Why does the server close the connection after processing one message?¶
Your connection handler exits after processing one message. Write a loop to process multiple messages.
For example, if your handler looks like this:
async def handler(websocket, path): print(websocket.recv())
change it like this:
async def handler(websocket, path): async for message in websocket: print(message)
Don’t feel bad if this happens to you — it’s the most common question in websockets’ issue tracker :-)
Why can only one client connect at a time?¶
Your connection handler blocks the event loop. Look for blocking calls. Any call that may take some time must be asynchronous.
For example, if you have:
async def handler(websocket, path): time.sleep(1)
change it to:
async def handler(websocket, path): await asyncio.sleep(1)
This is part of learning asyncio. It isn’t specific to websockets.
See also Python’s documentation about running blocking code.
How can I pass additional arguments to the connection handler?¶
You can bind additional arguments to the connection handler with
import asyncio import functools import websockets async def handler(websocket, path, extra_argument): ... bound_handler = functools.partial(handler, extra_argument='spam') start_server = websockets.serve(bound_handler, ...)
Another way to achieve this result is to define the
handler coroutine in
a scope where the
extra_argument variable exists instead of injecting it
through an argument.
How do I get the IP address of the client connecting to my server?¶
It’s available in
async def handler(websocket, path): remote_ip = websocket.remote_address
How do I set which IP addresses my server listens to?¶
Look at the
host argument of
serve() accepts the same arguments as
How do I close a connection properly?¶
websockets takes care of closing the connection when the handler exits.
How do I run a HTTP server and WebSocket server on the same port?¶
This isn’t supported.
Providing a HTTP server is out of scope for websockets. It only aims at providing a WebSocket server.
There’s limited support for returning HTTP responses with the
If you need more, pick a HTTP server and run it separately.
How do I close a connection properly?¶
The easiest is to use
connect() as a context manager:
async with connect(...) as websocket: ...
How do I do two things in parallel? How do I integrate with another coroutine?¶
This is also part of learning asyncio and not specific to websockets.
Keep track of the tasks and make sure they terminate or you cancel them when the connection terminates.
How do I create channels or topics?¶
websockets doesn’t have built-in publish / subscribe for these use cases.
Depending on the scale of your service, a simple in-memory implementation may do the job or you may need an external publish / subscribe component.
ConnectionClosedError: code = 1006 mean?¶
If you’re seeing this traceback in the logs of a server:
Error in connection handler Traceback (most recent call last): ... asyncio.streams.IncompleteReadError: 0 bytes read on a total of 2 expected bytes The above exception was the direct cause of the following exception: Traceback (most recent call last): ... websockets.exceptions.ConnectionClosedError: code = 1006 (connection closed abnormally [internal]), no reason
or if a client crashes with this traceback:
Traceback (most recent call last): ... ConnectionResetError: [Errno 54] Connection reset by peer The above exception was the direct cause of the following exception: Traceback (most recent call last): ... websockets.exceptions.ConnectionClosedError: code = 1006 (connection closed abnormally [internal]), no reason
it means that the TCP connection was lost. As a consequence, the WebSocket connection was closed without receiving a close frame, which is abnormal.
You can catch and handle
ConnectionClosed to prevent it
from being logged.
There are several reasons why long-lived connections may be lost:
End-user devices tend to lose network connectivity often and unpredictably because they can move out of wireless network coverage, get unplugged from a wired network, enter airplane mode, be put to sleep, etc.
HTTP load balancers or proxies that aren’t configured for long-lived connections may terminate connections after a short amount of time, usually 30 seconds.
If you’re facing a reproducible issue, enable debug logs to see when and how connections are closed.
How can I pass additional arguments to a custom protocol subclass?¶
You can bind additional arguments to the protocol factory with
import asyncio import functools import websockets class MyServerProtocol(websockets.WebSocketServerProtocol): def __init__(self, extra_argument, *args, **kwargs): super().__init__(*args, **kwargs) # do something with extra_argument create_protocol = functools.partial(MyServerProtocol, extra_argument='spam') start_server = websockets.serve(..., create_protocol=create_protocol)
This example was for a server. The same pattern applies on a client.
Why do I get the error:
module 'websockets' has no attribute '...'?¶
Often, this is because you created a script called
websockets.py in your
current working directory. Then
import websockets imports this module
instead of the websockets library.
No, there aren’t.
websockets provides high-level, coroutine-based APIs. Compared to callbacks, coroutines make it easier to manage control flow in concurrent code.
If you prefer callback-based APIs, you should use another library.
Can I use
websockets synchronously, without
You can convert every asynchronous call to a synchronous call by wrapping it
If this turns out to be impractical, you should use another library.
How do I set a timeout on
await asyncio.wait_for(websocket.recv(), timeout=10)
This technique works for most APIs, except for asynchronous context managers. See issue 574.
How do I keep idle connections open?¶
websockets sends pings at 20 seconds intervals to keep the connection open.
In closes the connection if it doesn’t get a pong within 20 seconds.
You can adjust this behavior with
How do I respond to pings?¶
websockets takes care of responding to pings with pongs.
Is there a Python 2 version?¶
No, there isn’t.
websockets builds upon asyncio which requires Python 3.