fix(audio): give ffprobe its own 45s deadline, a timeout is the file's fault (#49)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/adapters/audio/ffprobe.go

@@ -22,8 +22,14 @@ type FFprobe struct {
 	Bin string
 	// MaxOutput bounds how much of ffprobe's stdout is read; zero means DefaultMaxOutput.
 	MaxOutput int
+	// Timeout bounds one probe; zero means DefaultProbeTimeout. A probe is milliseconds of
+	// work on a real file, so one that runs this long is the FILE's doing (#49).
+	Timeout time.Duration
 }
 
+// DefaultProbeTimeout is the probe deadline when FFprobe.Timeout is unset.
+const DefaultProbeTimeout = 45 * time.Second
+
 // DefaultMaxOutput is far above the narrowed probe output of a legitimate file (a few
 // hundred bytes) and far below what a hostile one can make ffprobe print.
 const DefaultMaxOutput = 1 << 20
@@ -102,7 +108,13 @@ func (f *FFprobe) Probe(ctx context.Context, path string) (uploads.Probe, error)
 	}
 	args := append([]string{"-v", "error"}, inputRestrictions...)
 	args = append(args, "-print_format", "json", "-show_entries", probeEntries, path)
-	cmd := exec.CommandContext(ctx, bin, args...)
+	timeout := f.Timeout
+	if timeout <= 0 {
+		timeout = DefaultProbeTimeout
+	}
+	probeCtx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	cmd := exec.CommandContext(probeCtx, bin, args...)
 	cmd.WaitDelay = killGrace
 	maxOut := f.MaxOutput
 	if maxOut <= 0 {
@@ -111,9 +123,12 @@ func (f *FFprobe) Probe(ctx context.Context, path string) (uploads.Probe, error)
 	stdout, stderr := &capWriter{max: maxOut}, &headWriter{max: maxStderr}
 	cmd.Stdout, cmd.Stderr = stdout, stderr
 	if err := cmd.Run(); err != nil {
-		if ctxErr := ctx.Err(); ctxErr != nil {
+		if ctxErr := ctx.Err(); ctxErr != nil { // the caller gave up: not a verdict on the file
 			return uploads.Probe{}, fmt.Errorf("audio: ffprobe: %w", ctxErr)
 		}
+		if probeCtx.Err() != nil { // our own deadline passed while the caller was still waiting
+			return uploads.Probe{}, fmt.Errorf("%w: ffprobe did not finish within %s", uploads.ErrUnreadable, timeout)
+		}
 		if errors.Is(err, errOutputCap) {
 			return uploads.Probe{}, fmt.Errorf("%w: ffprobe printed more than %d bytes", uploads.ErrUnreadable, maxOut)
 		}