ws

RFC6455 WebSocket implementation in Go.

Features

• Zero-copy upgrade
• No intermediate allocations during I/O
• Low-level API which allows to build your own logic of packet handling and buffers reuse
• High-level wrappers and helpers around API in wsutil package, which allow to start fast without digging the protocol internals

Documentation

GoDoc.

Why

Existing WebSocket implementations do not allow users to reuse I/O buffers between connections in clear way. This library aims to export efficient low-level interface for working with the protocol without forcing only one way it could be used.

By the way, if you want get the higher-level tools, you can use wsutil package.

Status

Library is tagged as v1* so its API must not be broken during some improvements or refactoring.

This implementation of RFC6455 passes Autobahn Test Suite and currently has about 78% coverage.

Examples

Example applications using ws are developed in separate repository ws-examples.

Usage

The higher-level example of WebSocket echo server:

package main

import (
	"net/http"

	"github.com/gobwas/ws"
	"github.com/gobwas/ws/wsutil"
)

func main() {
	http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		conn, _, _, err := ws.UpgradeHTTP(r, w)
		if err != nil {
			// handle error
		}
		go func() {
			defer conn.Close()

			for {
				msg, op, err := wsutil.ReadClientData(conn)
				if err != nil {
					// handle error
				}
				err = wsutil.WriteServerMessage(conn, op, msg)
				if err != nil {
					// handle error
				}
			}
		}()
	}))
}

Lower-level, but still high-level example:

import (
	"net/http"
	"io"

	"github.com/gobwas/ws"
	"github.com/gobwas/ws/wsutil"
)

func main() {
	http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		conn, _, _, err := ws.UpgradeHTTP(r, w)
		if err != nil {
			// handle error
		}
		go func() {
			defer conn.Close()

			var (
				state  = ws.StateServerSide
				reader = wsutil.NewReader(conn, state)
				writer = wsutil.NewWriter(conn, state, ws.OpText)
			)
			for {
				header, err := reader.NextFrame()
				if err != nil {
					// handle error
				}

				// Reset writer to write frame with right operation code.
				writer.Reset(conn, state, header.OpCode)

				if _, err = io.Copy(writer, reader); err != nil {
					// handle error
				}
				if err = writer.Flush(); err != nil {
					// handle error
				}
			}
		}()
	}))
}

We can apply the same pattern to read and write structured responses through a JSON encoder and decoder.:

	...
	var (
		r = wsutil.NewReader(conn, ws.StateServerSide)
		w = wsutil.NewWriter(conn, ws.StateServerSide, ws.OpText)
		decoder = json.NewDecoder(r)
		encoder = json.NewEncoder(w)
	)
	for {
		if _, err = r.NextFrame(); err != nil {
			return err
		}
		var req Request
		if err := decoder.Decode(&req); err != nil {
			return err
		}
		var resp Response
		if err := encoder.Encode(&resp); err != nil {
			return err
		}
		if err = w.Flush(); err != nil {
			return err
		}
	}
	...

The lower-level example without wsutil:

package main

import (
	"net"
	"io"

	"github.com/gobwas/ws"
)

func main() {
	ln, err := net.Listen("tcp", "localhost:8080")
	if err != nil {
		log.Fatal(err)
	}

	for {
		conn, err := ln.Accept()
		if err != nil {
			// handle error
		}
		_, err = ws.Upgrade(conn)
		if err != nil {
			// handle error
		}

		go func() {
			defer conn.Close()

			for {
				header, err := ws.ReadHeader(conn)
				if err != nil {
					// handle error
				}

				payload := make([]byte, header.Length)
				_, err = io.ReadFull(conn, payload)
				if err != nil {
					// handle error
				}
				if header.Masked {
					ws.Cipher(payload, header.Mask, 0)
				}

				// Reset the Masked flag, server frames must not be masked as
				// RFC6455 says.
				header.Masked = false

				if err := ws.WriteHeader(conn, header); err != nil {
					// handle error
				}
				if _, err := conn.Write(payload); err != nil {
					// handle error
				}

				if header.OpCode == ws.OpClose {
					return
				}
			}
		}()
	}
}

Zero-copy upgrade

Zero-copy upgrade helps to avoid unnecessary allocations and copying while handling HTTP Upgrade request.

Processing of all non-websocket headers is made in place with use of registered user callbacks whose arguments are only valid until callback returns.

The simple example looks like this:

package main

import (
	"net"
	"log"

	"github.com/gobwas/ws"
)

func main() {
	ln, err := net.Listen("tcp", "localhost:8080")
	if err != nil {
		log.Fatal(err)
	}
	u := ws.Upgrader{
		OnHeader: func(key, value []byte) (err error) {
			log.Printf("non-websocket header: %q=%q", key, value)
			return
		},
	}
	for {
		conn, err := ln.Accept()
		if err != nil {
			// handle error
		}

		_, err = u.Upgrade(conn)
		if err != nil {
			// handle error
		}
	}
}

Usage of ws.Upgrader here brings ability to control incoming connections on tcp level and simply not to accept them by some logic.

Zero-copy upgrade is for high-load services which have to control many resources such as connections buffers.

The real life example could be like this:

package main

import (
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"runtime"

	"github.com/gobwas/httphead"
	"github.com/gobwas/ws"
)

func main() {
	ln, err := net.Listen("tcp", "localhost:8080")
	if err != nil {
		// handle error
	}

	// Prepare handshake header writer from http.Header mapping.
	header := ws.HandshakeHeaderHTTP(http.Header{
		"X-Go-Version": []string{runtime.Version()},
	})

	u := ws.Upgrader{
		OnHost: func(host []byte) error {
			if string(host) == "github.com" {
				return nil
			}
			return &ws.RejectConnectionError(
				ws.RejectionStatus(403),
				ws.RejectionHeader(ws.HandshakeHeaderString(
					"X-Want-Host: github.com",
				)),
			)
		},
		OnHeader: func(key, value []byte) error {
			if string(key) != "Cookie" {
				return
			}
			ok := httphead.ScanCookie(value, func(key, value []byte) bool {
				// Check session here or do some other stuff with cookies.
				// Maybe copy some values for future use.
				return true
			})
			if ok {
				return nil
			}
			return &ws.RejectConnectionError(
				ws.RejectionReason("bad cookie"),
				ws.RejectionStatus(400),
			)
		},
		OnBeforeUpgrade: func() (HandshakeHeader, error) {
			return header, nil
		},
	}
	for {
		conn, err := ln.Accept()
		if err != nil {
			log.Fatal(err)
		}
		_, err = u.Upgrade(conn)
		if err != nil {
			log.Printf("upgrade error: %s", err)
		}
	}
}