Fix WASI pipe to properly store read bytes in temp_buffer

lib/c-api/src/wasm_c_api/wasi/mod.rs

@@ -58,6 +58,7 @@ pub struct wasi_pipe_t {
     data: Option<Box<Arc<Mutex<WasiPipeDataWithDestructor>>>>,
 }
 
+#[derive(Debug)]
 struct WasiPipeDataWithDestructor {
     data: Vec<c_char>,
     // Buffer of already-read data that is being read into,
@@ -71,12 +72,17 @@ impl WasiPipeDataWithDestructor {
         &mut self,
         read_cb: WasiConsoleIoReadCallback,
         max_read: Option<usize>,
-    ) -> io::Result<Vec<u8>> {
+    ) -> io::Result<usize> {
         const BLOCK_SIZE: usize = 1024;
 
         let mut final_buf = Vec::new();
 
-        let max_read = max_read.unwrap_or(usize::MAX);
+        let max_to_read = max_read.unwrap_or(usize::MAX);
+        let max_read = max_to_read.saturating_sub(self.temp_buffer.len());
+        if max_read == 0 {
+            // there are n bytes being available to read in the temp_buffer
+            return Ok(max_to_read);
+        }
         let mut cur_read = 0;
 
         // Read bytes until either EOF is reached or max_read bytes are reached
@@ -107,15 +113,28 @@ impl WasiPipeDataWithDestructor {
                 ));
             }
 
-            if result == 0 {
+            let result = result as usize;
+            if result == 0 || result > temp_buffer.len() {
                 break; // EOF
             }
 
-            cur_read += temp_buffer.len();
-            final_buf.append(&mut temp_buffer);
+            cur_read += result;
+            final_buf.extend_from_slice(&temp_buffer[..result]);
         }
 
-        Ok(final_buf)
+        let final_buf_len = final_buf.len();
+
+        // store the bytes in temp_buffer
+        self.temp_buffer.extend_from_slice(&final_buf);
+
+        // temp_buffer.len() can be smaller than max_read in case we
+        // encounter EOF earlier than expected
+        assert!(self.temp_buffer.len() <= max_read);
+
+        // return how many bytes were just read
+        //
+        // caller has to clear temp_buffer to advance actual reading
+        Ok(final_buf_len)
     }
 }
 
@@ -161,26 +180,11 @@ impl io::Read for wasi_pipe_t {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let self_read = self.read;
         let mut data = self.get_data_mut("read")?;
-
-        // fill up buf by draining temp_buffer first, then read more bytes
-        let bytes_to_read = data.temp_buffer.len().min(buf.len());
-        let mut temp_buffer_drained: Vec<_> = data.temp_buffer.drain(..bytes_to_read).collect();
-        assert!(temp_buffer_drained.len() <= buf.len());
-
-        // If temp_buffer is exhausted, try reading the remaining bytes from the pipe
-        let mut bytes_read = bytes_to_read;
-        if buf.len() >= temp_buffer_drained.len() {
-            let secondary_bytes_to_read = data.temp_buffer.len().min(buf.len());
-            data.read_buffer(self_read, Some(secondary_bytes_to_read))?;
-            temp_buffer_drained
-                .append(&mut data.temp_buffer.drain(..secondary_bytes_to_read).collect());
-            bytes_read += secondary_bytes_to_read;
-        }
-
-        assert_eq!(buf.len(), temp_buffer_drained.len());
-        buf.clone_from_slice(&temp_buffer_drained);
-
-        Ok(bytes_read)
+        let _ = data.read_buffer(self_read, Some(buf.len()))?;
+        let bytes_to_read = buf.len().min(data.temp_buffer.len());
+        let bytes_read = data.temp_buffer.drain(..bytes_to_read).collect::<Vec<_>>();
+        buf[..bytes_read.len()].clone_from_slice(&bytes_read);
+        Ok(bytes_to_read)
     }
 }
 
@@ -278,7 +282,7 @@ impl VirtualFile for wasi_pipe_t {
     fn bytes_available_read(&self) -> Result<Option<usize>, FsError> {
         let self_read = self.read;
         let mut data = self.get_data_mut("bytes_available_read")?;
-        data.read_buffer(self_read, None)?;
+        let _ = data.read_buffer(self_read, None)?;
         Ok(Some(data.temp_buffer.len()))
     }
     fn bytes_available_write(&self) -> Result<Option<usize>, FsError> {
@@ -507,6 +511,36 @@ pub unsafe extern "C" fn wasi_pipe_flush(ptr: *mut wasi_pipe_t) -> i64 {
     }
 }
 
+#[test]
+fn test_wasi_pipe_with_destructor() {
+    let mut wasi_pipe_t_ptr = std::ptr::null_mut();
+    let second_wasi_pipe_t_ptr = unsafe { wasi_pipe_new(&mut wasi_pipe_t_ptr) };
+    let wasi_pipe_t_ptr = unsafe { &mut *wasi_pipe_t_ptr };
+    let second_wasi_pipe_t_ptr = unsafe { &mut *second_wasi_pipe_t_ptr };
+
+    let data = b"hello".into_iter().map(|v| *v as i8).collect::<Vec<_>>();
+    let result = unsafe { wasi_pipe_write_bytes(wasi_pipe_t_ptr, data.as_ptr(), data.len()) };
+    assert_eq!(result, 5);
+
+    let bytes_avail = wasi_pipe_t_ptr.bytes_available_read();
+    assert_eq!(bytes_avail, Ok(Some(0)));
+
+    let bytes_avail2 = second_wasi_pipe_t_ptr.bytes_available_read();
+    assert_eq!(bytes_avail2, Ok(Some(5)));
+
+    let mut read_str_ptr = std::ptr::null_mut();
+    let result = unsafe { wasi_pipe_read_str(second_wasi_pipe_t_ptr, &mut read_str_ptr) };
+    assert_eq!(result, 6); // hello\0
+    let buf_slice = unsafe { std::slice::from_raw_parts_mut(read_str_ptr, result as usize) };
+    assert_eq!(buf_slice[..5], data);
+
+    unsafe {
+        wasi_pipe_delete_str(read_str_ptr);
+    }
+    unsafe { wasi_pipe_delete(wasi_pipe_t_ptr) };
+    unsafe { wasi_pipe_delete(second_wasi_pipe_t_ptr) };
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn wasi_pipe_read_bytes(
     ptr: *const wasi_pipe_t,
@@ -553,12 +587,13 @@ unsafe fn wasi_pipe_read_bytes_internal(ptr: *const wasi_pipe_t, buf: &mut Vec<u
         }
     }
 
+    let len = target.len() as i64;
     *buf = target;
-    0
+    len
 }
 
 #[no_mangle]
-pub unsafe extern "C" fn wasi_pipe_read_str(ptr: *const wasi_pipe_t, buf: *mut *mut c_char) -> i64 {
+pub unsafe extern "C" fn wasi_pipe_read_str(ptr: *const wasi_pipe_t, buf: &mut *mut c_char) -> i64 {
     use std::ffi::CString;
 
     let mut target = Vec::new();