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Table of Contents

Class: WebSocketServer

This class represents a WebSocket server. It extends the EventEmitter.

new WebSocketServer(options[, callback])

  • options {Object}
    • allowSynchronousEvents {Boolean} Specifies whether any of the 'message', 'ping', and 'pong' events can be emitted multiple times in the same tick. Defaults to true. Setting it to false improves compatibility with the WHATWG standard but may negatively impact performance.
    • autoPong {Boolean} Specifies whether or not to automatically send a pong in response to a ping. Defaults to true.
    • backlog {Number} The maximum length of the queue of pending connections.
    • clientTracking {Boolean} Specifies whether or not to track clients.
    • closeTimeout {Number} Duration in milliseconds to wait for a graceful close after websocket.close() is called. If the limit is reached, the connection is forcibly terminated. Defaults to 30000.
    • handleProtocols {Function} A function which can be used to handle the WebSocket subprotocols. See description below.
    • host {String} The hostname where to bind the server.
    • maxPayload {Number} The maximum allowed message size in bytes. Defaults to 100 MiB (104857600 bytes).
    • noServer {Boolean} Enable no server mode.
    • path {String} Accept only connections matching this path.
    • perMessageDeflate {Boolean|Object} Enable/disable permessage-deflate.
    • port {Number} The port where to bind the server.
    • server {http.Server|https.Server} A pre-created Node.js HTTP/S server.
    • skipUTF8Validation {Boolean} Specifies whether or not to skip UTF-8 validation for text and close messages. Defaults to false. Set to true only if clients are trusted.
    • verifyClient {Function} A function which can be used to validate incoming connections. See description below. (Usage is discouraged: see Issue #337)
    • WebSocket {Function} Specifies the WebSocket class to be used. It must be extended from the original WebSocket. Defaults to WebSocket.
  • callback {Function}

Create a new server instance. One and only one of port, server or noServer must be provided or an error is thrown. An HTTP server is automatically created, started, and used if port is set. To use an external HTTP/S server instead, specify only server or noServer. In this case, the HTTP/S server must be started manually. The "noServer" mode allows the WebSocket server to be completely detached from the HTTP/S server. This makes it possible, for example, to share a single HTTP/S server between multiple WebSocket servers.

NOTE: Use of verifyClient is discouraged. Rather handle client authentication in the 'upgrade' event of the HTTP server. See examples for more details.

If verifyClient is not set, then the handshake is automatically accepted. If it has a single parameter, then ws will invoke it with the following argument:

  • info {Object}
    • origin {String} The value in the Origin header indicated by the client.
    • req {http.IncomingMessage} The client HTTP GET request.
    • secure {Boolean} true if req.socket.authorized or req.socket.encrypted is set.

The return value (Boolean) of the function determines whether or not to accept the handshake.

If verifyClient has two parameters, then ws will invoke it with the following arguments:

  • info {Object} Same as above.
  • cb {Function} A callback that must be called by the user upon inspection of the info fields. Arguments in this callback are:
    • result {Boolean} Whether or not to accept the handshake.
    • code {Number} When result is false, this field determines the HTTP error status code to be sent to the client.
    • name {String} When result is false, this field determines the HTTP reason phrase.
    • headers {Object} When result is false, this field determines additional HTTP headers to be sent to the client. For example, { 'Retry-After': 120 }.

handleProtocols takes two arguments:

  • protocols {Set} The list of WebSocket subprotocols indicated by the client in the Sec-WebSocket-Protocol header.
  • request {http.IncomingMessage} The client HTTP GET request.

The returned value sets the value of the Sec-WebSocket-Protocol header in the HTTP 101 response. If returned value is false, the header is not added in the response.

If handleProtocols is not set, then the first of the client's requested subprotocols is used.

perMessageDeflate can be used to control the behavior of permessage-deflate extension. The extension is disabled when false (default value). If an object is provided, then that is extension parameters:

  • serverNoContextTakeover {Boolean} Whether to use context takeover or not.
  • clientNoContextTakeover {Boolean} Acknowledge disabling of client context takeover.
  • serverMaxWindowBits {Number} The value of windowBits.
  • clientMaxWindowBits {Number} Request a custom client window size.
  • zlibDeflateOptions {Object} Additional options to pass to zlib on deflate.
  • zlibInflateOptions {Object} Additional options to pass to zlib on inflate.
  • threshold {Number} Payloads smaller than this will not be compressed if context takeover is disabled. Defaults to 1024 bytes.
  • concurrencyLimit {Number} The number of concurrent calls to zlib. Calls above this limit will be queued. Default 10. You usually won't need to touch this option. See this issue for more details.

If a property is empty, then either an offered configuration or a default value is used. When sending a fragmented message, the length of the first fragment is compared to the threshold. This determines if compression is used for the entire message.

callback will be added as a listener for the 'listening' event on the HTTP server when the port option is set.

Event: 'close'

Emitted when the server closes. This event depends on the 'close' event of HTTP server only when it is created internally. In all other cases, the event is emitted independently.

Event: 'connection'

  • websocket {WebSocket}
  • request {http.IncomingMessage}

Emitted when the handshake is complete. request is the http GET request sent by the client. Useful for parsing authority headers, cookie headers, and other information.

Event: 'error'

  • error {Error}

Emitted when an error occurs on the underlying server.

Event: 'headers'

  • headers {Array}
  • request {http.IncomingMessage}

Emitted before the response headers are written to the socket as part of the handshake. This allows you to inspect/modify the headers before they are sent.

Event: 'listening'

Emitted when the underlying server has been bound.

Event: 'wsClientError'

  • error {Error}
  • socket {net.Socket|tls.Socket}
  • request {http.IncomingMessage}

Emitted when an error occurs before the WebSocket connection is established. socket and request are respectively the socket and the HTTP request from which the error originated. The listener of this event is responsible for closing the socket. When the 'wsClientError' event is emitted there is no http.ServerResponse object, so any HTTP response, including the response headers and body, must be written directly to the socket. If there is no listener for this event, the socket is closed with a default 4xx response containing a descriptive error message.

server.address()

Returns an object with port, family, and address properties specifying the bound address, the address family name, and port of the server as reported by the operating system if listening on an IP socket. If the server is listening on a pipe or UNIX domain socket, the name is returned as a string.

server.clients

  • {Set}

A set that stores all connected clients. This property is only added when the clientTracking is truthy.

server.close([callback])

Prevent the server from accepting new connections and close the HTTP server if created internally. If an external HTTP server is used via the server or noServer constructor options, it must be closed manually. Existing connections are not closed automatically. The server emits a 'close' event when all connections are closed unless an external HTTP server is used and client tracking is disabled. In this case, the 'close' event is emitted in the next tick. The optional callback is called when the 'close' event occurs and receives an Error if the server is already closed.

server.handleUpgrade(request, socket, head, callback)

  • request {http.IncomingMessage} The client HTTP GET request.
  • socket {stream.Duplex} The network socket between the server and client.
  • head {Buffer} The first packet of the upgraded stream.
  • callback {Function}

Handle a HTTP upgrade request. When the HTTP server is created internally or when the HTTP server is passed via the server option, this method is called automatically. When operating in "noServer" mode, this method must be called manually.

If the upgrade is successful, the callback is called with two arguments:

  • websocket {WebSocket} A WebSocket object.
  • request {http.IncomingMessage} The client HTTP GET request.

server.shouldHandle(request)

  • request {http.IncomingMessage} The client HTTP GET request.

See if a given request should be handled by this server. By default, this method validates the pathname of the request, matching it against the path option if provided. The return value, true or false, determines whether or not to accept the handshake.

This method can be overridden when a custom handling logic is required.

Class: WebSocket

This class represents a WebSocket. It extends the EventEmitter.

Ready state constants

ConstantValueDescription
CONNECTING0The connection is not yet open.
OPEN1The connection is open and ready to communicate.
CLOSING2The connection is in the process of closing.
CLOSED3The connection is closed.

new WebSocket(address[, protocols][, options])

  • address {String|url.URL} The URL to which to connect.
  • protocols {String|Array} The list of subprotocols.
  • options {Object}
    • allowSynchronousEvents {Boolean} Specifies whether any of the 'message', 'ping', and 'pong' events can be emitted multiple times in the same tick. Defaults to true. Setting it to false improves compatibility with the WHATWG standard but may negatively impact performance.
    • autoPong {Boolean} Specifies whether or not to automatically send a pong in response to a ping. Defaults to true.
    • closeTimeout {Number} Duration in milliseconds to wait for a graceful close after websocket.close() is called. If the limit is reached, the connection is forcibly terminated. Defaults to 30000.
    • finishRequest {Function} A function which can be used to customize the headers of each HTTP request before it is sent. See description below.
    • followRedirects {Boolean} Whether or not to follow redirects. Defaults to false.
    • generateMask {Function} The function used to generate the masking key. It takes a Buffer that must be filled synchronously and is called before a message is sent, for each message. By default, the buffer is filled with cryptographically strong random bytes.
    • handshakeTimeout {Number} Timeout in milliseconds for the handshake request. This is reset after every redirection.
    • maxPayload {Number} The maximum allowed message size in bytes. Defaults to 100 MiB (104857600 bytes).
    • maxRedirects {Number} The maximum number of redirects allowed. Defaults to 10.
    • origin {String} Value of the Origin or Sec-WebSocket-Origin header depending on the protocolVersion.
    • perMessageDeflate {Boolean|Object} Enable/disable permessage-deflate.
    • protocolVersion {Number} Value of the Sec-WebSocket-Version header.
    • skipUTF8Validation {Boolean} Specifies whether or not to skip UTF-8 validation for text and close messages. Defaults to false. Set to true only if the server is trusted.
    • Any other option allowed in http.request() or https.request(). Options given do not have any effect if parsed from the URL given with the address parameter.

Create a new WebSocket instance.

perMessageDeflate default value is true. When using an object, parameters are the same of the server. The only difference is the direction of requests. For example, serverNoContextTakeover can be used to ask the server to disable context takeover.

finishRequest is called with arguments

  • request {http.ClientRequest}
  • websocket {WebSocket}

for each HTTP GET request (the initial one and any caused by redirects) when it is ready to be sent, to allow for last minute customization of the headers. If finishRequest is set, then it has the responsibility to call request.end() once it is done setting request headers. This is intended for niche use-cases where some headers can't be provided in advance e.g. because they depend on the underlying socket.

IPC connections

ws supports IPC connections. To connect to an IPC endpoint, use the following URL form:

  • On Unices

    ws+unix:/absolute/path/to/uds_socket:/pathname?search_params

  • On Windows

    ws+unix:\\.\pipe\pipe_name:/pathname?search_params

The character : is the separator between the IPC path (the UNIX domain socket path or the Windows named pipe) and the URL path. The IPC path must not include the characters : and ?, otherwise the URL is incorrectly parsed. If the URL path is omitted

ws+unix:/absolute/path/to/uds_socket

it defaults to /.

Event: 'close'

  • code {Number}
  • reason {Buffer}

Emitted when the connection is closed. code is a numeric value indicating the status code explaining why the connection has been closed. reason is a Buffer containing a human-readable string explaining why the connection has been closed.

Event: 'error'

  • error {Error}

Emitted when an error occurs. Errors may have a .code property, matching one of the string values defined below under Error codes.

Event: 'message'

  • data {ArrayBuffer|Blob|Buffer|Buffer[]}
  • isBinary {Boolean}

Emitted when a message is received. data is the message content. isBinary specifies whether the message is binary or not.

Event: 'open'

Emitted when the connection is established.

Event: 'ping'

  • data {Buffer}

Emitted when a ping is received.

Event: 'pong'

  • data {Buffer}

Emitted when a pong is received.

Event: 'redirect'

  • url {String}
  • request {http.ClientRequest}

Emitted before a redirect is followed. url is the redirect URL. request is the HTTP GET request with the headers queued. This event gives the ability to inspect confidential headers and remove them on a per-redirect basis using the request.getHeader() and request.removeHeader() API. The request object should be used only for this purpose. When there is at least one listener for this event, no header is removed by default, even if the redirect is to a different domain.

Event: 'unexpected-response'

  • request {http.ClientRequest}
  • response {http.IncomingMessage}

Emitted when the server response is not the expected one, for example a 401 response. This event gives the ability to read the response in order to extract useful information. If the server sends an invalid response and there isn't a listener for this event, an error is emitted.

Event: 'upgrade'

  • response {http.IncomingMessage}

Emitted when response headers are received from the server as part of the handshake. This allows you to read headers from the server, for example 'set-cookie' headers.

websocket.addEventListener(type, listener[, options])

  • type {String} A string representing the event type to listen for.
  • listener {Function|Object} The listener to add.
  • options {Object}
    • once {Boolean} A Boolean indicating that the listener should be invoked at most once after being added. If true, the listener would be automatically removed when invoked.

Register an event listener emulating the EventTarget interface. This method does nothing if type is not one of 'close', 'error', 'message', or 'open'.

websocket.binaryType

  • {String}

A string indicating the type of binary data being transmitted by the connection. This should be one of "nodebuffer", "arraybuffer", "blob", or "fragments". Defaults to "nodebuffer". Type "fragments" will emit the array of fragments as received from the sender, without copyfull concatenation, which is useful for the performance of binary protocols transferring large messages with multiple fragments.

websocket.bufferedAmount

  • {Number}

The number of bytes of data that have been queued using calls to send() but not yet transmitted to the network. This deviates from the HTML standard in the following ways:

  1. If the data is immediately sent, the value is 0.
  2. All framing bytes are included.

websocket.close([code[, reason]])

  • code {Number} A numeric value indicating the status code explaining why the connection is being closed.
  • reason {String|Buffer} The reason why the connection is closing.

Initiate a closing handshake.

websocket.isPaused

  • {Boolean}

Indicates whether the websocket is paused.

websocket.extensions

  • {Object}

An object containing the negotiated extensions.

websocket.onclose

  • {Function}

An event listener to be called when connection is closed. The listener receives a CloseEvent named "close".

websocket.onerror

  • {Function}

An event listener to be called when an error occurs. The listener receives an ErrorEvent named "error".

websocket.onmessage

  • {Function}

An event listener to be called when a message is received. The listener receives a MessageEvent named "message".

websocket.onopen

  • {Function}

An event listener to be called when the connection is established. The listener receives an OpenEvent named "open".

websocket.pause()

Pause the websocket causing it to stop emitting events. Some events can still be emitted after this is called, until all buffered data is consumed. This method is a noop if the ready state is CONNECTING or CLOSED.

websocket.ping([data[, mask]][, callback])

  • data {Array|Number|Object|String|ArrayBuffer|Buffer|DataView|TypedArray|Blob} The data to send in the ping frame.
  • mask {Boolean} Specifies whether data should be masked or not. Defaults to true when websocket is not a server client.
  • callback {Function} An optional callback which is invoked when the ping frame is written out. If an error occurs, the callback is called with the error as its first argument.

Send a ping. This method throws an error if the ready state is CONNECTING.

websocket.pong([data[, mask]][, callback])

  • data {Array|Number|Object|String|ArrayBuffer|Buffer|DataView|TypedArray|Blob} The data to send in the pong frame.
  • mask {Boolean} Specifies whether data should be masked or not. Defaults to true when websocket is not a server client.
  • callback {Function} An optional callback which is invoked when the pong frame is written out. If an error occurs, the callback is called with the error as its first argument.

Send a pong. This method throws an error if the ready state is CONNECTING.

websocket.protocol

  • {String}

The subprotocol selected by the server.

websocket.resume()

Make a paused socket resume emitting events. This method is a noop if the ready state is CONNECTING or CLOSED.

websocket.readyState

  • {Number}

The current state of the connection. This is one of the ready state constants.

websocket.removeEventListener(type, listener)

  • type {String} A string representing the event type to remove.
  • listener {Function|Object} The listener to remove.

Removes an event listener emulating the EventTarget interface. This method only removes listeners added with websocket.addEventListener().

websocket.send(data[, options][, callback])

  • data {Array|Number|Object|String|ArrayBuffer|Buffer|DataView|TypedArray|Blob} The data to send. Object values are only supported if they conform to the requirements of Buffer.from(). If those constraints are not met, a TypeError is thrown.
  • options {Object}
    • binary {Boolean} Specifies whether data should be sent as a binary or not. Default is autodetected.
    • compress {Boolean} Specifies whether data should be compressed or not. Defaults to true when permessage-deflate is enabled.
    • fin {Boolean} Specifies whether data is the last fragment of a message or not. Defaults to true.
    • mask {Boolean} Specifies whether data should be masked or not. Defaults to true when websocket is not a server client.
  • callback {Function} An optional callback which is invoked when data is written out. If an error occurs, the callback is called with the error as its first argument.

Send data through the connection. This method throws an error if the ready state is CONNECTING.

websocket.terminate()

Forcibly close the connection. Internally, this calls socket.destroy().

websocket.url

  • {String}

The URL of the WebSocket server. Server clients don't have this attribute.

createWebSocketStream(websocket[, options])

  • websocket {WebSocket} A WebSocket object.
  • options {Object} Options to pass to the Duplex constructor.

Returns a Duplex stream that allows to use the Node.js streams API on top of a given WebSocket.

Environment variables

WS_NO_BUFFER_UTIL

When set to a non-empty value, prevents the optional bufferutil dependency from being required.

WS_NO_UTF_8_VALIDATE

When set to a non-empty value, prevents the optional utf-8-validate dependency from being required.

Error codes

Errors emitted by the websocket may have a .code property, describing the specific type of error that has occurred:

WS_ERR_EXPECTED_FIN

A WebSocket frame was received with the FIN bit not set when it was expected.

WS_ERR_EXPECTED_MASK

An unmasked WebSocket frame was received by a WebSocket server.

WS_ERR_INVALID_CLOSE_CODE

A WebSocket close frame was received with an invalid close code.

WS_ERR_INVALID_CONTROL_PAYLOAD_LENGTH

A control frame with an invalid payload length was received.

WS_ERR_INVALID_OPCODE

A WebSocket frame was received with an invalid opcode.

WS_ERR_INVALID_UTF8

A text or close frame was received containing invalid UTF-8 data.

WS_ERR_UNEXPECTED_MASK

A masked WebSocket frame was received by a WebSocket client.

WS_ERR_UNEXPECTED_RSV_1

A WebSocket frame was received with the RSV1 bit set unexpectedly.

WS_ERR_UNEXPECTED_RSV_2_3

A WebSocket frame was received with the RSV2 or RSV3 bit set unexpectedly.

WS_ERR_UNSUPPORTED_DATA_PAYLOAD_LENGTH

A data frame was received with a length longer than the max supported length (2^53 - 1, due to JavaScript language limitations).

WS_ERR_UNSUPPORTED_MESSAGE_LENGTH

A message was received with a length longer than the maximum supported length, as configured by the maxPayload option.