Mojo-Websockets: WebSocket servers and clients

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1

Hello, I’m excited to share the mojo-websockets library for building websockets in Mojo in a similar way for those who are use to the Python websockets library.

Features

  • WebSocket Server and Client: Supports creating both WebSocket servers and clients.
  • Compatibility: API designed to be intuitive for developers familiar with the Python websockets library.
  • Sans/IO Layer: Implements a WebSocket Sans/IO layer pure Mojo and performs no I/O of its own.

The main TO-DO is the non-blocking communications support, as it’s waiting for the official Mojo async support.

Any feedback and contributions are highly appreciated!

7 Likes
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Always happy to see sans-io protocol implementations!

1 Like
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100%. Thanks to the Sans/IO I could add 200+ tests to check my implementation with no I/O connection at all

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Unfortunately, without proper async support in Mojo, the WebSocket server is not usable. In Lightbug, at least, the HTTP connections are quick if there is no keep-alive. However, websocket connections remain active for a whole lifetime.

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That’s great, good job!
There is also the autobahn websocket test suite i think :+1:

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I am trying to workaround the lack of async support trying to do it using threads. This is the PR I tried: Threading version to try to serve connections in parallel by msaelices · Pull Request #2 · msaelices/mojo-websockets · GitHub

The problem is these major issues:

  1. The thread context was deleted by Mojo and I don’t know how to properly fix it. I used the mark_destroyed trickery but I don’t know if there is a better approach (it should)
  2. There is a segfault related to the CPython interpreter. Don’t know how to fix it.

Do you have any clue? Thanks in advance.

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Most kinds of threading are going to break a lot of things. There’s no way to take the gil right now, so you can’t call python code. You also can’t access global variables.

I think it would be better to try to set up epoll or io_uring and take event handlers.

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Thanks for the suggestion. I’ve seen there is already a io_uring library in Mojo GitHub - dmitry-salin/io_uring: The io_uring library for Mojo

I’ve just adapted it to use the latest 25.1 version: Update code to support Mojo and Max 25.1 by msaelices · Pull Request #1 · dmitry-salin/io_uring · GitHub

When/If merged, I will add it to the official max community channel so I hope @Caroline will be happy about it

2 Likes
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The support of concurrent connections is already implemented in the io_uring branch. It’s blocked because of some PR for fixing the io_uring wrapper on the latest Max version, but it will be merged soon.

Thanks to @owenhilyard for the suggestion.

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I run this client code, and the response is limited to 1024 characters. How can I get longer responses?

from websockets.sync.client import connect

fn send_and_receive(msg: String) raises:
    with connect("ws://127.0.0.1:8000") as client:
        client.send_text(msg)
        print(">>> ", msg)
        response = client.recv_text()
        print("<<< ", response)

fn main() raises:
    send_and_receive("Hello world!")
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What version are you using? I’m in process of supporting Mojo 25.4 but the current buffer size is 64K not 1K, so it’s weird

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