RFC6455 WebSocket implementation in Go.
- 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
wsutilpackage, which allow to start fast without digging the protocol internals
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.
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.
Example applications using ws are developed in separate repository
ws-examples.
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 {
hdr, err = r.NextFrame()
if err != nil {
return err
}
if hdr.OpCode == ws.OpClose {
return io.EOF
}
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 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\r\n",
)),
)
},
OnHeader: func(key, value []byte) error {
if string(key) != "Cookie" {
return nil
}
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() (ws.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)
}
}
}