Client

Opening a connection

await websockets.client.connect(uri, *, create_protocol=None, ping_interval=20, ping_timeout=20, close_timeout=None, max_size=1048576, max_queue=32, read_limit=65536, write_limit=65536, loop=None, compression='deflate', origin=None, extensions=None, subprotocols=None, extra_headers=None, **kwargs)

Connect to the WebSocket server at the given uri.

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

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

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

In that case, the connection is closed when exiting the context.

connect() is a wrapper around the event loop’s create_connection() method. Unknown keyword arguments are passed to create_connection().

For example, you can set the ssl keyword argument to a SSLContext to enforce some TLS settings. When connecting to a wss:// URI, if this argument isn’t provided explicitly, ssl.create_default_context() is called to create a context.

You can connect to a different host and port from those found in uri by setting host and port keyword arguments. 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 HTTP header.

create_protocol defaults to WebSocketClientProtocol. It may be replaced by a wrapper or a subclass to customize the protocol that manages the connection.

The behavior of ping_interval, ping_timeout, close_timeout, max_size, max_queue, read_limit, and write_limit is described in WebSocketClientProtocol.

connect() also accepts the following optional arguments:

  • compression is a shortcut to configure compression extensions; by default it enables the “permessage-deflate” extension; set it to None to disable compression.

  • origin sets the Origin HTTP header.

  • extensions is a list of supported extensions in order of decreasing preference.

  • subprotocols is a list of supported subprotocols in order of decreasing preference.

  • extra_headers sets additional HTTP request headers; it can be a Headers instance, a Mapping, or an iterable of (name, value) pairs.

Raises

  • InvalidURI – if uri is invalid

  • InvalidHandshake – if the opening handshake fails

await websockets.client.unix_connect(path, uri='ws://localhost/', **kwargs)[source]

Similar to connect(), but for connecting to a Unix socket.

This function calls 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 (Optional[str]) – file system path to the Unix socket

  • uri (str) – WebSocket URI

Return type

Connect

Using a connection

class websockets.client.WebSocketClientProtocol(*, origin=None, extensions=None, subprotocols=None, extra_headers=None, **kwargs)[source]

Protocol subclass implementing a WebSocket client.

WebSocketClientProtocol:

  • performs the opening handshake to establish the connection;

  • provides recv() and send() coroutines for receiving and sending messages;

  • deals with control frames automatically;

  • performs the closing handshake to terminate the connection.

WebSocketClientProtocol supports asynchronous iteration:

async for message in websocket:
    await process(message)

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

Once the connection is open, a Ping frame is sent every ping_interval seconds. This serves as a keepalive. It helps keeping the connection open, especially in the presence of proxies with short timeouts on inactive connections. Set ping_interval to None to disable this behavior.

If the corresponding Pong frame isn’t received within ping_timeout seconds, the connection is considered unusable and is closed with code 1011. This ensures that the remote endpoint remains responsive. Set ping_timeout to None to disable this behavior.

The close_timeout parameter defines a maximum wait time for completing the closing handshake and terminating the TCP connection. For legacy reasons, close() completes in at most 5 * close_timeout seconds.

close_timeout needs to be a parameter of the protocol because websockets usually calls close() implicitly upon exit when connect() is used as a context manager.

To apply a timeout to any other API, wrap it in wait_for().

The max_size parameter enforces the maximum size for incoming messages in bytes. The default value is 1 MiB. None disables the limit. If a message larger than the maximum size is received, recv() will raise ConnectionClosedError and the connection will be closed with code 1009.

The max_queue parameter sets the maximum length of the queue that holds incoming messages. The default value is 32. None disables the limit. Messages are added to an in-memory queue when they’re received; then recv() pops from that queue. In order to prevent excessive memory consumption when messages are received faster than they can be processed, the queue must be bounded. If the queue fills up, the protocol stops processing incoming data until recv() is called. In this situation, various receive buffers (at least in asyncio and in the OS) will fill up, then the TCP receive window will shrink, slowing down transmission to avoid packet loss.

Since Python can use up to 4 bytes of memory to represent a single character, each connection may use up to 4 * max_size * max_queue bytes of memory to store incoming messages. By default, this is 128 MiB. You may want to lower the limits, depending on your application’s requirements.

The read_limit argument sets the high-water limit of the buffer for incoming bytes. The low-water limit is half the high-water limit. The default value is 64 KiB, half of asyncio’s default (based on the current implementation of StreamReader).

The write_limit argument sets the high-water limit of the buffer for outgoing bytes. The low-water limit is a quarter of the high-water limit. The default value is 64 KiB, equal to asyncio’s default (based on the current implementation of FlowControlMixin).

As soon as the HTTP request and response in the opening handshake are processed:

  • the request path is available in the path attribute;

  • the request and response HTTP headers are available in the request_headers and response_headers attributes, which are Headers instances.

If a subprotocol was negotiated, it’s available in the subprotocol attribute.

Once the connection is closed, the code is available in the close_code attribute and the reason in close_reason.

All attributes must be treated as read-only.

local_address

Local address of the connection as a (host, port) tuple.

When the connection isn’t open, local_address is None.

Return type

Any

remote_address

Remote address of the connection as a (host, port) tuple.

When the connection isn’t open, remote_address is None.

Return type

Any

open

True when the connection is usable.

It may be used to detect disconnections. However, this approach is discouraged per the EAFP principle.

When open is False, using the connection raises a ConnectionClosed exception.

Return type

bool

closed

True once the connection is closed.

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

Return type

bool

path

Path of the HTTP request.

Available once the connection is open.

request_headers

HTTP request headers as a Headers instance.

Available once the connection is open.

response_headers

HTTP response headers as a Headers instance.

Available once the connection is open.

subprotocol

Subprotocol, if one was negotiated.

Available once the connection is open.

close_code

WebSocket close code.

Available once the connection is closed.

close_reason

WebSocket close reason.

Available once the connection is closed.

await recv()

Receive the next message.

Return a str for a text frame and bytes for a binary frame.

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

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().

Raises
Return type

Union[str, bytes]

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. In that case the message is fragmented. 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 wish 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:

  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. Closing the connection has the same effect.

Raises

TypeError – for unsupported inputs

Return type

None

await ping(data=None)

Send a ping.

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

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

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

By default, the ping contains four random bytes. This payload may be overridden with the optional data argument which must be a string (which will be encoded to UTF-8) or a bytes-like object.

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.

Return type

Awaitable[None]

await pong(data=b'')

Send a pong.

An unsolicited pong may serve as a unidirectional heartbeat.

The payload may be set with the optional data argument which must be a string (which will be encoded to UTF-8) or a bytes-like object.

Canceling pong() is discouraged for the same reason as ping().

Return type

None

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(); close() already does it.

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 close the TCP connection.

Parameters

  • code (int) – WebSocket close code

  • reason (str) – WebSocket close reason

Return type

None

await wait_closed()

Wait until the connection is closed.

This is identical to closed, except it can be awaited.

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

Return type

None