# ws

## Table of Contents

- [Class: WebSocket.Server](#class-websocketserver)
  - [new WebSocket.Server(options[, callback])](#new-websocketserveroptions-callback)
  - [Event: 'close'](#event-close)
  - [Event: 'connection'](#event-connection)
  - [Event: 'error'](#event-error)
  - [Event: 'headers'](#event-headers)
  - [Event: 'listening'](#event-listening)
  - [server.address()](#serveraddress)
  - [server.clients](#serverclients)
  - [server.close([callback])](#serverclosecallback)
  - [server.handleUpgrade(request, socket, head, callback)](#serverhandleupgraderequest-socket-head-callback)
  - [server.shouldHandle(request)](#servershouldhandlerequest)
- [Class: WebSocket](#class-websocket)
  - [Ready state constants](#ready-state-constants)
  - [new WebSocket(address[, protocols][, options])](#new-websocketaddress-protocols-options)
    - [UNIX Domain Sockets](#unix-domain-sockets)
  - [Event: 'close'](#event-close-1)
  - [Event: 'error'](#event-error-1)
  - [Event: 'message'](#event-message)
  - [Event: 'open'](#event-open)
  - [Event: 'ping'](#event-ping)
  - [Event: 'pong'](#event-pong)
  - [Event: 'unexpected-response'](#event-unexpected-response)
  - [Event: 'upgrade'](#event-upgrade)
  - [websocket.addEventListener(type, listener[, options])](#websocketaddeventlistenertype-listener-options)
  - [websocket.binaryType](#websocketbinarytype)
  - [websocket.bufferedAmount](#websocketbufferedamount)
  - [websocket.close([code[, reason]])](#websocketclosecode-reason)
  - [websocket.extensions](#websocketextensions)
  - [websocket.onclose](#websocketonclose)
  - [websocket.onerror](#websocketonerror)
  - [websocket.onmessage](#websocketonmessage)
  - [websocket.onopen](#websocketonopen)
  - [websocket.ping([data[, mask]][, callback])](#websocketpingdata-mask-callback)
  - [websocket.pong([data[, mask]][, callback])](#websocketpongdata-mask-callback)
  - [websocket.protocol](#websocketprotocol)
  - [websocket.readyState](#websocketreadystate)
  - [websocket.removeEventListener(type, listener)](#websocketremoveeventlistenertype-listener)
  - [websocket.send(data[, options][, callback])](#websocketsenddata-options-callback)
  - [websocket.terminate()](#websocketterminate)
  - [websocket.url](#websocketurl)
- [WebSocket.createWebSocketStream(websocket[, options])](#websocketcreatewebsocketstreamwebsocket-options)

## Class: WebSocket.Server

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

### new WebSocket.Server(options[, callback])

- `options` {Object}
  - `host` {String} The hostname where to bind the server.
  - `port` {Number} The port where to bind the server.
  - `backlog` {Number} The maximum length of the queue of pending connections.
  - `server` {http.Server|https.Server} A pre-created Node.js HTTP/S server.
  - `verifyClient` {Function} A function which can be used to validate incoming
    connections. See description below. (Usage is discouraged: see
    [Issue #337](https://github.com/websockets/ws/issues/377#issuecomment-462152231))
  - `handleProtocols` {Function} A function which can be used to handle the
    WebSocket subprotocols. See description below.
  - `path` {String} Accept only connections matching this path.
  - `noServer` {Boolean} Enable no server mode.
  - `clientTracking` {Boolean} Specifies whether or not to track clients.
  - `perMessageDeflate` {Boolean|Object} Enable/disable permessage-deflate.
  - `maxPayload` {Number} The maximum allowed message size in bytes.
- `callback` {Function}

Create a new server instance. 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
completly 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
is provided with a single argument then that is:

- `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.connection.authorized` or
    `req.connection.encrypted` is set.

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

if `verifyClient` is provided with two arguments then those are:

- `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` {Array} 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][permessage-deflate]. 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][zlib-options] to pass to
  zlib on deflate.
- `zlibInflateOptions` {Object} [Additional options][zlib-options] to pass to
  zlib on inflate.
- `threshold` {Number} Payloads smaller than this will not be compressed.
  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][concurrency-limit] 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 not operating in "noServer" mode.

### 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'

- `socket` {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.

### 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. Please note that this property is only
added when the `clientTracking` is truthy.

### server.close([callback])

Close the HTTP server if created internally, terminate all clients and call
callback when done. If an external HTTP server is used via the `server` or
`noServer` constructor options, it must be closed manually.

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

- `request` {http.IncomingMessage} The client HTTP GET request.
- `socket` {net.Socket} 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 a `WebSocket` object
as parameter.

### 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

| Constant   | Value | Description                                      |
| ---------- | ----- | ------------------------------------------------ |
| CONNECTING | 0     | The connection is not yet open.                  |
| OPEN       | 1     | The connection is open and ready to communicate. |
| CLOSING    | 2     | The connection is in the process of closing.     |
| CLOSED     | 3     | The 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}
  - `followRedirects` {Boolean} Whether or not to follow redirects. Defaults to
    `false`.
  - `handshakeTimeout` {Number} Timeout in milliseconds for the handshake
    request. This is reset after every redirection.
  - `maxRedirects` {Number} The maximum number of redirects allowed. Defaults
    to 10.
  - `perMessageDeflate` {Boolean|Object} Enable/disable permessage-deflate.
  - `protocolVersion` {Number} Value of the `Sec-WebSocket-Version` header.
  - `origin` {String} Value of the `Origin` or `Sec-WebSocket-Origin` header
    depending on the `protocolVersion`.
  - `maxPayload` {Number} The maximum allowed message size in bytes.
  - Any other option allowed in [http.request()][] or [https.request()][].

`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.

Create a new WebSocket instance.

#### UNIX Domain Sockets

`ws` supports making requests to UNIX domain sockets. To make one, use the
following URL scheme:

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

Note that `:` is the separator between the socket path and the URL path. If the
URL path is omitted

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

it defaults to `/`.

### Event: 'close'

- `code` {Number}
- `reason` {String}

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
human-readable string explaining why the connection has been closed.

### Event: 'error'

- `error` {Error}

Emitted when an error occurs.

### Event: 'message'

- `data` {String|Buffer|ArrayBuffer|Buffer[]}

Emitted when a message is received from the server.

### Event: 'open'

Emitted when the connection is established.

### Event: 'ping'

- `data` {Buffer}

Emitted when a ping is received from the server.

### Event: 'pong'

- `data` {Buffer}

Emitted when a pong is received from the server.

### 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} 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.

### websocket.binaryType

- {String}

A string indicating the type of binary data being transmitted by the connection.
This should be one of "nodebuffer", "arraybuffer" 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.

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

- `code` {Number} A numeric value indicating the status code explaining why the
  connection is being closed.
- `reason` {String} A human-readable string explaining why the connection is
  closing.

Initiate a closing handshake.

### 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 from the server. 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.ping([data[, mask]][, callback])

- `data` {Any} 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.

Send a ping.

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

- `data` {Any} 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.

Send a pong.

### websocket.protocol

- {String}

The subprotocol selected by the server.

### 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} The listener to remove.

Removes an event listener emulating the `EventTarget` interface.

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

- `data` {Any} The data to send.
- `options` {Object}
  - `compress` {Boolean} Specifies whether `data` should be compressed or not.
    Defaults to `true` when permessage-deflate is enabled.
  - `binary` {Boolean} Specifies whether `data` should be sent as a binary or
    not. Default is autodetected.
  - `mask` {Boolean} Specifies whether `data` should be masked or not. Defaults
    to `true` when `websocket` is not a server client.
  - `fin` {Boolean} Specifies whether `data` is the last fragment of a message
    or not. Defaults to `true`.
- `callback` {Function} An optional callback which is invoked when `data` is
  written out.

Send `data` through the connection.

### websocket.terminate()

Forcibly close the connection.

### websocket.url

- {String}

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

## WebSocket.createWebSocketStream(websocket[, options])

- `websocket` {WebSocket} A `WebSocket` object.
- `options` {Object} [Options][duplex-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`.

[concurrency-limit]: https://github.com/websockets/ws/issues/1202
[duplex-options]:
  https://nodejs.org/api/stream.html#stream_new_stream_duplex_options
[http.request()]:
  https://nodejs.org/api/http.html#http_http_request_options_callback
[https.request()]:
  https://nodejs.org/api/https.html#https_https_request_options_callback
[permessage-deflate]:
  https://tools.ietf.org/html/draft-ietf-hybi-permessage-compression-19
[zlib-options]: https://nodejs.org/api/zlib.html#zlib_class_options