Description

Package websocket implements the WebSocket protocol defined in RFC 6455.

Overview

The Conn type represents a WebSocket connection. A server application uses the Upgrade function from an Upgrader object with a HTTP request handler to get a pointer to 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 {
        return
    }
    if err = conn.WriteMessage(messageType, p); err != nil {
        return err
    }
}

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 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 ping and pong messages by invoking a callback function set with SetPingHandler and SetPongHandler methods. These callback functions can be invoked from the ReadMessage method, the NextReader method or from a call to the data message reader returned from NextReader.

Connections handle received close messages by returning an error from the ReadMessage method, the NextReader method or from a call to the data message reader returned from NextReader.

Concurrency

Connections do not support concurrent calls to the write methods (NextWriter, SetWriteDeadline, WriteMessage) or concurrent calls to the read methods methods (NextReader, SetReadDeadline, ReadMessage). Connections do support a concurrent reader and writer.

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

Read is Required

The application must read the connection to process ping and close 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
        }
    }
}

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 not equal to the Host request header.

An application can allow connections from any origin by specifying a function that always returns true:

 var upgrader = websocket.Upgrader{
   CheckOrigin: func(r *http.Request) bool { return true },
}

The deprecated Upgrade function does not enforce an origin policy. It's the application's responsibility to check the Origin header before calling Upgrade.

websocket is referenced in 1 repository

github.com/yudai/gotty