WebSocket::write_message will no longer buffer unlimited messages - it will only buffer a configurable number of outbound messages. Needed for snapview/tokio-tungstenite#35.

Cargo.toml

@@ -7,9 +7,9 @@ authors = ["Alexey Galakhov"]
 license = "MIT/Apache-2.0"
 readme = "README.md"
 homepage = "https://github.com/snapview/tungstenite-rs"
-documentation = "https://docs.rs/tungstenite/0.5.3"
+documentation = "https://docs.rs/tungstenite/0.5.4"
 repository = "https://github.com/snapview/tungstenite-rs"
-version = "0.5.3"
+version = "0.5.4"
 
 [features]
 default = ["tls"]

src/error.rs

@@ -12,6 +12,7 @@ use std::string;
 use httparse;
 
 use protocol::frame::CloseFrame;
+use protocol::Message;
 
 #[cfg(feature="tls")]
 pub mod tls {
@@ -36,6 +37,8 @@ pub enum Error {
     Capacity(Cow<'static, str>),
     /// Protocol violation
     Protocol(Cow<'static, str>),
+    /// Message send queue full
+    SendQueueFull(Message),
     /// UTF coding error
     Utf8,
     /// Invlid URL.
@@ -59,6 +62,7 @@ impl fmt::Display for Error {
             Error::Tls(ref err) => write!(f, "TLS error: {}", err),
             Error::Capacity(ref msg) => write!(f, "Space limit exceeded: {}", msg),
             Error::Protocol(ref msg) => write!(f, "WebSocket protocol error: {}", msg),
+            Error::SendQueueFull(_) => write!(f, "Send queue is full"),
             Error::Utf8 => write!(f, "UTF-8 encoding error"),
             Error::Url(ref msg) => write!(f, "URL error: {}", msg),
             Error::Http(code) => write!(f, "HTTP code: {}", code),
@@ -75,6 +79,7 @@ impl ErrorTrait for Error {
             Error::Tls(ref err) => err.description(),
             Error::Capacity(ref msg) => msg.borrow(),
             Error::Protocol(ref msg) => msg.borrow(),
+            Error::SendQueueFull(_) => "Send queue is full",
             Error::Utf8 => "",
             Error::Url(ref msg) => msg.borrow(),
             Error::Http(_) => "",

src/protocol/mod.rs

@@ -42,6 +42,7 @@ pub struct WebSocket<Stream> {
     incomplete: Option<IncompleteMessage>,
     /// Send: a data send queue.
     send_queue: VecDeque<Frame>,
+    max_send_queue: usize,
     /// Send: an OOB pong message.
     pong: Option<Frame>,
 }
@@ -74,6 +75,7 @@ impl<Stream> WebSocket<Stream> {
             state: WebSocketState::Active,
             incomplete: None,
             send_queue: VecDeque::new(),
+            max_send_queue: 1,
             pong: None,
         }
     }
@@ -101,13 +103,20 @@ impl<Stream: Read + Write> 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.
+    /// WebSocket will buffer a configurable number of messages at a time, except to reply to Ping
+    /// and Close requests. If the WebSocket's send queue is full, SendQueueFull will be returned
+    /// along with the passed message. Otherwise, the message is queued and Ok(()) is returned.
     ///
     /// Note that only the last pong frame is stored to be sent, and only the
-    /// most recent pong frame is sent if multiple pong frames are queued up.
+    /// most recent pong frame is sent if multiple pong frames are queued
     pub fn write_message(&mut self, message: Message) -> Result<()> {
+        // Try to make some room for the new message
+        self.write_pending().no_block()?;
+
+        if self.send_queue.len() >= self.max_send_queue {
+            return Err(Error::SendQueueFull(message));
+        }
+
         let frame = match message {
             Message::Text(data) => {
                 Frame::message(data.into(), OpCode::Data(OpData::Text), true)
@@ -122,13 +131,13 @@ impl<Stream: Read + Write> WebSocket<Stream> {
             }
         };
         self.send_queue.push_back(frame);
-        self.write_pending()
+        Ok(())
     }
 
     /// 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().
+    /// There is no need to call it again.
     pub fn close(&mut self, code: Option<CloseFrame>) -> Result<()> {
         if let WebSocketState::Active = self.state {
             self.state = WebSocketState::ClosedByUs;
@@ -151,7 +160,7 @@ impl<Stream: Read + Write> WebSocket<Stream> {
         // 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) {
+        if let Some(pong) = self.pong.take() {
             self.send_one_frame(pong)?;
         }
         // If we have any unsent frames, send them.
@@ -159,21 +168,20 @@ impl<Stream: Read + Write> WebSocket<Stream> {
             self.send_one_frame(data)?;
         }
 
+        // If we get to this point, the send queue is empty and the underlying socket is still
+        // willing to take more data.
+
         // If we're closing and there is nothing to send anymore, we should close the connection.
-        if self.send_queue.is_empty() {
-            if let WebSocketState::ClosedByPeer(ref mut frame) = self.state {
-                // 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(replace(frame, None))),
-                }
-            } else {
-                Ok(())
+        if let WebSocketState::ClosedByPeer(ref mut frame) = self.state {
+            // 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(frame.take())),
             }
         } else {
             Ok(())
@@ -262,7 +270,7 @@ impl<Stream: Read + Write> WebSocket<Stream> {
                                 return Err(Error::Protocol("Continue frame but nothing to continue".into()))
                             }
                             if fin {
-                                Ok(Some(replace(&mut self.incomplete, None).unwrap().complete()?))
+                                Ok(Some(self.incomplete.take().unwrap().complete()?))
                             } else {
                                 Ok(None)
                             }
@@ -381,9 +389,9 @@ impl<Stream: Read + Write> WebSocket<Stream> {
                 if err.kind() == IoErrorKind::ConnectionReset {
                     match self.state {
                         WebSocketState::ClosedByPeer(ref mut frame) =>
-                            Error::ConnectionClosed(replace(frame, None)),
+                            Error::ConnectionClosed(frame.take()),
                         WebSocketState::CloseAcknowledged(ref mut frame) =>
-                            Error::ConnectionClosed(replace(frame, None)),
+                            Error::ConnectionClosed(frame.take()),
                         _ => Error::Io(err),
                     }
                 } else {