This is a follow-on to my SimpleX CLI Docker Setup post. If you read that, you might remember the socat workaround I used to get around the WebSocket server only binding to localhost:

command: >
  sh -c "socat TCP-LISTEN:5225,fork,bind=0.0.0.0 TCP:127.0.0.1:5226 &
         simplex-chat -p 5226"

It worked, but it always felt like a hack. The underlying issue was that simplex-chat hardcodes the bind address to 127.0.0.1 when you use the -p flag.

Understanding the Default

This localhost-only binding is a reasonable security decision. SimpleX is designed primarily for private communication between people on mobile devices - not for bots and automation. Binding to localhost means only local processes can connect to the WebSocket API, which is sensible when you’re running the CLI directly on a machine you control.

But for those of us running SimpleX in containers, or interested in exploring its potential for automated messaging and notifications, this becomes a constraint.

The Contribution

I’m fairly new to open source, but I figured I’d try submitting a small PR rather than maintaining my own patched binary. The change adds an optional --chat-server-host flag:

simplex-chat -p 5225 --chat-server-host 0.0.0.0

The secure default stays unchanged - without the flag, it still binds to 127.0.0.1. The option just allows users who understand the implications to bind more broadly when their deployment requires it.

PR #6609 is now open.

Why I Care About This

I’d like to see more experimentation with SimpleX for bot and automation use cases. The protocol’s privacy properties - no user identifiers, decentralised architecture, end-to-end encryption - seem valuable beyond just person-to-person chat. Notifications, alerts, home automation, CI/CD updates… there’s potential here.

I recognise that’s not the project’s primary focus, and that’s fine. But making the CLI a bit more container-friendly might lower the barrier for others who want to explore these ideas.

If the PR gets merged, I can finally remove the socat workaround from my Docker setup. If not, I’ve learned a lot from reading through the codebase. Either way, worth the attempt.