websocket

package
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 Go to latest Published: Apr 28, 2023 License: MIT Imports: 25 Imported by: 0

Documentation

Overview

Package websocket implements the WebSocket protocol defined in RFC 6455.

Overview

The Conn type represents a WebSocket connection. A server application calls the Upgrader.Upgrade method from an HTTP request handler to get a *Conn: 

var upgrader = websocket.Upgrader{
    ReadBufferSize:  1024,
    WriteBufferSize: 1024,
}

func handler(w http.ResponseWriter, r *http.Request) {
    conn, err := upgrader.Upgrade(w, r, nil)
    if err != nil {
        log.Println(err)
        return
    }
    ... Use conn to send and receive messages.
}

Call the connection's WriteMessage and ReadMessage methods to send and receive messages as a slice of bytes. This snippet of code shows how to echo messages using these methods: 

for {
    messageType, p, err := conn.ReadMessage()
    if err != nil {
        log.Println(err)
        return
    }
    if err := conn.WriteMessage(messageType, p); err != nil {
        log.Println(err)
        return
    }
}

In above snippet of code, p is a []byte and messageType is an int with value websocket.BinaryMessage or websocket.TextMessage.

An application can also send and receive messages using the io.WriteCloser and io.Reader interfaces. To send a message, call the connection NextWriter method to get an io.WriteCloser, write the message to the writer and close the writer when done. To receive a message, call the connection NextReader method to get an io.Reader and read until io.EOF is returned. This snippet shows how to echo messages using the NextWriter and NextReader methods: 

for {
    messageType, r, err := conn.NextReader()
    if err != nil {
        return
    }
    w, err := conn.NextWriter(messageType)
    if err != nil {
        return err
    }
    if _, err := io.Copy(w, r); err != nil {
        return err
    }
    if err := w.Close(); err != nil {
        return err
    }
}

Data Messages

The WebSocket protocol distinguishes between text and binary data messages. Text messages are interpreted as UTF-8 encoded text. The interpretation of binary messages is left to the application.

This package uses the TextMessage and BinaryMessage integer constants to identify the two data message types. The ReadMessage and NextReader methods return the type of the received message. The messageType argument to the WriteMessage and NextWriter methods specifies the type of a sent message.

It is the application's responsibility to ensure that text messages are valid UTF-8 encoded text.

Control Messages

The WebSocket protocol defines three types of control messages: close, ping and pong. Call the connection WriteControl, WriteMessage or NextWriter methods to send a control message to the peer.

Connections handle received close messages by calling the handler function set with the SetCloseHandler method and by returning a *CloseError from the NextReader, ReadMessage or the message Read method. The default close handler sends a close message to the peer.

Connections handle received ping messages by calling the handler function set with the SetPingHandler method. The default ping handler sends a pong message to the peer.

Connections handle received pong messages by calling the handler function set with the SetPongHandler method. The default pong handler does nothing. If an application sends ping messages, then the application should set a pong handler to receive the corresponding pong.

The control message handler functions are called from the NextReader, ReadMessage and message reader Read methods. The default close and ping handlers can block these methods for a short time when the handler writes to the connection.

The application must read the connection to process close, ping and pong messages sent from the peer. If the application is not otherwise interested in messages from the peer, then the application should start a goroutine to read and discard messages from the peer. A simple example is: 

func readLoop(c *websocket.Conn) {
    for {
        if _, _, err := c.NextReader(); err != nil {
            c.Close()
            break
        }
    }
}

Concurrency

Connections support one concurrent reader and one concurrent writer.

Applications are responsible for ensuring that no more than one goroutine calls the write methods (NextWriter, SetWriteDeadline, WriteMessage, WriteJSON, EnableWriteCompression, SetCompressionLevel) concurrently and that no more than one goroutine calls the read methods (NextReader, SetReadDeadline, ReadMessage, ReadJSON, SetPongHandler, SetPingHandler) concurrently.

The Close and WriteControl methods can be called concurrently with all other methods.

Origin Considerations

Web browsers allow Javascript applications to open a WebSocket connection to any host. It's up to the server to enforce an origin policy using the Origin request header sent by the browser.

The Upgrader calls the function specified in the CheckOrigin field to check the origin. If the CheckOrigin function returns false, then the Upgrade method fails the WebSocket handshake with HTTP status 403.

If the CheckOrigin field is nil, then the Upgrader uses a safe default: fail the handshake if the Origin request header is present and the Origin host is not equal to the Host request header.

The deprecated package-level Upgrade function does not perform origin checking. The application is responsible for checking the Origin header before calling the Upgrade function.

Compression EXPERIMENTAL

Per message compression extensions (RFC 7692) are experimentally supported by this package in a limited capacity. Setting the EnableCompression option to true in Dialer or Upgrader will attempt to negotiate per message deflate support. 

var upgrader = websocket.Upgrader{
    EnableCompression: true,
}

If compression was successfully negotiated with the connection's peer, any message received in compressed form will be automatically decompressed. All Read methods will return uncompressed bytes.

Per message compression of messages written to a connection can be enabled or disabled by calling the corresponding Conn method: 

conn.EnableWriteCompression(false)

Currently this package does not support compression with "context takeover". This means that messages must be compressed and decompressed in isolation, without retaining sliding window or dictionary state across messages. For more details refer to RFC 7692.

Use of compression is experimental and may result in decreased performance.

Index

Constants

View Source 
const (
	CloseNormalClosure           = 1000
	CloseGoingAway               = 1001
	CloseProtocolError           = 1002
	CloseUnsupportedData         = 1003
	CloseNoStatusReceived        = 1005
	CloseAbnormalClosure         = 1006
	CloseInvalidFramePayloadData = 1007
	ClosePolicyViolation         = 1008
	CloseMessageTooBig           = 1009
	CloseMandatoryExtension      = 1010
	CloseInternalServerErr       = 1011
	CloseServiceRestart          = 1012
	CloseTryAgainLater           = 1013
	CloseTLSHandshake            = 1015
)

Close codes defined in RFC 6455, section 11.7.

View Source 
const (
	// TextMessage denotes a text data message. The text message payload is
	// interpreted as UTF-8 encoded text data.
	TextMessage = 1

	// BinaryMessage denotes a binary data message.
	BinaryMessage = 2

	// CloseMessage denotes a close control message. The optional message
	// payload contains a numeric code and text. Use the FormatCloseMessage
	// function to format a close message payload.
	CloseMessage = 8

	// PingMessage denotes a ping control message. The optional message payload
	// is UTF-8 encoded text.
	PingMessage = 9

	// PongMessage denotes a pong control message. The optional message payload
	// is UTF-8 encoded text.
	PongMessage = 10
)

The message types are defined in RFC 6455, section 11.8.

Variables

View Source 
var DefaultDialer = &Dialer{
	Proxy:            http.ProxyFromEnvironment,
	HandshakeTimeout: 45 * time.Second,
}

DefaultDialer is a dialer with all fields set to the default values.

View Source 
var ErrBadHandshake = errors.New("websocket: bad handshake")

ErrBadHandshake is returned when the server response to opening handshake is invalid.

View Source 
var ErrCloseSent = errors.New("websocket: close sent")

ErrCloseSent is returned when the application writes a message to the connection after sending a close message.

View Source 
var ErrReadLimit = errors.New("websocket: read limit exceeded")

ErrReadLimit is returned when reading a message that is larger than the read limit set for the connection.

Functions

func FormatCloseMessage 

func FormatCloseMessage(closeCode int, text string) []byte

FormatCloseMessage formats closeCode and text as a WebSocket close message. An empty message is returned for code CloseNoStatusReceived.

func IsCloseError 

func IsCloseError(err error, codes ...int) bool

IsCloseError returns boolean indicating whether the error is a *CloseError with one of the specified codes.

func IsUnexpectedCloseError 

func IsUnexpectedCloseError(err error, expectedCodes ...int) bool

IsUnexpectedCloseError returns boolean indicating whether the error is a *CloseError with a code not in the list of expected codes.

func IsWebSocketUpgrade 

func IsWebSocketUpgrade(r *http.Request) bool

IsWebSocketUpgrade returns true if the client requested upgrade to the WebSocket protocol.

func ReadJSON deprecated 

func ReadJSON(c *Conn, v interface{}) error

ReadJSON reads the next JSON-encoded message from the connection and stores it in the value pointed to by v.

Deprecated: Use c.ReadJSON instead.

func Subprotocols 

func Subprotocols(r *http.Request) []string

Subprotocols returns the subprotocols requested by the client in the Sec-Websocket-Protocol header.

func WriteJSON deprecated 

func WriteJSON(c *Conn, v interface{}) error

WriteJSON writes the JSON encoding of v as a message.

Deprecated: Use c.WriteJSON instead.

Types

type BufferPool 

type BufferPool interface {
	// Get gets a value from the pool or returns nil if the pool is empty.
	Get() interface{}
	// Put adds a value to the pool.
	Put(interface{})
}

BufferPool represents a pool of buffers. The *sync.Pool type satisfies this interface. The type of the value stored in a pool is not specified.

type CloseError 

type CloseError struct {
	// Code is defined in RFC 6455, section 11.7.
	Code int

	// Text is the optional text payload.
	Text string
}

CloseError represents a close message.

func (*CloseError) Error 

func (e *CloseError) Error() string

type Conn 

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

The Conn type represents a WebSocket connection.

func NewClient deprecated 

func NewClient(netConn net.Conn, u *url.URL, requestHeader http.Header, readBufSize, writeBufSize int) (c *Conn, response *http.Response, err error)

NewClient creates a new client connection using the given net connection. The URL u specifies the host and request URI. Use requestHeader to specify the origin (Origin), subprotocols (Sec-WebSocket-Protocol) and cookies (Cookie). Use the response.Header to get the selected subprotocol (Sec-WebSocket-Protocol) and cookies (Set-Cookie).

If the WebSocket handshake fails, ErrBadHandshake is returned along with a non-nil *http.Response so that callers can handle redirects, authentication, etc.

Deprecated: Use Dialer instead.

func Upgrade deprecated 

func Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header, readBufSize, writeBufSize int) (*Conn, error)

Upgrade upgrades the HTTP server connection to the WebSocket protocol.

Deprecated: Use websocket.Upgrader instead.

Upgrade does not perform origin checking. The application is responsible for checking the Origin header before calling Upgrade. An example implementation of the same origin policy check is: 

if req.Header.Get("Origin") != "http://"+req.Host {
	http.Error(w, "Origin not allowed", http.StatusForbidden)
	return
}

If the endpoint supports subprotocols, then the application is responsible for negotiating the protocol used on the connection. Use the Subprotocols() function to get the subprotocols requested by the client. Use the Sec-Websocket-Protocol response header to specify the subprotocol selected by the application.

The responseHeader is included in the response to the client's upgrade request. Use the responseHeader to specify cookies (Set-Cookie) and the negotiated subprotocol (Sec-Websocket-Protocol).

The connection buffers IO to the underlying network connection. The readBufSize and writeBufSize parameters specify the size of the buffers to use. Messages can be larger than the buffers.

If the request is not a valid WebSocket handshake, then Upgrade returns an error of type HandshakeError. Applications should handle this error by replying to the client with an HTTP error response.

func (*Conn) Close 

func (c *Conn) Close() error

Close closes the underlying network connection without sending or waiting for a close message.

func (*Conn) CloseHandler 

func (c *Conn) CloseHandler() func(code int, text string) error

CloseHandler returns the current close handler

func (*Conn) EnableWriteCompression 

func (c *Conn) EnableWriteCompression(enable bool)

EnableWriteCompression enables and disables write compression of subsequent text and binary messages. This function is a noop if compression was not negotiated with the peer.

func (*Conn) LocalAddr 

func (c *Conn) LocalAddr() net.Addr

LocalAddr returns the local network address.

func (*Conn) NextReader 

func (c *Conn) NextReader() (messageType int, r io.Reader, err error)

NextReader returns the next data message received from the peer. The returned messageType is either TextMessage or BinaryMessage.

There can be at most one open reader on a connection. NextReader discards the previous message if the application has not already consumed it.

Applications must break out of the application's read loop when this method returns a non-nil error value. Errors returned from this method are permanent. Once this method returns a non-nil error, all subsequent calls to this method return the same error.

func (*Conn) NextWriter 

func (c *Conn) NextWriter(messageType int) (io.WriteCloser, error)

NextWriter returns a writer for the next message to send. The writer's Close method flushes the complete message to the network.

There can be at most one open writer on a connection. NextWriter closes the previous writer if the application has not already done so.

All message types (TextMessage, BinaryMessage, CloseMessage, PingMessage and PongMessage) are supported.

func (*Conn) PingHandler 

func (c *Conn) PingHandler() func(appData string) error

PingHandler returns the current ping handler

func (*Conn) PongHandler 

func (c *Conn) PongHandler() func(appData string) error

PongHandler returns the current pong handler

func (*Conn) ReadJSON 

func (c *Conn) ReadJSON(v interface{}) error

ReadJSON reads the next JSON-encoded message from the connection and stores it in the value pointed to by v.

See the documentation for the encoding/json Unmarshal function for details about the conversion of JSON to a Go value.

func (*Conn) ReadMessage 

func (c *Conn) ReadMessage() (messageType int, p []byte, err error)

ReadMessage is a helper method for getting a reader using NextReader and reading from that reader to a buffer.

func (*Conn) RemoteAddr 

func (c *Conn) RemoteAddr() net.Addr

RemoteAddr returns the remote network address.

func (*Conn) SetCloseHandler 

func (c *Conn) SetCloseHandler(h func(code int, text string) error)

SetCloseHandler sets the handler for close messages received from the peer. The code argument to h is the received close code or CloseNoStatusReceived if the close message is empty. The default close handler sends a close message back to the peer.

The handler function is called from the NextReader, ReadMessage and message reader Read methods. The application must read the connection to process close messages as described in the section on Control Messages above.

The connection read methods return a CloseError when a close message is received. Most applications should handle close messages as part of their normal error handling. Applications should only set a close handler when the application must perform some action before sending a close message back to the peer.

func (*Conn) SetCompressionLevel 

func (c *Conn) SetCompressionLevel(level int) error

SetCompressionLevel sets the flate compression level for subsequent text and binary messages. This function is a noop if compression was not negotiated with the peer. See the compress/flate package for a description of compression levels.

func (*Conn) SetPingHandler 

func (c *Conn) SetPingHandler(h func(appData string) error)

SetPingHandler sets the handler for ping messages received from the peer. The appData argument to h is the PING message application data. The default ping handler sends a pong to the peer.

The handler function is called from the NextReader, ReadMessage and message reader Read methods. The application must read the connection to process ping messages as described in the section on Control Messages above.

func (*Conn) SetPongHandler 

func (c *Conn) SetPongHandler(h func(appData string) error)

SetPongHandler sets the handler for pong messages received from the peer. The appData argument to h is the PONG message application data. The default pong handler does nothing.

The handler function is called from the NextReader, ReadMessage and message reader Read methods. The application must read the connection to process pong messages as described in the section on Control Messages above.

func (*Conn) SetReadDeadline 

func (c *Conn) SetReadDeadline(t time.Time) error

SetReadDeadline sets the read deadline on the underlying network connection. After a read has timed out, the websocket connection state is corrupt and all future reads will return an error. A zero value for t means reads will not time out.

func (*Conn) SetReadLimit 

func (c *Conn) SetReadLimit(limit int64)

SetReadLimit sets the maximum size for a message read from the peer. If a message exceeds the limit, the connection sends a close message to the peer and returns ErrReadLimit to the application.

func (*Conn) SetWriteDeadline 

func (c *Conn) SetWriteDeadline(t time.Time) error

SetWriteDeadline sets the write deadline on the underlying network connection. After a write has timed out, the websocket state is corrupt and all future writes will return an error. A zero value for t means writes will not time out.

func (*Conn) Subprotocol 

func (c *Conn) Subprotocol() string

Subprotocol returns the negotiated protocol for the connection.

func (*Conn) UnderlyingConn 

func (c *Conn) UnderlyingConn() net.Conn

UnderlyingConn returns the internal net.Conn. This can be used to further modifications to connection specific flags.

func (*Conn) WriteControl 

func (c *Conn) WriteControl(messageType int, data []byte, deadline time.Time) error

WriteControl writes a control message with the given deadline. The allowed message types are CloseMessage, PingMessage and PongMessage.

func (*Conn) WriteJSON 

func (c *Conn) WriteJSON(v interface{}) error

WriteJSON writes the JSON encoding of v as a message.

See the documentation for encoding/json Marshal for details about the conversion of Go values to JSON.

func (*Conn) WriteMessage 

func (c *Conn) WriteMessage(messageType int, data []byte) error

WriteMessage is a helper method for getting a writer using NextWriter, writing the message and closing the writer.

func (*Conn) WritePong 

func (c *Conn) WritePong() error

func (*Conn) WritePreparedMessage 

func (c *Conn) WritePreparedMessage(pm *PreparedMessage) error

WritePreparedMessage writes prepared message into connection.

type Dialer 

type Dialer struct {
	// NetDial specifies the dial function for creating TCP connections. If
	// NetDial is nil, net.Dial is used.
	NetDial func(network, addr string) (net.Conn, error)

	// NetDialContext specifies the dial function for creating TCP connections. If
	// NetDialContext is nil, net.DialContext is used.
	NetDialContext func(ctx context.Context, network, addr string) (net.Conn, error)

	// Proxy specifies a function to return a proxy for a given
	// Request. If the function returns a non-nil error, the
	// request is aborted with the provided error.
	// If Proxy is nil or returns a nil *URL, no proxy is used.
	Proxy func(*http.Request) (*url.URL, error)

	// TLSClientConfig specifies the TLS configuration to use with tls.Client.
	// If nil, the default configuration is used.
	TLSClientConfig *tls.Config

	// HandshakeTimeout specifies the duration for the handshake to complete.
	HandshakeTimeout time.Duration

	// ReadBufferSize and WriteBufferSize specify I/O buffer sizes. If a buffer
	// size is zero, then a useful default size is used. The I/O buffer sizes
	// do not limit the size of the messages that can be sent or received.
	ReadBufferSize, WriteBufferSize int

	// WriteBufferPool is a pool of buffers for write operations. If the value
	// is not set, then write buffers are allocated to the connection for the
	// lifetime of the connection.
	//
	// A pool is most useful when the application has a modest volume of writes
	// across a large number of connections.
	//
	// Applications should use a single pool for each unique value of
	// WriteBufferSize.
	WriteBufferPool BufferPool

	// Subprotocols specifies the client's requested subprotocols.
	Subprotocols []string

	// EnableCompression specifies if the client should attempt to negotiate
	// per message compression (RFC 7692). Setting this value to true does not
	// guarantee that compression will be supported. Currently only "no context
	// takeover" modes are supported.
	EnableCompression bool

	// Jar specifies the cookie jar.
	// If Jar is nil, cookies are not sent in requests and ignored
	// in responses.
	Jar http.CookieJar
}

A Dialer contains options for connecting to WebSocket server.

func (*Dialer) Dial 

func (d *Dialer) Dial(urlStr string, requestHeader http.Header) (*Conn, *http.Response, error)

Dial creates a new client connection by calling DialContext with a background context.

func (*Dialer) DialContext 

func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader http.Header) (*Conn, *http.Response, error)

DialContext creates a new client connection. Use requestHeader to specify the origin (Origin), subprotocols (Sec-WebSocket-Protocol) and cookies (Cookie). Use the response.Header to get the selected subprotocol (Sec-WebSocket-Protocol) and cookies (Set-Cookie).

The context will be used in the request and in the Dialer

If the WebSocket handshake fails, ErrBadHandshake is returned along with a non-nil *http.Response so that callers can handle redirects, authentication, etcetera. The response body may not contain the entire response and does not need to be closed by the application.

type HandshakeError 

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

HandshakeError describes an error with the handshake from the peer.

func (HandshakeError) Error 

func (e HandshakeError) Error() string

type PreparedMessage 

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

PreparedMessage caches on the wire representations of a message payload. Use PreparedMessage to efficiently send a message payload to multiple connections. PreparedMessage is especially useful when compression is used because the CPU and memory expensive compression operation can be executed once for a given set of compression options.

func NewPreparedMessage 

func NewPreparedMessage(messageType int, data []byte) (*PreparedMessage, error)

NewPreparedMessage returns an initialized PreparedMessage. You can then send it to connection using WritePreparedMessage method. Valid wire representation will be calculated lazily only once for a set of current connection options.

type Upgrader 

type Upgrader struct {
	// HandshakeTimeout specifies the duration for the handshake to complete.
	HandshakeTimeout time.Duration

	// ReadBufferSize and WriteBufferSize specify I/O buffer sizes. If a buffer
	// size is zero, then buffers allocated by the HTTP server are used. The
	// I/O buffer sizes do not limit the size of the messages that can be sent
	// or received.
	ReadBufferSize, WriteBufferSize int

	// WriteBufferPool is a pool of buffers for write operations. If the value
	// is not set, then write buffers are allocated to the connection for the
	// lifetime of the connection.
	//
	// A pool is most useful when the application has a modest volume of writes
	// across a large number of connections.
	//
	// Applications should use a single pool for each unique value of
	// WriteBufferSize.
	WriteBufferPool BufferPool

	// Subprotocols specifies the server's supported protocols in order of
	// preference. If this field is not nil, then the Upgrade method negotiates a
	// subprotocol by selecting the first match in this list with a protocol
	// requested by the client. If there's no match, then no protocol is
	// negotiated (the Sec-Websocket-Protocol header is not included in the
	// handshake response).
	Subprotocols []string

	// Error specifies the function for generating HTTP error responses. If Error
	// is nil, then http.Error is used to generate the HTTP response.
	Error func(w http.ResponseWriter, r *http.Request, status int, reason error)

	// CheckOrigin returns true if the request Origin header is acceptable. If
	// CheckOrigin is nil, then a safe default is used: return false if the
	// Origin request header is present and the origin host is not equal to
	// request Host header.
	//
	// A CheckOrigin function should carefully validate the request origin to
	// prevent cross-site request forgery.
	CheckOrigin func(r *http.Request) bool

	// EnableCompression specify if the server should attempt to negotiate per
	// message compression (RFC 7692). Setting this value to true does not
	// guarantee that compression will be supported. Currently only "no context
	// takeover" modes are supported.
	EnableCompression bool
}

Upgrader specifies parameters for upgrading an HTTP connection to a WebSocket connection.

func (*Upgrader) Upgrade 

func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header) (*Conn, error)

Upgrade upgrades the HTTP server connection to the WebSocket protocol.

The responseHeader is included in the response to the client's upgrade request. Use the responseHeader to specify cookies (Set-Cookie) and the application negotiated subprotocol (Sec-WebSocket-Protocol).

If the upgrade fails, then Upgrade replies to the client with an HTTP error response.

Source Files

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