Add real mpv-backed jukebox controller (JSON IPC), tested against real mpv

internal/jukebox/mpv.go

@@ -0,0 +1,185 @@
+// Package jukebox implements Subsonic's jukeboxControl endpoint using
+// mpv as the actual server-side playback backend, driven over mpv's
+// JSON IPC socket (--input-ipc-server). If mpv isn't installed, the
+// jukebox is simply unavailable — VibeSonic never fakes playback.
+package jukebox
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+// mpvClient owns one mpv process and its JSON IPC connection.
+type mpvClient struct {
+	mpvPath    string
+	socketPath string
+
+	mu    sync.Mutex
+	cmd   *exec.Cmd
+	conn  net.Conn
+	reqID int64
+
+	// pending correlates in-flight requests (by request_id) to the
+	// goroutine waiting for their response; mpv's IPC is a single
+	// bidirectional stream so responses must be demultiplexed.
+	pendingMu sync.Mutex
+	pending   map[int64]chan mpvResponse
+
+	closed atomic.Bool
+}
+
+type mpvResponse struct {
+	Error     string `json:"error"`
+	Data      any    `json:"data"`
+	RequestID int64  `json:"request_id"`
+}
+
+func newMPVClient(mpvPath string) *mpvClient {
+	if mpvPath == "" {
+		mpvPath = "mpv"
+	}
+	return &mpvClient{mpvPath: mpvPath, pending: make(map[int64]chan mpvResponse)}
+}
+
+func (c *mpvClient) start() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.cmd != nil {
+		return nil // already running
+	}
+
+	dir, err := os.MkdirTemp("", "vibesonic-mpv-")
+	if err != nil {
+		return err
+	}
+	c.socketPath = filepath.Join(dir, "mpv.sock")
+
+	cmd := exec.Command(c.mpvPath,
+		"--idle=yes",
+		"--no-video",
+		"--no-terminal",
+		"--really-quiet",
+		"--input-ipc-server="+c.socketPath,
+	)
+	if err := cmd.Start(); err != nil {
+		os.RemoveAll(dir)
+		return fmt.Errorf("starting mpv: %w", err)
+	}
+	c.cmd = cmd
+
+	var conn net.Conn
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		conn, err = net.Dial("unix", c.socketPath)
+		if err == nil {
+			break
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	if conn == nil {
+		_ = cmd.Process.Kill()
+		os.RemoveAll(dir)
+		return fmt.Errorf("connecting to mpv IPC socket: %w", err)
+	}
+	c.conn = conn
+
+	go c.readLoop()
+	return nil
+}
+
+func (c *mpvClient) readLoop() {
+	scanner := bufio.NewScanner(c.conn)
+	scanner.Buffer(make([]byte, 0, 64*1024), 1<<20)
+	for scanner.Scan() {
+		var resp mpvResponse
+		if err := json.Unmarshal(scanner.Bytes(), &resp); err != nil {
+			continue // ignore event lines / anything we can't parse
+		}
+		if resp.RequestID == 0 {
+			continue // an mpv event, not a command reply
+		}
+		c.pendingMu.Lock()
+		ch, ok := c.pending[resp.RequestID]
+		if ok {
+			delete(c.pending, resp.RequestID)
+		}
+		c.pendingMu.Unlock()
+		if ok {
+			ch <- resp
+		}
+	}
+}
+
+func (c *mpvClient) command(args ...any) (any, error) {
+	if err := c.start(); err != nil {
+		return nil, err
+	}
+	id := atomic.AddInt64(&c.reqID, 1)
+	payload := map[string]any{"command": args, "request_id": id}
+	encoded, err := json.Marshal(payload)
+	if err != nil {
+		return nil, err
+	}
+
+	ch := make(chan mpvResponse, 1)
+	c.pendingMu.Lock()
+	c.pending[id] = ch
+	c.pendingMu.Unlock()
+
+	c.mu.Lock()
+	_, werr := c.conn.Write(append(encoded, '\n'))
+	c.mu.Unlock()
+	if werr != nil {
+		c.pendingMu.Lock()
+		delete(c.pending, id)
+		c.pendingMu.Unlock()
+		return nil, werr
+	}
+
+	select {
+	case resp := <-ch:
+		if resp.Error != "" && resp.Error != "success" {
+			return nil, fmt.Errorf("mpv: %s", resp.Error)
+		}
+		return resp.Data, nil
+	case <-time.After(5 * time.Second):
+		c.pendingMu.Lock()
+		delete(c.pending, id)
+		c.pendingMu.Unlock()
+		return nil, fmt.Errorf("mpv command timed out")
+	}
+}
+
+func (c *mpvClient) getProperty(name string) (any, error) {
+	return c.command("get_property", name)
+}
+
+func (c *mpvClient) setProperty(name string, value any) error {
+	_, err := c.command("set_property", name, value)
+	return err
+}
+
+func (c *mpvClient) close() {
+	if c.closed.Swap(true) {
+		return
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.conn != nil {
+		c.conn.Close()
+	}
+	if c.cmd != nil && c.cmd.Process != nil {
+		_ = c.cmd.Process.Kill()
+	}
+	if c.socketPath != "" {
+		os.RemoveAll(filepath.Dir(c.socketPath))
+	}
+}