juanfont/headscale

[Bug] Internal server error on /debug/registration-cache

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#2714 opened on Aug 4, 2025

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Description

Is this a support request?

  • This is not a support request

Is there an existing issue for this?

  • I have searched the existing issues

Current Behavior

An internal server error is displayed when /debug/registration-cache is requested and there are pending registrations.

Expected Behavior

Display the current registration cache.

Steps To Reproduce

  1. Start a new, interactive registration. The client shows the usual setup instructions to complete the setup by registering the new node using the headscale CLI
  2. Request the registration-cache of the debug interface 
    $ curl http://localhost:9090/debug/registration-cache
internal server error
  3. Notice the corresponding log entry on the server: 
    ERR http internal server error error="json: unsupported type: chan *types.Node" code=500

Environment

- OS: Debian 12
- Headscale version: 0.26.1
- Tailscale version: 1.84.2

Runtime environment

  • Headscale is behind a (reverse) proxy
  • Headscale runs in a container

Debug information

Not required.

Contributor guide

Tech stack
go
Domain
backendapi
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic GoUnderstanding of JSON serialization
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
The error occurs in the /debug/registration cache endpoint when there are pending registrations. The log shows "json: unsupported type: chan *types.Node", indicating that a channel is being marshaled into JSON. Locate the handler for this endpoint in the source code (likely in a file like debug.go or similar) and modify the response to avoid including the channel. Instead, convert the channel data to a serializable format (e.g., slice) before returning.