Add tests for the readonly component

components/readonly/Cargo.toml

@@ -8,4 +8,11 @@ license = "Apache-2.0"
 crate-type = ["cdylib"]
 
 [dependencies]
+componentized-rt = { workspace = true, features = ["executor"] }
 wit-bindgen = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }
+test-harness = { workspace = true }
+tokio = { workspace = true }
+wasmtime = { workspace = true }

components/readonly/README.md

@@ -1,3 +1,7 @@
 # `readonly`
 
-Virtualizes the wasi:filesystem interfaces making the exported file system read-only.
+Virtualizes the `wasi:filesystem` interfaces making the exported file system read-only.
+
+Every operation that reads the filesystem is passed through, every operation that would change it fails with `read-only`, including opening a descriptor with flags that would allow a change. `sync` and `sync-data` are denied as well.
+
+`write-via-stream` and `append-via-stream` are synchronous and resolve their result on a background thread, so the host must support component model threads, e.g. `wasmtime -W component-model-threading`.

components/readonly/build.rs

@@ -0,0 +1,7 @@
+fn main() {
+    // componentized_rt::executor's thread is started with thread.new-indirect, which calls through
+    // the exported function table
+    if std::env::var("CARGO_CFG_TARGET_FAMILY").as_deref() == Ok("wasm") {
+        println!("cargo:rustc-link-arg-cdylib=--export-table");
+    }
+}

components/readonly/src/lib.rs

@@ -1,5 +1,3 @@
-use std::path::PathBuf;
-
 use exports::wasi::filesystem::preopens::Guest as Preopens;
 use exports::wasi::filesystem::types::{
     Advice, Descriptor, DescriptorBorrow, DescriptorFlags, DescriptorStat, DescriptorType,
@@ -17,7 +15,7 @@ impl Preopens for FilesystemReadOnly {
         preopens::get_directories()
             .into_iter()
             .map(|(fd, path)| {
-                let fd = Descriptor::new(ReadOnlyDescriptor::new(fd, path.clone().into()));
+                let fd = Descriptor::new(ReadOnlyDescriptor::new(fd));
                 (fd, path)
             })
             .collect()
@@ -30,12 +28,11 @@ impl Types for FilesystemReadOnly {
 
 struct ReadOnlyDescriptor {
     fd: types::Descriptor,
-    path: PathBuf,
 }
 
 impl ReadOnlyDescriptor {
-    fn new(fd: types::Descriptor, path: PathBuf) -> Self {
-        Self { fd, path }
+    fn new(fd: types::Descriptor) -> Self {
+        Self { fd }
     }
 }
 
@@ -55,18 +52,14 @@ impl exports::wasi::filesystem::types::GuestDescriptor for ReadOnlyDescriptor {
         _data: wit_bindgen::StreamReader<u8>,
         _offset: Filesize,
     ) -> wit_bindgen::FutureReader<Result<(), ErrorCode>> {
-        let (tx, rx) = wit_future::new(|| Err(ErrorCode::ReadOnly));
-        tx.write(Err(ErrorCode::ReadOnly));
-        rx
+        read_only()
     }
 
     fn append_via_stream(
         &self,
         _data: wit_bindgen::StreamReader<u8>,
     ) -> wit_bindgen::FutureReader<Result<(), ErrorCode>> {
-        let (tx, rx) = wit_future::new(|| Err(ErrorCode::ReadOnly));
-        tx.write(Err(ErrorCode::ReadOnly));
-        rx
+        read_only()
     }
 
     async fn advise(
@@ -171,6 +164,7 @@ impl exports::wasi::filesystem::types::GuestDescriptor for ReadOnlyDescriptor {
             || flags.contains(DescriptorFlags::FILE_INTEGRITY_SYNC)
             || flags.contains(DescriptorFlags::DATA_INTEGRITY_SYNC)
             || flags.contains(DescriptorFlags::REQUESTED_WRITE_SYNC)
+            || flags.contains(DescriptorFlags::MUTATE_DIRECTORY)
         {
             return Err(ErrorCode::ReadOnly);
         }
@@ -180,10 +174,7 @@ impl exports::wasi::filesystem::types::GuestDescriptor for ReadOnlyDescriptor {
             .open_at(path_flags, path.clone(), open_flags, flags)
             .await
         {
-            Ok(fd) => Ok(Descriptor::new(ReadOnlyDescriptor::new(
-                fd,
-                self.path.clone().join(path),
-            ))),
+            Ok(fd) => Ok(Descriptor::new(ReadOnlyDescriptor::new(fd))),
             Err(error_code) => Err(error_code),
         }
     }
@@ -231,6 +222,17 @@ impl exports::wasi::filesystem::types::GuestDescriptor for ReadOnlyDescriptor {
     }
 }
 
+/// A future resolved to `read-only`, for the sync exports that return a future.
+fn read_only() -> wit_bindgen::FutureReader<Result<(), ErrorCode>> {
+    let (tx, rx) = wit_future::new(|| Err(ErrorCode::ReadOnly));
+    // a sync export can't wait for the write, the reader has not been returned yet, so the write
+    // completes in the background
+    componentized_rt::executor::spawn(async move {
+        let _ = tx.write(Err(ErrorCode::ReadOnly)).await;
+    });
+    rx
+}
+
 wit_bindgen::generate!({
     path: "../wit",
     world: "filesystem",