protocol: add write_pending() functions

The semantics of write_message() and write_frame()
is changed accordingly.

src/protocol/frame/mod.rs

@@ -66,12 +66,22 @@ impl<Stream> FrameSocket<Stream>
     where Stream: Write
 {
     /// Write a frame to stream.
+    ///
+    /// This function guarantees that the frame is queued regardless of any errors.
+    /// There is no need to resend the frame. In order to handle WouldBlock or Incomplete,
+    /// call write_pending() afterwards.
     pub fn write_frame(&mut self, frame: Frame) -> Result<()> {
         debug!("writing frame {}", frame);
         self.out_buffer.reserve(frame.len());
-        frame.format(&mut self.out_buffer)?;
-        let len = self.stream.write(&self.out_buffer)?;
-        self.out_buffer.drain(0..len);
+        frame.format(&mut self.out_buffer).expect("Bug: can't write to vector");
+        self.write_pending()
+    }
+    /// Complete pending write, if any.
+    pub fn write_pending(&mut self) -> Result<()> {
+        while !self.out_buffer.is_empty() {
+            let len = self.stream.write(&self.out_buffer)?;
+            self.out_buffer.drain(0..len);
+        }
         Ok(())
     }
 }

src/protocol/mod.rs

@@ -55,9 +55,14 @@ impl<Stream> WebSocket<Stream>
     }
 
     /// Read a message from stream, if possible.
+    ///
+    /// This function sends pong and close responses automatically.
+    /// However, it never blocks on write.
     pub fn read_message(&mut self) -> Result<Message> {
         loop {
-            self.send_pending().no_block()?;
+            // Since we may get ping or close, we need to reply to the messages even during read.
+            // Thus we call write_pending() but ignore its blocking.
+            self.write_pending().no_block()?;
             // If we get here, either write blocks or we have nothing to write.
             // Thus if read blocks, just let it return WouldBlock.
             if let Some(message) = self.read_message_frame()? {
@@ -68,6 +73,10 @@ impl<Stream> WebSocket<Stream>
     }
 
     /// Send a message to stream, if possible.
+    ///
+    /// This function guarantees that the frame is queued regardless of any errors.
+    /// There is no need to resend the frame. In order to handle WouldBlock or Incomplete,
+    /// call write_pending() afterwards.
     pub fn write_message(&mut self, message: Message) -> Result<()> {
         let frame = {
             let opcode = match message {
@@ -77,11 +86,13 @@ impl<Stream> WebSocket<Stream>
             Frame::message(message.into_data(), OpCode::Data(opcode), true)
         };
         self.send_queue.push_back(frame);
-        self.send_pending().no_block()?;
-        Ok(())
+        self.write_pending()
     }
 
     /// Close the connection.
+    ///
+    /// This function guarantees that the close frame will be queued.
+    /// There is no need to call it again, just like write_message().
     pub fn close(&mut self) -> Result<()> {
         match self.state {
             WebSocketState::Active => {
@@ -93,8 +104,41 @@ impl<Stream> WebSocket<Stream>
                 // already closed, nothing to do
             }
         }
-        self.send_pending().no_block()?;
-        Ok(())
+        self.write_pending()
+    }
+
+    /// Flush the pending send queue.
+    pub fn write_pending(&mut self) -> Result<()> {
+        // First, make sure we have no pending frame sending.
+        self.socket.write_pending()?;
+
+        // Upon receipt of a Ping frame, an endpoint MUST send a Pong frame in
+        // response, unless it already received a Close frame. It SHOULD
+        // respond with Pong frame as soon as is practical. (RFC 6455)
+        if let Some(pong) = replace(&mut self.pong, None) {
+            self.send_one_frame(pong)?;
+        }
+        // If we have any unsent frames, send them.
+        while let Some(data) = self.send_queue.pop_front() {
+            self.send_one_frame(data)?;
+        }
+
+        // If we're closing and there is nothing to send anymore, we should close the connection.
+        match self.state {
+            WebSocketState::ClosedByPeer if self.send_queue.is_empty() => {
+                // The underlying TCP connection, in most normal cases, SHOULD be closed
+                // first by the server, so that it holds the TIME_WAIT state and not the
+                // client (as this would prevent it from re-opening the connection for 2
+                // maximum segment lifetimes (2MSL), while there is no corresponding
+                // server impact as a TIME_WAIT connection is immediately reopened upon
+                // a new SYN with a higher seq number). (RFC 6455)
+                match self.role {
+                    Role::Client => Ok(()),
+                    Role::Server => Err(Error::ConnectionClosed),
+                }
+            }
+            _ => Ok(()),
+        }
     }
 
     /// Convert a frame socket into a WebSocket.
@@ -288,37 +332,6 @@ impl<Stream> WebSocket<Stream>
         Ok(())
     }
 
-    /// Flush the pending send queue.
-    fn send_pending(&mut self) -> Result<()> {
-        // Upon receipt of a Ping frame, an endpoint MUST send a Pong frame in
-        // response, unless it already received a Close frame. It SHOULD
-        // respond with Pong frame as soon as is practical. (RFC 6455)
-        if let Some(pong) = replace(&mut self.pong, None) {
-            self.send_one_frame(pong)?;
-        }
-        // If we have any unsent frames, send them.
-        while let Some(data) = self.send_queue.pop_front() {
-            self.send_one_frame(data)?;
-        }
-
-        // If we're closing and there is nothing to send anymore, we should close the connection.
-        match self.state {
-            WebSocketState::ClosedByPeer if self.send_queue.is_empty() => {
-                // The underlying TCP connection, in most normal cases, SHOULD be closed
-                // first by the server, so that it holds the TIME_WAIT state and not the
-                // client (as this would prevent it from re-opening the connection for 2
-                // maximum segment lifetimes (2MSL), while there is no corresponding
-                // server impact as a TIME_WAIT connection is immediately reopened upon
-                // a new SYN with a higher seq number). (RFC 6455)
-                match self.role {
-                    Role::Client => Ok(()),
-                    Role::Server => Err(Error::ConnectionClosed),
-                }
-            }
-            _ => Ok(()),
-        }
-    }
-
     /// Send a single pending frame.
     fn send_one_frame(&mut self, mut frame: Frame) -> Result<()> {
         match self.role {
@@ -330,8 +343,7 @@ impl<Stream> WebSocket<Stream>
                 frame.set_mask();
             }
         }
-        self.socket.write_frame(frame)?;
-        Ok(())
+        self.socket.write_frame(frame)
     }
 
 }