Support Windows Device Paths in WASI

crates/livesplit-auto-splitting/Cargo.toml

@@ -23,14 +23,14 @@ sysinfo = { version = "0.30.0", default-features = false, features = [
   "multithread",
 ] }
 time = { version = "0.3.3", default-features = false }
-wasmtime = { version = "16.0.0", default-features = false, features = [
+wasmtime = { version = "17.0.0", default-features = false, features = [
   "cranelift",
   "parallel-compilation",
 ] }
-wasmtime-wasi = { version = "16.0.0", default-features = false, features = [
+wasmtime-wasi = { version = "17.0.0", default-features = false, features = [
   "sync",
 ] }
-wasi-common = "16.0.0"
+wasi-common = "17.0.0"
 
 [target.'cfg(windows)'.dependencies]
 windows-sys = { version = "0.52.0", features = ["Win32_Storage_FileSystem"] }

crates/livesplit-auto-splitting/README.md

@@ -532,9 +532,10 @@ support:
 
 - `stdout` / `stderr` / `stdin` are unbound. Those streams currently do
   nothing.
-- The file system is currently almost entirely empty. The host's file system
-  is accessible through `/mnt`. It is entirely read-only. Windows paths are
-  mapped to `/mnt/c`, `/mnt/d`, etc. to match WSL.
+- The file system is currently almost entirely empty. The host's file system is
+  accessible through `/mnt`. It is entirely read-only. Windows paths are mapped
+  to `/mnt/c`, `/mnt/d`, etc. to match WSL. Additionally `/mnt/device` maps to
+  `\\?\` on Windows to access additional paths.
 - There are no environment variables.
 - There are no command line arguments.
 - There is no networking.

crates/livesplit-auto-splitting/src/lib.rs

@@ -534,7 +534,8 @@
 //!   nothing.
 //! - The file system is currently almost entirely empty. The host's file system
 //!   is accessible through `/mnt`. It is entirely read-only. Windows paths are
-//!   mapped to `/mnt/c`, `/mnt/d`, etc. to match WSL.
+//!   mapped to `/mnt/c`, `/mnt/d`, etc. to match WSL. Additionally
+//!   `/mnt/device` maps to `\\?\` on Windows to access additional paths.
 //! - There are no environment variables.
 //! - There are no command line arguments.
 //! - There is no networking.

crates/livesplit-auto-splitting/src/runtime/api/wasi.rs

@@ -33,7 +33,7 @@ pub fn build(script_path: Option<&Path>) -> WasiCtx {
             drives &= !(1 << drive_idx);
             let drive = drive_idx as u8 + b'a';
             if let Ok(path) = wasmtime_wasi::Dir::open_ambient_dir(
-                str::from_utf8(&[drive, b':', b'\\']).unwrap(),
+                str::from_utf8(&[b'\\', b'\\', b'?', b'\\', drive, b':', b'\\']).unwrap(),
                 ambient_authority(),
             ) {
                 wasi.push_dir(
@@ -43,6 +43,9 @@ pub fn build(script_path: Option<&Path>) -> WasiCtx {
                 .unwrap();
             }
         }
+
+        wasi.push_dir(Box::new(DeviceDir), PathBuf::from("/mnt/device"))
+            .unwrap();
     }
     #[cfg(not(windows))]
     {
@@ -128,3 +131,65 @@ impl WasiDir for ReadOnlyDir {
         self.0.get_path_filestat(path, follow_symlinks).await
     }
 }
+
+#[cfg(windows)]
+struct DeviceDir;
+
+#[cfg(windows)]
+#[async_trait::async_trait]
+impl WasiDir for DeviceDir {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+
+    async fn open_file(
+        &self,
+        symlink_follow: bool,
+        path: &str,
+        oflags: OFlags,
+        read: bool,
+        write: bool,
+        fdflags: FdFlags,
+    ) -> Result<OpenResult, wasi_common::Error> {
+        let (dir, file) = device_path(path)?;
+        dir.open_file(symlink_follow, file, oflags, read, write, fdflags)
+            .await
+    }
+
+    // FIXME: cap-primitives/src/windows/fs/get_path tries to strip `\\?\`,
+    // which breaks paths that aren't valid without it, such as UNC paths:
+    // https://github.com/bytecodealliance/cap-std/issues/348
+
+    async fn read_link(&self, path: &str) -> Result<PathBuf, wasi_common::Error> {
+        let (dir, file) = device_path(path)?;
+        dir.read_link(file).await
+    }
+
+    async fn get_path_filestat(
+        &self,
+        path: &str,
+        follow_symlinks: bool,
+    ) -> Result<Filestat, wasi_common::Error> {
+        let (dir, file) = device_path(path)?;
+        dir.get_path_filestat(file, follow_symlinks).await
+    }
+}
+
+#[cfg(windows)]
+fn device_path(path: &str) -> Result<(ReadOnlyDir, &str), wasi_common::Error> {
+    let (parent, file) = path
+        .strip_suffix('/')
+        .unwrap_or(path)
+        .rsplit_once('/')
+        .ok_or_else(wasi_common::Error::not_supported)?;
+
+    let parent = wasi_path::to_native(&format!("/mnt/device/{parent}"), true)
+        .ok_or_else(wasi_common::Error::not_supported)?;
+
+    let dir = wasmtime_wasi::dir::Dir::from_cap_std(
+        wasmtime_wasi::Dir::open_ambient_dir(parent, ambient_authority())
+            .map_err(|_| wasi_common::Error::not_supported())?,
+    );
+
+    Ok((ReadOnlyDir(dir), file))
+}