Server (`threading`)¶

Creating a server¶

websockets.sync.server.serve(handler, host=None, port=None, *, sock=None, ssl=None, origins=None, extensions=None, subprotocols=None, select_subprotocol=None, compression='deflate', process_request=None, process_response=None, server_header='Python/3.14 websockets/16.0', 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]¶

Create a WebSocket server listening on host and port.

Whenever a client connects, the server creates a ServerConnection, performs the opening handshake, and delegates to the handler.

The handler receives the ServerConnection instance, which you can use 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.

This function returns a Server whose API mirrors BaseServer. Treat it as a context manager to ensure that it will be closed and call serve_forever() to serve requests:

from websockets.sync.server import serve

def handler(websocket):
    ...

with serve(handler, ...) as server:
    server.serve_forever()

Parameters:

handler (Callable[[ServerConnection], None]) – Connection handler. It receives the WebSocket connection, which is a ServerConnection, in argument.
host (str | None) – Network interfaces the server binds to. See create_server() for details.
port (int | None) – TCP port the server listens on. See create_server() for details.
sock (socket | None) – Preexisting TCP socket. sock replaces host and port. You may call socket.create_server() to create a suitable TCP socket.
ssl (SSLContext | None) – Configuration for enabling TLS on the connection.
origins (Sequence[Origin | Pattern[str] | None] | None) – Acceptable values of the Origin header, for defending against Cross-Site WebSocket Hijacking attacks. Values can be str to test for an exact match or regular expressions compiled by re.compile() to test against a pattern. Include None in the list if the lack of an origin is acceptable.
extensions (Sequence[ServerExtensionFactory] | 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.
select_subprotocol (Callable[[ServerConnection, Sequence[Subprotocol]], Subprotocol | None] | None) – Callback for selecting a subprotocol among those supported by the client and the server. It receives a ServerConnection (not a ServerProtocol!) instance and a list of subprotocols offered by the client. Other than the first argument, it has the same behavior as the ServerProtocol.select_subprotocol method.
compression (str | None) – The “permessage-deflate” extension is enabled by default. Set compression to None to disable it. See the compression guide for details.
process_request (Callable[[ServerConnection, Request], Response | None] | None) – Intercept the request during the opening handshake. Return an HTTP response to force the response. Return None to continue normally. When you force an HTTP 101 Continue response, the handshake is successful. Else, the connection is aborted.
process_response (Callable[[ServerConnection, Request, Response], Response | None] | None) – Intercept the response during the opening handshake. Modify the response or return a new HTTP response to force the response. Return None to continue normally. When you force an HTTP 101 Continue response, the handshake is successful. Else, the connection is aborted.
server_header (str | None) – Value of the Server response header. It defaults to "Python/x.y.z websockets/X.Y". Setting it to None removes the header.
open_timeout (float | None) – Timeout for opening connections 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 connections in seconds. None disables the timeout.
max_size (int | None | tuple[int | None, int | None]) – Maximum size of incoming messages in bytes. None disables the limit. You may pass a (max_message_size, max_fragment_size) tuple to set different limits for messages and fragments when you expect long messages sent in short fragments.
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 server. It defaults to logging.getLogger("websockets.server"). See the logging guide for details.
create_connection (type[ServerConnection] | None) – Factory for the ServerConnection managing the connection. Set it to a wrapper or a subclass to customize connection handling.

Any other keyword arguments are passed to create_server().

websockets.sync.server.unix_serve(handler, path=None, **kwargs)[source]¶

Create a WebSocket server listening on a Unix socket.

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

It’s only available on Unix.

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

Parameters:

handler (Callable[[ServerConnection], None]) – Connection handler. It receives the WebSocket connection, which is a ServerConnection, in argument.
path (str | None) – File system path to the Unix socket.

Routing connections¶

websockets.sync.router.route(url_map, *args, server_name=None, ssl=None, create_router=None, **kwargs)[source]¶

Create a WebSocket server dispatching connections to different handlers.

This feature requires the third-party library werkzeug:

$ pip install werkzeug

route() accepts the same arguments as serve(), except as described below.

The first argument is a werkzeug.routing.Map that maps URL patterns to connection handlers. In addition to the connection, handlers receive parameters captured in the URL as keyword arguments.

Here’s an example:

from websockets.sync.router import route
from werkzeug.routing import Map, Rule

def channel_handler(websocket, channel_id):
    ...

url_map = Map([
    Rule("/channel/<uuid:channel_id>", endpoint=channel_handler),
    ...
])

with route(url_map, ...) as server:
    server.serve_forever()

Refer to the documentation of werkzeug.routing for details.

If you define redirects with Rule(..., redirect_to=...) in the URL map, when the server runs behind a reverse proxy that modifies the Host header or terminates TLS, you need additional configuration:

Set server_name to the name of the server as seen by clients. When not provided, websockets uses the value of the Host header.
Set ssl=True to generate wss:// URIs without enabling TLS. Under the hood, this bind the URL map with a url_scheme of wss:// instead of ws://.

There is no need to specify websocket=True in each rule. It is added automatically.

Parameters:

url_map (Map) – Mapping of URL patterns to connection handlers.
server_name (str | None) – Name of the server as seen by clients. If None, websockets uses the value of the Host header.
ssl (SSLContext | Literal[True] | None) – Configuration for enabling TLS on the connection. Set it to True if a reverse proxy terminates TLS connections.
create_router (type[Router] | None) – Factory for the Router dispatching requests to handlers. Set it to a wrapper or a subclass to customize routing.

websockets.sync.router.unix_route(url_map, path=None, **kwargs)[source]¶

Create a WebSocket Unix server dispatching connections to different handlers.

unix_route() combines the behaviors of route() and unix_serve().

Parameters:

url_map (Map) – Mapping of URL patterns to connection handlers.
path (str | None) – File system path to the Unix socket.

class websockets.sync.router.Router(url_map, server_name=None, url_scheme='ws')[source]¶

WebSocket router supporting route().

Running a server¶

class websockets.sync.server.Server(socket, handler, logger=None)[source]¶

WebSocket server returned by serve().

This class mirrors the API of BaseServer, notably the serve_forever() and shutdown() methods, as well as the context manager protocol.

Parameters:

socket (socket.socket) – Server socket listening for new connections.
handler (Callable[[socket.socket, Any], None]) – Handler for one connection. Receives the socket and address returned by accept().
logger (LoggerLike | None) – Logger for this server. It defaults to logging.getLogger("websockets.server"). See the logging guide for details.

serve_forever()[source]¶

See socketserver.BaseServer.serve_forever().

This method doesn’t return. Calling shutdown() from another thread stops the server.

Typical use:

with serve(...) as server:
    server.serve_forever()

shutdown()[source]¶

See socketserver.BaseServer.shutdown().

fileno()[source]¶

See socketserver.BaseServer.fileno().

Using a connection¶

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

threading implementation of a WebSocket server connection.

ServerConnection 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 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 serve().

Parameters:

socket (socket.socket) – Socket connected to a WebSocket client.
protocol (ServerProtocol) – Sans-I/O connection.

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.

When the message is fragmented, recv() waits until all fragments are received, reassembles them, and returns 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 strings (str). This may be useful for servers that send binary frames instead of text frames.

Raises:

ConnectionClosed – When the connection is closed.
ConcurrencyError – If two threads call recv() or recv_streaming() concurrently.

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 yield bytestrings (bytes). This improves performance when decoding isn’t needed.
Set decode=True to force UTF-8 decoding of Binary frames and yield strings (str). This may be useful for servers that send binary frames instead of text frames.

Raises:

ConnectionClosed – When the connection is closed.
ConcurrencyError – If two threads call recv() or recv_streaming() concurrently.

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 an UTF-8 bytestring or bytes-like object (bytes, bytearray, or memoryview) in 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:

Raises:

ConnectionClosed – When the connection is closed.
ConcurrencyError – If the connection is sending a fragmented message.
TypeError – If message doesn’t have a supported type.

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.

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

Parameters:

code (CloseCode | 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 | bytearray | memoryview | 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_received = ws.ping()
# only if you want to wait for the corresponding pong
pong_received.wait()

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 | bytearray | memoryview) – Payload of the pong. A str will be encoded to UTF-8.
Raises:: ConnectionClosed – When the connection is closed.

respond(status, text)[source]¶

Create a plain text HTTP response.

process_request and process_response may call this method to return an HTTP response instead of performing the WebSocket opening handshake.

You can modify the response before returning it, for example by changing HTTP headers.

Parameters:

status (HTTPStatus | int) – HTTP status code.
text (str) – HTTP response body; it will be encoded to UTF-8.

Returns:

HTTP response to send to the client.

Return type:

Response

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().

latency: float¶

Latency of the connection, in seconds.

Latency is defined as the round-trip time of the connection. It is measured by sending a Ping frame and waiting for a matching Pong frame. Before the first measurement, latency is 0.0.

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().

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.

HTTP Basic Authentication¶

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

websockets.sync.server.basic_auth(realm='', credentials=None, check_credentials=None)[source]¶

Factory for process_request to enforce HTTP Basic Authentication.

basic_auth() is designed to integrate with serve() as follows:

from websockets.sync.server import basic_auth, serve

with serve(
    ...,
    process_request=basic_auth(
        realm="my dev server",
        credentials=("hello", "iloveyou"),
    ),
):

If authentication succeeds, the connection’s username attribute is set. If it fails, the server responds with an HTTP 401 Unauthorized status.

One of credentials or check_credentials must be provided; not both.

Parameters:

realm (str) – 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 (tuple[str, str] | Iterable[tuple[str, str]] | None) – Hard coded authorized credentials. It can be a (username, password) pair or a list of such pairs.
check_credentials (Callable[[str, str], bool] | None) – Function that verifies credentials. It receives username and password arguments and returns whether they’re valid.

Raises:

TypeError – If credentials or check_credentials is wrong.
ValueError – If credentials and check_credentials are both provided or both not provided.

Server (threading)¶

Creating a server¶

Routing connections¶

Running a server¶

Using a connection¶

HTTP Basic Authentication¶

Server (`threading`)¶