[libos] Fix error handling of sendfile

src/libos/src/fs/file_ops/sendfile.rs

@@ -22,28 +22,66 @@ pub fn do_sendfile(
         None => in_file.seek(SeekFrom::Current(0))?,
     } as usize;
 
-    // read from specified offset and write new offset back
-    let mut bytes_read = 0;
-    while bytes_read < count {
-        let len = min(buffer.len(), count - bytes_read);
-        let read_len = in_file.read_at(read_offset, &mut buffer[..len])?;
-        if read_len == 0 {
-            break;
-        }
-        bytes_read += read_len;
-        read_offset += read_len;
+    // write_file is used to write buffer into out_file, the closure avoids complex loop structure
+    let mut write_file = |buffer: &[u8]| -> Result<usize> {
+        let buffer_len = buffer.len();
         let mut bytes_written = 0;
-        while bytes_written < read_len {
-            let write_len = out_file.write(&buffer[bytes_written..read_len])?;
-            if write_len == 0 {
-                return_errno!(EBADF, "sendfile write return 0");
+        let mut write_error = None;
+
+        while bytes_written < buffer_len {
+            match out_file.write(&buffer[bytes_written..]) {
+                Ok(write_len) => {
+                    debug_assert!(write_len > 0);
+                    bytes_written += write_len;
+                }
+                Err(e) => {
+                    // handle sendmsg return err
+                    write_error = Some(e);
+                    break;
+                }
+            }
+        }
+
+        if bytes_written > 0 {
+            Ok(bytes_written)
+        } else {
+            // if bytes_written = 0, write_error must be Some(e).
+            Err(write_error.unwrap())
+        }
+    };
+
+    // read from specified offset and write new offset back
+    let mut bytes_sent = 0;
+    let mut send_error = None;
+    while bytes_sent < count {
+        let len = min(buffer.len(), count - bytes_sent);
+
+        match in_file.read_at(read_offset, &mut buffer[..len]) {
+            Ok(read_len) if read_len > 0 => match write_file(&buffer[..read_len]) {
+                Ok(write_len) => {
+                    bytes_sent += write_len;
+                    read_offset += write_len;
+                }
+                Err(e) => {
+                    send_error = Some(e);
+                    break;
+                }
+            },
+            Ok(..) => break,
+            Err(e) => {
+                send_error = Some(e);
+                break;
             }
-            bytes_written += write_len;
         }
     }
 
     if offset.is_none() {
-        in_file.seek(SeekFrom::Current(bytes_read as i64))?;
+        in_file.seek(SeekFrom::Current(bytes_sent as i64))?;
+    }
+
+    if bytes_sent > 0 {
+        Ok((bytes_sent, read_offset))
+    } else {
+        send_error.map_or_else(|| Ok((0, read_offset)), |e| Err(e))
     }
-    Ok((bytes_read, read_offset))
 }