A lightweight and scalable asynchronous WebSocket listener
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README.md

Build status WebSocketListener


Please read

This project is considered completed. Reported bugs will be fixed, but there is no plans for new features.

@deniszykov has continued its development, adding support for other platforms in his fork deniszykov/WebSocketListener.


The WebSocketListener class provides simple methods that listen for and accept incoming WebSocket connection requests asynchronously. It is a lightweight listener with an API very similar to the System.Net.TcpListener class. It does not use the Microsoft's System.Net.WebSockets namespace.

It works with .NET Standard 2.0 since Version 3.0.0. Version 2.2.4 is .NET/Mono 4.5 compatible.

WebSocketListener has been designed to provide WebSocket connectivity to other applications, in the same way that System.Net.TcpListener provides TCP connectivity. It is not a communication framework on its own and it does not provide any kind of publisher/subscriber pattern or reliable messaging beyond TCP.

  • It can work with both Text or Binary messages.
  • It supports wss://(secure). More info.
  • It supports per-message deflate compression. More info.
  • It can work with multiple WebSocket standards simultaneously. More info
  • It is extensible. More info.
  • It is asynchronous.
  • It supports Mono. More info
  • It has the Ping/Pong functionality built-in.
  • It can measure connection latency. More info
  • It can work with cookies and custom HTTP response statuses. More info
  • It detects and disconnects half open connections.
  • It allows to send and receive messages as streams. WebSocket messages are represented as delimited stream-like objects, that allows integration with other .NET objects like e.g. StreamReader and StreamWriter. Two different WebSocket messages, yield two different streams.
  • Messages reads and writes are streamed. Big messages are not held in memory during reads or writes.
  • It handles partial frames transparently. The WebSocket specification states that a single message can be sent across multiple individual frames. The message stream will allow to read all the message data, no matter if it was sent in a single or multiple frames.
  • It handles interleaved control frames transparently. The WebSocket specification states that control frames can appear interleaved with data frames, including between partial frames of the same message. The message stream will allow to read just the message data, it will skip the control frames.

Take a look on the performance and load tests on a simple 'echo' server.

Featured example

This echo server example uses NGINX to serve static files and WebSocket connections through the same port, providing SSL termination for both. It uses Docker and .Net Core 2.0.

Quickstart

Install

WebSocketListener is available through NuGet

PM> Install-Package vtortola.WebSocketListener

Set up

Setting up a server and start listening for clients is very similar to a TcpListener. An listening endpoint and a WebSocket standard is the minimum needed to set up a server.

var server = new WebSocketListener(new IPEndPoint(IPAddress.Any, 8006));
server.Standards.RegisterStandard(new WebSocketFactoryRfc6455());
server.StartAsync();

The class vtortola.WebSockets.Rfc6455.WebSocketFactoryRfc6455 gives support to the RFC 6455, that is the WebSocket standard used at the moment. Future standards can be added in the same way.

Optionally, you can also:

Accepting clients

Once the server has started, clients can be awaited asynchronously. When a client connects, a WebSocket object will be returned:

var client = await server.AcceptWebSocketAsync(cancellationToken);

The client provides means to read and write messages. With the client, as in the underlying NetworkStream, is possible to write and read at the same time even from different threads, but is not possible to read from two or more threads at the same time, same for writing.

AcceptWebSocketAsync should be in a loop to continuously accept new clients, also wrapped in a try/catch since errors in the negotiation process will be thrown here. Take a look to the simple host tutorial.

Receiving messages

With the client we can await a message as a readonly stream:

var messageReadStream = await client.ReadMessageAsync(cancellationToken);

Messages are a stream-like objects, so is it possible to use regular .NET framework tools to work with them. The WebSocketMessageReadStream.MessageType property indicates the kind of content the message contains, so it can be used to select a different handling approach.

The returned WebSocketMessageReadStream object will contain information from the header, like type of message (Text or Binary) but not the message content, neither the message length, since a frame only contains the frame length rather than the total message length, therefore that information could be missleading.

A text message can be read with a simple StreamReader. It is worth remember that according to the WebSockets specs, it always uses UTF8 for text enconding:

if(messageReadStream.MessageType == WebSocketMessageType.Text)
{
   var msgContent = string.Empty;
   using (var sr = new StreamReader(messageReadStream, Encoding.UTF8))
        msgContent = await sr.ReadToEndAsync();
}

ReadMessageAsync should go in a loop, to read messages continuously. Writes and read can be performed at the same time. Take a look to the simple host tutorial.

Also, a binary message can be read using regular .NET techniques:

if(messageReadStream.MessageType == WebSocketMessageType.Binary)
{
   using (var ms = new MemoryStream())
   {
       await messageReadStream.CopyToAsync(ms);
   }
}

Sending messages

Writing messages is also easy. The WebSocketMessageReadStream.CreateMessageWriter method allows to create a write only message:

using (var messageWriterStream = client.CreateMessageWriter(WebSocketMessageType.Text))

Once a message writer is created, regular .NET tools can be used to write in it:

using (var sw = new StreamWriter(messageWriterStream, Encoding.UTF8))
{
   await sw.WriteAsync("Hello World!");
}

Also binary messages:

using (var messageWriter = ws.CreateMessageWriter(WebSocketMessageType.Binary))
   await myFileStream.CopyToAsync(messageWriter);

Example

Take a look on the WebSocketListener samples.

The MIT License (MIT)

Copyright (c) 2014 vtortola

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.