Server - websockets 10.3 documentation
Description: asyncio: Starting a server: Stopping a server: Using a connection: Basic authentication: websockets supports HTTP Basic Authentication according to RFC 7235 and RFC 7617. Sans-I/O:

Hide navigation sidebar
Hide table of contents sidebar
Back to top
Toggle table of contents sidebar

# Server

## asyncio

### Starting a server

await websockets.server.serve(ws_handler, host=None, port=None, *, create_protocol=None, logger=None, compression='deflate', origins=None, extensions=None, subprotocols=None, extra_headers=None, process_request=None, select_subprotocol=None, ping_interval=20, ping_timeout=20, close_timeout=10, max_size=2 ** 20, max_queue=2 ** 5, read_limit=2 ** 16, write_limit=2 ** 16, **kwds)

  Start a WebSocket server listening on `host` and `port`.

  Whenever a client connects, the server creates a `WebSocketServerProtocol`, performs the opening handshake, and delegates to the connection handler, `ws_handler`.

  The handler receives the `WebSocketServerProtocol` and uses it to send and receive messages.

  Once the handler completes, either normally or with an exception, the server performs the closing handshake and closes the connection.

  Awaiting `serve()` yields a `WebSocketServer`. This object provides `close()` and `wait_closed()` methods for shutting down the server.

  `serve()` can be used as an asynchronous context manager:

      stop = asyncio.Future()  # set this future to exit the server

      async with serve(...):
          await stop

  The server is shut down automatically when exiting the context.

  Parameters

    - ws_handler (Union[Callable[[WebSocketServerProtocol], Awaitable[Any]], Callable[[WebSocketServerProtocol, str], Awaitable[Any]]]) – connection handler. It receives the WebSocket connection, which is a `WebSocketServerProtocol`, in argument.

    - host (Optional[Union[str, Sequence[str]]]) – network interfaces the server is bound to; see `create_server()` for details.

    - port (Optional[int]) – TCP port the server listens on; see `create_server()` for details.

    - create_protocol (Optional[Callable[[Any], WebSocketServerProtocol]]) – factory for the `asyncio.Protocol` managing the connection; defaults to `WebSocketServerProtocol`; may be set to a wrapper or a subclass to customize connection handling.

    - logger (Optional[LoggerLike]) – logger for this server; defaults to `logging.getLogger("websockets.server")`; see the logging guide for details.

    - compression (Optional[str]) – shortcut that enables the “permessage-deflate” extension by default; may be set to `None` to disable compression; see the compression guide for details.

    - origins (Optional[Sequence[Optional[Origin]]]) – acceptable values of the `Origin` header; include `None` in the list if the lack of an origin is acceptable. This is useful for defending against Cross-Site WebSocket Hijacking attacks.

    - extensions (Optional[Sequence[ServerExtensionFactory]]) – list of supported extensions, in order in which they should be tried.

    - subprotocols (Optional[Sequence[Subprotocol]]) – list of supported subprotocols, in order of decreasing preference.

    - extra_headers (Union[HeadersLike, Callable[[str, Headers], HeadersLike]]) – arbitrary HTTP headers to add to the request; this can be a `HeadersLike` or a callable taking the request path and headers in arguments and returning a `HeadersLike`.

    - process_request (Optional[Callable[[str, Headers], Awaitable[Optional[Tuple[http.HTTPStatus, HeadersLike, bytes]]]]]) – intercept HTTP request before the opening handshake; see `process_request()` for details.

    - select_subprotocol (Optional[Callable[[Sequence[Subprotocol], Sequence[Subprotocol]], Subprotocol]]) – select a subprotocol supported by the client; see `select_subprotocol()` for details.

  See `WebSocketCommonProtocol` for the documentation of `ping_interval`, `ping_timeout`, `close_timeout`, `max_size`, `max_queue`, `read_limit`, and `write_limit`.

  Any other keyword arguments are passed the event loop’s `create_server()` method.

  For example:

  - You can set `ssl` to a `SSLContext` to enable TLS.

  - You can set `sock` to a `socket` that you created outside of websockets.

  Returns

    WebSocket server.

  Return type

    WebSocketServer

await websockets.server.unix_serve(ws_handler, path=None, *, create_protocol=None, logger=None, compression='deflate', origins=None, extensions=None, subprotocols=None, extra_headers=None, process_request=None, select_subprotocol=None, ping_interval=20, ping_timeout=20, close_timeout=10, max_size=2 ** 20, max_queue=2 ** 5, read_limit=2 ** 16, write_limit=2 ** 16, **kwds)

  Similar to `serve()`, but for listening on Unix sockets.

  This function builds upon the event loop’s `create_unix_server()` method.

  It is only available on Unix.

  It’s useful for deploying a server behind a reverse proxy such as nginx.

  Parameters

    path (Optional[str]) – file system path to the Unix socket.

### Stopping a server

class websockets.server.WebSocketServer(logger=None)

  WebSocket server returned by `serve()`.

  This class provides the same interface as `Server`, notably the `close()` and `wait_closed()` methods.

  It keeps track of WebSocket connections in order to close them properly when shutting down.

  Parameters

    logger (Optional[LoggerLike]) – logger for this server; defaults to `logging.getLogger("websockets.server")`; see the logging guide for details.

  close()

    Close the server.

    This method:

    - closes the underlying `Server`;

    - rejects new WebSocket connections with an HTTP 503 (service unavailable) error; this happens when the server accepted the TCP connection but didn’t complete the WebSocket opening handshake prior to closing;

    - closes open WebSocket connections with close code 1001 (going away).

    `close()` is idempotent.

  await wait_closed()

    Wait until the server is closed.

    When `wait_closed()` returns, all TCP connections are closed and all connection handlers have returned.

    To ensure a fast shutdown, a connection handler should always be awaiting at least one of:

    - `recv()`: when the connection is closed, it raises `ConnectionClosedOK`;

    - `wait_closed()`: when the connection is closed, it returns.

    Then the connection handler is immediately notified of the shutdown; it can clean up and exit.

  get_loop()

    See `asyncio.Server.get_loop()`.

  is_serving()

    See `asyncio.Server.is_serving()`.

  await start_serving()

    See `asyncio.Server.start_serving()`.

  await serve_forever()

    See `asyncio.Server.serve_forever()`.

  sockets

    See `asyncio.Server.sockets`.

### Using a connection

class websockets.server.WebSocketServerProtocol(ws_handler, ws_server, *, logger=None, origins=None, extensions=None, subprotocols=None, extra_headers=None, process_request=None, select_subprotocol=None, ping_interval=20, ping_timeout=20, close_timeout=10, max_size=2 ** 20, max_queue=2 ** 5, read_limit=2 ** 16, write_limit=2 ** 16)

  WebSocket server connection.

  `WebSocketServerProtocol` provides `recv()` and `send()` coroutines for receiving and sending messages.

  It supports asynchronous iteration to receive messages:

      async for message in websocket:
          await process(message)

  The iterator exits normally when the connection is closed with close code 1000 (OK) or 1001 (going away). It raises a `ConnectionClosedError` when the connection is closed with any other code.

  You may customize the opening handshake in a subclass by overriding `process_request()` or `select_subprotocol()`.

  Parameters

    ws_server (WebSocketServer) – WebSocket server that created this connection.

  See `serve()` for the documentation of `ws_handler`, `logger`, `origins`, `extensions`, `subprotocols`, and `extra_headers`.

  See `WebSocketCommonProtocol` for the documentation of `ping_interval`, `ping_timeout`, `close_timeout`, `max_size`, `max_queue`, `read_limit`, and `write_limit`.

  await recv()

    Receive the next message.

    When the connection is closed, `recv()` raises `ConnectionClosed`. Specifically, it raises `ConnectionClosedOK` after a normal connection closure and `ConnectionClosedError` after a protocol error or a network failure. This is how you detect the end of the message stream.

    Canceling `recv()` is safe. There’s no risk of losing the next message. The next invocation of `recv()` will return it.

    This makes it possible to enforce a timeout by wrapping `recv()` in `wait_for()`.

    Returns

      A string (`str`) for a Text frame. A bytestring (`bytes`) for a Binary frame.

    Return type

      Data

    Raises

      - ConnectionClosed – when the connection is closed.

      - RuntimeError – if two coroutines call `recv()` concurrently.

  await send(message)

    Send a message.

    A string (`str`) is sent as a Text frame. A bytestring or bytes-like object (`bytes`, `bytearray`, or `memoryview`) is sent as a Binary frame.

    `send()` also accepts an iterable or an asynchronous iterable of strings, bytestrings, or bytes-like objects to enable fragmentation. Each item is treated as a message fragment and sent in its own frame. All items must be of the same type, or else `send()` will raise a `TypeError` and the connection will be closed.

    `send()` rejects dict-like objects because this is often an error. (If you want to send the keys of a dict-like object as fragments, call its `keys()` method and pass the result to `send()`.)

    Canceling `send()` is discouraged. Instead, you should close the connection with `close()`. Indeed, there are only two situations where `send()` may yield control to the event loop and then get canceled; in both cases, `close()` has the same effect and is more clear:

    1. The write buffer is full. If you don’t want to wait until enough data is sent, your only alternative is to close the connection. `close()` will likely time out then abort the TCP connection.

    2. `message` is an asynchronous iterator that yields control. Stopping in the middle of a fragmented message will cause a protocol error and the connection will be closed.

    When the connection is closed, `send()` raises `ConnectionClosed`. Specifically, it raises `ConnectionClosedOK` after a normal connection closure and `ConnectionClosedError` after a protocol error or a network failure.

    Parameters

      message (Union[Data, Iterable[Data], AsyncIterable[Data]) – message to send.

    Raises

      - ConnectionClosed – when the connection is closed.

      - TypeError – if `message` doesn’t have a supported type.

  await close(code=1000, reason='')

    Perform the closing handshake.

    `close()` waits for the other end to complete the handshake and for the TCP connection to terminate. As a consequence, there’s no need to await `wait_closed()` after `close()`.

    `close()` is idempotent: it doesn’t do anything once the connection is closed.

    Wrapping `close()` in `create_task()` is safe, given that errors during connection termination aren’t particularly useful.

    Canceling `close()` is discouraged. If it takes too long, you can set a shorter `close_timeout`. If you don’t want to wait, let the Python process exit, then the OS will take care of closing the TCP connection.

    Parameters

      - code (int) – WebSocket close code.

      - reason (str) – WebSocket close reason.

  await wait_closed()

    Wait until the connection is closed.

    This coroutine is identical to the `closed` attribute, except it can be awaited.

    This can make it easier to detect connection termination, regardless of its cause, in tasks that interact with the WebSocket connection.

  await ping(data=None)

    Send a Ping.

    A ping may serve as a keepalive or as a check that the remote endpoint received all messages up to this point

    Canceling `ping()` is discouraged. If `ping()` doesn’t return immediately, it means the write buffer is full. If you don’t want to wait, you should close the connection.

    Canceling the `Future` returned by `ping()` has no effect.

    Parameters

      data (Optional[Data]) – payload of the ping; a string will be encoded to UTF-8; or `None` to generate a payload containing four random bytes.

    Returns

      A future that will be completed when the corresponding pong is received. You can ignore it if you don’t intend to wait.

          pong_waiter = await ws.ping()
          await pong_waiter  # only if you want to wait for the pong

    Return type

      Future

    Raises

      - ConnectionClosed – when the connection is closed.

      - RuntimeError – if another ping was sent with the same data and the corresponding pong wasn’t received yet.

  await pong(data=b'')

    Send a Pong.

    An unsolicited pong may serve as a unidirectional heartbeat.

    Canceling `pong()` is discouraged. If `pong()` doesn’t return immediately, it means the write buffer is full. If you don’t want to wait, you should close the connection.

    Parameters

      data (Data) – payload of the pong; a string will be encoded to UTF-8.

    Raises

      ConnectionClosed – when the connection is closed.

  You can customize the opening handshake in a subclass by overriding these methods:

  await process_request(path, request_headers)

    Intercept the HTTP request and return an HTTP response if appropriate.

    You may override this method in a `WebSocketServerProtocol` subclass, for example:

    - to return a HTTP 200 OK response on a given path; then a load balancer can use this path for a health check;

    - to authenticate the request and return a HTTP 401 Unauthorized or a HTTP 403 Forbidden when authentication fails.

    You may also override this method with the `process_request` argument of `serve()` and `WebSocketServerProtocol`. This is equivalent, except `process_request` won’t have access to the protocol instance, so it can’t store information for later use.

    `process_request()` is expected to complete quickly. If it may run for a long time, then it should await `wait_closed()` and exit if `wait_closed()` completes, or else it could prevent the server from shutting down.

    Parameters

      - path (str) – request path, including optional query string.

      - request_headers (websockets.datastructures.Headers) – request headers.

    Returns

      `None` to continue the WebSocket handshake normally.

      An HTTP response, represented by a 3-uple of the response status, headers, and body, to abort the WebSocket handshake and return that HTTP response instead.

    Return type

      Optional[Tuple[http.HTTPStatus, HeadersLike, bytes]]

  select_subprotocol(client_subprotocols, server_subprotocols)

    Pick a subprotocol among those offered by the client.

    If several subprotocols are supported by the client and the server, the default implementation selects the preferred subprotocol by giving equal value to the priorities of the client and the server. If no subprotocol is supported by the client and the server, it proceeds without a subprotocol.

    This is unlikely to be the most useful implementation in practice. Many servers providing a subprotocol will require that the client uses that subprotocol. Such rules can be implemented in a subclass.

    You may also override this method with the `select_subprotocol` argument of `serve()` and `WebSocketServerProtocol`.

    Parameters

      - client_subprotocols (Sequence[websockets.typing.Subprotocol]) – list of subprotocols offered by the client.

      - server_subprotocols (Sequence[websockets.typing.Subprotocol]) – list of subprotocols available on the server.

    Returns

      Selected subprotocol.

      `None` to continue without a subprotocol.

    Return type

      Optional[Subprotocol]

  WebSocket connection objects also provide these attributes:

  id: uuid.UUID

    Unique identifier of the connection. Useful in logs.

  logger: LoggerLike

    Logger for this connection.

  property local_address: Any

    Local address of the connection.

    For IPv4 connections, this is a `(host, port)` tuple.

    The format of the address depends on the address family; see `getsockname()`.

    `None` if the TCP connection isn’t established yet.

  property remote_address: Any

    Remote address of the connection.

    For IPv4 connections, this is a `(host, port)` tuple.

    The format of the address depends on the address family; see `getpeername()`.

    `None` if the TCP connection isn’t established yet.

  property open: bool

    `True` when the connection is open; `False` otherwise.

    This attribute may be used to detect disconnections. However, this approach is discouraged per the EAFP principle. Instead, you should handle `ConnectionClosed` exceptions.

  property closed: bool

    `True` when the connection is closed; `False` otherwise.

    Be aware that both `open` and `closed` are `False` during the opening and closing sequences.

  The following attributes are available after the opening handshake, once the WebSocket connection is open:

  path: str

    Path of the opening handshake request.

  request_headers: Headers

    Opening handshake request headers.

  response_headers: Headers

    Opening handshake response headers.

  subprotocol: Optional[Subprotocol]

    Subprotocol, if one was negotiated.

  The following attributes are available after the closing handshake, once the WebSocket connection is closed:

  property close_code: Optional[int]

    WebSocket close code, defined in section 7.1.5 of RFC 6455.

    `None` if the connection isn’t closed yet.

  property close_reason: Optional[str]

    WebSocket close reason, defined in section 7.1.6 of RFC 6455.

    `None` if the connection isn’t closed yet.

### Basic authentication

websockets supports HTTP Basic Authentication according to RFC 7235 and RFC 7617.

websockets.auth.basic_auth_protocol_factory(realm=None, credentials=None, check_credentials=None, create_protocol=None)

  Protocol factory that enforces HTTP Basic Auth.

  `basic_auth_protocol_factory()` is designed to integrate with `serve()` like this:

      websockets.serve(
          ...,
          create_protocol=websockets.basic_auth_protocol_factory(
              realm="my dev server",
              credentials=("hello", "iloveyou"),
          )
      )

  Parameters

    - realm (Optional[str]) – indicates the scope of protection. It should contain only ASCII characters because the encoding of non-ASCII characters is undefined. Refer to section 2.2 of RFC 7235 for details.

    - credentials (Optional[Union[Tuple[str, str], Iterable[Tuple[str, str]]]]) – defines hard coded authorized credentials. It can be a `(username, password)` pair or a list of such pairs.

    - check_credentials (Optional[Callable[[str, str], Awaitable[bool]]]) – defines a coroutine that verifies credentials. This coroutine receives `username` and `password` arguments and returns a `bool`. One of `credentials` or `check_credentials` must be provided but not both.

    - create_protocol (Optional[Callable[[Any], websockets.legacy.auth.BasicAuthWebSocketServerProtocol]]) – factory that creates the protocol. By default, this is `BasicAuthWebSocketServerProtocol`. It can be replaced by a subclass.

  Raises

    TypeError – if the `credentials` or `check_credentials` argument is wrong.

class websockets.auth.BasicAuthWebSocketServerProtocol(*args, realm=None, check_credentials=None, **kwargs)

  WebSocket server protocol that enforces HTTP Basic Auth.

  realm: str = ''

    Scope of protection.

    If provided, it should contain only ASCII characters because the encoding of non-ASCII characters is undefined.

  username: Optional[str] = None

    Username of the authenticated user.

  await check_credentials(username, password)

    Check whether credentials are authorized.

    This coroutine may be overridden in a subclass, for example to authenticate against a database or an external service.

    Parameters

      - username (str) – HTTP Basic Auth username.

      - password (str) – HTTP Basic Auth password.

    Returns

      `True` if the handshake should continue; `False` if it should fail with a HTTP 401 error.

    Return type

      bool

## Sans-I/O

class websockets.server.ServerConnection(origins=None, extensions=None, subprotocols=None, state=State.CONNECTING, max_size=2 ** 20, logger=None)

  Sans-I/O implementation of a WebSocket server connection.

  Parameters

    - origins (Optional[Sequence[Optional[Origin]]]) – acceptable values of the `Origin` header; include `None` in the list if the lack of an origin is acceptable. This is useful for defending against Cross-Site WebSocket Hijacking attacks.

    - extensions (List[websockets.extensions.base.Extension]) – list of supported extensions, in order in which they should be tried.

    - subprotocols (Optional[Sequence[Subprotocol]]) – list of supported subprotocols, in order of decreasing preference.

    - state (State) – initial state of the WebSocket connection.

    - max_size (Optional[int]) – maximum size of incoming messages in bytes; `None` to disable the limit.

    - logger (Union[logging.Logger, logging.LoggerAdapter]) – logger for this connection; defaults to `logging.getLogger("websockets.client")`; see the logging guide for details.

  receive_data(data)

    Receive data from the network.

    After calling this method:

    - You must call `data_to_send()` and send this data to the network.

    - You should call `events_received()` and process resulting events.

    Raises

      EOFError – if `receive_eof()` was called earlier.

  receive_eof()

    Receive the end of the data stream from the network.

    After calling this method:

    - You must call `data_to_send()` and send this data to the network.

    - You aren’t expected to call `events_received()`; it won’t return any new events.

    Raises

      EOFError – if `receive_eof()` was called earlier.

  accept(request)

    Create a handshake response to accept the connection.

    If the connection cannot be established, the handshake response actually rejects the handshake.

    You must send the handshake response with `send_response()`.

    You can modify it before sending it, for example to add HTTP headers.

    Parameters

      request (websockets.http11.Request) – WebSocket handshake request event received from the client.

    Returns

      WebSocket handshake response event to send to the client.

    Return type

      Response

  reject(status, text)

    Create a handshake response to reject the connection.

    A short plain text response is the best fallback when failing to establish a WebSocket connection.

    You must send the handshake response with `send_response()`.

    You can modify it before sending it, for example to alter HTTP headers.

    Parameters

      - status (http.HTTPStatus) – HTTP status code.

      - text (str) – HTTP response body; will be encoded to UTF-8.

    Returns

      WebSocket handshake response event to send to the client.

    Return type

      Response

  send_response(response)

    Send a handshake response to the client.

    Parameters

      response (websockets.http11.Response) – WebSocket handshake response event to send.

  send_continuation(data, fin)

    Send a Continuation frame.

    Parameters

      - data (bytes) – payload containing the same kind of data as the initial frame.

      - fin (bool) – FIN bit; set it to `True` if this is the last frame of a fragmented message and to `False` otherwise.

    Raises

      ProtocolError – if a fragmented message isn’t in progress.

  send_text(data, fin=True)

    Send a Text frame.

    Parameters

      - data (bytes) – payload containing text encoded with UTF-8.

      - fin (bool) – FIN bit; set it to `False` if this is the first frame of a fragmented message.

    Raises

      ProtocolError – if a fragmented message is in progress.

  send_binary(data, fin=True)

    Send a Binary frame.

    Parameters

      - data (bytes) – payload containing arbitrary binary data.

      - fin (bool) – FIN bit; set it to `False` if this is the first frame of a fragmented message.

    Raises

      ProtocolError – if a fragmented message is in progress.

  send_close(code=None, reason='')

    Send a Close frame.

    Parameters

      - code (Optional[int]) – close code.

      - reason (str) – close reason.

    Raises

      ProtocolError – if a fragmented message is being sent, if the code isn’t valid, or if a reason is provided without a code

  send_ping(data)

    Send a Ping frame.

    Parameters

      data (bytes) – payload containing arbitrary binary data.

  send_pong(data)

    Send a Pong frame.

    Parameters

      data (bytes) – payload containing arbitrary binary data.

  fail(code, reason='')

    Fail the WebSocket connection.

    Parameters

      - code (int) – close code

      - reason (str) – close reason

    Raises

      ProtocolError – if the code isn’t valid.

  events_received()

    Fetch events generated from data received from the network.

    Call this method immediately after any of the `receive_*()` methods.

    Process resulting events, likely by passing them to the application.

    Returns

      Events read from the connection.

    Return type

      List[Event]

  data_to_send()

    Obtain data to send to the network.

    Call this method immediately after any of the `receive_*()`, `send_*()`, or `fail()` methods.

    Write resulting data to the connection.

    The empty bytestring `SEND_EOF` signals the end of the data stream. When you receive it, half-close the TCP connection.

    Returns

      Data to write to the connection.

    Return type

      List[bytes]

  close_expected()

    Tell if the TCP connection is expected to close soon.

    Call this method immediately after any of the `receive_*()` or `fail()` methods.

    If it returns `True`, schedule closing the TCP connection after a short timeout if the other side hasn’t already closed it.

    Returns

      Whether the TCP connection is expected to close soon.

    Return type

      bool

  id: uuid.UUID

    Unique identifier of the connection. Useful in logs.

  logger: LoggerLike

    Logger for this connection.

  property state: websockets.connection.State

    WebSocket connection state.

    Defined in 4.1, 4.2, 7.1.3, and 7.1.4 of RFC 6455.

  handshake_exc: Optional[Exception]

    Exception to raise if the opening handshake failed.

    `None` if the opening handshake succeeded.

  property close_code: Optional[int]

    WebSocket close code.

    `None` if the connection isn’t closed yet.

  property close_reason: Optional[str]

    WebSocket close reason.

    `None` if the connection isn’t closed yet.

  property close_exc: websockets.exceptions.ConnectionClosed

    Exception to raise when trying to interact with a closed connection.

    Don’t raise this exception while the connection `state` is `CLOSING`; wait until it’s `CLOSED`.

    Indeed, the exception includes the close code and reason, which are known only once the connection is closed.

    Raises

      AssertionError – if the connection isn’t closed yet.