use virtual stdio

which works except for the lifetime issues, i think the trap still holds
an Rc to the store?

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

@@ -2,17 +2,29 @@ use anyhow::Context;
 use std::convert::TryFrom;
 use std::fs::File;
 use std::path::Path;
-use wasi_c2::WasiCtx;
+use wasi_c2::{
+    virt::pipe::{ReadPipe, WritePipe},
+    WasiCtx,
+};
 use wasmtime::{Linker, Module, Store};
 
 pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> anyhow::Result<()> {
+    let stdout = WritePipe::new_in_memory();
+    let stderr = WritePipe::new_in_memory();
+
+    let r = {
         let store = Store::default();
 
-    // Create our wasi context with pretty standard arguments/inheritance/etc.
+        // Create our wasi context.
         // Additionally register any preopened directories if we have them.
         let mut builder = wasi_c2::WasiCtx::builder();
 
-    builder.arg(bin_name)?.arg(".")?.inherit_stdio();
+        builder
+            .arg(bin_name)?
+            .arg(".")?
+            .stdin(Box::new(ReadPipe::from(Vec::new())))
+            .stdout(Box::new(stdout.clone()))
+            .stderr(Box::new(stderr.clone()));
 
         if let Some(workspace) = workspace {
             let dirfd =
@@ -21,16 +33,6 @@ pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> any
             builder.preopened_dir(Box::new(preopen_dir), ".")?;
         }
 
-    /*
-        // The nonstandard thing we do with `WasiCtxBuilder` is to ensure that
-        // `stdin` is always an unreadable pipe. This is expected in the test suite
-        // 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()?;
-        let file = reader_to_file(reader);
-        let handle = OsOther::try_from(file).context("failed to create OsOther from PipeReader")?;
-        builder.stdin(handle);
-    */
         let snapshot1 = wasi_c2_wasmtime::Wasi::new(&store, builder.build()?);
 
         let mut linker = Linker::new(&store);
@@ -44,7 +46,27 @@ pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> any
             .and_then(|m| m.get_default(""))
             .and_then(|f| f.get0::<()>())
             .and_then(|f| f().map_err(Into::into))
-        .context(format!("error while testing Wasm module '{}'", bin_name,))
+    };
+    match r {
+        Ok(()) => Ok(()),
+        Err(trap) => {
+            let stdout = stdout
+                .try_into_inner()
+                .expect("sole ref to stdout")
+                .into_inner();
+            if !stdout.is_empty() {
+                println!("guest stdout:\n{}\n===", String::from_utf8_lossy(&stdout));
+            }
+            let stderr = stderr
+                .try_into_inner()
+                .expect("sole ref to stderr")
+                .into_inner();
+            if !stderr.is_empty() {
+                println!("guest stderr:\n{}\n===", String::from_utf8_lossy(&stderr));
+            }
+            Err(trap.context(format!("error while testing Wasm module '{}'", bin_name,)))
+        }
+    }
 }
 
 #[cfg(unix)]

crates/wasi-c2/src/ctx.rs

@@ -69,31 +69,48 @@ impl WasiCtxBuilder {
     pub fn build(self) -> Result<WasiCtx, Error> {
         Ok(self.0)
     }
+
     pub fn arg(&mut self, arg: &str) -> Result<&mut Self, StringArrayError> {
         self.0.args.push(arg.to_owned())?;
         Ok(self)
     }
-    pub fn inherit_stdio(&mut self) -> &mut Self {
+
+    pub fn stdin(&mut self, f: Box<dyn WasiFile>) -> &mut Self {
         self.0.insert_file(
             0,
-            Box::new(crate::stdio::stdin()),
-            FileCaps::READ,
+            f,
+            FileCaps::READ, // XXX probably more rights are ok
             FileCaps::READ,
         );
+        self
+    }
+
+    pub fn stdout(&mut self, f: Box<dyn WasiFile>) -> &mut Self {
         self.0.insert_file(
             1,
-            Box::new(crate::stdio::stdout()),
-            FileCaps::WRITE,
-            FileCaps::WRITE,
-        );
-        self.0.insert_file(
-            2,
-            Box::new(crate::stdio::stderr()),
-            FileCaps::WRITE,
+            f,
+            FileCaps::WRITE, // XXX probably more rights are ok
             FileCaps::WRITE,
         );
         self
     }
+
+    pub fn stderr(&mut self, f: Box<dyn WasiFile>) -> &mut Self {
+        self.0.insert_file(
+            2,
+            f,
+            FileCaps::WRITE, // XXX probably more rights are ok
+            FileCaps::WRITE,
+        );
+        self
+    }
+
+    pub fn inherit_stdio(&mut self) -> &mut Self {
+        self.stdin(Box::new(crate::stdio::stdin()))
+            .stdout(Box::new(crate::stdio::stdout()))
+            .stderr(Box::new(crate::stdio::stderr()))
+    }
+
     pub fn preopened_dir(
         &mut self,
         dir: Box<dyn WasiDir>,