Client (threading)

Opening a connection

websockets.sync.client.connect(uri, *, sock=None, ssl=None, server_hostname=None, origin=None, extensions=None, subprotocols=None, compression='deflate', additional_headers=None, user_agent_header='Python/3.10 websockets/15.0', proxy=True, proxy_ssl=None, proxy_server_hostname=None, open_timeout=10, ping_interval=20, ping_timeout=20, close_timeout=10, max_size=1048576, max_queue=16, logger=None, create_connection=None, **kwargs)[source]

Connect to the WebSocket server at uri.

This function returns a ClientConnection instance, which you can use to send and receive messages.

connect() may be used as a context manager:

from websockets.sync.client import connect

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

The connection is closed automatically when exiting the context.

Parameters:

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

  • sock (socket | None) – Preexisting TCP socket. sock overrides the host and port from uri. You may call socket.create_connection() to create a suitable TCP socket.

  • ssl (SSLContext | None) – Configuration for enabling TLS on the connection.

  • server_hostname (str | None) – Host name for the TLS handshake. server_hostname overrides the host name from uri.

  • origin (Origin | None) – Value of the Origin header, for servers that require it.

  • extensions (Sequence[ClientExtensionFactory] | None) – List of supported extensions, in order in which they should be negotiated and run.

  • subprotocols (Sequence[Subprotocol] | None) – List of supported subprotocols, in order of decreasing preference.

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

  • additional_headers (HeadersLike | None) – Arbitrary HTTP headers to add to the handshake request.

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

  • proxy (str | Literal[True] | None) – If a proxy is configured, it is used by default. Set proxy to None to disable the proxy or to the address of a proxy to override the system configuration. See the proxy docs for details.

  • proxy_ssl (SSLContext | None) – Configuration for enabling TLS on the proxy connection.

  • proxy_server_hostname (str | None) – Host name for the TLS handshake with the proxy. proxy_server_hostname overrides the host name from proxy.

  • open_timeout (float | None) – Timeout for opening the connection in seconds. None disables the timeout.

  • ping_interval (float | None) – Interval between keepalive pings in seconds. None disables keepalive.

  • ping_timeout (float | None) – Timeout for keepalive pings in seconds. None disables timeouts.

  • close_timeout (float | None) – Timeout for closing the connection in seconds. None disables the timeout.

  • max_size (int | None) – Maximum size of incoming messages in bytes. None disables the limit.

  • max_queue (int | None | tuple[int | None, int | None]) – High-water mark of the buffer where frames are received. It defaults to 16 frames. The low-water mark defaults to max_queue // 4. You may pass a (high, low) tuple to set the high-water and low-water marks. If you want to disable flow control entirely, you may set it to None, although that’s a bad idea.

  • logger (Logger | LoggerAdapter | None) – Logger for this client. It defaults to logging.getLogger("websockets.client"). See the logging guide for details.

  • create_connection (type[ClientConnection] | None) – Factory for the ClientConnection managing the connection. Set it to a wrapper or a subclass to customize connection handling.

Any other keyword arguments are passed to create_connection().

Raises:
websockets.sync.client.unix_connect(path=None, uri=None, **kwargs)[source]

Connect to a WebSocket server listening on a Unix socket.

This function accepts the same keyword arguments as connect().

It’s 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 | None) – URI of the WebSocket server. uri defaults to ws://localhost/ or, when a ssl is provided, to wss://localhost/.

Using a connection

class websockets.sync.client.ClientConnection(socket, protocol, *, ping_interval=20, ping_timeout=20, close_timeout=10, max_queue=16)[source]

threading implementation of a WebSocket client connection.

ClientConnection provides recv() and send() methods for receiving and sending messages.

It supports iteration to receive messages:

for message in websocket:
    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.

The ping_interval, ping_timeout, close_timeout, and max_queue arguments have the same meaning as in connect().

Parameters:
for ... in __iter__()[source]

Iterate on incoming messages.

The iterator calls recv() and yields messages in an infinite loop.

It exits when the connection is closed normally. It raises a ConnectionClosedError exception after a protocol error or a network failure.

recv(timeout=None, decode=None)[source]

Receive the next message.

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

If timeout is None, block until a message is received. If timeout is set, wait up to timeout seconds for a message to be received and return it, else raise TimeoutError. If timeout is 0 or negative, check if a message has been received already and return it, else raise TimeoutError.

If the message is fragmented, wait until all fragments are received, reassemble them, and return the whole message.

Parameters:

  • timeout (float | None) – Timeout for receiving a message in seconds.

  • decode (bool | None) – Set this flag to override the default behavior of returning str or bytes. See below for details.

Returns:

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

You may override this behavior with the decode argument:

  • Set decode=False to disable UTF-8 decoding of Text frames and return a bytestring (bytes). This improves performance when decoding isn’t needed, for example if the message contains JSON and you’re using a JSON library that expects a bytestring.

  • Set decode=True to force UTF-8 decoding of Binary frames and return a string (str). This may be useful for servers that send binary frames instead of text frames.

Raises:
Return type:

str | bytes

for ... in recv_streaming(decode=None)[source]

Receive the next message frame by frame.

This method is designed for receiving fragmented messages. It returns an iterator that yields each fragment as it is received. This iterator must be fully consumed. Else, future calls to recv() or recv_streaming() will raise ConcurrencyError, making the connection unusable.

recv_streaming() raises the same exceptions as recv().

Parameters:

decode (bool | None) – Set this flag to override the default behavior of returning str or bytes. See below for details.

Returns:

An iterator of strings (str) for a Text frame or bytestrings (bytes) for a Binary frame.

You may override this behavior with the decode argument:

  • Set decode=False to disable UTF-8 decoding of Text frames and return bytestrings (bytes). This may be useful to optimize performance when decoding isn’t needed.

  • Set decode=True to force UTF-8 decoding of Binary frames and return strings (str). This is useful for servers that send binary frames instead of text frames.

Raises:
Return type:

Iterator[str | bytes]

send(message, text=None)[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.

You may override this behavior with the text argument:

  • Set text=True to send a bytestring or bytes-like object (bytes, bytearray, or memoryview) as a Text frame. This improves performance when the message is already UTF-8 encoded, for example if the message contains JSON and you’re using a JSON library that produces a bytestring.

  • Set text=False to send a string (str) in a Binary frame. This may be useful for servers that expect binary frames instead of text frames.

send() also accepts an 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 really want to send the keys of a dict-like object as fragments, call its keys() method and pass the result to send().)

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]) – Message to send.

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

Perform the closing handshake.

close() waits for the other end to complete the handshake, for the TCP connection to terminate, and for all incoming messages to be read with recv().

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

Parameters:

  • code (int) – WebSocket close code.

  • reason (str) – WebSocket close reason.

ping(data=None, ack_on_close=False)[source]

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

Parameters:

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

  • ack_on_close (bool) – when this option is True, the event will also be set when the connection is closed. While this avoids getting stuck waiting for a pong that will never arrive, it requires checking that the state of the connection is still OPEN to confirm that a pong was received, rather than the connection being closed.

Returns:

An event that will be set when the corresponding pong is received. You can ignore it if you don’t intend to wait.

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

Raises:

  • ConnectionClosed – When the connection is closed.

  • ConcurrencyError – If another ping was sent with the same data and the corresponding pong wasn’t received yet.

Return type:

Event

pong(data=b'')[source]

Send a Pong.

An unsolicited pong may serve as a unidirectional heartbeat.

Parameters:

data (str | bytes) – Payload of the pong. A str 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().

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().

property state: State

State of the WebSocket connection, defined in RFC 6455.

This attribute is provided for completeness. Typical applications shouldn’t check its value. Instead, they should call recv() or send() and handle ConnectionClosed exceptions.

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

request: Request | None

Opening handshake request.

response: Response | None

Opening handshake response.

property subprotocol: Subprotocol | None

Subprotocol negotiated during the opening handshake.

None if no subprotocol was negotiated.

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

property close_code: int | None

State of the WebSocket connection, defined in RFC 6455.

This attribute is provided for completeness. Typical applications shouldn’t check its value. Instead, they should inspect attributes of ConnectionClosed exceptions.

property close_reason: str | None

State of the WebSocket connection, defined in RFC 6455.

This attribute is provided for completeness. Typical applications shouldn’t check its value. Instead, they should inspect attributes of ConnectionClosed exceptions.