Merge pull request #977 from peterhuene/wasi-c-api

Implement a WASI instantiation C API.

crates/api/src/types.rs

@@ -168,7 +168,7 @@ fn from_wasmtime_abiparam(param: &ir::AbiParam) -> Option<ValType> {
 /// A descriptor for a function in a WebAssembly module.
 ///
 /// WebAssembly functions can have 0 or more parameters and results.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct FuncType {
     params: Box<[ValType]>,
     results: Box<[ValType]>,

crates/c-api/Cargo.toml

@@ -18,3 +18,5 @@ doctest = false
 
 [dependencies]
 wasmtime = { path = "../api" }
+wasi-common = { path = "../wasi-common" }
+wasmtime-wasi = { path = "../wasi" }

crates/c-api/include/wasi.h

@@ -0,0 +1,70 @@
+// WASI C API
+
+#ifndef WASI_H
+#define WASI_H
+
+#include "wasm.h"
+
+#ifndef WASI_API_EXTERN
+#ifdef _WIN32
+#define WASI_API_EXTERN __declspec(dllimport)
+#else
+#define WASI_API_EXTERN
+#endif
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define own
+
+#define WASI_DECLARE_OWN(name) \
+  typedef struct wasi_##name##_t wasi_##name##_t; \
+  WASI_API_EXTERN void wasi_##name##_delete(own wasi_##name##_t*);
+
+// WASI config
+
+WASI_DECLARE_OWN(config)
+
+WASI_API_EXTERN own wasi_config_t* wasi_config_new();
+
+WASI_API_EXTERN void wasi_config_set_argv(wasi_config_t* config, int argc, const char* argv[]);
+WASI_API_EXTERN void wasi_config_inherit_argv(wasi_config_t* config);
+
+WASI_API_EXTERN void wasi_config_set_env(wasi_config_t* config, int envc, const char* names[], const char* values[]);
+WASI_API_EXTERN void wasi_config_inherit_env(wasi_config_t* config);
+
+WASI_API_EXTERN bool wasi_config_set_stdin_file(wasi_config_t* config, const char* path);
+WASI_API_EXTERN void wasi_config_inherit_stdin(wasi_config_t* config);
+
+WASI_API_EXTERN bool wasi_config_set_stdout_file(wasi_config_t* config, const char* path);
+WASI_API_EXTERN void wasi_config_inherit_stdout(wasi_config_t* config);
+
+WASI_API_EXTERN bool wasi_config_set_stderr_file(wasi_config_t* config, const char* path);
+WASI_API_EXTERN void wasi_config_inherit_stderr(wasi_config_t* config);
+
+WASI_API_EXTERN bool wasi_config_preopen_dir(wasi_config_t* config, const char* path, const char* guest_path);
+
+// WASI instance
+
+WASI_DECLARE_OWN(instance)
+
+WASI_API_EXTERN own wasi_instance_t* wasi_instance_new(
+  wasm_store_t* store,
+  own wasi_config_t* config,
+  own wasm_trap_t** trap
+);
+
+WASI_API_EXTERN const wasm_extern_t* wasi_instance_bind_import(
+  const wasi_instance_t* instance,
+  const wasm_importtype_t* import
+);
+
+#undef own
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // #ifdef WASI_H

crates/c-api/src/lib.rs

@@ -15,6 +15,12 @@ use wasmtime::{
     Table, TableType, Trap, Val, ValType,
 };
 
+mod ext;
+mod wasi;
+
+pub use crate::ext::*;
+pub use crate::wasi::*;
+
 macro_rules! declare_vec {
     ($name:ident, $elem_ty:path) => {
         #[repr(C)]
@@ -1025,7 +1031,7 @@ pub unsafe extern "C" fn wasm_trap_new(
     if message[message.len() - 1] != 0 {
         panic!("wasm_trap_new message stringz expected");
     }
-    let message = String::from_utf8_lossy(message);
+    let message = String::from_utf8_lossy(&message[..message.len() - 1]);
     let trap = Box::new(wasm_trap_t {
         trap: HostRef::new(Trap::new(message)),
     });
@@ -1777,7 +1783,3 @@ pub unsafe extern "C" fn wasm_valtype_vec_copy(
     let slice = slice::from_raw_parts((*src).data, (*src).size);
     (*out).set_from_slice(slice);
 }
-
-mod ext;
-
-pub use crate::ext::*;

crates/c-api/src/wasi.rs

@@ -0,0 +1,239 @@
+//! The WASI embedding API definitions for Wasmtime.
+use crate::{wasm_extern_t, wasm_importtype_t, wasm_store_t, wasm_trap_t, ExternHost, ExternType};
+use std::collections::HashMap;
+use std::ffi::CStr;
+use std::fs::File;
+use std::os::raw::{c_char, c_int};
+use std::path::Path;
+use std::slice;
+use wasi_common::{preopen_dir, WasiCtxBuilder};
+use wasmtime::{HostRef, Trap};
+use wasmtime_wasi::Wasi;
+
+unsafe fn cstr_to_path<'a>(path: *const c_char) -> Option<&'a Path> {
+    CStr::from_ptr(path).to_str().map(Path::new).ok()
+}
+
+unsafe fn open_file(path: *const c_char) -> Option<File> {
+    File::open(cstr_to_path(path)?).ok()
+}
+
+unsafe fn create_file(path: *const c_char) -> Option<File> {
+    File::create(cstr_to_path(path)?).ok()
+}
+
+#[repr(C)]
+pub struct wasi_config_t {
+    builder: WasiCtxBuilder,
+}
+
+impl wasi_config_t {}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_new() -> *mut wasi_config_t {
+    Box::into_raw(Box::new(wasi_config_t {
+        builder: WasiCtxBuilder::new(),
+    }))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_delete(config: *mut wasi_config_t) {
+    drop(Box::from_raw(config));
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_set_argv(
+    config: *mut wasi_config_t,
+    argc: c_int,
+    argv: *const *const c_char,
+) {
+    (*config).builder.args(
+        slice::from_raw_parts(argv, argc as usize)
+            .iter()
+            .map(|a| slice::from_raw_parts(*a as *const u8, CStr::from_ptr(*a).to_bytes().len())),
+    );
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_inherit_argv(config: *mut wasi_config_t) {
+    (*config).builder.inherit_args();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_set_env(
+    config: *mut wasi_config_t,
+    envc: c_int,
+    names: *const *const c_char,
+    values: *const *const c_char,
+) {
+    let names = slice::from_raw_parts(names, envc as usize);
+    let values = slice::from_raw_parts(values, envc as usize);
+
+    (*config).builder.envs(
+        names
+            .iter()
+            .map(|p| CStr::from_ptr(*p).to_bytes())
+            .zip(values.iter().map(|p| CStr::from_ptr(*p).to_bytes())),
+    );
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_inherit_env(config: *mut wasi_config_t) {
+    (*config).builder.inherit_env();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_set_stdin_file(
+    config: *mut wasi_config_t,
+    path: *const c_char,
+) -> bool {
+    let file = match open_file(path) {
+        Some(f) => f,
+        None => return false,
+    };
+
+    (*config).builder.stdin(file);
+
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_inherit_stdin(config: *mut wasi_config_t) {
+    (*config).builder.inherit_stdin();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_set_stdout_file(
+    config: *mut wasi_config_t,
+    path: *const c_char,
+) -> bool {
+    let file = match create_file(path) {
+        Some(f) => f,
+        None => return false,
+    };
+
+    (*config).builder.stdout(file);
+
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_inherit_stdout(config: *mut wasi_config_t) {
+    (*config).builder.inherit_stdout();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_set_stderr_file(
+    config: *mut wasi_config_t,
+    path: *const c_char,
+) -> bool {
+    let file = match create_file(path) {
+        Some(f) => f,
+        None => return false,
+    };
+
+    (*config).builder.stderr(file);
+
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_inherit_stderr(config: *mut wasi_config_t) {
+    (*config).builder.inherit_stderr();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_config_preopen_dir(
+    config: *mut wasi_config_t,
+    path: *const c_char,
+    guest_path: *const c_char,
+) -> bool {
+    let guest_path = match cstr_to_path(guest_path) {
+        Some(p) => p,
+        None => return false,
+    };
+
+    let dir = match cstr_to_path(path) {
+        Some(p) => match preopen_dir(p) {
+            Ok(d) => d,
+            Err(_) => return false,
+        },
+        None => return false,
+    };
+
+    (*config).builder.preopened_dir(dir, guest_path);
+
+    true
+}
+
+#[repr(C)]
+pub struct wasi_instance_t {
+    wasi: Wasi,
+    export_cache: HashMap<String, Box<wasm_extern_t>>,
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_instance_new(
+    store: *mut wasm_store_t,
+    config: *mut wasi_config_t,
+    trap: *mut *mut wasm_trap_t,
+) -> *mut wasi_instance_t {
+    let store = &(*store).store.borrow();
+    let mut config = Box::from_raw(config);
+
+    match config.builder.build() {
+        Ok(ctx) => Box::into_raw(Box::new(wasi_instance_t {
+            wasi: Wasi::new(store, ctx),
+            export_cache: HashMap::new(),
+        })),
+        Err(e) => {
+            (*trap) = Box::into_raw(Box::new(wasm_trap_t {
+                trap: HostRef::new(Trap::new(e.to_string())),
+            }));
+
+            std::ptr::null_mut()
+        }
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_instance_delete(instance: *mut wasi_instance_t) {
+    drop(Box::from_raw(instance));
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn wasi_instance_bind_import(
+    instance: *mut wasi_instance_t,
+    import: *const wasm_importtype_t,
+) -> *const wasm_extern_t {
+    // TODO: support previous versions?
+    if (*import).ty.module() != "wasi_snapshot_preview1" {
+        return std::ptr::null_mut();
+    }
+
+    // The import should be a function (WASI only exports functions)
+    let func_type = match (*import).ty.ty() {
+        ExternType::Func(f) => f,
+        _ => return std::ptr::null_mut(),
+    };
+
+    let name = (*import).ty.name();
+
+    match (*instance).wasi.get_export(name) {
+        Some(export) => {
+            if export.ty() != func_type {
+                return std::ptr::null_mut();
+            }
+
+            &**(*instance)
+                .export_cache
+                .entry(name.to_string())
+                .or_insert_with(|| {
+                    Box::new(wasm_extern_t {
+                        which: ExternHost::Func(HostRef::new(export.clone())),
+                    })
+                }) as *const wasm_extern_t
+        }
+        None => std::ptr::null_mut(),
+    }
+}

crates/misc/dotnet/docs/articles/intro.md

@@ -142,13 +142,12 @@ namespace Tutorial
     {
         static void Main(string[] args)
         {
-            using (var engine = new Engine())
-            using (var store = engine.CreateStore())
-            using (var module = store.CreateModule("hello.wasm"))
-            using (dynamic instance = module.Instantiate(new Host()))
-            {
-                instance.run();
-            }
+            using var engine = new Engine();
+            using var store = engine.CreateStore();
+            using var module = store.CreateModule("hello.wasm");
+            using dynamic instance = module.Instantiate(new Host());
+
+            instance.run();
         }
     }
 }
@@ -166,10 +165,8 @@ Alternatively, the `run` function could be invoked without using the runtime bin
 
 ```c#
 ...
-using (var instance = module.Instantiate(new Host()))
-{
-    instance.Externs.Functions[0].Invoke();
-}
+using var instance = module.Instantiate(new Host());
+instance.Externs.Functions[0].Invoke();
 ...
 ```
 

crates/misc/dotnet/examples/global/Program.cs

@@ -21,13 +21,12 @@ namespace HelloExample
     {
         static void Main(string[] args)
         {
-            using (var engine = new Engine())
-            using (var store = engine.CreateStore())
-            using (var module = store.CreateModule("global.wasm"))
-            using (dynamic instance = module.Instantiate(new Host()))
-            {
-                instance.run(20);
-            }
+            using var engine = new Engine();
+            using var store = engine.CreateStore();
+            using var module = store.CreateModule("global.wasm");
+            using dynamic instance = module.Instantiate(new Host());
+
+            instance.run(20);
         }
     }
 }

crates/misc/dotnet/examples/hello/Program.cs

@@ -18,13 +18,12 @@ namespace HelloExample
     {
         static void Main(string[] args)
         {
-            using (var engine = new Engine())
-            using (var store = engine.CreateStore())
-            using (var module = store.CreateModule("hello.wasm"))
-            using (dynamic instance = module.Instantiate(new Host()))
-            {
-                instance.run();
-            }
+            using var engine = new Engine();
+            using var store = engine.CreateStore();
+            using var module = store.CreateModule("hello.wasm");
+            using dynamic instance = module.Instantiate(new Host());
+
+            instance.run();
         }
     }
 }

crates/misc/dotnet/examples/memory/Program.cs

@@ -19,13 +19,12 @@ namespace HelloExample
     {
         static void Main(string[] args)
         {
-            using (var engine = new Engine())
-            using (var store = engine.CreateStore())
-            using (var module = store.CreateModule("memory.wasm"))
-            using (dynamic instance = module.Instantiate(new Host()))
-            {
-                instance.run();
-            }
+            using var engine = new Engine();
+            using var store = engine.CreateStore();
+            using var module = store.CreateModule("memory.wasm");
+            using dynamic instance = module.Instantiate(new Host());
+
+            instance.run();
         }
     }
 }

crates/misc/dotnet/src/Bindings/Binding.cs

@@ -10,35 +10,37 @@ namespace Wasmtime.Bindings
     /// <summary>
     /// Represents an abstract host binding.
     /// </summary>
-    public abstract class Binding
+    internal abstract class Binding
     {
-        internal abstract SafeHandle Bind(Store store, IHost host);
+        public abstract SafeHandle Bind(Store store, IHost host);
 
-        internal static void ThrowBindingException(Import import, MemberInfo member, string message)
+        public static WasmtimeException CreateBindingException(Import import, MemberInfo member, string message)
         {
-            throw new WasmtimeException($"Unable to bind '{member.DeclaringType.Name}.{member.Name}' to WebAssembly import '{import}': {message}.");
+            return new WasmtimeException($"Unable to bind '{member.DeclaringType.Name}.{member.Name}' to WebAssembly import '{import}': {message}.");
         }
 
-        internal static List<Binding> GetImportBindings(IHost host, Module module)
+        public static List<Binding> GetImportBindings(Module module, Wasi wasi = null, IHost host = null)
         {
-            if (host is null)
-            {
-                throw new ArgumentNullException(nameof(host));
-            }
-
             if (module is null)
             {
                 throw new ArgumentNullException(nameof(module));
             }
 
-            var flags = BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly;
-            var type = host.GetType();
-            var methods = type.GetMethods(flags).Where(m => !m.IsSpecialName && Attribute.IsDefined(m, typeof(ImportAttribute)));
-            var fields = type.GetFields(flags).Where(m => !m.IsSpecialName && Attribute.IsDefined(m, typeof(ImportAttribute)));
-
             var bindings = new List<Binding>();
+            var flags = BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly;
+            var type = host?.GetType();
+            var methods = type?.GetMethods(flags).Where(m => !m.IsSpecialName && Attribute.IsDefined(m, typeof(ImportAttribute)));
+            var fields = type?.GetFields(flags).Where(m => !m.IsSpecialName && Attribute.IsDefined(m, typeof(ImportAttribute)));
+
             foreach (var import in module.Imports.All)
             {
+                var wasiBinding = wasi?.Bind(import);
+                if (!(wasiBinding is null))
+                {
+                    bindings.Add(wasiBinding);
+                    continue;
+                }
+
                 switch (import)
                 {
                     case FunctionImport func:
@@ -63,7 +65,7 @@ namespace Wasmtime.Bindings
 
         private static FunctionBinding BindFunction(FunctionImport import, IEnumerable<MethodInfo> methods)
         {
-            var method = methods.Where(m =>
+            var method = methods?.Where(m =>
                 {
                     var attribute = (ImportAttribute)m.GetCustomAttribute(typeof(ImportAttribute));
                     if (attribute is null)
@@ -88,7 +90,7 @@ namespace Wasmtime.Bindings
 
         private static GlobalBinding BindGlobal(GlobalImport import, IEnumerable<FieldInfo> fields)
         {
-            var field = fields.Where(f =>
+            var field = fields?.Where(f =>
                 {
                     var attribute = (ImportAttribute)f.GetCustomAttribute(typeof(ImportAttribute));
                     return attribute.Name == import.Name &&
@@ -108,7 +110,7 @@ namespace Wasmtime.Bindings
 
         private static MemoryBinding BindMemory(MemoryImport import, IEnumerable<FieldInfo> fields)
         {
-            var field = fields.Where(f =>
+            var field = fields?.Where(f =>
                 {
                     var attribute = (ImportAttribute)f.GetCustomAttribute(typeof(ImportAttribute));
                     return attribute.Name == import.Name &&

crates/misc/dotnet/src/Bindings/FunctionBinding.cs

@@ -11,7 +11,7 @@ namespace Wasmtime.Bindings
     /// <summary>
     /// Represents a host function binding.
     /// </summary>
-    public class FunctionBinding : Binding
+    internal class FunctionBinding : Binding
     {
         /// <summary>
         /// Constructs a new function binding.
@@ -46,23 +46,18 @@ namespace Wasmtime.Bindings
         /// </summary>
         public MethodInfo Method { get; private set; }
 
-        internal override SafeHandle Bind(Store store, IHost host)
+        public override SafeHandle Bind(Store store, IHost host)
         {
             unsafe
             {
-                if (_callback != null)
-                {
-                    throw new InvalidOperationException("Cannot bind more than once.");
-                }
-
-                _callback = CreateCallback(store, host);
-
                 var parameters = Interop.ToValueTypeVec(Import.Parameters);
                 var results = Interop.ToValueTypeVec(Import.Results);
-                using (var funcType = Interop.wasm_functype_new(ref parameters, ref results))
-                {
-                    return Interop.wasm_func_new(store.Handle, funcType, _callback);
-                }
+                using var funcType = Interop.wasm_functype_new(ref parameters, ref results);
+                var callback = CreateCallback(store, host);
+                var func = Interop.wasm_func_new(store.Handle, funcType, callback);
+                // Store the callback with the safe handle to keep the delegate GC reachable
+                func.Callback = callback;
+                return func;
             }
         }
 
@@ -70,17 +65,17 @@ namespace Wasmtime.Bindings
         {
             if (Method.IsStatic)
             {
-                ThrowBindingException(Import, Method, "method cannot be static");
+                throw CreateBindingException(Import, Method, "method cannot be static");
             }
 
             if (Method.IsGenericMethod)
             {
-                ThrowBindingException(Import, Method, "method cannot be generic");
+                throw CreateBindingException(Import, Method, "method cannot be generic");
             }
 
             if (Method.IsConstructor)
             {
-                ThrowBindingException(Import, Method, "method cannot be a constructor");
+                throw CreateBindingException(Import, Method, "method cannot be a constructor");
             }
 
             ValidateParameters();
@@ -93,7 +88,7 @@ namespace Wasmtime.Bindings
             var parameters = Method.GetParameters();
             if (parameters.Length != Import.Parameters.Count)
             {
-                ThrowBindingException(
+                throw CreateBindingException(
                     Import,
                     Method,
                     $"parameter mismatch: import requires {Import.Parameters.Count} but the method has {parameters.Length}");
@@ -106,18 +101,18 @@ namespace Wasmtime.Bindings
                 {
                     if (parameter.IsOut)
                     {
-                        ThrowBindingException(Import, Method, $"parameter '{parameter.Name}' cannot be an 'out' parameter");
+                        throw CreateBindingException(Import, Method, $"parameter '{parameter.Name}' cannot be an 'out' parameter");
                     }
                     else
                     {
-                        ThrowBindingException(Import, Method, $"parameter '{parameter.Name}' cannot be a 'ref' parameter");
+                        throw CreateBindingException(Import, Method, $"parameter '{parameter.Name}' cannot be a 'ref' parameter");
                     }
                 }
 
                 var expected = Import.Parameters[i];
                 if (!Interop.TryGetValueKind(parameter.ParameterType, out var kind) || !Interop.IsMatchingKind(kind, expected))
                 {
-                    ThrowBindingException(Import, Method, $"method parameter '{parameter.Name}' is expected to be of type '{Interop.ToString(expected)}'");
+                    throw CreateBindingException(Import, Method, $"method parameter '{parameter.Name}' is expected to be of type '{Interop.ToString(expected)}'");
                 }
             }
         }
@@ -129,7 +124,7 @@ namespace Wasmtime.Bindings
             {
                 if (Method.ReturnType != typeof(void))
                 {
-                    ThrowBindingException(Import, Method, "method must return void");
+                    throw CreateBindingException(Import, Method, "method must return void");
                 }
             }
             else if (resultsCount == 1)
@@ -137,14 +132,14 @@ namespace Wasmtime.Bindings
                 var expected = Import.Results[0];
                 if (!Interop.TryGetValueKind(Method.ReturnType, out var kind) || !Interop.IsMatchingKind(kind, expected))
                 {
-                    ThrowBindingException(Import, Method, $"return type is expected to be '{Interop.ToString(expected)}'");
+                    throw CreateBindingException(Import, Method, $"return type is expected to be '{Interop.ToString(expected)}'");
                 }
             }
             else
             {
                 if (!IsTupleOfSize(Method.ReturnType, resultsCount))
                 {
-                    ThrowBindingException(Import, Method, $"return type is expected to be a tuple of size {resultsCount}");
+                    throw CreateBindingException(Import, Method, $"return type is expected to be a tuple of size {resultsCount}");
                 }
 
                 var typeArguments =
@@ -163,7 +158,7 @@ namespace Wasmtime.Bindings
                     var expected = Import.Results[i];
                     if (!Interop.TryGetValueKind(typeArgument, out var kind) || !Interop.IsMatchingKind(kind, expected))
                     {
-                        ThrowBindingException(Import, Method, $"return tuple item #{i} is expected to be of type '{Interop.ToString(expected)}'");
+                        throw CreateBindingException(Import, Method, $"return tuple item #{i} is expected to be of type '{Interop.ToString(expected)}'");
                     }
 
                     ++i;
@@ -340,7 +335,5 @@ namespace Wasmtime.Bindings
                     throw new NotSupportedException("Unsupported return value type.");
             }
         }
-
-        private Interop.WasmFuncCallback _callback;
     }
 }

crates/misc/dotnet/src/Bindings/GlobalBinding.cs

@@ -8,7 +8,7 @@ namespace Wasmtime.Bindings
     /// <summary>
     /// Represents a host global binding.
     /// </summary>
-    public class GlobalBinding : Binding
+    internal class GlobalBinding : Binding
     {
         /// <summary>
         /// Constructs a new global binding.
@@ -43,12 +43,12 @@ namespace Wasmtime.Bindings
         /// </summary>
         public FieldInfo Field { get; private set; }
 
-        internal override SafeHandle Bind(Store store, IHost host)
+        public override SafeHandle Bind(Store store, IHost host)
         {
             unsafe
             {
                 dynamic global = Field.GetValue(host);
-                if (global.Handle != null)
+                if (!(global.Handle is null))
                 {
                     throw new InvalidOperationException("Cannot bind more than once.");
                 }
@@ -59,14 +59,14 @@ namespace Wasmtime.Bindings
                 var valueTypeHandle = valueType.DangerousGetHandle();
                 valueType.SetHandleAsInvalid();
 
-                using (var globalType = Interop.wasm_globaltype_new(
+                using var globalType = Interop.wasm_globaltype_new(
                     valueTypeHandle,
-                    Import.IsMutable ? Interop.wasm_mutability_t.WASM_VAR : Interop.wasm_mutability_t.WASM_CONST))
-                {
-                    var handle = Interop.wasm_global_new(store.Handle, globalType, &v);
-                    global.Handle = handle;
-                    return handle;
-                }
+                    Import.IsMutable ? Interop.wasm_mutability_t.WASM_VAR : Interop.wasm_mutability_t.WASM_CONST
+                );
+
+                var handle = Interop.wasm_global_new(store.Handle, globalType, &v);
+                global.Handle = handle;
+                return handle;
             }
         }
 
@@ -74,17 +74,17 @@ namespace Wasmtime.Bindings
         {
             if (Field.IsStatic)
             {
-                ThrowBindingException(Import, Field, "field cannot be static");
+                throw CreateBindingException(Import, Field, "field cannot be static");
             }
 
             if (!Field.IsInitOnly)
             {
-                ThrowBindingException(Import, Field, "field must be readonly");
+                throw CreateBindingException(Import, Field, "field must be readonly");
             }
 
             if (!Field.FieldType.IsGenericType)
             {
-                ThrowBindingException(Import, Field, "field is expected to be of type 'Global<T>'");
+                throw CreateBindingException(Import, Field, "field is expected to be of type 'Global<T>'");
             }
 
             var definition = Field.FieldType.GetGenericTypeDefinition();
@@ -92,19 +92,19 @@ namespace Wasmtime.Bindings
             {
                 if (Import.IsMutable)
                 {
-                    ThrowBindingException(Import, Field, "the import is mutable (use the 'MutableGlobal' type)");
+                    throw CreateBindingException(Import, Field, "the import is mutable (use the 'MutableGlobal' type)");
                 }
             }
             else if (definition == typeof(MutableGlobal<>))
             {
                 if (!Import.IsMutable)
                 {
-                    ThrowBindingException(Import, Field, "the import is constant (use the 'Global' type)");
+                    throw CreateBindingException(Import, Field, "the import is constant (use the 'Global' type)");
                 }
             }
             else
             {
-                ThrowBindingException(Import, Field, "field is expected to be of type 'Global<T>' or 'MutableGlobal<T>'");
+                throw CreateBindingException(Import, Field, "field is expected to be of type 'Global<T>' or 'MutableGlobal<T>'");
             }
 
             var arg = Field.FieldType.GetGenericArguments()[0];
@@ -113,12 +113,12 @@ namespace Wasmtime.Bindings
             {
                 if (!Interop.IsMatchingKind(kind, Import.Kind))
                 {
-                    ThrowBindingException(Import, Field, $"global type argument is expected to be of type '{Interop.ToString(Import.Kind)}'");
+                    throw CreateBindingException(Import, Field, $"global type argument is expected to be of type '{Interop.ToString(Import.Kind)}'");
                 }
             }
             else
             {
-                ThrowBindingException(Import, Field, $"'{arg}' is not a valid global type");
+                throw CreateBindingException(Import, Field, $"'{arg}' is not a valid global type");
             }
         }
     }

crates/misc/dotnet/src/Bindings/MemoryBinding.cs

@@ -8,7 +8,7 @@ namespace Wasmtime.Bindings
     /// <summary>
     /// Represents a host memory binding.
     /// </summary>
-    public class MemoryBinding : Binding
+    internal class MemoryBinding : Binding
     {
         /// <summary>
         /// Constructs a new memory binding.
@@ -43,10 +43,10 @@ namespace Wasmtime.Bindings
         /// </summary>
         public FieldInfo Field { get; private set; }
 
-        internal override SafeHandle Bind(Store store, IHost host)
+        public override SafeHandle Bind(Store store, IHost host)
         {
             Memory memory = (Memory)Field.GetValue(host);
-            if (memory.Handle != null)
+            if (!(memory.Handle is null))
             {
                 throw new InvalidOperationException("Cannot bind more than once.");
             }
@@ -56,11 +56,11 @@ namespace Wasmtime.Bindings
 
             if (min != Import.Minimum)
             {
-                ThrowBindingException(Import, Field, $"Memory does not have the expected minimum of {Import.Minimum} page(s)");
+                throw CreateBindingException(Import, Field, $"Memory does not have the expected minimum of {Import.Minimum} page(s)");
             }
             if (max != Import.Maximum)
             {
-                ThrowBindingException(Import, Field, $"Memory does not have the expected maximum of {Import.Maximum} page(s)");
+                throw CreateBindingException(Import, Field, $"Memory does not have the expected maximum of {Import.Maximum} page(s)");
             }
 
             unsafe
@@ -68,12 +68,11 @@ namespace Wasmtime.Bindings
                 Interop.wasm_limits_t limits = new Interop.wasm_limits_t();
                 limits.min = min;
                 limits.max = max;
-                using (var memoryType = Interop.wasm_memorytype_new(&limits))
-                {
-                    var handle = Interop.wasm_memory_new(store.Handle, memoryType);
-                    memory.Handle = handle;
-                    return handle;
-                }
+
+                using var memoryType = Interop.wasm_memorytype_new(&limits);
+                var handle = Interop.wasm_memory_new(store.Handle, memoryType);
+                memory.Handle = handle;
+                return handle;
             }
         }
 
@@ -81,17 +80,17 @@ namespace Wasmtime.Bindings
         {
             if (Field.IsStatic)
             {
-                ThrowBindingException(Import, Field, "field cannot be static");
+                throw CreateBindingException(Import, Field, "field cannot be static");
             }
 
             if (!Field.IsInitOnly)
             {
-                ThrowBindingException(Import, Field, "field must be readonly");
+                throw CreateBindingException(Import, Field, "field must be readonly");
             }
 
             if (Field.FieldType != typeof(Memory))
             {
-                ThrowBindingException(Import, Field, "field is expected to be of type 'Memory'");
+                throw CreateBindingException(Import, Field, "field is expected to be of type 'Memory'");
             }
         }
     }

crates/misc/dotnet/src/Bindings/WasiBinding.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace Wasmtime.Bindings
+{
+    /// <summary>
+    /// Represents a binding to a WASI export.
+    /// </summary>
+    internal class WasiBinding : Binding
+    {
+        public WasiBinding(IntPtr handle)
+        {
+            _handle = handle;
+        }
+
+        public override SafeHandle Bind(Store store, IHost host)
+        {
+            return new Interop.WasiExportHandle(_handle);
+        }
+
+        private IntPtr _handle;
+    }
+}

crates/misc/dotnet/src/Externs/ExternMemory.cs

@@ -63,6 +63,23 @@ namespace Wasmtime.Externs
             return Encoding.UTF8.GetString(Span.Slice(address, length));
         }
 
+        /// <summary>
+        /// Reads a null-terminated UTF-8 string from memory.
+        /// </summary>
+        /// <param name="address">The zero-based address to read from.</param>
+        /// <returns>Returns the string read from memory.</returns>
+        public string ReadNullTerminatedString(int address)
+        {
+            var slice = Span.Slice(address);
+            var terminator = slice.IndexOf((byte)0);
+            if (terminator == -1)
+            {
+                throw new InvalidOperationException("string is not null terminated");
+            }
+
+            return Encoding.UTF8.GetString(slice.Slice(0, terminator));
+        }
+
         /// <summary>
         /// Writes a UTF-8 string at the given address.
         /// </summary>

crates/misc/dotnet/src/IHost.cs

@@ -14,12 +14,5 @@ namespace Wasmtime
         /// </summary>
         /// <remarks>A host can only bind to one module instance at a time.</remarks>
         Instance Instance { get; set; }
-
-        /// <summary>
-        /// Gets the import bindings of the host given a WebAssembly module.
-        /// </summary>
-        /// <param name="module">The WebAssembly module to get the import bindings for.</param>
-        /// <returns>Returns the list of import bindings for the host.</returns>
-        List<Binding> GetImportBindings(Module module) => Binding.GetImportBindings(this, module);
     }
 }

crates/misc/dotnet/src/Imports/Import.cs

@@ -12,10 +12,12 @@ namespace Wasmtime.Imports
         {
             unsafe
             {
-                var moduleName = Interop.wasm_importtype_module(importType);
+                Handle = importType;
+
+                var moduleName = Interop.wasm_importtype_module(Handle);
                 ModuleName = Marshal.PtrToStringUTF8((IntPtr)moduleName->data, (int)moduleName->size);
 
-                var name = Interop.wasm_importtype_name(importType);
+                var name = Interop.wasm_importtype_name(Handle);
                 Name = Marshal.PtrToStringUTF8((IntPtr)name->data, (int)name->size);
             }
         }
@@ -30,6 +32,8 @@ namespace Wasmtime.Imports
         /// </summary>
         public string Name { get; private set; }
 
+        internal IntPtr Handle { get; private set; }
+
         /// <inheritdoc/>
         public override string ToString()
         {

crates/misc/dotnet/src/Imports/Imports.cs

@@ -6,69 +6,72 @@ namespace Wasmtime.Imports
     /// <summary>
     /// Represents imported functions, globals, tables, and memories to a WebAssembly module.
     /// </summary>
-    public class Imports
+    public class Imports : IDisposable
     {
         internal Imports(Module module)
         {
             Interop.wasm_importtype_vec_t imports;
             Interop.wasm_module_imports(module.Handle, out imports);
 
-            try
+            var all = new List<Import>((int)imports.size);
+            var functions = new List<FunctionImport>();
+            var globals = new List<GlobalImport>();
+            var tables = new List<TableImport>();
+            var memories = new List<MemoryImport>();
+
+            for (int i = 0; i < (int)imports.size; ++i)
             {
-                var all = new List<Import>((int)imports.size);
-                var functions = new List<FunctionImport>();
-                var globals = new List<GlobalImport>();
-                var tables = new List<TableImport>();
-                var memories = new List<MemoryImport>();
-
-                for (int i = 0; i < (int)imports.size; ++i)
+                unsafe
                 {
-                    unsafe
+                    var importType = imports.data[i];
+                    var externType = Interop.wasm_importtype_type(importType);
+
+                    switch (Interop.wasm_externtype_kind(externType))
                     {
-                        var importType = imports.data[i];
-                        var externType = Interop.wasm_importtype_type(importType);
+                        case Interop.wasm_externkind_t.WASM_EXTERN_FUNC:
+                            var function = new FunctionImport(importType, externType);
+                            functions.Add(function);
+                            all.Add(function);
+                            break;
 
-                        switch (Interop.wasm_externtype_kind(externType))
-                        {
-                            case Interop.wasm_externkind_t.WASM_EXTERN_FUNC:
-                                var function = new FunctionImport(importType, externType);
-                                functions.Add(function);
-                                all.Add(function);
-                                break;
+                        case Interop.wasm_externkind_t.WASM_EXTERN_GLOBAL:
+                            var global = new GlobalImport(importType, externType);
+                            globals.Add(global);
+                            all.Add(global);
+                            break;
 
-                            case Interop.wasm_externkind_t.WASM_EXTERN_GLOBAL:
-                                var global = new GlobalImport(importType, externType);
-                                globals.Add(global);
-                                all.Add(global);
-                                break;
+                        case Interop.wasm_externkind_t.WASM_EXTERN_TABLE:
+                            var table = new TableImport(importType, externType);
+                            tables.Add(table);
+                            all.Add(table);
+                            break;
 
-                            case Interop.wasm_externkind_t.WASM_EXTERN_TABLE:
-                                var table = new TableImport(importType, externType);
-                                tables.Add(table);
-                                all.Add(table);
-                                break;
+                        case Interop.wasm_externkind_t.WASM_EXTERN_MEMORY:
+                            var memory = new MemoryImport(importType, externType);
+                            memories.Add(memory);
+                            all.Add(memory);
+                            break;
 
-                            case Interop.wasm_externkind_t.WASM_EXTERN_MEMORY:
-                                var memory = new MemoryImport(importType, externType);
-                                memories.Add(memory);
-                                all.Add(memory);
-                                break;
-
-                            default:
-                                throw new NotSupportedException("Unsupported import extern type.");
-                        }
+                        default:
+                            throw new NotSupportedException("Unsupported import extern type.");
                     }
                 }
-
-                Functions = functions;
-                Globals = globals;
-                Tables = tables;
-                Memories = memories;
-                All = all;
             }
-            finally
+
+            Functions = functions;
+            Globals = globals;
+            Tables = tables;
+            Memories = memories;
+            All = all;
+        }
+
+        /// <inheritdoc/>
+        public unsafe void Dispose()
+        {
+            if (!(_imports.data is null))
             {
-                Interop.wasm_importtype_vec_delete(ref imports);
+                Interop.wasm_importtype_vec_delete(ref _imports);
+                _imports.data = null;
             }
         }
 
@@ -93,5 +96,7 @@ namespace Wasmtime.Imports
         public IReadOnlyList<MemoryImport> Memories { get; private set; }
 
         internal IReadOnlyList<Import> All { get; private set; }
+
+        private Interop.wasm_importtype_vec_t _imports;
     }
 }

crates/misc/dotnet/src/Instance.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using System.Runtime.InteropServices;
 using System.Dynamic;
 using Wasmtime.Externs;
+using Wasmtime.Bindings;
 
 namespace Wasmtime
 {
@@ -12,22 +13,23 @@ namespace Wasmtime
     /// </summary>
     public class Instance : DynamicObject, IDisposable
     {
-        internal Instance(Module module, IHost host)
+        internal Instance(Module module, Wasi wasi = null, IHost host = null)
         {
             Host = host;
             Module = module;
 
-            //Save the bindings to root the objects.
-            //Otherwise the GC may collect the delegates from ExternFunction for example.
-            _bindings = host.GetImportBindings(module);
-            var handles = _bindings.Select(b => b.Bind(module.Store, host)).ToList();
+            // Save the bindings to root the objects.
+            // Otherwise the GC may collect the callback delegates from FunctionHandles for example.
+            _bindings = Binding.GetImportBindings(module, wasi, host)
+                    .Select(b => b.Bind(module.Store, host))
+                    .ToArray();
 
             unsafe
             {
                 Handle = Interop.wasm_instance_new(
                     Module.Store.Handle,
                     Module.Handle,
-                    handles.Select(h => ToExtern(h)).ToArray(),
+                    _bindings.Select(h => ToExtern(h)).ToArray(),
                     out var trap);
 
                 if (trap != IntPtr.Zero)
@@ -41,12 +43,6 @@ namespace Wasmtime
                 throw new WasmtimeException($"Failed to instantiate module '{module.Name}'.");
             }
 
-            // Dispose of all function handles (not needed at runtime)
-            foreach (var h in handles.Where(h => h is Interop.FunctionHandle))
-            {
-                h.Dispose();
-            }
-
             Interop.wasm_instance_exports(Handle, out _externs);
 
             Externs = new Wasmtime.Externs.Externs(Module.Exports, _externs);
@@ -71,17 +67,27 @@ namespace Wasmtime
         public Wasmtime.Externs.Externs Externs { get; private set; }
 
         /// <inheritdoc/>
-        public void Dispose()
+        public unsafe void Dispose()
         {
             if (!Handle.IsInvalid)
             {
                 Handle.Dispose();
                 Handle.SetHandleAsInvalid();
             }
-            if (_externs.size != UIntPtr.Zero)
+
+            if (!(_bindings is null))
+            {
+                foreach (var binding in _bindings)
+                {
+                    binding.Dispose();
+                }
+                _bindings = null;
+            }
+
+            if (!(_externs.data is null))
             {
                 Interop.wasm_extern_vec_delete(ref _externs);
-                _externs.size = UIntPtr.Zero;
+                _externs.data = null;
             }
         }
 
@@ -134,15 +140,18 @@ namespace Wasmtime
                 case Interop.MemoryHandle m:
                     return Interop.wasm_memory_as_extern(m);
 
+                case Interop.WasiExportHandle w:
+                    return w.DangerousGetHandle();
+
                 default:
                     throw new NotSupportedException("Unexpected handle type.");
             }
         }
 
         internal Interop.InstanceHandle Handle { get; private set; }
+        private SafeHandle[] _bindings;
         private Interop.wasm_extern_vec_t _externs;
         private Dictionary<string, ExternFunction> _functions;
         private Dictionary<string, ExternGlobal> _globals;
-        private List<Bindings.Binding> _bindings;
     }
 }

crates/misc/dotnet/src/Interop.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace Wasmtime
 {
@@ -10,6 +11,8 @@ namespace Wasmtime
     /// <remarks>See https://github.com/WebAssembly/wasm-c-api/blob/master/include/wasm.h for the C API reference.</remarks>
     internal static class Interop
     {
+        const string LibraryName = "wasmtime";
+
         internal class EngineHandle : SafeHandle
         {
             public EngineHandle() : base(IntPtr.Zero, true)
@@ -61,6 +64,8 @@ namespace Wasmtime
             {
             }
 
+            public WasmFuncCallback Callback { get; set; } = null;
+
             public override bool IsInvalid => handle == IntPtr.Zero;
 
             protected override bool ReleaseHandle()
@@ -175,6 +180,51 @@ namespace Wasmtime
             }
         }
 
+        internal class WasiConfigHandle : SafeHandle
+        {
+            public WasiConfigHandle() : base(IntPtr.Zero, true)
+            {
+            }
+
+            public override bool IsInvalid => handle == IntPtr.Zero;
+
+            protected override bool ReleaseHandle()
+            {
+                Interop.wasi_config_delete(handle);
+                return true;
+            }
+        }
+
+        internal class WasiInstanceHandle : SafeHandle
+        {
+            public WasiInstanceHandle() : base(IntPtr.Zero, true)
+            {
+            }
+
+            public override bool IsInvalid => handle == IntPtr.Zero;
+
+            protected override bool ReleaseHandle()
+            {
+                Interop.wasi_instance_delete(handle);
+                return true;
+            }
+        }
+
+        internal class WasiExportHandle : SafeHandle
+        {
+            public WasiExportHandle(IntPtr handle) : base(IntPtr.Zero, false /* not owned */)
+            {
+                SetHandle(handle);
+            }
+
+            public override bool IsInvalid => handle == IntPtr.Zero;
+
+            protected override bool ReleaseHandle()
+            {
+                return true;
+            }
+        }
+
         [StructLayout(LayoutKind.Sequential)]
         internal unsafe struct wasm_byte_vec_t
         {
@@ -440,323 +490,415 @@ namespace Wasmtime
             return vec;
         }
 
+        internal static unsafe (byte*[], GCHandle[]) ToUTF8PtrArray(IList<string> strings)
+        {
+            // Unfortunately .NET cannot currently marshal string[] as UTF-8
+            // See: https://github.com/dotnet/runtime/issues/7315
+            // Therefore, we need to marshal the strings manually
+            var handles = new GCHandle[strings.Count];
+            var ptrs = new byte*[strings.Count];
+            for (int i = 0; i < strings.Count; ++i)
+            {
+                handles[i] = GCHandle.Alloc(
+                    Encoding.UTF8.GetBytes(strings[i] + '\0'),
+                    GCHandleType.Pinned
+                );
+                ptrs[i] = (byte*)handles[i].AddrOfPinnedObject();
+            }
+
+            return (ptrs, handles);
+        }
+
         // Engine imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern EngineHandle wasm_engine_new();
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_engine_delete(IntPtr engine);
 
         // Store imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern StoreHandle wasm_store_new(EngineHandle engine);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_store_delete(IntPtr engine);
 
         // Byte vec imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_byte_vec_new_empty(out wasm_byte_vec_t vec);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_byte_vec_new_uninitialized(out wasm_byte_vec_t vec, UIntPtr length);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_byte_vec_new(out wasm_byte_vec_t vec, UIntPtr length, byte[] data);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_byte_vec_copy(out wasm_byte_vec_t vec, ref wasm_byte_vec_t src);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_byte_vec_delete(ref wasm_byte_vec_t vec);
 
         // Value type vec imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_valtype_vec_new_empty(out wasm_valtype_vec_t vec);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_valtype_vec_new_uninitialized(out wasm_valtype_vec_t vec, UIntPtr length);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_valtype_vec_new(out wasm_valtype_vec_t vec, UIntPtr length, IntPtr[] data);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_valtype_vec_copy(out wasm_valtype_vec_t vec, ref wasm_valtype_vec_t src);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_valtype_vec_delete(ref wasm_valtype_vec_t vec);
 
         // Extern vec imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_extern_vec_new_empty(out wasm_extern_vec_t vec);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_extern_vec_new_uninitialized(out wasm_extern_vec_t vec, UIntPtr length);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_extern_vec_new(out wasm_extern_vec_t vec, UIntPtr length, IntPtr[] data);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_extern_vec_copy(out wasm_extern_vec_t vec, ref wasm_extern_vec_t src);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_extern_vec_delete(ref wasm_extern_vec_t vec);
 
         // Import type vec imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_importtype_vec_new_empty(out wasm_importtype_vec_t vec);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_importtype_vec_new_uninitialized(out wasm_importtype_vec_t vec, UIntPtr length);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_importtype_vec_new(out wasm_importtype_vec_t vec, UIntPtr length, IntPtr[] data);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_importtype_vec_copy(out wasm_importtype_vec_t vec, ref wasm_importtype_vec_t src);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_importtype_vec_delete(ref wasm_importtype_vec_t vec);
 
         // Export type vec imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_exporttype_vec_new_empty(out wasm_exporttype_vec_t vec);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_exporttype_vec_new_uninitialized(out wasm_exporttype_vec_t vec, UIntPtr length);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_exporttype_vec_new(out wasm_exporttype_vec_t vec, UIntPtr length, IntPtr[] data);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_exporttype_vec_copy(out wasm_exporttype_vec_t vec, ref wasm_exporttype_vec_t src);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_exporttype_vec_delete(ref wasm_exporttype_vec_t vec);
 
         // Import type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe wasm_byte_vec_t* wasm_importtype_module(IntPtr importType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe wasm_byte_vec_t* wasm_importtype_name(IntPtr importType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe IntPtr wasm_importtype_type(IntPtr importType);
 
         // Export type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe wasm_byte_vec_t* wasm_exporttype_name(IntPtr exportType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe IntPtr wasm_exporttype_type(IntPtr exportType);
 
         // Module imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern ModuleHandle wasm_module_new(StoreHandle store, ref wasm_byte_vec_t bytes);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_module_imports(ModuleHandle module, out wasm_importtype_vec_t imports);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_module_exports(ModuleHandle module, out wasm_exporttype_vec_t exports);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_module_delete(IntPtr module);
 
         // Value type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern ValueTypeHandle wasm_valtype_new(wasm_valkind_t kind);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_valtype_delete(IntPtr valueType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern ValueKind wasm_valtype_kind(IntPtr valueType);
 
         // Extern imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern wasm_externkind_t wasm_extern_kind(IntPtr ext);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_extern_type(IntPtr ext);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_extern_as_func(IntPtr ext);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_extern_as_global(IntPtr ext);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_extern_as_table(IntPtr ext);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_extern_as_memory(IntPtr ext);
 
         // Extern type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern wasm_externkind_t wasm_externtype_kind(IntPtr externType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_externtype_as_functype_const(IntPtr externType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_externtype_as_globaltype_const(IntPtr externType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_externtype_as_tabletype_const(IntPtr externType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_externtype_as_memorytype_const(IntPtr externType);
 
         // Function imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern FunctionHandle wasm_func_new(StoreHandle store, FuncTypeHandle type, WasmFuncCallback callback);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_func_delete(IntPtr function);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern IntPtr wasm_func_call(IntPtr function, wasm_val_t* args, wasm_val_t* results);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_func_as_extern(FunctionHandle function);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_global_as_extern(GlobalHandle global);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_memory_as_extern(MemoryHandle memory);
 
         // Function type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe wasm_valtype_vec_t* wasm_functype_params(IntPtr funcType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe wasm_valtype_vec_t* wasm_functype_results(IntPtr funcType);
 
         // Instance imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe InstanceHandle wasm_instance_new(StoreHandle store, ModuleHandle module, IntPtr[] imports, out IntPtr trap);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_instance_delete(IntPtr ext);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_instance_exports(InstanceHandle instance, out wasm_extern_vec_t exports);
 
         // Function type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern FuncTypeHandle wasm_functype_new(ref wasm_valtype_vec_t parameters, ref wasm_valtype_vec_t results);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_functype_delete(IntPtr functype);
 
         // Global type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern GlobalTypeHandle wasm_globaltype_new(IntPtr valueType, wasm_mutability_t mutability);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_globaltype_delete(IntPtr globalType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_globaltype_content(IntPtr globalType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern wasm_mutability_t wasm_globaltype_mutability(IntPtr globalType);
 
         // Memory type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe MemoryTypeHandle wasm_memorytype_new(wasm_limits_t* limits);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_memorytype_delete(IntPtr memoryType);
 
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern unsafe wasm_limits_t* wasm_memorytype_limits(MemoryTypeHandle memoryType);
 
         // Trap imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_trap_new(StoreHandle store, ref wasm_byte_vec_t message);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_trap_delete(IntPtr trap);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_trap_message(IntPtr trap, out wasm_byte_vec_t message);
 
         // Table type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_tabletype_element(IntPtr tableType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern wasm_limits_t* wasm_tabletype_limits(IntPtr tableType);
 
         // Memory type imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern wasm_limits_t* wasm_memorytype_limits(IntPtr memoryType);
 
         // Global imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern GlobalHandle wasm_global_new(StoreHandle handle, GlobalTypeHandle globalType, wasm_val_t* initialValue);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_global_delete(IntPtr global);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_global_type(IntPtr global);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern void wasm_global_get(IntPtr global, wasm_val_t* value);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern void wasm_global_set(IntPtr global, wasm_val_t* value);
 
         // Memory imports
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern MemoryHandle wasm_memory_new(StoreHandle handle, MemoryTypeHandle memoryType);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern void wasm_memory_delete(IntPtr memory);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern IntPtr wasm_memory_type(MemoryHandle memory);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static unsafe extern byte* wasm_memory_data(IntPtr memory);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern UIntPtr wasm_memory_data_size(IntPtr memory);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern uint wasm_memory_size(MemoryHandle memory);
 
-        [DllImport("wasmtime")]
+        [DllImport(LibraryName)]
         public static extern bool wasm_memory_grow(MemoryHandle memory, uint delta);
+
+        // WASI config
+
+        [DllImport(LibraryName)]
+        public static extern WasiConfigHandle wasi_config_new();
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_config_delete(IntPtr config);
+
+        [DllImport(LibraryName)]
+        public unsafe static extern void wasi_config_set_argv(WasiConfigHandle config, int argc, byte*[] argv);
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_config_inherit_argv(WasiConfigHandle config);
+
+        [DllImport(LibraryName)]
+        public static extern unsafe void wasi_config_set_env(
+            WasiConfigHandle config,
+            int envc,
+            byte*[] names,
+            byte*[] values
+        );
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_config_inherit_env(WasiConfigHandle config);
+
+        [DllImport(LibraryName)]
+        public static extern bool wasi_config_set_stdin_file(
+            WasiConfigHandle config,
+            [MarshalAs(UnmanagedType.LPUTF8Str)] string path
+        ); 
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_config_inherit_stdin(WasiConfigHandle config);
+
+        [DllImport(LibraryName)]
+        public static extern bool wasi_config_set_stdout_file(
+            WasiConfigHandle config,
+            [MarshalAs(UnmanagedType.LPUTF8Str)] string path
+        ); 
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_config_inherit_stdout(WasiConfigHandle config);
+
+        [DllImport(LibraryName)]
+        public static extern bool wasi_config_set_stderr_file(
+            WasiConfigHandle config,
+            [MarshalAs(UnmanagedType.LPUTF8Str)] string path
+        ); 
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_config_inherit_stderr(WasiConfigHandle config);
+
+        [DllImport(LibraryName)]
+        public static extern bool wasi_config_preopen_dir(
+            WasiConfigHandle config,
+            [MarshalAs(UnmanagedType.LPUTF8Str)] string path,
+            [MarshalAs(UnmanagedType.LPUTF8Str)] string guestPath
+        );
+
+        // WASI instance
+        [DllImport(LibraryName)]
+        public static extern WasiInstanceHandle wasi_instance_new(
+            StoreHandle store,
+            WasiConfigHandle config,
+            out IntPtr trap
+        );
+
+        [DllImport(LibraryName)]
+        public static extern void wasi_instance_delete(IntPtr instance);
+
+        [DllImport(LibraryName)]
+        public static extern IntPtr wasi_instance_bind_import(WasiInstanceHandle instance, IntPtr importType);
     }
 }

crates/misc/dotnet/src/Module.cs

@@ -49,20 +49,33 @@ namespace Wasmtime
         /// </summary>
         /// <param name="host">The host to use for the WebAssembly module's instance.</param>
         /// <returns>Returns a new <see cref="Instance" />.</returns>
-        public Instance Instantiate(IHost host)
+        public Instance Instantiate(IHost host = null)
         {
-            if (host is null)
-            {
-                throw new ArgumentNullException(nameof(host));
-            }
+            return Instantiate(null, host);
+        }
 
-            if (host.Instance != null)
+        /// <summary>
+        /// Instantiates a WebAssembly module for the given host.
+        /// </summary>
+        /// <param name="wasi">The WASI instance to use for WASI imports.</param>
+        /// <param name="host">The host to use for the WebAssembly module's instance.</param>
+        /// <returns>Returns a new <see cref="Instance" />.</returns>
+        public Instance Instantiate(Wasi wasi, IHost host = null)
+        {
+            if (!(host?.Instance is null))
             {
                 throw new InvalidOperationException("The host has already been associated with an instantiated module.");
             }
 
-            host.Instance = new Instance(this, host);
-            return host.Instance;
+            var instance = new Instance(this, wasi, host);
+
+            if (!(host is null))
+            {
+                host.Instance = instance;
+                return instance;
+            }
+
+            return instance;
         }
 
         /// <summary>
@@ -94,6 +107,11 @@ namespace Wasmtime
                 Handle.Dispose();
                 Handle.SetHandleAsInvalid();
             }
+            if (!(Imports is null))
+            {
+                Imports.Dispose();
+                Imports = null;
+            }
         }
 
         internal Interop.ModuleHandle Handle { get; private set; }

crates/misc/dotnet/src/TrapException.cs

@@ -29,9 +29,11 @@ namespace Wasmtime
                 Interop.wasm_trap_message(trap, out var bytes);
                 var byteSpan = new ReadOnlySpan<byte>(bytes.data, checked((int)bytes.size));
 
-                int indexOfNull = byteSpan.IndexOf((byte)0);
+                int indexOfNull = byteSpan.LastIndexOf((byte)0);
                 if (indexOfNull != -1)
+                {
                     byteSpan = byteSpan.Slice(0, indexOfNull);
+                }
 
                 var message = Encoding.UTF8.GetString(byteSpan);
                 Interop.wasm_byte_vec_delete(ref bytes);

crates/misc/dotnet/src/Wasi.cs

@@ -0,0 +1,44 @@
+using System;
+using Wasmtime.Bindings;
+using Wasmtime.Imports;
+
+namespace Wasmtime
+{
+    public class Wasi
+    {
+        /// <summary>
+        /// Creates a default <see cref="Wasi"/> instance.
+        /// </summary>
+        public Wasi(Store store) :
+            this(
+                (store ?? throw new ArgumentNullException(nameof(store))).Handle,
+                Interop.wasi_config_new()
+            )
+        {
+        }
+
+        internal Wasi(Interop.StoreHandle store, Interop.WasiConfigHandle config)
+        {
+            IntPtr trap;
+            Handle = Interop.wasi_instance_new(store, config, out trap);
+            config.SetHandleAsInvalid();
+
+            if (trap != IntPtr.Zero)
+            {
+                throw TrapException.FromOwnedTrap(trap);
+            }
+        }
+
+        internal WasiBinding Bind(Import import)
+        {
+            var export = Interop.wasi_instance_bind_import(Handle, import.Handle);
+            if (export == IntPtr.Zero)
+            {
+                return null;
+            }
+            return new WasiBinding(export);
+        }
+
+        internal Interop.WasiInstanceHandle Handle { get; private set; }
+    }   
+}

crates/misc/dotnet/src/WasiBuilder.cs

@@ -0,0 +1,409 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Wasmtime
+{
+    /// <summary>
+    /// Represents a build of WASI instances.
+    /// </summary>
+    public class WasiBuilder
+    {
+        /// <summary>
+        /// Constructs a new <see cref="WasiBuilder" />.
+        /// </summary>
+        public WasiBuilder()
+        {
+        }
+
+        /// <summary>
+        /// Adds a command line argument to the builder.
+        /// </summary>
+        /// <param name="arg">The command line argument to add.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithArg(string arg)
+        {
+            if (arg is null)
+            {
+                throw new ArgumentNullException(nameof(arg));
+            }
+
+            if (_inheritArgs)
+            {
+                _args.Clear();
+                _inheritArgs = false;
+            }
+
+            _args.Add(arg);
+            return this;
+        }
+
+        /// <summary>
+        /// Adds multiple command line arguments to the builder.
+        /// </summary>
+        /// <param name="args">The command line arguments to add.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithArgs(IEnumerable<string> args)
+        {
+            if (args is null)
+            {
+                throw new ArgumentNullException(nameof(args));
+            }
+
+            if (_inheritArgs)
+            {
+                _args.Clear();
+                _inheritArgs = false;
+            }
+            
+            foreach (var arg in args)
+            {
+                _args.Add(arg);
+            }
+            return this;
+        }
+
+        /// <summary>
+        /// Adds multiple command line arguments to the builder.
+        /// </summary>
+        /// <param name="args">The command line arguments to add.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithArgs(params string[] args)
+        {
+            return WithArgs((IEnumerable<string>)args);
+        }
+
+        /// <summary>
+        /// Sets the builder to inherit command line arguments.
+        /// </summary>
+        /// <remarks>Any explicitly specified command line arguments will be removed.</remarks>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithInheritedArgs()
+        {
+            _inheritArgs = true;
+            _args.Clear();
+            _args.AddRange(Environment.GetCommandLineArgs());
+            return this;
+        }
+
+        /// <summary>
+        /// Adds an environment variable to the builder.
+        /// </summary>
+        /// <param name="name">The name of the environment variable.</param>
+        /// <param name="value">The value of the environment variable.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithEnvironmentVariable(string name, string value)
+        {
+            if (name is null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+            if (value is null)
+            {
+                throw new ArgumentNullException(nameof(value));
+            }
+
+            if (string.IsNullOrEmpty(name))
+            {
+                throw new ArgumentException("Environment variable name cannot be empty.", nameof(name));
+            }
+
+            _inheritEnv = false;
+            _vars.Add((name, value));
+            return this;
+        }
+
+        /// <summary>
+        /// Adds multiple environment variables to the builder.
+        /// </summary>
+        /// <param name="vars">The name-value tuples of the environment variables to add.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithEnvironmentVariables(IEnumerable<(string,string)> vars)
+        {
+            if (vars is null)
+            {
+                throw new ArgumentNullException(nameof(vars));
+            }
+
+            _inheritEnv = false;
+           
+            foreach (var v in vars)
+            {
+                _vars.Add(v);
+            }
+
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to inherit environment variables.
+        /// </summary>
+        /// <remarks>Any explicitly specified environment variables will be removed.</remarks>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithInheritedEnvironment()
+        {
+            _inheritEnv = true;
+            _vars.Clear();
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to use the given file path as stdin.
+        /// </summary>
+        /// <param name="path">The file to use as stdin.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithStandardInput(string path)
+        {
+            if (string.IsNullOrEmpty(path))
+            {
+                throw new ArgumentException("The path cannot be null or empty.", nameof(path));
+            }
+
+            _inheritStandardInput = false;
+            _standardInputPath = path;
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to inherit stdin.
+        /// </summary>
+        /// <remarks>Any explicitly specified stdin file will be removed.</remarks>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithInheritedStandardInput()
+        {
+            _inheritStandardInput = true;
+            _standardInputPath = null;
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to use the given file path as stdout.
+        /// </summary>
+        /// <param name="path">The file to use as stdout.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithStandardOutput(string path)
+        {
+            if (string.IsNullOrEmpty(path))
+            {
+                throw new ArgumentException("The path cannot be null or empty.", nameof(path));
+            }
+
+            _inheritStandardOutput = false;
+            _standardOutputPath = path;
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to inherit stdout.
+        /// </summary>
+        /// <remarks>Any explicitly specified stdout file will be removed.</remarks>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithInheritedStandardOutput()
+        {
+            _inheritStandardOutput = true;
+            _standardOutputPath = null;
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to use the given file path as stderr.
+        /// </summary>
+        /// <param name="path">The file to use as stderr.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithStandardError(string path)
+        {
+            if (string.IsNullOrEmpty(path))
+            {
+                throw new ArgumentException("The path cannot be null or empty.", nameof(path));
+            }
+
+            _inheritStandardError = false;
+            _standardErrorPath = path;
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the builder to inherit stderr.
+        /// </summary>
+        /// <remarks>Any explicitly specified stderr file will be removed.</remarks>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithInheritedStandardError()
+        {
+            _inheritStandardError = true;
+            _standardErrorPath = null;
+            return this;
+        }
+
+        /// <summary>
+        /// Adds a preopen directory to the builder.
+        /// </summary>
+        /// <param name="path">The path to the directory to add.</param>
+        /// <param name="guestPath">The path the guest will use to open the directory.</param>
+        /// <returns>Returns the current builder.</returns>
+        public WasiBuilder WithPreopenedDirectory(string path, string guestPath)
+        {
+            if (string.IsNullOrEmpty(path))
+            {
+                throw new ArgumentException("The path cannot be null or empty.", nameof(path));
+            }
+            if (string.IsNullOrEmpty(guestPath))
+            {
+                throw new ArgumentException("The guest path cannot be null or empty.", nameof(guestPath));
+            }
+
+            _preopenDirs.Add((path, guestPath));
+            return this;
+        }
+
+        /// <summary>
+        /// Builds the <see cref="Wasi" /> instance.
+        /// </summary>
+        /// <param name="store">The <see cref="Store" /> to use.</param>
+        /// <returns>Returns the new <see cref="Wasi" /> instance.</returns>
+        public Wasi Build(Store store)
+        {
+            var config = Interop.wasi_config_new();
+
+            SetConfigArgs(config);
+            SetEnvironmentVariables(config);
+            SetStandardIn(config);
+            SetStandardOut(config);
+            SetStandardError(config);
+            SetPreopenDirectories(config);
+            
+            return new Wasi(store.Handle, config);
+        }
+
+        private unsafe void SetConfigArgs(Interop.WasiConfigHandle config)
+        {
+            // Don't call wasi_config_inherit_argv as the command line to the .NET program may not be
+            // the same as the process' command line (e.g. `dotnet foo.dll foo bar baz` => "foo.dll foo bar baz").
+            if (_args.Count == 0)
+            {
+                return;
+            }
+
+            var (args, handles) = Interop.ToUTF8PtrArray(_args);
+            
+            try
+            {
+                Interop.wasi_config_set_argv(config, _args.Count, args);
+            }
+            finally
+            {
+                foreach (var handle in handles)
+                {
+                    handle.Free();
+                }
+            }
+        }
+
+        private unsafe void SetEnvironmentVariables(Interop.WasiConfigHandle config)
+        {
+            if (_inheritEnv)
+            {
+                Interop.wasi_config_inherit_env(config);
+                return;
+            }
+
+            if (_vars.Count == 0)
+            {
+                return;
+            }
+
+            var (names, nameHandles) = Interop.ToUTF8PtrArray(_vars.Select(var => var.Name).ToArray());
+            var (values, valueHandles) = Interop.ToUTF8PtrArray(_vars.Select(var => var.Value).ToArray());
+            
+            try
+            {
+                Interop.wasi_config_set_env(config, _vars.Count, names, values);
+            }
+            finally
+            {
+                foreach (var handle in nameHandles)
+                {
+                    handle.Free();
+                }
+
+                foreach (var handle in valueHandles)
+                {
+                    handle.Free();
+                }
+            }
+        }
+
+        private void SetStandardIn(Interop.WasiConfigHandle config)
+        {
+            if (_inheritStandardInput)
+            {
+                Interop.wasi_config_inherit_stdin(config);
+                return;
+            }
+
+            if (!string.IsNullOrEmpty(_standardInputPath))
+            {
+                if (!Interop.wasi_config_set_stdin_file(config, _standardInputPath))
+                {
+                    throw new InvalidOperationException($"Failed to set stdin to file '{_standardInputPath}'.");
+                }
+            }
+        }
+
+        private void SetStandardOut(Interop.WasiConfigHandle config)
+        {
+            if (_inheritStandardOutput)
+            {
+                Interop.wasi_config_inherit_stdout(config);
+                return;
+            }
+
+            if (!string.IsNullOrEmpty(_standardOutputPath))
+            {
+                if (!Interop.wasi_config_set_stdout_file(config, _standardOutputPath))
+                {
+                    throw new InvalidOperationException($"Failed to set stdout to file '{_standardOutputPath}'.");
+                }
+            }
+        }
+        
+        private void SetStandardError(Interop.WasiConfigHandle config)
+        {
+            if (_inheritStandardError)
+            {
+                Interop.wasi_config_inherit_stderr(config);
+                return;
+            }
+
+            if (!string.IsNullOrEmpty(_standardErrorPath))
+            {
+                if (!Interop.wasi_config_set_stderr_file(config, _standardErrorPath))
+                {
+                    throw new InvalidOperationException($"Failed to set stderr to file '{_standardErrorPath}'.");
+                }
+            }
+        }
+
+        private void SetPreopenDirectories(Interop.WasiConfigHandle config)
+        {
+            foreach (var dir in _preopenDirs)
+            {
+                if (!Interop.wasi_config_preopen_dir(config, dir.Path, dir.GuestPath))
+                {
+                    throw new InvalidOperationException($"Failed to preopen directory '{dir.Path}'.");
+                }
+            }
+        }
+
+        private readonly List<string> _args = new List<string>();
+        private readonly List<(string Name, string Value)> _vars = new List<(string, string)>();
+        private string _standardInputPath;
+        private string _standardOutputPath;
+        private string _standardErrorPath;
+        private readonly List<(string Path, string GuestPath)> _preopenDirs = new List<(string, string)>();
+        private bool _inheritArgs = false;
+        private bool _inheritEnv = false;
+        private bool _inheritStandardInput = false;
+        private bool _inheritStandardOutput = false;
+        private bool _inheritStandardError = false;
+    }   
+}

crates/misc/dotnet/tests/Fixtures/ModuleFixture.cs

@@ -15,19 +15,19 @@ namespace Wasmtime.Tests
 
         public void Dispose()
         {
-            if (Module != null)
+            if (!(Module is null))
             {
                 Module.Dispose();
                 Module = null;
             }
 
-            if (Store != null)
+            if (!(Store is null))
             {
                 Store.Dispose();
                 Store = null;
             }
 
-            if (Engine != null)
+            if (!(Engine is null))
             {
                 Engine.Dispose();
                 Engine = null;

crates/misc/dotnet/tests/FunctionThunkingTests.cs

@@ -12,7 +12,7 @@ namespace Wasmtime.Tests
 
     public class FunctionThunkingTests : IClassFixture<FunctionThunkingFixture>
     {
-        const string THROW_MESSAGE = "Test error messages for wasmtime dotnet bidnings unit tests.";
+        const string THROW_MESSAGE = "Test error message for wasmtime dotnet unit tests.";
 
         class MyHost : IHost
         {
@@ -36,36 +36,34 @@ namespace Wasmtime.Tests
         public void ItBindsImportMethodsAndCallsThemCorrectly()
         {
             var host = new MyHost();
-            using (var instance = Fixture.Module.Instantiate(host))
-            {
-                var add_func = instance.Externs.Functions.Where(f => f.Name == "add_wrapper").Single();
-                int invoke_add(int x, int y) => (int)add_func.Invoke(new object[] { x, y });
+            using var instance = Fixture.Module.Instantiate(host);
 
-                invoke_add(40, 2).Should().Be(42);
-                invoke_add(22, 5).Should().Be(27);
+            var add_func = instance.Externs.Functions.Where(f => f.Name == "add_wrapper").Single();
+            int invoke_add(int x, int y) => (int)add_func.Invoke(new object[] { x, y });
 
-                //Collect garbage to make sure delegate function pointers pasted to wasmtime are rooted.
-                GC.Collect();
-                GC.WaitForPendingFinalizers();
+            invoke_add(40, 2).Should().Be(42);
+            invoke_add(22, 5).Should().Be(27);
 
-                invoke_add(1970, 50).Should().Be(2020);
-            }
+            //Collect garbage to make sure delegate function pointers pasted to wasmtime are rooted.
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+
+            invoke_add(1970, 50).Should().Be(2020);
         }
 
         [Fact]
-        public void ItPropegatesExceptionsToCallersViaTraps()
+        public void ItPropagatesExceptionsToCallersViaTraps()
         {
             var host = new MyHost();
-            using (var instance = Fixture.Module.Instantiate(host))
-            {
-                var throw_func = instance.Externs.Functions.Where(f => f.Name == "do_throw_wrapper").Single();
-                Action action = () => throw_func.Invoke();
+            using var instance = Fixture.Module.Instantiate(host);
 
-                action
-                    .Should()
-                    .Throw<TrapException>()
-                    .WithMessage(THROW_MESSAGE);
-            }
+            var throw_func = instance.Externs.Functions.Where(f => f.Name == "do_throw_wrapper").Single();
+            Action action = () => throw_func.Invoke();
+
+            action
+                .Should()
+                .Throw<TrapException>()
+                .WithMessage(THROW_MESSAGE);
         }
     }
 }

crates/misc/dotnet/tests/GlobalExportsTests.cs

@@ -46,124 +46,123 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItCreatesExternsForTheGlobals()
         {
-            using (var instance = Fixture.Module.Instantiate(new Host()))
-            {
-                dynamic dyn = instance;
-                var globals = instance.Externs.Globals;
-                globals.Count.Should().Be(8);
+            using var instance = Fixture.Module.Instantiate(new Host());
 
-                var i32 = globals[0];
-                i32.Name.Should().Be("global_i32");
-                i32.Kind.Should().Be(ValueKind.Int32);
-                i32.IsMutable.Should().Be(false);
-                i32.Value.Should().Be(0);
+            dynamic dyn = instance;
+            var globals = instance.Externs.Globals;
+            globals.Count.Should().Be(8);
 
-                var i32Mut = globals[1];
-                i32Mut.Name.Should().Be("global_i32_mut");
-                i32Mut.Kind.Should().Be(ValueKind.Int32);
-                i32Mut.IsMutable.Should().Be(true);
-                i32Mut.Value.Should().Be(1);
-                i32Mut.Value = 11;
-                i32Mut.Value.Should().Be(11);
-                dyn.global_i32_mut = 12;
-                ((int)dyn.global_i32_mut).Should().Be(12);
-                i32Mut.Value.Should().Be(12);
+            var i32 = globals[0];
+            i32.Name.Should().Be("global_i32");
+            i32.Kind.Should().Be(ValueKind.Int32);
+            i32.IsMutable.Should().Be(false);
+            i32.Value.Should().Be(0);
 
-                var i64 = globals[2];
-                i64.Name.Should().Be("global_i64");
-                i64.Kind.Should().Be(ValueKind.Int64);
-                i64.IsMutable.Should().Be(false);
-                i64.Value.Should().Be(2);
+            var i32Mut = globals[1];
+            i32Mut.Name.Should().Be("global_i32_mut");
+            i32Mut.Kind.Should().Be(ValueKind.Int32);
+            i32Mut.IsMutable.Should().Be(true);
+            i32Mut.Value.Should().Be(1);
+            i32Mut.Value = 11;
+            i32Mut.Value.Should().Be(11);
+            dyn.global_i32_mut = 12;
+            ((int)dyn.global_i32_mut).Should().Be(12);
+            i32Mut.Value.Should().Be(12);
 
-                var i64Mut = globals[3];
-                i64Mut.Name.Should().Be("global_i64_mut");
-                i64Mut.Kind.Should().Be(ValueKind.Int64);
-                i64Mut.IsMutable.Should().Be(true);
-                i64Mut.Value.Should().Be(3);
-                i64Mut.Value = 13;
-                i64Mut.Value.Should().Be(13);
-                dyn.global_i64_mut = 14;
-                ((long)dyn.global_i64_mut).Should().Be(14);
-                i64Mut.Value.Should().Be(14);
+            var i64 = globals[2];
+            i64.Name.Should().Be("global_i64");
+            i64.Kind.Should().Be(ValueKind.Int64);
+            i64.IsMutable.Should().Be(false);
+            i64.Value.Should().Be(2);
 
-                var f32 = globals[4];
-                f32.Name.Should().Be("global_f32");
-                f32.Kind.Should().Be(ValueKind.Float32);
-                f32.IsMutable.Should().Be(false);
-                f32.Value.Should().Be(4);
+            var i64Mut = globals[3];
+            i64Mut.Name.Should().Be("global_i64_mut");
+            i64Mut.Kind.Should().Be(ValueKind.Int64);
+            i64Mut.IsMutable.Should().Be(true);
+            i64Mut.Value.Should().Be(3);
+            i64Mut.Value = 13;
+            i64Mut.Value.Should().Be(13);
+            dyn.global_i64_mut = 14;
+            ((long)dyn.global_i64_mut).Should().Be(14);
+            i64Mut.Value.Should().Be(14);
 
-                var f32Mut = globals[5];
-                f32Mut.Name.Should().Be("global_f32_mut");
-                f32Mut.Kind.Should().Be(ValueKind.Float32);
-                f32Mut.IsMutable.Should().Be(true);
-                f32Mut.Value.Should().Be(5);
-                f32Mut.Value = 15;
-                f32Mut.Value.Should().Be(15);
-                dyn.global_f32_mut = 16;
-                ((float)dyn.global_f32_mut).Should().Be(16);
-                f32Mut.Value.Should().Be(16);
+            var f32 = globals[4];
+            f32.Name.Should().Be("global_f32");
+            f32.Kind.Should().Be(ValueKind.Float32);
+            f32.IsMutable.Should().Be(false);
+            f32.Value.Should().Be(4);
 
-                var f64 = globals[6];
-                f64.Name.Should().Be("global_f64");
-                f64.Kind.Should().Be(ValueKind.Float64);
-                f64.IsMutable.Should().Be(false);
-                f64.Value.Should().Be(6);
+            var f32Mut = globals[5];
+            f32Mut.Name.Should().Be("global_f32_mut");
+            f32Mut.Kind.Should().Be(ValueKind.Float32);
+            f32Mut.IsMutable.Should().Be(true);
+            f32Mut.Value.Should().Be(5);
+            f32Mut.Value = 15;
+            f32Mut.Value.Should().Be(15);
+            dyn.global_f32_mut = 16;
+            ((float)dyn.global_f32_mut).Should().Be(16);
+            f32Mut.Value.Should().Be(16);
 
-                var f64Mut = globals[7];
-                f64Mut.Name.Should().Be("global_f64_mut");
-                f64Mut.Kind.Should().Be(ValueKind.Float64);
-                f64Mut.IsMutable.Should().Be(true);
-                f64Mut.Value.Should().Be(7);
-                f64Mut.Value = 17;
-                f64Mut.Value.Should().Be(17);
-                dyn.global_f64_mut = 17;
-                ((double)dyn.global_f64_mut).Should().Be(17);
-                f64Mut.Value.Should().Be(17);
+            var f64 = globals[6];
+            f64.Name.Should().Be("global_f64");
+            f64.Kind.Should().Be(ValueKind.Float64);
+            f64.IsMutable.Should().Be(false);
+            f64.Value.Should().Be(6);
 
-                Action action = () => i32.Value = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_i32' cannot be modified.");
-                action = () => dyn.global_i32 = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_i32' cannot be modified.");
+            var f64Mut = globals[7];
+            f64Mut.Name.Should().Be("global_f64_mut");
+            f64Mut.Kind.Should().Be(ValueKind.Float64);
+            f64Mut.IsMutable.Should().Be(true);
+            f64Mut.Value.Should().Be(7);
+            f64Mut.Value = 17;
+            f64Mut.Value.Should().Be(17);
+            dyn.global_f64_mut = 17;
+            ((double)dyn.global_f64_mut).Should().Be(17);
+            f64Mut.Value.Should().Be(17);
 
-                action = () => i64.Value = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_i64' cannot be modified.");
-                action = () => dyn.global_i64 = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_i64' cannot be modified.");
+            Action action = () => i32.Value = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_i32' cannot be modified.");
+            action = () => dyn.global_i32 = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_i32' cannot be modified.");
 
-                action = () => f32.Value = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_f32' cannot be modified.");
-                action = () => dyn.global_f32 = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_f32' cannot be modified.");
+            action = () => i64.Value = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_i64' cannot be modified.");
+            action = () => dyn.global_i64 = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_i64' cannot be modified.");
 
-                action = () => f64.Value = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_f64' cannot be modified.");
-                action = () => dyn.global_f64 = 0;
-                action
-                    .Should()
-                    .Throw<InvalidOperationException>()
-                    .WithMessage("The value of global 'global_f64' cannot be modified.");
-            }
+            action = () => f32.Value = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_f32' cannot be modified.");
+            action = () => dyn.global_f32 = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_f32' cannot be modified.");
+
+            action = () => f64.Value = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_f64' cannot be modified.");
+            action = () => dyn.global_f64 = 0;
+            action
+                .Should()
+                .Throw<InvalidOperationException>()
+                .WithMessage("The value of global 'global_f64' cannot be modified.");
         }
 
         public static IEnumerable<object[]> GetGlobalExports()

crates/misc/dotnet/tests/GlobalImportBindingTests.cs

@@ -118,7 +118,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithMissingImport()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new NoImportsHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new NoImportsHost()); };
 
             action
                 .Should()
@@ -129,7 +129,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithStaticField()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new GlobalIsStaticHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new GlobalIsStaticHost()); };
 
             action
                 .Should()
@@ -140,7 +140,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithNonReadOnlyField()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new GlobalIsNotReadOnlyHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new GlobalIsNotReadOnlyHost()); };
 
             action
                 .Should()
@@ -151,7 +151,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithInvalidType()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new NotAGlobalHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new NotAGlobalHost()); };
 
             action
                 .Should()
@@ -162,7 +162,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithInvalidGlobalType()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new NotAValidGlobalTypeHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new NotAValidGlobalTypeHost()); };
 
             action
                 .Should()
@@ -173,7 +173,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithGlobalTypeMismatch()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new TypeMismatchHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new TypeMismatchHost()); };
 
             action
                 .Should()
@@ -184,7 +184,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWhenGlobalIsNotMut()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new NotMutHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new NotMutHost()); };
 
             action
                 .Should()
@@ -195,7 +195,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWhenGlobalIsMut()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new MutHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new MutHost()); };
 
             action
                 .Should()
@@ -207,53 +207,52 @@ namespace Wasmtime.Tests
         public void ItBindsTheGlobalsCorrectly()
         {
             var host = new ValidHost();
-            using (dynamic instance = Fixture.Module.Instantiate(host))
-            {
-                host.Int32Mut.Value.Should().Be(0);
-                ((int)instance.get_global_i32_mut()).Should().Be(0);
-                host.Int32.Value.Should().Be(1);
-                ((int)instance.get_global_i32()).Should().Be(1);
-                host.Int64Mut.Value.Should().Be(2);
-                ((long)instance.get_global_i64_mut()).Should().Be(2);
-                host.Int64.Value.Should().Be(3);
-                ((long)instance.get_global_i64()).Should().Be(3);
-                host.Float32Mut.Value.Should().Be(4);
-                ((float)instance.get_global_f32_mut()).Should().Be(4);
-                host.Float32.Value.Should().Be(5);
-                ((float)instance.get_global_f32()).Should().Be(5);
-                host.Float64Mut.Value.Should().Be(6);
-                ((double)instance.get_global_f64_mut()).Should().Be(6);
-                host.Float64.Value.Should().Be(7);
-                ((double)instance.get_global_f64()).Should().Be(7);
+            using dynamic instance = Fixture.Module.Instantiate(host);
 
-                host.Int32Mut.Value = 10;
-                host.Int32Mut.Value.Should().Be(10);
-                ((int)instance.get_global_i32_mut()).Should().Be(10);
-                instance.set_global_i32_mut(11);
-                host.Int32Mut.Value.Should().Be(11);
-                ((int)instance.get_global_i32_mut()).Should().Be(11);
+            host.Int32Mut.Value.Should().Be(0);
+            ((int)instance.get_global_i32_mut()).Should().Be(0);
+            host.Int32.Value.Should().Be(1);
+            ((int)instance.get_global_i32()).Should().Be(1);
+            host.Int64Mut.Value.Should().Be(2);
+            ((long)instance.get_global_i64_mut()).Should().Be(2);
+            host.Int64.Value.Should().Be(3);
+            ((long)instance.get_global_i64()).Should().Be(3);
+            host.Float32Mut.Value.Should().Be(4);
+            ((float)instance.get_global_f32_mut()).Should().Be(4);
+            host.Float32.Value.Should().Be(5);
+            ((float)instance.get_global_f32()).Should().Be(5);
+            host.Float64Mut.Value.Should().Be(6);
+            ((double)instance.get_global_f64_mut()).Should().Be(6);
+            host.Float64.Value.Should().Be(7);
+            ((double)instance.get_global_f64()).Should().Be(7);
 
-                host.Int64Mut.Value = 12;
-                host.Int64Mut.Value.Should().Be(12);
-                ((long)instance.get_global_i64_mut()).Should().Be(12);
-                instance.set_global_i64_mut(13);
-                host.Int64Mut.Value.Should().Be(13);
-                ((long)instance.get_global_i64_mut()).Should().Be(13);
+            host.Int32Mut.Value = 10;
+            host.Int32Mut.Value.Should().Be(10);
+            ((int)instance.get_global_i32_mut()).Should().Be(10);
+            instance.set_global_i32_mut(11);
+            host.Int32Mut.Value.Should().Be(11);
+            ((int)instance.get_global_i32_mut()).Should().Be(11);
 
-                host.Float32Mut.Value = 14;
-                host.Float32Mut.Value.Should().Be(14);
-                ((float)instance.get_global_f32_mut()).Should().Be(14);
-                instance.set_global_f32_mut(15);
-                host.Float32Mut.Value.Should().Be(15);
-                ((float)instance.get_global_f32_mut()).Should().Be(15);
+            host.Int64Mut.Value = 12;
+            host.Int64Mut.Value.Should().Be(12);
+            ((long)instance.get_global_i64_mut()).Should().Be(12);
+            instance.set_global_i64_mut(13);
+            host.Int64Mut.Value.Should().Be(13);
+            ((long)instance.get_global_i64_mut()).Should().Be(13);
 
-                host.Float64Mut.Value = 16;
-                host.Float64Mut.Value.Should().Be(16);
-                ((double)instance.get_global_f64_mut()).Should().Be(16);
-                instance.set_global_f64_mut(17);
-                host.Float64Mut.Value.Should().Be(17);
-                ((double)instance.get_global_f64_mut()).Should().Be(17);
-            }
+            host.Float32Mut.Value = 14;
+            host.Float32Mut.Value.Should().Be(14);
+            ((float)instance.get_global_f32_mut()).Should().Be(14);
+            instance.set_global_f32_mut(15);
+            host.Float32Mut.Value.Should().Be(15);
+            ((float)instance.get_global_f32_mut()).Should().Be(15);
+
+            host.Float64Mut.Value = 16;
+            host.Float64Mut.Value.Should().Be(16);
+            ((double)instance.get_global_f64_mut()).Should().Be(16);
+            instance.set_global_f64_mut(17);
+            host.Float64Mut.Value.Should().Be(17);
+            ((double)instance.get_global_f64_mut()).Should().Be(17);
         }
     }
 }

crates/misc/dotnet/tests/MemoryExportsTests.cs

@@ -45,43 +45,42 @@ namespace Wasmtime.Tests
         public void ItCreatesExternsForTheMemories()
         {
             var host = new Host();
-            using (var instance = Fixture.Module.Instantiate(host))
-            {
-                instance.Externs.Memories.Count.Should().Be(1);
+            using var instance = Fixture.Module.Instantiate(host);
 
-                var memory = instance.Externs.Memories[0];
-                memory.ReadString(0, 11).Should().Be("Hello World");
-                int written = memory.WriteString(0, "WebAssembly Rocks!");
-                memory.ReadString(0, written).Should().Be("WebAssembly Rocks!");
+            instance.Externs.Memories.Count.Should().Be(1);
 
-                memory.ReadByte(20).Should().Be(1);
-                memory.WriteByte(20, 11);
-                memory.ReadByte(20).Should().Be(11);
+            var memory = instance.Externs.Memories[0];
+            memory.ReadString(0, 11).Should().Be("Hello World");
+            int written = memory.WriteString(0, "WebAssembly Rocks!");
+            memory.ReadString(0, written).Should().Be("WebAssembly Rocks!");
 
-                memory.ReadInt16(21).Should().Be(2);
-                memory.WriteInt16(21, 12);
-                memory.ReadInt16(21).Should().Be(12);
+            memory.ReadByte(20).Should().Be(1);
+            memory.WriteByte(20, 11);
+            memory.ReadByte(20).Should().Be(11);
 
-                memory.ReadInt32(23).Should().Be(3);
-                memory.WriteInt32(23, 13);
-                memory.ReadInt32(23).Should().Be(13);
+            memory.ReadInt16(21).Should().Be(2);
+            memory.WriteInt16(21, 12);
+            memory.ReadInt16(21).Should().Be(12);
 
-                memory.ReadInt64(27).Should().Be(4);
-                memory.WriteInt64(27, 14);
-                memory.ReadInt64(27).Should().Be(14);
+            memory.ReadInt32(23).Should().Be(3);
+            memory.WriteInt32(23, 13);
+            memory.ReadInt32(23).Should().Be(13);
 
-                memory.ReadSingle(35).Should().Be(5);
-                memory.WriteSingle(35, 15);
-                memory.ReadSingle(35).Should().Be(15);
+            memory.ReadInt64(27).Should().Be(4);
+            memory.WriteInt64(27, 14);
+            memory.ReadInt64(27).Should().Be(14);
 
-                memory.ReadDouble(39).Should().Be(6);
-                memory.WriteDouble(39, 16);
-                memory.ReadDouble(39).Should().Be(16);
+            memory.ReadSingle(35).Should().Be(5);
+            memory.WriteSingle(35, 15);
+            memory.ReadSingle(35).Should().Be(15);
 
-                memory.ReadIntPtr(48).Should().Be((IntPtr)7);
-                memory.WriteIntPtr(48, (IntPtr)17);
-                memory.ReadIntPtr(48).Should().Be((IntPtr)17);
-            }
+            memory.ReadDouble(39).Should().Be(6);
+            memory.WriteDouble(39, 16);
+            memory.ReadDouble(39).Should().Be(16);
+
+            memory.ReadIntPtr(48).Should().Be((IntPtr)7);
+            memory.WriteIntPtr(48, (IntPtr)17);
+            memory.ReadIntPtr(48).Should().Be((IntPtr)17);
         }
 
         public static IEnumerable<object[]> GetMemoryExports()

crates/misc/dotnet/tests/MemoryImportBindingTests.cs

@@ -74,7 +74,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithMissingImport()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new MissingImportsHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new MissingImportsHost()); };
 
             action
                 .Should()
@@ -85,7 +85,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithStaticField()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new MemoryIsStaticHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new MemoryIsStaticHost()); };
 
             action
                 .Should()
@@ -96,7 +96,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithNonReadOnlyField()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new MemoryIsNotReadOnlyHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new MemoryIsNotReadOnlyHost()); };
 
             action
                 .Should()
@@ -107,7 +107,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWithInvalidType()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new NotAMemoryHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new NotAMemoryHost()); };
 
             action
                 .Should()
@@ -118,7 +118,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWhenMemoryHasInvalidMinimum()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new InvalidMinimumHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new InvalidMinimumHost()); };
 
             action
                 .Should()
@@ -129,7 +129,7 @@ namespace Wasmtime.Tests
         [Fact]
         public void ItFailsToInstantiateWhenMemoryHasInvalidMaximum()
         {
-            Action action = () => { using (var instance = Fixture.Module.Instantiate(new InvalidMaximumHost())) { } };
+            Action action = () => { using var instance = Fixture.Module.Instantiate(new InvalidMaximumHost()); };
 
             action
                 .Should()
@@ -141,47 +141,46 @@ namespace Wasmtime.Tests
         public void ItBindsTheGlobalsCorrectly()
         {
             var host = new ValidHost();
-            using (dynamic instance = Fixture.Module.Instantiate(host))
-            {
-                host.Mem.ReadString(0, 11).Should().Be("Hello World");
-                int written = host.Mem.WriteString(0, "WebAssembly Rocks!");
-                host.Mem.ReadString(0, written).Should().Be("WebAssembly Rocks!");
+            using dynamic instance = Fixture.Module.Instantiate(host);
 
-                host.Mem.ReadByte(20).Should().Be(1);
-                host.Mem.WriteByte(20, 11);
-                host.Mem.ReadByte(20).Should().Be(11);
-                ((byte)instance.ReadByte()).Should().Be(11);
+            host.Mem.ReadString(0, 11).Should().Be("Hello World");
+            int written = host.Mem.WriteString(0, "WebAssembly Rocks!");
+            host.Mem.ReadString(0, written).Should().Be("WebAssembly Rocks!");
 
-                host.Mem.ReadInt16(21).Should().Be(2);
-                host.Mem.WriteInt16(21, 12);
-                host.Mem.ReadInt16(21).Should().Be(12);
-                ((short)instance.ReadInt16()).Should().Be(12);
+            host.Mem.ReadByte(20).Should().Be(1);
+            host.Mem.WriteByte(20, 11);
+            host.Mem.ReadByte(20).Should().Be(11);
+            ((byte)instance.ReadByte()).Should().Be(11);
 
-                host.Mem.ReadInt32(23).Should().Be(3);
-                host.Mem.WriteInt32(23, 13);
-                host.Mem.ReadInt32(23).Should().Be(13);
-                ((int)instance.ReadInt32()).Should().Be(13);
+            host.Mem.ReadInt16(21).Should().Be(2);
+            host.Mem.WriteInt16(21, 12);
+            host.Mem.ReadInt16(21).Should().Be(12);
+            ((short)instance.ReadInt16()).Should().Be(12);
 
-                host.Mem.ReadInt64(27).Should().Be(4);
-                host.Mem.WriteInt64(27, 14);
-                host.Mem.ReadInt64(27).Should().Be(14);
-                ((long)instance.ReadInt64()).Should().Be(14);
+            host.Mem.ReadInt32(23).Should().Be(3);
+            host.Mem.WriteInt32(23, 13);
+            host.Mem.ReadInt32(23).Should().Be(13);
+            ((int)instance.ReadInt32()).Should().Be(13);
 
-                host.Mem.ReadSingle(35).Should().Be(5);
-                host.Mem.WriteSingle(35, 15);
-                host.Mem.ReadSingle(35).Should().Be(15);
-                ((float)instance.ReadFloat32()).Should().Be(15);
+            host.Mem.ReadInt64(27).Should().Be(4);
+            host.Mem.WriteInt64(27, 14);
+            host.Mem.ReadInt64(27).Should().Be(14);
+            ((long)instance.ReadInt64()).Should().Be(14);
 
-                host.Mem.ReadDouble(39).Should().Be(6);
-                host.Mem.WriteDouble(39, 16);
-                host.Mem.ReadDouble(39).Should().Be(16);
-                ((double)instance.ReadFloat64()).Should().Be(16);
+            host.Mem.ReadSingle(35).Should().Be(5);
+            host.Mem.WriteSingle(35, 15);
+            host.Mem.ReadSingle(35).Should().Be(15);
+            ((float)instance.ReadFloat32()).Should().Be(15);
 
-                host.Mem.ReadIntPtr(48).Should().Be((IntPtr)7);
-                host.Mem.WriteIntPtr(48, (IntPtr)17);
-                host.Mem.ReadIntPtr(48).Should().Be((IntPtr)17);
-                ((IntPtr)instance.ReadIntPtr()).Should().Be((IntPtr)17);
-            }
+            host.Mem.ReadDouble(39).Should().Be(6);
+            host.Mem.WriteDouble(39, 16);
+            host.Mem.ReadDouble(39).Should().Be(16);
+            ((double)instance.ReadFloat64()).Should().Be(16);
+
+            host.Mem.ReadIntPtr(48).Should().Be((IntPtr)7);
+            host.Mem.WriteIntPtr(48, (IntPtr)17);
+            host.Mem.ReadIntPtr(48).Should().Be((IntPtr)17);
+            ((IntPtr)instance.ReadIntPtr()).Should().Be((IntPtr)17);
         }
     }
 }

crates/misc/dotnet/tests/Modules/Wasi.wat

@@ -0,0 +1,66 @@
+(module
+  (type $t0 (func (param i32 i32) (result i32)))
+  (type $t1 (func (param i32 i32 i32 i32) (result i32)))
+  (type $t2 (func (param i32) (result i32)))
+  (type $t3 (func (param i32 i32 i32 i32 i32 i64 i64 i32 i32) (result i32)))
+  (import "wasi_snapshot_preview1" "environ_sizes_get" (func $wasi_snapshot_preview1.environ_sizes_get (type $t0)))
+  (import "wasi_snapshot_preview1" "environ_get" (func $wasi_snapshot_preview1.environ_get (type $t0)))
+  (import "wasi_snapshot_preview1" "args_sizes_get" (func $wasi_snapshot_preview1.args_sizes_get (type $t0)))
+  (import "wasi_snapshot_preview1" "args_get" (func $wasi_snapshot_preview1.args_get (type $t0)))
+  (import "wasi_snapshot_preview1" "fd_write" (func $wasi_snapshot_preview1.fd_write (type $t1)))
+  (import "wasi_snapshot_preview1" "fd_read" (func $wasi_snapshot_preview1.fd_read (type $t1)))
+  (import "wasi_snapshot_preview1" "fd_close" (func $wasi_snapshot_preview1.fd_close (type $t2)))
+  (import "wasi_snapshot_preview1" "path_open" (func $wasi_snapshot_preview1.path_open (type $t3)))
+  (memory $memory 1)
+  (export "memory" (memory 0))
+  (func $call_environ_sizes_get (type $t0) (param $p0 i32) (param $p1 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    call $wasi_snapshot_preview1.environ_sizes_get)
+  (func $call_environ_get (type $t0) (param $p0 i32) (param $p1 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    call $wasi_snapshot_preview1.environ_get)
+  (func $call_args_sizes_get (type $t0) (param $p0 i32) (param $p1 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    call $wasi_snapshot_preview1.args_sizes_get)
+  (func $call_args_get (type $t0) (param $p0 i32) (param $p1 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    call $wasi_snapshot_preview1.args_get)
+  (func $call_fd_write (type $t1) (param $p0 i32) (param $p1 i32) (param $p2 i32) (param $p3 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    local.get $p2
+    local.get $p3
+    call $wasi_snapshot_preview1.fd_write)
+  (func $call_fd_read (type $t1) (param $p0 i32) (param $p1 i32) (param $p2 i32) (param $p3 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    local.get $p2
+    local.get $p3
+    call $wasi_snapshot_preview1.fd_read)
+  (func $call_fd_close (type $t2) (param $p0 i32) (result i32)
+    local.get $p0
+    call $wasi_snapshot_preview1.fd_close)
+  (func $call_path_open (type $t3) (param $p0 i32) (param $p1 i32) (param $p2 i32) (param $p3 i32) (param $p4 i32) (param $p5 i64) (param $p6 i64) (param $p7 i32) (param $p8 i32) (result i32)
+    local.get $p0
+    local.get $p1
+    local.get $p2
+    local.get $p3
+    local.get $p4
+    local.get $p5
+    local.get $p6
+    local.get $p7
+    local.get $p8
+    call $wasi_snapshot_preview1.path_open)
+  (export "call_environ_sizes_get" (func $call_environ_sizes_get))
+  (export "call_environ_get" (func $call_environ_get))
+  (export "call_args_sizes_get" (func $call_args_sizes_get))
+  (export "call_args_get" (func $call_args_get))
+  (export "call_fd_write" (func $call_fd_write))
+  (export "call_fd_read" (func $call_fd_read))
+  (export "call_fd_close" (func $call_fd_close))
+  (export "call_path_open" (func $call_path_open))
+)

crates/misc/dotnet/tests/TempFile.cs

@@ -0,0 +1,24 @@
+using System;
+using System.IO;
+
+namespace Wasmtime.Tests
+{
+    internal class TempFile : IDisposable
+    {
+        public TempFile()
+        {
+            Path = System.IO.Path.GetTempFileName();
+        }
+
+        public void Dispose()
+        {
+            if (Path != null)
+            {
+                File.Delete(Path);
+                Path = null;
+            }
+        }
+
+        public string Path { get; private set; }
+    }
+}

crates/misc/dotnet/tests/WasiTests.cs

@@ -0,0 +1,246 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.IO;
+using FluentAssertions;
+using Xunit;
+
+namespace Wasmtime.Tests
+{
+    public class WasiFixture : ModuleFixture
+    {
+        protected override string ModuleFileName => "Wasi.wasm";
+    }
+
+    public class WasiTests : IClassFixture<WasiFixture>
+    {
+        public WasiTests(WasiFixture fixture)
+        {
+            Fixture = fixture;
+        }
+
+        private WasiFixture Fixture { get; set; }
+
+        [Fact]
+        public void ItHasNoEnvironmentByDefault()
+        {
+            using var instance = Fixture.Module.Instantiate(new Wasi(Fixture.Module.Store));
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+
+            Assert.Equal(0, inst.call_environ_sizes_get(0, 4));
+            Assert.Equal(0, memory.ReadInt32(0));
+            Assert.Equal(0, memory.ReadInt32(4));
+        }
+
+        [Fact]
+        public void ItHasSpecifiedEnvironment()
+        {
+            var env = new Dictionary<string, string>() {
+                {"FOO", "BAR"},
+                {"WASM", "IS"},
+                {"VERY", "COOL"},
+            };
+
+            var wasi = new WasiBuilder()
+                .WithEnvironmentVariables(env.Select(kvp => (kvp.Key, kvp.Value)))
+                .Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+
+            Assert.Equal(0, inst.call_environ_sizes_get(0, 4));
+            Assert.Equal(env.Count, memory.ReadInt32(0));
+            Assert.Equal(env.Sum(kvp => kvp.Key.Length + kvp.Value.Length + 2), memory.ReadInt32(4));
+            Assert.Equal(0, inst.call_environ_get(0, 4 * env.Count));
+
+            for (int i = 0; i < env.Count; ++i)
+            {
+                var kvp = memory.ReadNullTerminatedString(memory.ReadInt32(i * 4)).Split("=");
+                Assert.Equal(env[kvp[0]], kvp[1]);
+            }
+        }
+
+        [Fact]
+        public void ItInheritsEnvironment()
+        {
+            var wasi = new WasiBuilder()
+                .WithInheritedEnvironment()
+                .Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+
+            Assert.Equal(0, inst.call_environ_sizes_get(0, 4));
+            Assert.Equal(Environment.GetEnvironmentVariables().Keys.Count, memory.ReadInt32(0));
+        }
+
+        [Fact]
+        public void ItHasNoArgumentsByDefault()
+        {
+            using var instance = Fixture.Module.Instantiate(new Wasi(Fixture.Module.Store));
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+
+            Assert.Equal(0, inst.call_args_sizes_get(0, 4));
+            Assert.Equal(0, memory.ReadInt32(0));
+            Assert.Equal(0, memory.ReadInt32(4));
+        }
+
+        [Fact]
+        public void ItHasSpecifiedArguments()
+        {
+            var args = new List<string>() {
+                "WASM",
+                "IS",
+                "VERY",
+                "COOL"
+            };
+
+            var wasi = new WasiBuilder()
+                .WithArgs(args)
+                .Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+
+            Assert.Equal(0, inst.call_args_sizes_get(0, 4));
+            Assert.Equal(args.Count, memory.ReadInt32(0));
+            Assert.Equal(args.Sum(a => a.Length + 1), memory.ReadInt32(4));
+            Assert.Equal(0, inst.call_args_get(0, 4 * args.Count));
+
+            for (int i = 0; i < args.Count; ++i)
+            {
+                var arg = memory.ReadNullTerminatedString(memory.ReadInt32(i * 4));
+                Assert.Equal(args[i], arg);
+            }
+        }
+
+        [Fact]
+        public void ItInheritsArguments()
+        {
+            var wasi = new WasiBuilder()
+                .WithInheritedArgs()
+                .Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+
+            Assert.Equal(0, inst.call_args_sizes_get(0, 4));
+            Assert.Equal(Environment.GetCommandLineArgs().Length, memory.ReadInt32(0));
+        }
+
+        [Fact]
+        public void ItSetsStdIn()
+        {
+            const string MESSAGE = "WASM IS VERY COOL";
+
+            using var file = new TempFile();
+            File.WriteAllText(file.Path, MESSAGE);
+
+            var wasi = new WasiBuilder()
+                .WithStandardInput(file.Path)
+                .Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+            memory.WriteInt32(0, 8);
+            memory.WriteInt32(4, MESSAGE.Length);
+
+            Assert.Equal(0, inst.call_fd_read(0, 0, 1, 32));
+            Assert.Equal(MESSAGE.Length, memory.ReadInt32(32));
+            Assert.Equal(MESSAGE, memory.ReadString(8, MESSAGE.Length));
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        public void ItSetsStdOutAndStdErr(int fd)
+        {
+            const string MESSAGE = "WASM IS VERY COOL";
+
+            using var file = new TempFile();
+
+            var builder = new WasiBuilder();
+            if (fd == 1)
+            {
+                builder.WithStandardOutput(file.Path);
+            }
+            else if (fd == 2)
+            {
+                builder.WithStandardError(file.Path);
+            }
+
+            var wasi = builder.Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+            memory.WriteInt32(0, 8);
+            memory.WriteInt32(4, MESSAGE.Length);
+            memory.WriteString(8, MESSAGE);
+
+            Assert.Equal(0, inst.call_fd_write(fd, 0, 1, 32));
+            Assert.Equal(MESSAGE.Length, memory.ReadInt32(32));
+            Assert.Equal(0, inst.call_fd_close(fd));
+            Assert.Equal(MESSAGE, File.ReadAllText(file.Path));
+        }
+
+        [Fact]
+        public void ItSetsPreopenDirectories()
+        {
+            const string MESSAGE = "WASM IS VERY COOL";
+
+            using var file = new TempFile();
+
+            var wasi = new WasiBuilder()
+                .WithPreopenedDirectory(Path.GetDirectoryName(file.Path), "/foo")
+                .Build(Fixture.Module.Store);
+
+            using var instance = Fixture.Module.Instantiate(wasi);
+            dynamic inst = instance;
+
+            var memory = instance.Externs.Memories[0];
+            var fileName = Path.GetFileName(file.Path);
+            memory.WriteString(0, fileName);
+
+            Assert.Equal(0, inst.call_path_open(
+                    3,
+                    0,
+                    0,
+                    fileName.Length,
+                    0,
+                    0x40 /* RIGHTS_FD_WRITE */,
+                    0,
+                    0,
+                    64
+                )
+            );
+
+            var fileFd = (int) memory.ReadInt32(64);
+            Assert.True(fileFd > 3);
+
+            memory.WriteInt32(0, 8);
+            memory.WriteInt32(4, MESSAGE.Length);
+            memory.WriteString(8, MESSAGE);
+
+            Assert.Equal(0, inst.call_fd_write(fileFd, 0, 1, 64));
+            Assert.Equal(MESSAGE.Length, memory.ReadInt32(64));
+            Assert.Equal(0, inst.call_fd_close(fileFd));
+            Assert.Equal(MESSAGE, File.ReadAllText(file.Path));
+        }
+    }
+}

crates/test-programs/tests/wasm_tests/runtime.rs

@@ -19,12 +19,12 @@ pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> any
 
     // Create our wasi context with pretty standard arguments/inheritance/etc.
     // Additionally register andy preopened directories if we have them.
-    let mut builder = wasi_common::WasiCtxBuilder::new()
-        .arg(bin_name)
-        .arg(".")
-        .inherit_stdio();
+    let mut builder = wasi_common::WasiCtxBuilder::new();
+
+    builder.arg(bin_name).arg(".").inherit_stdio();
+
     for (dir, file) in get_preopens(workspace)? {
-        builder = builder.preopened_dir(file, dir);
+        builder.preopened_dir(file, dir);
     }
 
     // The nonstandard thing we do with `WasiCtxBuilder` is to ensure that
@@ -32,7 +32,7 @@ pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> any
     // where `stdin` is never ready to be read. In some CI systems, however,
     // stdin is closed which causes tests to fail.
     let (reader, _writer) = os_pipe::pipe()?;
-    builder = builder.stdin(reader_to_file(reader));
+    builder.stdin(reader_to_file(reader));
     let snapshot1 = wasmtime_wasi::Wasi::new(&store, builder.build()?);
     let module = Module::new(&store, &data).context("failed to create wasm module")?;
     let imports = module

crates/wasi-common/src/ctx.rs

@@ -60,38 +60,38 @@ impl PendingCString {
 
 /// A builder allowing customizable construction of `WasiCtx` instances.
 pub struct WasiCtxBuilder {
-    fds: HashMap<wasi::__wasi_fd_t, PendingFdEntry>,
-    preopens: Vec<(PathBuf, File)>,
-    args: Vec<PendingCString>,
-    env: HashMap<PendingCString, PendingCString>,
+    fds: Option<HashMap<wasi::__wasi_fd_t, PendingFdEntry>>,
+    preopens: Option<Vec<(PathBuf, File)>>,
+    args: Option<Vec<PendingCString>>,
+    env: Option<HashMap<PendingCString, PendingCString>>,
 }
 
 impl WasiCtxBuilder {
     /// Builder for a new `WasiCtx`.
     pub fn new() -> Self {
-        let mut builder = Self {
-            fds: HashMap::new(),
-            preopens: Vec::new(),
-            args: vec![],
-            env: HashMap::new(),
-        };
+        let mut fds = HashMap::new();
 
-        builder.fds.insert(0, PendingFdEntry::Thunk(FdEntry::null));
-        builder.fds.insert(1, PendingFdEntry::Thunk(FdEntry::null));
-        builder.fds.insert(2, PendingFdEntry::Thunk(FdEntry::null));
+        fds.insert(0, PendingFdEntry::Thunk(FdEntry::null));
+        fds.insert(1, PendingFdEntry::Thunk(FdEntry::null));
+        fds.insert(2, PendingFdEntry::Thunk(FdEntry::null));
 
-        builder
+        Self {
+            fds: Some(fds),
+            preopens: Some(Vec::new()),
+            args: Some(Vec::new()),
+            env: Some(HashMap::new()),
+        }
     }
 
     /// Add arguments to the command-line arguments list.
     ///
     /// Arguments must be valid UTF-8 with no NUL bytes, or else `WasiCtxBuilder::build()` will fail
     /// with `Error::EILSEQ`.
-    pub fn args<S: AsRef<[u8]>>(mut self, args: impl IntoIterator<Item = S>) -> Self {
-        self.args = args
-            .into_iter()
-            .map(|arg| arg.as_ref().to_vec().into())
-            .collect();
+    pub fn args<S: AsRef<[u8]>>(&mut self, args: impl IntoIterator<Item = S>) -> &mut Self {
+        self.args
+            .as_mut()
+            .unwrap()
+            .extend(args.into_iter().map(|a| a.as_ref().to_vec().into()));
         self
     }
 
@@ -99,8 +99,11 @@ impl WasiCtxBuilder {
     ///
     /// Arguments must be valid UTF-8 with no NUL bytes, or else `WasiCtxBuilder::build()` will fail
     /// with `Error::EILSEQ`.
-    pub fn arg<S: AsRef<[u8]>>(mut self, arg: S) -> Self {
-        self.args.push(arg.as_ref().to_vec().into());
+    pub fn arg<S: AsRef<[u8]>>(&mut self, arg: S) -> &mut Self {
+        self.args
+            .as_mut()
+            .unwrap()
+            .push(arg.as_ref().to_vec().into());
         self
     }
 
@@ -108,19 +111,46 @@ impl WasiCtxBuilder {
     ///
     /// If any arguments from the host process contain invalid UTF-8, `WasiCtxBuilder::build()` will
     /// fail with `Error::EILSEQ`.
-    pub fn inherit_args(mut self) -> Self {
-        self.args = env::args_os().map(PendingCString::OsString).collect();
+    pub fn inherit_args(&mut self) -> &mut Self {
+        let args = self.args.as_mut().unwrap();
+        args.clear();
+        args.extend(env::args_os().map(PendingCString::OsString));
+        self
+    }
+
+    /// Inherit stdin from the host process.
+    pub fn inherit_stdin(&mut self) -> &mut Self {
+        self.fds
+            .as_mut()
+            .unwrap()
+            .insert(0, PendingFdEntry::Thunk(FdEntry::duplicate_stdin));
+        self
+    }
+
+    /// Inherit stdout from the host process.
+    pub fn inherit_stdout(&mut self) -> &mut Self {
+        self.fds
+            .as_mut()
+            .unwrap()
+            .insert(1, PendingFdEntry::Thunk(FdEntry::duplicate_stdout));
+        self
+    }
+
+    /// Inherit stdout from the host process.
+    pub fn inherit_stderr(&mut self) -> &mut Self {
+        self.fds
+            .as_mut()
+            .unwrap()
+            .insert(2, PendingFdEntry::Thunk(FdEntry::duplicate_stderr));
         self
     }
 
     /// Inherit the stdin, stdout, and stderr streams from the host process.
-    pub fn inherit_stdio(mut self) -> Self {
-        self.fds
-            .insert(0, PendingFdEntry::Thunk(FdEntry::duplicate_stdin));
-        self.fds
-            .insert(1, PendingFdEntry::Thunk(FdEntry::duplicate_stdout));
-        self.fds
-            .insert(2, PendingFdEntry::Thunk(FdEntry::duplicate_stderr));
+    pub fn inherit_stdio(&mut self) -> &mut Self {
+        let fds = self.fds.as_mut().unwrap();
+        fds.insert(0, PendingFdEntry::Thunk(FdEntry::duplicate_stdin));
+        fds.insert(1, PendingFdEntry::Thunk(FdEntry::duplicate_stdout));
+        fds.insert(2, PendingFdEntry::Thunk(FdEntry::duplicate_stderr));
         self
     }
 
@@ -129,10 +159,10 @@ impl WasiCtxBuilder {
     /// If any environment variables from the host process contain invalid Unicode (UTF-16 for
     /// Windows, UTF-8 for other platforms), `WasiCtxBuilder::build()` will fail with
     /// `Error::EILSEQ`.
-    pub fn inherit_env(mut self) -> Self {
-        self.env = std::env::vars_os()
-            .map(|(k, v)| (k.into(), v.into()))
-            .collect();
+    pub fn inherit_env(&mut self) -> &mut Self {
+        let env = self.env.as_mut().unwrap();
+        env.clear();
+        env.extend(std::env::vars_os().map(|(k, v)| (k.into(), v.into())));
         self
     }
 
@@ -140,8 +170,10 @@ impl WasiCtxBuilder {
     ///
     /// Environment variable keys and values must be valid UTF-8 with no NUL bytes, or else
     /// `WasiCtxBuilder::build()` will fail with `Error::EILSEQ`.
-    pub fn env<S: AsRef<[u8]>>(mut self, k: S, v: S) -> Self {
+    pub fn env<S: AsRef<[u8]>>(&mut self, k: S, v: S) -> &mut Self {
         self.env
+            .as_mut()
+            .unwrap()
             .insert(k.as_ref().to_vec().into(), v.as_ref().to_vec().into());
         self
     }
@@ -151,40 +183,49 @@ impl WasiCtxBuilder {
     /// Environment variable keys and values must be valid UTF-8 with no NUL bytes, or else
     /// `WasiCtxBuilder::build()` will fail with `Error::EILSEQ`.
     pub fn envs<S: AsRef<[u8]>, T: Borrow<(S, S)>>(
-        mut self,
+        &mut self,
         envs: impl IntoIterator<Item = T>,
-    ) -> Self {
-        self.env = envs
-            .into_iter()
-            .map(|t| {
-                let (k, v) = t.borrow();
-                (k.as_ref().to_vec().into(), v.as_ref().to_vec().into())
-            })
-            .collect();
+    ) -> &mut Self {
+        self.env.as_mut().unwrap().extend(envs.into_iter().map(|t| {
+            let (k, v) = t.borrow();
+            (k.as_ref().to_vec().into(), v.as_ref().to_vec().into())
+        }));
         self
     }
 
     /// Provide a File to use as stdin
-    pub fn stdin(mut self, file: File) -> Self {
-        self.fds.insert(0, PendingFdEntry::File(file));
+    pub fn stdin(&mut self, file: File) -> &mut Self {
+        self.fds
+            .as_mut()
+            .unwrap()
+            .insert(0, PendingFdEntry::File(file));
         self
     }
 
     /// Provide a File to use as stdout
-    pub fn stdout(mut self, file: File) -> Self {
-        self.fds.insert(1, PendingFdEntry::File(file));
+    pub fn stdout(&mut self, file: File) -> &mut Self {
+        self.fds
+            .as_mut()
+            .unwrap()
+            .insert(1, PendingFdEntry::File(file));
         self
     }
 
     /// Provide a File to use as stderr
-    pub fn stderr(mut self, file: File) -> Self {
-        self.fds.insert(2, PendingFdEntry::File(file));
+    pub fn stderr(&mut self, file: File) -> &mut Self {
+        self.fds
+            .as_mut()
+            .unwrap()
+            .insert(2, PendingFdEntry::File(file));
         self
     }
 
     /// Add a preopened directory.
-    pub fn preopened_dir<P: AsRef<Path>>(mut self, dir: File, guest_path: P) -> Self {
-        self.preopens.push((guest_path.as_ref().to_owned(), dir));
+    pub fn preopened_dir<P: AsRef<Path>>(&mut self, dir: File, guest_path: P) -> &mut Self {
+        self.preopens
+            .as_mut()
+            .unwrap()
+            .push((guest_path.as_ref().to_owned(), dir));
         self
     }
 
@@ -192,17 +233,21 @@ impl WasiCtxBuilder {
     ///
     /// If any of the arguments or environment variables in this builder cannot be converted into
     /// `CString`s, either due to NUL bytes or Unicode conversions, this returns `Error::EILSEQ`.
-    pub fn build(self) -> Result<WasiCtx> {
+    pub fn build(&mut self) -> Result<WasiCtx> {
         // Process arguments and environment variables into `CString`s, failing quickly if they
         // contain any NUL bytes, or if conversion from `OsString` fails.
         let args = self
             .args
+            .take()
+            .ok_or(Error::EINVAL)?
             .into_iter()
             .map(|arg| arg.into_utf8_cstring())
             .collect::<Result<Vec<CString>>>()?;
 
         let env = self
             .env
+            .take()
+            .ok_or(Error::EINVAL)?
             .into_iter()
             .map(|(k, v)| {
                 k.into_string().and_then(|mut pair| {
@@ -219,7 +264,7 @@ impl WasiCtxBuilder {
 
         let mut fds: HashMap<wasi::__wasi_fd_t, FdEntry> = HashMap::new();
         // Populate the non-preopen fds.
-        for (fd, pending) in self.fds {
+        for (fd, pending) in self.fds.take().ok_or(Error::EINVAL)? {
             log::debug!("WasiCtx inserting ({:?}, {:?})", fd, pending);
             match pending {
                 PendingFdEntry::Thunk(f) => {
@@ -234,7 +279,7 @@ impl WasiCtxBuilder {
         // so we start from there. This variable is initially 2, though, because the loop
         // immediately does the increment and check for overflow.
         let mut preopen_fd: wasi::__wasi_fd_t = 2;
-        for (guest_path, dir) in self.preopens {
+        for (guest_path, dir) in self.preopens.take().ok_or(Error::EINVAL)? {
             // We do the increment at the beginning of the loop body, so that we don't overflow
             // unnecessarily if we have exactly the maximum number of file descriptors.
             preopen_fd = preopen_fd.checked_add(1).ok_or(Error::ENFILE)?;