websocket

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README

websocket

Go Reference Go Coverage

websocket is a minimal and idiomatic WebSocket library for Go.

Install

go get github.com/coder/websocket

[!NOTE] Coder now maintains this project as explained in this blog post. We're grateful to nhooyr for authoring and maintaining this project from 2019 to 2024.

Highlights

Roadmap

See GitHub issues for minor issues but the major future enhancements are:

  • Perfect examples #217
  • wstest.Pipe for in memory testing #340
  • Ping pong heartbeat helper #267
  • Ping pong instrumentation callbacks #246
  • Graceful shutdown helpers #209
  • Assembly for WebSocket masking #16
    • WIP at #326, about 3x faster
  • HTTP/2 #4
  • The holy grail #402

Examples

For a production quality example that demonstrates the complete API, see the echo example.

For a full stack example, see the chat example.

Server
http.HandlerFunc(func (w http.ResponseWriter, r *http.Request) {
	c, err := websocket.Accept(w, r, nil)
	if err != nil {
		// ...
	}
	defer c.CloseNow()

	ctx, cancel := context.WithTimeout(r.Context(), time.Second*10)
	defer cancel()

	var v interface{}
	err = wsjson.Read(ctx, c, &v)
	if err != nil {
		// ...
	}

	log.Printf("received: %v", v)

	c.Close(websocket.StatusNormalClosure, "")
})
Client
ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
defer cancel()

c, _, err := websocket.Dial(ctx, "ws://localhost:8080", nil)
if err != nil {
	// ...
}
defer c.CloseNow()

err = wsjson.Write(ctx, c, "hi")
if err != nil {
	// ...
}

c.Close(websocket.StatusNormalClosure, "")

Comparison

gorilla/websocket

Advantages of gorilla/websocket:

  • Mature and widely used
  • Prepared writes
  • Configurable buffer sizes
  • No extra goroutine per connection to support cancellation with context.Context. This costs github.com/coder/websocket 2 KB of memory per connection.

Advantages of github.com/coder/websocket:

golang.org/x/net/websocket

golang.org/x/net/websocket is deprecated. See golang/go/issues/18152.

The net.Conn can help in transitioning to github.com/coder/websocket.

gobwas/ws

gobwas/ws has an extremely flexible API that allows it to be used in an event driven style for performance. See the author's blog post.

However it is quite bloated. See https://pkg.go.dev/github.com/gobwas/ws

When writing idiomatic Go, github.com/coder/websocket will be faster and easier to use.

lesismal/nbio

lesismal/nbio is similar to gobwas/ws in that the API is event driven for performance reasons.

However it is quite bloated. See https://pkg.go.dev/github.com/lesismal/nbio

When writing idiomatic Go, github.com/coder/websocket will be faster and easier to use.

Documentation

Overview

Package websocket implements the RFC 6455 WebSocket protocol.

https://tools.ietf.org/html/rfc6455

Use Dial to dial a WebSocket server.

Use Accept to accept a WebSocket client.

Conn represents the resulting WebSocket connection.

The examples are the best way to understand how to correctly use the library.

The wsjson subpackage contain helpers for JSON and protobuf messages.

More documentation at https://github.com/coder/websocket.

Wasm

The client side supports compiling to Wasm. It wraps the WebSocket browser API.

See https://developer.mozilla.org/en-US/docs/Web/API/WebSocket

Some important caveats to be aware of:

  • Accept always errors out
  • Conn.Ping is no-op
  • Conn.CloseNow is Close(StatusGoingAway, "")
  • HTTPClient, HTTPHeader and CompressionMode in DialOptions are no-op
  • *http.Response from Dial is &http.Response{} with a 101 status code on success
Example (CrossOrigin) 
package main

import (
	"log"
	"net/http"

	"github.com/coder/websocket"
)

func main() {
	// This handler demonstrates how to safely accept cross origin WebSockets
	// from the origin example.com.
	fn := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		c, err := websocket.Accept(w, r, &websocket.AcceptOptions{
			OriginPatterns: []string{"example.com"},
		})
		if err != nil {
			log.Println(err)
			return
		}
		c.Close(websocket.StatusNormalClosure, "cross origin WebSocket accepted")
	})

	err := http.ListenAndServe("localhost:8080", fn)
	log.Fatal(err)
}

Output:
Example (Echo)

This example demonstrates a echo server. 

package main

import ()

func main() {
	// https://github.com/nhooyr/websocket/tree/master/internal/examples/echo
}

Output:
Example (FullStackChat)

This example demonstrates full stack chat with an automated test. 

package main

import ()

func main() {
	// https://github.com/nhooyr/websocket/tree/master/internal/examples/chat
}

Output:
Example (WriteOnly) 
package main

import (
	"context"
	"log"
	"net/http"
	"time"

	"github.com/coder/websocket"
	"github.com/coder/websocket/wsjson"
)

func main() {
	// This handler demonstrates how to correctly handle a write only WebSocket connection.
	// i.e you only expect to write messages and do not expect to read any messages.
	fn := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		c, err := websocket.Accept(w, r, nil)
		if err != nil {
			log.Println(err)
			return
		}
		defer c.CloseNow()

		ctx, cancel := context.WithTimeout(r.Context(), time.Minute*10)
		defer cancel()

		ctx = c.CloseRead(ctx)

		t := time.NewTicker(time.Second * 30)
		defer t.Stop()

		for {
			select {
			case <-ctx.Done():
				c.Close(websocket.StatusNormalClosure, "")
				return
			case <-t.C:
				err = wsjson.Write(ctx, c, "hi")
				if err != nil {
					log.Println(err)
					return
				}
			}
		}
	})

	err := http.ListenAndServe("localhost:8080", fn)
	log.Fatal(err)
}

Output:

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func NetConn 

func NetConn(ctx context.Context, c *Conn, msgType MessageType) net.Conn

NetConn converts a *websocket.Conn into a net.Conn.

It's for tunneling arbitrary protocols over WebSockets. Few users of the library will need this but it's tricky to implement correctly and so provided in the library. See https://github.com/nhooyr/websocket/issues/100.

Every Write to the net.Conn will correspond to a message write of the given type on *websocket.Conn.

The passed ctx bounds the lifetime of the net.Conn. If cancelled, all reads and writes on the net.Conn will be cancelled.

If a message is read that is not of the correct type, the connection will be closed with StatusUnsupportedData and an error will be returned.

Close will close the *websocket.Conn with StatusNormalClosure.

When a deadline is hit and there is an active read or write goroutine, the connection will be closed. This is different from most net.Conn implementations where only the reading/writing goroutines are interrupted but the connection is kept alive.

The Addr methods will return the real addresses for connections obtained from websocket.Accept. But for connections obtained from websocket.Dial, a mock net.Addr will be returned that gives "websocket" for Network() and "websocket/unknown-addr" for String(). This is because websocket.Dial only exposes a io.ReadWriteCloser instead of the full net.Conn to us.

When running as WASM, the Addr methods will always return the mock address described above.

A received StatusNormalClosure or StatusGoingAway close frame will be translated to io.EOF when reading.

Furthermore, the ReadLimit is set to -1 to disable it.

Types

type AcceptOptions 

type AcceptOptions struct {
	// Subprotocols lists the WebSocket subprotocols that Accept will negotiate with the client.
	// The empty subprotocol will always be negotiated as per RFC 6455. If you would like to
	// reject it, close the connection when c.Subprotocol() == "".
	Subprotocols []string

	// InsecureSkipVerify is used to disable Accept's origin verification behaviour.
	//
	// You probably want to use OriginPatterns instead.
	InsecureSkipVerify bool

	// OriginPatterns lists the host patterns for authorized origins.
	// The request host is always authorized.
	// Use this to enable cross origin WebSockets.
	//
	// i.e javascript running on example.com wants to access a WebSocket server at chat.example.com.
	// In such a case, example.com is the origin and chat.example.com is the request host.
	// One would set this field to []string{"example.com"} to authorize example.com to connect.
	//
	// Each pattern is matched case insensitively against the request origin host
	// with filepath.Match.
	// See https://golang.org/pkg/path/filepath/#Match
	//
	// Please ensure you understand the ramifications of enabling this.
	// If used incorrectly your WebSocket server will be open to CSRF attacks.
	//
	// Do not use * as a pattern to allow any origin, prefer to use InsecureSkipVerify instead
	// to bring attention to the danger of such a setting.
	OriginPatterns []string

	// CompressionMode controls the compression mode.
	// Defaults to CompressionDisabled.
	//
	// See docs on CompressionMode for details.
	CompressionMode CompressionMode

	// CompressionThreshold controls the minimum size of a message before compression is applied.
	//
	// Defaults to 512 bytes for CompressionNoContextTakeover and 128 bytes
	// for CompressionContextTakeover.
	CompressionThreshold int
}

AcceptOptions represents Accept's options.

type CloseError 

type CloseError struct {
	Code   StatusCode
	Reason string
}

CloseError is returned when the connection is closed with a status and reason.

Use Go 1.13's errors.As to check for this error. Also see the CloseStatus helper.

func (CloseError) Error 

func (ce CloseError) Error() string

type CompressionMode 

type CompressionMode int

CompressionMode represents the modes available to the permessage-deflate extension. See https://tools.ietf.org/html/rfc7692

Works in all modern browsers except Safari which does not implement the permessage-deflate extension.

Compression is only used if the peer supports the mode selected. 

const (
	// CompressionDisabled disables the negotiation of the permessage-deflate extension.
	//
	// This is the default. Do not enable compression without benchmarking for your particular use case first.
	CompressionDisabled CompressionMode = iota

	// CompressionContextTakeover compresses each message greater than 128 bytes reusing the 32 KB sliding window from
	// previous messages. i.e compression context across messages is preserved.
	//
	// As most WebSocket protocols are text based and repetitive, this compression mode can be very efficient.
	//
	// The memory overhead is a fixed 32 KB sliding window, a fixed 1.2 MB flate.Writer and a sync.Pool of 40 KB flate.Reader's
	// that are used when reading and then returned.
	//
	// Thus, it uses more memory than CompressionNoContextTakeover but compresses more efficiently.
	//
	// If the peer does not support CompressionContextTakeover then we will fall back to CompressionNoContextTakeover.
	CompressionContextTakeover

	// CompressionNoContextTakeover compresses each message greater than 512 bytes. Each message is compressed with
	// a new 1.2 MB flate.Writer pulled from a sync.Pool. Each message is read with a 40 KB flate.Reader pulled from
	// a sync.Pool.
	//
	// This means less efficient compression as the sliding window from previous messages will not be used but the
	// memory overhead will be lower as there will be no fixed cost for the flate.Writer nor the 32 KB sliding window.
	// Especially if the connections are long lived and seldom written to.
	//
	// Thus, it uses less memory than CompressionContextTakeover but compresses less efficiently.
	//
	// If the peer does not support CompressionNoContextTakeover then we will fall back to CompressionDisabled.
	CompressionNoContextTakeover
)

type Conn 

type Conn struct {
	// contains filtered or unexported fields
}

Conn represents a WebSocket connection. All methods may be called concurrently except for Reader and Read.

You must always read from the connection. Otherwise control frames will not be handled. See Reader and CloseRead.

Be sure to call Close on the connection when you are finished with it to release associated resources.

On any error from any method, the connection is closed with an appropriate reason.

This applies to context expirations as well unfortunately. See https://github.com/nhooyr/websocket/issues/242#issuecomment-633182220

func Accept 

func Accept(w http.ResponseWriter, r *http.Request, opts *AcceptOptions) (*Conn, error)

Accept accepts a WebSocket handshake from a client and upgrades the the connection to a WebSocket.

Accept will not allow cross origin requests by default. See the InsecureSkipVerify and OriginPatterns options to allow cross origin requests.

Accept will write a response to w on all errors.

Example 
package main

import (
	"context"
	"log"
	"net/http"
	"time"

	"github.com/coder/websocket"
	"github.com/coder/websocket/wsjson"
)

func main() {
	// This handler accepts a WebSocket connection, reads a single JSON
	// message from the client and then closes the connection.

	fn := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		c, err := websocket.Accept(w, r, nil)
		if err != nil {
			log.Println(err)
			return
		}
		defer c.CloseNow()

		ctx, cancel := context.WithTimeout(r.Context(), time.Second*10)
		defer cancel()

		var v interface{}
		err = wsjson.Read(ctx, c, &v)
		if err != nil {
			log.Println(err)
			return
		}

		c.Close(websocket.StatusNormalClosure, "")
	})

	err := http.ListenAndServe("localhost:8080", fn)
	log.Fatal(err)
}

Output:

func Dial 

func Dial(ctx context.Context, u string, opts *DialOptions) (*Conn, *http.Response, error)

Dial performs a WebSocket handshake on url.

The response is the WebSocket handshake response from the server. You never need to close resp.Body yourself.

If an error occurs, the returned response may be non nil. However, you can only read the first 1024 bytes of the body.

This function requires at least Go 1.12 as it uses a new feature in net/http to perform WebSocket handshakes. See docs on the HTTPClient option and https://github.com/golang/go/issues/26937#issuecomment-415855861

URLs with http/https schemes will work and are interpreted as ws/wss.

Example 
package main

import (
	"context"
	"log"
	"time"

	"github.com/coder/websocket"
	"github.com/coder/websocket/wsjson"
)

func main() {
	// Dials a server, writes a single JSON message and then
	// closes the connection.

	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	c, _, err := websocket.Dial(ctx, "ws://localhost:8080", nil)
	if err != nil {
		log.Fatal(err)
	}
	defer c.CloseNow()

	err = wsjson.Write(ctx, c, "hi")
	if err != nil {
		log.Fatal(err)
	}

	c.Close(websocket.StatusNormalClosure, "")
}

Output:

func (*Conn) Close 

func (c *Conn) Close(code StatusCode, reason string) (err error)

Close performs the WebSocket close handshake with the given status code and reason.

It will write a WebSocket close frame with a timeout of 5s and then wait 5s for the peer to send a close frame. All data messages received from the peer during the close handshake will be discarded.

The connection can only be closed once. Additional calls to Close are no-ops.

The maximum length of reason must be 125 bytes. Avoid sending a dynamic reason.

Close will unblock all goroutines interacting with the connection once complete.

func (*Conn) CloseNow 

func (c *Conn) CloseNow() (err error)

CloseNow closes the WebSocket connection without attempting a close handshake. Use when you do not want the overhead of the close handshake.

func (*Conn) CloseRead 

func (c *Conn) CloseRead(ctx context.Context) context.Context

CloseRead starts a goroutine to read from the connection until it is closed or a data message is received.

Once CloseRead is called you cannot read any messages from the connection. The returned context will be cancelled when the connection is closed.

If a data message is received, the connection will be closed with StatusPolicyViolation.

Call CloseRead when you do not expect to read any more messages. Since it actively reads from the connection, it will ensure that ping, pong and close frames are responded to. This means c.Ping and c.Close will still work as expected.

This function is idempotent.

func (*Conn) Ping 

func (c *Conn) Ping(ctx context.Context) error

Ping sends a ping to the peer and waits for a pong. Use this to measure latency or ensure the peer is responsive. Ping must be called concurrently with Reader as it does not read from the connection but instead waits for a Reader call to read the pong.

TCP Keepalives should suffice for most use cases.

Example 
package main

import (
	"context"
	"log"
	"time"

	"github.com/coder/websocket"
)

func main() {
	// Dials a server and pings it 5 times.

	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	c, _, err := websocket.Dial(ctx, "ws://localhost:8080", nil)
	if err != nil {
		log.Fatal(err)
	}
	defer c.CloseNow()

	// Required to read the Pongs from the server.
	ctx = c.CloseRead(ctx)

	for i := 0; i < 5; i++ {
		err = c.Ping(ctx)
		if err != nil {
			log.Fatal(err)
		}
	}

	c.Close(websocket.StatusNormalClosure, "")
}

Output:

func (*Conn) Read 

func (c *Conn) Read(ctx context.Context) (MessageType, []byte, error)

Read is a convenience method around Reader to read a single message from the connection.

func (*Conn) Reader 

func (c *Conn) Reader(ctx context.Context) (MessageType, io.Reader, error)

Reader reads from the connection until there is a WebSocket data message to be read. It will handle ping, pong and close frames as appropriate.

It returns the type of the message and an io.Reader to read it. The passed context will also bound the reader. Ensure you read to EOF otherwise the connection will hang.

Call CloseRead if you do not expect any data messages from the peer.

Only one Reader may be open at a time.

If you need a separate timeout on the Reader call and the Read itself, use time.AfterFunc to cancel the context passed in. See https://github.com/nhooyr/websocket/issues/87#issue-451703332 Most users should not need this.

func (*Conn) SetReadLimit 

func (c *Conn) SetReadLimit(n int64)

SetReadLimit sets the max number of bytes to read for a single message. It applies to the Reader and Read methods.

By default, the connection has a message read limit of 32768 bytes.

When the limit is hit, the connection will be closed with StatusMessageTooBig.

Set to -1 to disable.

func (*Conn) Subprotocol 

func (c *Conn) Subprotocol() string

Subprotocol returns the negotiated subprotocol. An empty string means the default protocol.

func (*Conn) Write 

func (c *Conn) Write(ctx context.Context, typ MessageType, p []byte) error

Write writes a message to the connection.

See the Writer method if you want to stream a message.

If compression is disabled or the compression threshold is not met, then it will write the message in a single frame.

func (*Conn) Writer 

func (c *Conn) Writer(ctx context.Context, typ MessageType) (io.WriteCloser, error)

Writer returns a writer bounded by the context that will write a WebSocket message of type dataType to the connection.

You must close the writer once you have written the entire message.

Only one writer can be open at a time, multiple calls will block until the previous writer is closed.

type DialOptions 

type DialOptions struct {
	// HTTPClient is used for the connection.
	// Its Transport must return writable bodies for WebSocket handshakes.
	// http.Transport does beginning with Go 1.12.
	HTTPClient *http.Client

	// HTTPHeader specifies the HTTP headers included in the handshake request.
	HTTPHeader http.Header

	// Host optionally overrides the Host HTTP header to send. If empty, the value
	// of URL.Host will be used.
	Host string

	// Subprotocols lists the WebSocket subprotocols to negotiate with the server.
	Subprotocols []string

	// CompressionMode controls the compression mode.
	// Defaults to CompressionDisabled.
	//
	// See docs on CompressionMode for details.
	CompressionMode CompressionMode

	// CompressionThreshold controls the minimum size of a message before compression is applied.
	//
	// Defaults to 512 bytes for CompressionNoContextTakeover and 128 bytes
	// for CompressionContextTakeover.
	CompressionThreshold int
}

DialOptions represents Dial's options.

type MessageType 

type MessageType int

MessageType represents the type of a WebSocket message. See https://tools.ietf.org/html/rfc6455#section-5.6 

const (
	// MessageText is for UTF-8 encoded text messages like JSON.
	MessageText MessageType = iota + 1
	// MessageBinary is for binary messages like protobufs.
	MessageBinary
)

MessageType constants.

func (MessageType) String 

func (i MessageType) String() string

type StatusCode 

type StatusCode int

StatusCode represents a WebSocket status code. https://tools.ietf.org/html/rfc6455#section-7.4 

const (
	StatusNormalClosure   StatusCode = 1000
	StatusGoingAway       StatusCode = 1001
	StatusProtocolError   StatusCode = 1002
	StatusUnsupportedData StatusCode = 1003

	// StatusNoStatusRcvd cannot be sent in a close message.
	// It is reserved for when a close message is received without
	// a status code.
	StatusNoStatusRcvd StatusCode = 1005

	// StatusAbnormalClosure is exported for use only with Wasm.
	// In non Wasm Go, the returned error will indicate whether the
	// connection was closed abnormally.
	StatusAbnormalClosure StatusCode = 1006

	StatusInvalidFramePayloadData StatusCode = 1007
	StatusPolicyViolation         StatusCode = 1008
	StatusMessageTooBig           StatusCode = 1009
	StatusMandatoryExtension      StatusCode = 1010
	StatusInternalError           StatusCode = 1011
	StatusServiceRestart          StatusCode = 1012
	StatusTryAgainLater           StatusCode = 1013
	StatusBadGateway              StatusCode = 1014

	// StatusTLSHandshake is only exported for use with Wasm.
	// In non Wasm Go, the returned error will indicate whether there was
	// a TLS handshake failure.
	StatusTLSHandshake StatusCode = 1015
)

https://www.iana.org/assignments/websocket/websocket.xhtml#close-code-number

These are only the status codes defined by the protocol.

You can define custom codes in the 3000-4999 range. The 3000-3999 range is reserved for use by libraries, frameworks and applications. The 4000-4999 range is reserved for private use.

func CloseStatus 

func CloseStatus(err error) StatusCode

CloseStatus is a convenience wrapper around Go 1.13's errors.As to grab the status code from a CloseError.

-1 will be returned if the passed error is nil or not a CloseError.

Example 
package main

import (
	"context"
	"log"
	"time"

	"github.com/coder/websocket"
)

func main() {
	// Dials a server and then expects to be disconnected with status code
	// websocket.StatusNormalClosure.

	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	c, _, err := websocket.Dial(ctx, "ws://localhost:8080", nil)
	if err != nil {
		log.Fatal(err)
	}
	defer c.CloseNow()

	_, _, err = c.Reader(ctx)
	if websocket.CloseStatus(err) != websocket.StatusNormalClosure {
		log.Fatalf("expected to be disconnected with StatusNormalClosure but got: %v", err)
	}
}

Output:

func (StatusCode) String 

func (i StatusCode) String() string

Source Files

View all Source files

Directories

Path Synopsis
internal
bpool
errd
test
Package test contains subpackages only used in tests.
 Package test contains subpackages only used in tests.
test/assert
test/wstest
test/xrand
util
wsjs
Package wsjs implements typed access to the browser javascript WebSocket API.
 Package wsjs implements typed access to the browser javascript WebSocket API.
xsync
thirdparty Module
Package wsjson provides helpers for reading and writing JSON messages.
 Package wsjson provides helpers for reading and writing JSON messages.

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