Add REST API server with TLS support, scoped authentication tokens, and preferences UI

[mccartyp]

Summary

Addresses #15741

This introduces a full REST API server for Mixxx, enabling external applications to query and control the DJ software over HTTP/HTTPS.

• REST API server built on Qt HttpServer with versioned endpoints (/api/v1/) for controlling decks, playlists, AutoDJ, and mixer state. Supports bulk commands (207 multi-status aggregation), Server-Sent Events streaming for real-time status updates, and a /api/v1/schema discovery endpoint.
• Authentication and TLS: Scoped token-based auth with read/write permissions, auto-generated self-signed TLS certificates for HTTPS, CORS allowlist, and enforced TLS for write-capable tokens.
• Preferences UI: New REST API page in Preferences with token management (create, copy, show/hide toggle), TLS configuration with certificate info and regeneration, listener address/port settings, and contextual tooltips and helper text.
• Qt cross-version compatibility: Version guards for QJsonArray::reserve (Qt 6.9+/6.11+), QDateTime::setTimeZone, QHttpServer bind return types, and QHttpHeaders migration across Qt 5 and Qt 6.x.

New and modified files (23 files, ~3000+ lines)

REST API Core (src/network/rest/)

File	Description
restapigateway.cpp/.h	API gateway handling all REST endpoints (~1200 lines)
restserver.cpp/.h	HTTP/HTTPS server with TLS support
restservercontroller.cpp/.h	Server lifecycle management
restservervalidator.cpp/.h	Request validation and HTTPS capability checks
certificategenerator.cpp/.h	Self-signed TLS certificate generation
restscopes.h	Token scope definitions
README.md	API endpoint documentation

Preferences & Settings

File	Description
src/preferences/dialog/dlgprefrestserver.cpp/.h	Preferences dialog
src/preferences/dialog/dlgprefrestserverdlg.ui	Qt Designer UI layout
src/preferences/restserversettings.cpp/.h	REST server settings persistence

Integration, Utilities, Assets

File	Description
src/coreservices.cpp/.h	REST server integration into Mixxx startup
src/util/ratelimitedlogger.cpp/.h	Rate-limited logging utility
src/test/restserver_test.cpp	REST API unit tests
res/images/preferences/*/ic_preferences_rest_api.svg	Dark/light theme icons
CMakeLists.txt	REST API build targets
res/mixxx.qrc	Resource file updated with new icons

[mccartyp]

Hello sir,

Thanks for the request — I’ve added a couple of short demo videos to show the REST API in use. The first video below demonstrates the API from the command line using a small scripted sequence of requests, showing request/response behavior and direct interaction with Mixxx state.

The second video shows integration with the Bitfocus Companion ecosystem using a development module (https://github.com/mccartyp/companion-module-mixxx). Companion integration is particularly relevant in event production environments, as it enables flexible, distributed control of Mixxx via Stream Deck hardware (https://www.elgato.com/en/stream-deck). For context, Bitfocus Companion provides a large ecosystem of integrations for audio, lighting, video, and control systems commonly used in live production, with a public module directory at https://bitfocus.io/companion. I plan to submit the Mixxx Companion module referenced above for inclusion in the distribution if the REST API is eventually merged and available for users.

I’ll be rebasing this PR shortly as I've had to refactor some of the code to ensure compatibility with earlier Qt versions (< 6.5.0). The changes have now been tested on Ubuntu 24.04 and Debian 13/Trixie. Please let me know if you’d like to see additional endpoints or scenarios demonstrated or have any feedback on the effort itself. No doubt there is much room for improvement.

Lastly, I’ve also included several screenshots of the Preferences dialog highlighting how the REST API is configured and enabled.

Thanks,
Patrick

Mixxx REST API Demo Video

Mixxx-Ubuntu_24.04.mp4

Mixxx REST API Demo Video with Companion

Mixxx-Ubuntu_24.04_Companion.mp4

Mixxx REST API Preferences

[bigpresh]

This is brilliant!

This is one thing I've been really missing and wanting from Mixxx.

One use case I have in mind is a karaoke setup - a script watching Mixxx status, and, if a karoke track begins to play on either deck and a .cdg file with a matching name is found, causing VLC on a second screen to start playing that and ensure the timestamps stay roughly in sync (using VLC's API)

I've done some initial testing on my Ubuntu 24.04 box using a recent build from the Actions build workflow and it appears to be working nicely so far - I've not exercised it hard so far though and not yet tested controlling Mixxx through it, only watching status e.g. GET /api/v1/status etc.

I think this will be a very powerful feature for Mixxx, opening up lots of useful integrations.

[mccartyp]

@bigpresh Glad it's useful for you. For your use case instead of polling via GET /api/v1/status, you might consider attaching to the SSE endpoint GET /api/v1/stream/status, which is a persistent stream of events and updates, as described in the README in the /src/network/rest directory:

• GET /api/v1/stream/status — server-sent events stream that emits status deltas at the configured interval. Requires status:read. Each event uses event: status and a JSON payload in data: containing only changed top-level fields since the last update (removed fields are sent as null). The first event includes the full status payload.