add wasmtime adapter and stdio wrappers

the stdio wrappers will not work on windows, but thats a whole other can
of worms anyway

crates/wasi-c2/src/ctx.rs

@@ -1,6 +1,7 @@
 use crate::dir::{DirCaps, DirEntry, WasiDir};
 use crate::file::{FileCaps, FileEntry, WasiFile};
 use crate::table::Table;
+use crate::Error;
 use std::cell::{RefCell, RefMut};
 use std::path::PathBuf;
 use std::rc::Rc;
@@ -10,6 +11,10 @@ pub struct WasiCtx {
 }
 
 impl WasiCtx {
+    pub fn builder() -> WasiCtxBuilder {
+        WasiCtxBuilder(WasiCtx::new())
+    }
+
     pub fn new() -> Self {
         WasiCtx {
             table: Rc::new(RefCell::new(Table::new())),
@@ -52,3 +57,36 @@ impl WasiCtx {
         self.table.borrow_mut()
     }
 }
+
+pub struct WasiCtxBuilder(WasiCtx);
+
+impl WasiCtxBuilder {
+    pub fn build(self) -> Result<WasiCtx, Error> {
+        Ok(self.0)
+    }
+    pub fn arg(&mut self, _arg: &str) -> &mut Self {
+        // Intentionally left blank. We do not handle arguments yet.
+        self
+    }
+    pub fn inherit_stdio(&mut self) -> &mut Self {
+        self.0.insert_file(
+            0,
+            Box::new(crate::stdio::stdin()),
+            FileCaps::READ,
+            FileCaps::READ,
+        );
+        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,
+            FileCaps::WRITE,
+        );
+        self
+    }
+}

crates/wasi-c2/src/lib.rs

@@ -5,7 +5,10 @@ mod dir;
 mod error;
 mod file;
 pub mod snapshots;
+pub mod stdio;
 pub mod table;
 
 pub use ctx::WasiCtx;
+pub use dir::{DirCaps, WasiDir};
 pub use error::Error;
+pub use file::{FileCaps, WasiFile};

crates/wasi-c2/src/stdio.rs

@@ -0,0 +1,124 @@
+use crate::file::{FdFlags, Filestat, Filetype, OFlags, WasiFile};
+use crate::Error;
+#[cfg(unix)]
+use std::os::unix::io::{AsRawFd, RawFd};
+
+pub struct Stdin(std::io::Stdin);
+
+pub fn stdin() -> Stdin {
+    Stdin(std::io::stdin())
+}
+
+#[cfg(unix)]
+impl AsRawFd for Stdin {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0.as_raw_fd()
+    }
+}
+
+impl WasiFile for Stdin {
+    fn datasync(&self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn sync(&self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn get_filetype(&self) -> Result<Filetype, Error> {
+        Ok(Filetype::CharacterDevice)
+    }
+    fn get_fdflags(&self) -> Result<FdFlags, Error> {
+        todo!()
+    }
+    fn get_oflags(&self) -> Result<OFlags, Error> {
+        todo!()
+    }
+    fn set_oflags(&self, _flags: OFlags) -> Result<(), Error> {
+        todo!()
+    }
+    fn get_filestat(&self) -> Result<Filestat, Error> {
+        todo!()
+    }
+    fn set_filestat_size(&self, _size: u64) -> Result<(), Error> {
+        todo!()
+    }
+}
+
+pub struct Stdout(std::io::Stdout);
+
+pub fn stdout() -> Stdout {
+    Stdout(std::io::stdout())
+}
+
+#[cfg(unix)]
+impl AsRawFd for Stdout {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0.as_raw_fd()
+    }
+}
+
+impl WasiFile for Stdout {
+    fn datasync(&self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn sync(&self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn get_filetype(&self) -> Result<Filetype, Error> {
+        Ok(Filetype::CharacterDevice)
+    }
+    fn get_fdflags(&self) -> Result<FdFlags, Error> {
+        todo!()
+    }
+    fn get_oflags(&self) -> Result<OFlags, Error> {
+        todo!()
+    }
+    fn set_oflags(&self, _flags: OFlags) -> Result<(), Error> {
+        todo!()
+    }
+    fn get_filestat(&self) -> Result<Filestat, Error> {
+        todo!()
+    }
+    fn set_filestat_size(&self, _size: u64) -> Result<(), Error> {
+        todo!()
+    }
+}
+
+pub struct Stderr(std::io::Stderr);
+
+pub fn stderr() -> Stderr {
+    Stderr(std::io::stderr())
+}
+
+#[cfg(unix)]
+impl AsRawFd for Stderr {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0.as_raw_fd()
+    }
+}
+
+impl WasiFile for Stderr {
+    fn datasync(&self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn sync(&self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn get_filetype(&self) -> Result<Filetype, Error> {
+        Ok(Filetype::CharacterDevice)
+    }
+    fn get_fdflags(&self) -> Result<FdFlags, Error> {
+        todo!()
+    }
+    fn get_oflags(&self) -> Result<OFlags, Error> {
+        todo!()
+    }
+    fn set_oflags(&self, _flags: OFlags) -> Result<(), Error> {
+        todo!()
+    }
+    fn get_filestat(&self) -> Result<Filestat, Error> {
+        todo!()
+    }
+    fn set_filestat_size(&self, _size: u64) -> Result<(), Error> {
+        todo!()
+    }
+}