Client (asyncio) - websockets 12.0 documentation
Description: Opening a connection: Using a connection:

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# Client (`asyncio`)

## Opening a connection

await websockets.client.connect(uri, *, create_protocol=None, logger=None, compression='deflate', origin=None, extensions=None, subprotocols=None, extra_headers=None, user_agent_header='Python/x.y.z websockets/X.Y', open_timeout=10, 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)

  Connect to the WebSocket server at `uri`.

  Awaiting `connect()` yields a `WebSocketClientProtocol` which can then be used to send and receive messages.

  `connect()` can be used as a asynchronous context manager:

      async with websockets.connect(...) as websocket:
          ...

  The connection is closed automatically when exiting the context.

  `connect()` can be used as an infinite asynchronous iterator to reconnect automatically on errors:

      async for websocket in websockets.connect(...):
          try:
              ...
          except websockets.ConnectionClosed:
              continue

  The connection is closed automatically after each iteration of the loop.

  If an error occurs while establishing the connection, `connect()` retries with exponential backoff. The backoff delay starts at three seconds and increases up to one minute.

  If an error occurs in the body of the loop, you can handle the exception and `connect()` will reconnect with the next iteration; or you can let the exception bubble up and break out of the loop. This lets you decide which errors trigger a reconnection and which errors are fatal.

  Parameters:

    - uri (str) – URI of the WebSocket server.

    - create_protocol (Optional[Callable[..., WebSocketClientProtocol]]) – Factory for the `asyncio.Protocol` managing the connection. It defaults to `WebSocketClientProtocol`. Set it to a wrapper or a subclass to customize connection handling.

    - logger (Optional[LoggerLike]) – Logger for this client. It defaults to `logging.getLogger("websockets.client")`. See the logging guide for details.

    - compression (Optional[str]) – The “permessage-deflate” extension is enabled by default. Set `compression` to `None` to disable it. See the compression guide for details.

    - origin (Optional[Origin]) – Value of the `Origin` header, for servers that require it.

    - extensions (Optional[Sequence[ClientExtensionFactory]]) – List of supported extensions, in order in which they should be negotiated and run.

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

    - extra_headers (Optional[HeadersLike]) – Arbitrary HTTP headers to add to the handshake request.

    - user_agent_header (Optional[str]) – Value of the `User-Agent` request header. It defaults to `"Python/x.y.z websockets/X.Y"`. Setting it to `None` removes the header.

    - open_timeout (Optional[float]) – Timeout for opening the connection in seconds. `None` disables the timeout.

  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_connection()` method.

  For example:

  - You can set `ssl` to a `SSLContext` to enforce TLS settings. When connecting to a `wss://` URI, if `ssl` isn’t provided, a TLS context is created with `create_default_context()`.

  - You can set `host` and `port` to connect to a different host and port from those found in `uri`. This only changes the destination of the TCP connection. The host name from `uri` is still used in the TLS handshake for secure connections and in the `Host` header.

  Raises:

    - InvalidURI – If `uri` isn’t a valid WebSocket URI.

    - OSError – If the TCP connection fails.

    - InvalidHandshake – If the opening handshake fails.

    - TimeoutError – If the opening handshake times out.

await websockets.client.unix_connect(path, uri='ws://localhost/', *, create_protocol=None, logger=None, compression='deflate', origin=None, extensions=None, subprotocols=None, extra_headers=None, user_agent_header='Python/x.y.z websockets/X.Y', open_timeout=10, 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 `connect()`, but for connecting to a Unix socket.

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

  It is only available on Unix.

  It’s mainly useful for debugging servers listening on Unix sockets.

  Parameters:

    - path (str | None) – File system path to the Unix socket.

    - uri (str) – URI of the WebSocket server; the host is used in the TLS handshake for secure connections and in the `Host` header.

## Using a connection

class websockets.client.WebSocketClientProtocol(*, logger=None, origin=None, extensions=None, subprotocols=None, extra_headers=None, user_agent_header='Python/x.y.z websockets/X.Y', 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 client connection.

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

  It supports asynchronous iteration to receive incoming 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) or without a close code. It raises a `ConnectionClosedError` when the connection is closed with any other code.

  See `connect()` for the documentation of `logger`, `origin`, `extensions`, `subprotocols`, `extra_headers`, and `user_agent_header`.

  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 `timeout()` or `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=CloseCode.NORMAL_CLOSURE, 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, as a check that the remote endpoint received all messages up to this point, or to measure `latency`.

    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. The result of the future is the latency of the connection in seconds.

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

    Return type:

      Future[float]

    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.

  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.

  latency: float

    Latency of the connection, in seconds.

    This value is updated after sending a ping frame and receiving a matching pong frame. Before the first ping, `latency` is `0`.

    By default, websockets enables a keepalive mechanism that sends ping frames automatically at regular intervals. You can also send ping frames and measure latency with `ping()`.

  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: Subprotocol | None

    Subprotocol, if one was negotiated.

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

  property close_code: int | None

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

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

  property close_reason: str | None

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

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