CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository. This guidance is aimed at Claude Code but may also be suitable for other AI tooling, such as GitHub Copilot and OpenAI Codex.

Project Overview

sendspin-go is the Go implementation of the Sendspin Protocol for synchronized multi-room audio streaming. It ships as a library (pkg/) plus two CLI binaries: sendspin-player (root main.go) and sendspin-server (./cmd/sendspin-server). The Python sibling is aiosendspin; the two implementations are wire-compatible and share the role-family vocabulary (player, controller, metadata, artwork, visualizer).

Note: If uncertain about how something in Sendspin is supposed to work, fetch and refer to the protocol specification for authoritative implementation details.

Commands

Native deps: libopus only. FLAC is pure-Go (mewkiz/flac); the Makefile, CI, and release pipelines all build with GOFLAGS=-tags=nolibopusfile so gopkg.in/hraban/opus.v2's opus.Stream parts (the only consumer of libopusfile) are skipped and the binary doesn't link libopusfile at runtime. Use ./install-deps.sh (handles brew/apt/dnf/pacman) or the per-OS commands in README.md. ffmpeg is only required for HLS/m3u8 server input. If you ever need to build with the opus.Stream API, override the tag: make BUILDTAGS= test.

make                            # Build sendspin-player + sendspin-server
make player                     # Build sendspin-player only
make server                     # Build sendspin-server only
make test                       # go test ./...
make test-coverage              # -race + HTML coverage report
make lint                       # golangci-lint --timeout=5m
make conformance                # Run protocol conformance suite (clones ../conformance on first run; needs uv)
go test ./pkg/sendspin -run TestPlayer_Connect -race -v   # Single test

Pre-commit (.pre-commit-config.yaml) runs gofmt, goimports, go-mod-tidy, golangci-lint, and go test -race -v ./... on every commit. Run pre-commit before pushing any commit to ensure it is valid.

Architecture

Library-first. The public API in pkg/ is what consumers import; the CLI binaries are thin wrappers. internal/ is private to the module by Go's rules — only pkg/sendspin legitimately reaches into it.

Public layers (`pkg/`)

pkg/sendspin (receiver.go, player.go, server.go): High-level API. The library splits the player into a Receiver (connect, handshake, clock sync, decode, schedule — emits <-chan audio.Buffer) and a Player (a thin wrapper composing Receiver + pkg/audio/output.Output). Use Receiver directly for visualizers, DSP, or custom output backends — no audio device required. Each Receiver/Player owns its own *sync.ClockSync; the package-level SetGlobalClockSync / ServerMicrosNow shims are deprecated.
pkg/audio (types.go, resample.go, plus decode/, encode/, output/ subpackages): Core Format and Buffer types, sample conversion, linear resampler, codec encoders/decoders (PCM, Opus, FLAC). output ships a single malgo backend; the oto backend was removed in v1.2.
pkg/protocol (messages.go, client.go, server_conn.go): Wire messages plus Client (player side) and ServerConn (CGO-free helpers for serving binary frames).
pkg/sync (clock.go, timefilter.go): ClockSync plus TimeFilter, the 2D Kalman filter tracking offset and drift per the Sendspin time-filter spec. This is what makes hi-res multi-room sync actually work; do not regress it without re-running make conformance.
pkg/discovery (mdns.go): mDNS browse/advertise.

Server-side group / role model (`pkg/sendspin`)

Two-level architecture, mirroring aiosendspin so the wire behavior matches across implementations.

Group (group.go): Owns the typed event bus for one playback group. Publishes ClientJoinedEvent, ClientLeftEvent, ClientStateChangedEvent, GroupStateChangedEvent, etc. ClientJoinedEvent carries a live *ServerClient (the connection is fully alive at publish); ClientLeftEvent intentionally drops the pointer because the client is mid-teardown.
GroupRole (group_role.go): One implementation per role family, coordinating across all member roles in the group. Built-in implementations: ControllerGroupRole (role_controller.go), MetadataGroupRole (role_metadata.go), PlayerGroupRole (role_player.go). Add new server-side behavior by writing a new GroupRole and registering it via activateRoles, not by editing server_dispatch.go directly.
ServerClient (server_client.go): Per-connection state with typed accessors (State(), Volume(), Muted(), Codec()). Message dispatch lives in server_dispatch.go, audio streaming in server_stream.go, and per-client send-ahead pacing in buffer_tracker.go.

Audio Pipeline

Server: AudioSource → codec negotiation per client (Opus/FLAC/PCM)
                   → 20 ms chunks tagged monotonic-µs server timestamps
                   → sent ~500 ms ahead → WebSocket binary frames
Player: protocol.Client → pkg/sync (Kalman-mapped local time)
                       → Scheduler priority queue (200 ms startup buffer)
                       → pkg/audio/output.Malgo

Binary message-type IDs encode role bits 7–2 / slot bits 1–0 per spec. Binary messages use a 9-byte header (1B message type + 8B timestamp_us); audio chunk = type 4. Artwork has its own slot via protocol.StreamStart.Artwork.

Configuration & Daemon Mode

pkg/sendspin/config.go provides PlayerConfigFile / ServerConfigFile plus LoadPlayerConfig / LoadServerConfig and ApplyEnvAndFile. Precedence is CLI > env (SENDSPIN_PLAYER_* / SENDSPIN_SERVER_*) > YAML file > built-in default. Default search paths: $SENDSPIN_*_CONFIG, ~/.config/sendspin/*.yaml, /etc/sendspin/*.yaml. Both binaries accept --config and --daemon (the latter logs to stdout for journalctl). Annotated examples and systemd units live in dist/config/ and dist/systemd/; make install-{player,server}-daemon installs them.

Internal layout (`internal/`)

internal/server: Audio engine, source decoders, Opus/FLAC encoders, resampler, server TUI. pkg/sendspin.Server is a façade over this.
internal/ui: bubbletea models, hotkey/device-picker widgets shared by both binaries.
internal/discovery: mDNS plumbing (TXT parsing, browse loops) used by pkg/discovery.
internal/version: ldflags version target.

The legacy internal/{app,artwork,audio,client,player,protocol,sync} packages were deleted in the v1.2 "rip-legacy-cli" sweep. Do not reintroduce that layering.

Code Style

Go ≥1.24. Module path is github.com/Sendspin/sendspin-go.
Every .go file starts with two // ABOUTME: header lines summarizing its purpose. Match this on new files.
Linting: golangci-lint with gosimple, govet, ineffassign, unused, gofmt, goimports, misspell, errcheck enabled; staticcheck intentionally disabled.
Conventional commits: type(scope): subject (feat, fix, refactor, test, chore, docs, style, build, ci).

Testing

Tests are co-located (_test.go next to source).
Integration tests use the _integration_test.go suffix (e.g. flac_integration_test.go, client_discovery_integration_test.go).
Wire-format / message-type / negotiation changes must keep make conformance green. The harness lives in Sendspin/conformance and is symlinked into this checkout on first run.
Audio invariants — 20 ms chunks (50/s), microsecond timestamps, 9-byte binary header — are interop-critical. Don't change without running the conformance suite against aiosendspin.

Contribution & AI Policy

This project follows the Open Home Foundation AI Policy:

No autonomous agents. PRs from autonomous agents will be closed.
Human-in-the-loop required. All contributions must be reviewed and understood by the contributor before submission.
Disclose AI-generated text. Quote it with > blocks and accompany it with your own commentary explaining relevance and implications.

PRs target main. Recent design notes worth consulting before touching the relevant area: docs/2026-04-12-layered-architecture-design.md, docs/CLOCK_SYNC_ANALYSIS.md, docs/FORMAT_NEGOTIATION_FIX.md, docs/superpowers/plans/.

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