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)[source]#

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:
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)[source]#

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)[source]#

WebSocket client connection.

WebSocketClientProtocol 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) 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()[source]#

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.

Raises:
Return type:

str | bytes

await send(message)[source]#

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 (str | bytes | Iterable[str | bytes] | AsyncIterable[str | bytes]) – Message to send.

Raises:
await close(code=CloseCode.NORMAL_CLOSURE, reason='')[source]#

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()[source]#

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)[source]#

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 (str | bytes | None) – Payload of the ping. A string will be encoded to UTF-8. If data is None, the payload is 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

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.

Return type:

Awaitable[float]

await pong(data=b'')[source]#

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 (str | bytes) – 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.