Fix file writes in preview 2 implementation (#7394)

* add a preview1_file_write test to show behavior of large file writes

reproduces #7390

* filesystem output-stream: update position cursor

crates/test-programs/src/bin/preview1_file_write.rs

@@ -0,0 +1,106 @@
+use std::{env, process};
+use test_programs::preview1::open_scratch_directory;
+
+unsafe fn test_file_long_write(dir_fd: wasi::Fd, filename: &str) {
+    // Open a file for writing
+    let file_fd = wasi::path_open(
+        dir_fd,
+        0,
+        filename,
+        wasi::OFLAGS_CREAT,
+        wasi::RIGHTS_FD_WRITE,
+        0,
+        0,
+    )
+    .expect("creating a file for writing");
+
+    let mut content = Vec::new();
+    // 16 byte string, 4096 times, is 64k
+    for n in 0..4096 {
+        let chunk = format!("123456789 {n:05} ");
+        assert_eq!(chunk.as_str().as_bytes().len(), 16);
+        content.extend_from_slice(chunk.as_str().as_bytes());
+    }
+
+    // Write to the file
+    let nwritten = wasi::fd_write(
+        file_fd,
+        &[wasi::Ciovec {
+            buf: content.as_slice().as_ptr() as *const _,
+            buf_len: content.len(),
+        }],
+    )
+    .expect("writing file content");
+    assert_eq!(nwritten, content.len(), "nwritten bytes check");
+
+    let stat = wasi::fd_filestat_get(file_fd).expect("reading file stats");
+    assert_eq!(
+        stat.size,
+        content.len() as u64,
+        "file should be size of content",
+    );
+
+    wasi::fd_close(file_fd).expect("closing the file");
+    // Open the file for reading
+    let file_fd = wasi::path_open(dir_fd, 0, filename, 0, wasi::RIGHTS_FD_READ, 0, 0)
+        .expect("open the file for reading");
+
+    // Read the file's contents
+    let buffer = &mut [0u8; 100];
+    let nread = wasi::fd_read(
+        file_fd,
+        &[wasi::Iovec {
+            buf: buffer.as_mut_ptr(),
+            buf_len: buffer.len(),
+        }],
+    )
+    .expect("reading first chunk file content");
+
+    assert_eq!(nread, buffer.len(), "read first chunk");
+    assert_eq!(
+        buffer,
+        &content[..buffer.len()],
+        "contents of first read chunk"
+    );
+
+    let end_cursor = content.len() - buffer.len();
+    wasi::fd_seek(file_fd, end_cursor as i64, wasi::WHENCE_SET)
+        .expect("seeking to end of file minus buffer size");
+
+    let nread = wasi::fd_read(
+        file_fd,
+        &[wasi::Iovec {
+            buf: buffer.as_mut_ptr(),
+            buf_len: buffer.len(),
+        }],
+    )
+    .expect("reading end chunk of file content");
+
+    assert_eq!(nread, buffer.len(), "read end chunk len");
+    assert_eq!(buffer, &content[end_cursor..], "contents of end read chunk");
+
+    wasi::fd_close(file_fd).expect("closing the file");
+}
+
+fn main() {
+    let mut args = env::args();
+    let prog = args.next().unwrap();
+    let arg = if let Some(arg) = args.next() {
+        arg
+    } else {
+        eprintln!("usage: {} <scratch directory>", prog);
+        process::exit(1);
+    };
+
+    // Open scratch directory
+    let dir_fd = match open_scratch_directory(&arg) {
+        Ok(dir_fd) => dir_fd,
+        Err(err) => {
+            eprintln!("{}", err);
+            process::exit(1)
+        }
+    };
+
+    // Run the tests.
+    unsafe { test_file_long_write(dir_fd, "long_write.txt") }
+}

crates/wasi-common/tests/all/async_.rs

@@ -291,3 +291,7 @@ async fn preview1_path_open_preopen() {
 async fn preview1_unicode_output() {
     run(PREVIEW1_UNICODE_OUTPUT, true).await.unwrap()
 }
+#[test_log::test(tokio::test(flavor = "multi_thread"))]
+async fn preview1_file_write() {
+    run(PREVIEW1_FILE_WRITE, true).await.unwrap()
+}

crates/wasi-common/tests/all/sync.rs

@@ -273,3 +273,7 @@ fn preview1_path_open_preopen() {
 fn preview1_unicode_output() {
     run(PREVIEW1_UNICODE_OUTPUT, true).unwrap()
 }
+#[test_log::test]
+fn preview1_file_write() {
+    run(PREVIEW1_FILE_WRITE, true).unwrap()
+}

crates/wasi/src/preview2/filesystem.rs

@@ -189,7 +189,7 @@ enum OutputState {
     Ready,
     /// Allows join future to be awaited in a cancellable manner. Gone variant indicates
     /// no task is currently outstanding.
-    Waiting(AbortOnDropJoinHandle<io::Result<()>>),
+    Waiting(AbortOnDropJoinHandle<io::Result<usize>>),
     /// The last I/O operation failed with this error.
     Error(io::Error),
     Closed,
@@ -233,22 +233,26 @@ impl HostOutputStream for FileOutputStream {
         let m = self.mode;
         let task = spawn_blocking(move || match m {
             FileOutputMode::Position(mut p) => {
+                let mut total = 0;
                 let mut buf = buf;
                 while !buf.is_empty() {
                     let nwritten = f.write_at(buf.as_ref(), p)?;
                     // afterwards buf contains [nwritten, len):
                     let _ = buf.split_to(nwritten);
                     p += nwritten as u64;
+                    total += nwritten;
                 }
-                Ok(())
+                Ok(total)
             }
             FileOutputMode::Append => {
+                let mut total = 0;
                 let mut buf = buf;
                 while !buf.is_empty() {
                     let nwritten = f.append(buf.as_ref())?;
                     let _ = buf.split_to(nwritten);
+                    total += nwritten;
                 }
-                Ok(())
+                Ok(total)
             }
         });
         self.state = OutputState::Waiting(task);
@@ -285,7 +289,12 @@ impl Subscribe for FileOutputStream {
     async fn ready(&mut self) {
         if let OutputState::Waiting(task) = &mut self.state {
             self.state = match task.await {
-                Ok(()) => OutputState::Ready,
+                Ok(nwritten) => {
+                    if let FileOutputMode::Position(ref mut p) = &mut self.mode {
+                        *p += nwritten as u64;
+                    }
+                    OutputState::Ready
+                }
                 Err(e) => OutputState::Error(e),
             };
         }

crates/wasi/tests/all/async_.rs

@@ -287,6 +287,10 @@ async fn preview1_path_open_preopen() {
 async fn preview1_unicode_output() {
     run(PREVIEW1_UNICODE_OUTPUT_COMPONENT, true).await.unwrap()
 }
+#[test_log::test(tokio::test(flavor = "multi_thread"))]
+async fn preview1_file_write() {
+    run(PREVIEW1_FILE_WRITE_COMPONENT, false).await.unwrap()
+}
 
 #[test_log::test(tokio::test(flavor = "multi_thread"))]
 async fn preview2_sleep() {

crates/wasi/tests/all/preview1.rs

@@ -245,3 +245,7 @@ async fn preview1_path_open_preopen() {
 async fn preview1_unicode_output() {
     run(PREVIEW1_UNICODE_OUTPUT, true).await.unwrap()
 }
+#[test_log::test(tokio::test(flavor = "multi_thread"))]
+async fn preview1_file_write() {
+    run(PREVIEW1_FILE_WRITE, true).await.unwrap()
+}

crates/wasi/tests/all/sync.rs

@@ -232,6 +232,10 @@ fn preview1_path_open_preopen() {
 fn preview1_unicode_output() {
     run(PREVIEW1_UNICODE_OUTPUT_COMPONENT, true).unwrap()
 }
+#[test_log::test]
+fn preview1_file_write() {
+    run(PREVIEW1_FILE_WRITE_COMPONENT, false).unwrap()
+}
 
 #[test_log::test]
 fn preview2_sleep() {