FAQ

What about Python 2 support?

Release 0.59.0 was the last main release supporting Python 2. All future releases 1.X.X and beyond will only support Python 3.

Why is this library slow?

The send and validate_utf8 methods are very slow in pure Python. You can disable UTF8 validation in this library (and receive a performance enhancement) with the skip_utf8_validation parameter. If you want to get better performance, install wsaccel. While websocket-client does not depend on wsaccel, it will be used if available. wsaccel doubles the speed of UTF8 validation and offers a very minor 10% performance boost when masking the payload data as part of the send process. Numpy used to be a suggested alternative, but issue #687 found it didn’t help.

How to troubleshoot an unclear callback error?

To get more information about a callback error, you can specify a custom on_error() function that raises errors to provide more information. Sample code of such a solution is shown below, although the example URL provided will probably not trigger an error under normal circumstances. Issue #377 discussed this topic previously.

>>> import websocket
>>>
>>> def on_message(ws, message):
...     print(message)
>>> def on_error(wsapp, err):
...     print("Got a an error: ", err)
>>> wsapp = websocket.WebSocketApp("ws://echo.websocket.events/",
... on_message = on_message,
... on_error=on_error)
>>> wsapp.run_forever()

How to solve the “connection is already closed” error?

The WebSocketConnectionClosedException, which returns the message “Connection is already closed.”, occurs when a WebSocket function such as send() or recv() is called but the WebSocket connection is already closed. One way to handle exceptions in Python is by using a try/except statement, which allows you to control what your program does if the WebSocket connection is closed when you try to use it. In order to properly carry out further functions with your WebSocket connection after the connection has closed, you will need to reconnect the WebSocket, using connect() or create_connection() (from the _core.py file). The WebSocketApp run_forever() function automatically tries to reconnect when the connection is lost if a dispatcher parameter is provided to the run_forever() function.

What’s going on with the naming of this library?

To install this library, you use pip install websocket-client, while import websocket imports this library, and PyPi lists the package as websocket_client. Why is it so confusing? To see the original issue about the choice of import websocket, see issue #60 and to read about websocket-client vs. websocket_client, see issue #147

Is WebSocket Compression using the permessage-deflate extension supported?

No, RFC 7692 for WebSocket Compression is unfortunately not supported by the websocket-client library at this time. You can view the currently supported WebSocket features in the latest autobahn compliance HTML report, found under the compliance folder. If you use the Sec-WebSocket-Extensions: permessage-deflate header with websocket-client, you will probably encounter errors, such as the ones described in issue #314.

I get the error ‘utf8’ codec can’t decode byte 0x81 in position 0

This error is caused when you receive a character that is not a UTF-8 character, so the UTF-8 decoding fails. You can set skip_utf8_validation to false, but if this does not work, you can change the encoding to ISO-8859-1 which was a workaround suggested in [issue 481](https://github.com/websocket-client/websocket-client/issues/481#issuecomment-1112506666).

If a connection is re-established after getting disconnected, does the new connection continue where the previous one dropped off?

The answer to this question depends on how the WebSocket server handles new connections. If the server keeps a list of recently dropped WebSocket connection sessions, then it may allow you to recontinue your WebSocket connection where you left off before disconnecting. However, this requires extra effort from the server and may create security issues. For these reasons it is rare to encounter such a WebSocket server. The server would need to identify each connecting client with authentication and keep track of which data was received using a method like TCP’s SYN/ACK. That’s a lot of overhead for a lightweight protocol! Both HTTP and WebSocket connections use TCP sockets, and when a new WebSocket connection is created, it uses a new TCP socket. Therefore, at the TCP layer, the default behavior is to give each WebSocket connection a separate TCP socket. This means the re-established connection after a disconnect is the same as a completely new connection. Another way to think about this is: what should the server do if you create two WebSocket connections from the same client to the same server? The easiest solution for the server is to treat each connection separately, unless the WebSocket uses an authentication method to identify individual clients connecting to the server.

What is the difference between recv_frame(), recv_data_frame(), and recv_data()?

This is explained in issue #688. This information is useful if you do NOT want to use run_forever() but want to have similar functionality. In short, recv_data() is the recommended choice and you will need to manage ping/pong on your own, while run_forever() handles ping/pong by default.

How to disable ssl cert verification?

Set the sslopt to {"cert_reqs": ssl.CERT_NONE}. The same sslopt argument is provided for all examples seen below.

WebSocketApp example

>>> import websocket, ssl
>>> ws = websocket.WebSocketApp("wss://echo.websocket.events")
>>> ws.run_forever(sslopt={"cert_reqs": ssl.CERT_NONE})

create_connection example

>>> import websocket, ssl
>>> ws = websocket.create_connection("wss://echo.websocket.events",
... sslopt={"cert_reqs": ssl.CERT_NONE})

WebSocket example

>>> import websocket, ssl
>>> ws = websocket.WebSocket(sslopt={"cert_reqs": ssl.CERT_NONE})
>>> ws.connect("wss://echo.websocket.events")

How to disable hostname verification?

Please set sslopt to {"check_hostname": False}. (since v0.18.0)

WebSocketApp example

>>> import websocket
>>> ws = websocket.WebSocketApp("wss://echo.websocket.events")
>>> ws.run_forever(sslopt={"check_hostname": False})

create_connection example

>>> import websocket
>>> ws = websocket.create_connection("wss://echo.websocket.events",
... sslopt={"check_hostname": False})

WebSocket example

>>> import websocket
>>> ws = websocket.WebSocket(sslopt={"check_hostname": False})
>>> ws.connect("wss://echo.websocket.events")

What else can I do with sslopts?

The sslopt parameter is a dictionary to which the following keys can be assigned:

If any other SSL options are required, they can be used by creating a custom SSLContext from the python SSL library and then passing that in as the value of the context key. (since v1.2.2)

For example, if you wanted to load all of the default CA verification certificates, but also add your own additional custom CAs (of which the certs are located in the file “my_extra_CAs.cer”), you could do this:

>>> import ssl
>>> my_context = ssl.create_default_context()
>>> my_context.load_verify_locations('my_extra_CAs.cer')  
>>> ws.run_forever(sslopt={'context': my_context})

Note that when passing in a custom context, all of the other context-related options are ignored. In other words, only the server_hostname, do_handshake_on_connect, and suppress_ragged_eofs options can be used in conjunction with context.

How to enable SNI?

SNI support is available for Python 2.7.9+ and 3.2+. It will be enabled automatically whenever possible.

Why don’t I receive all the server’s message(s)?

Depending on how long your connection exists, it can help to ping the server to keep the connection alive. See issue #200 for possible solutions.

Using Subprotocols

The WebSocket RFC outlines the usage of subprotocols. The subprotocol can be specified as in the example below:

>>> import websocket
>>> ws = websocket.create_connection("ws://echo.websocket.events", subprotocols=["binary", "base64"])