From 4d14ad812cc2536032a468939039b08caeb041b1 Mon Sep 17 00:00:00 2001
From: Deluan <deluan@navidrome.org>
Date: Wed, 25 Mar 2026 08:03:21 -0400
Subject: [PATCH] feat(stream): integrate TranscodingThrottle into NewStream

---
 core/stream/media_streamer.go      | 16 +++++++++++--
 core/stream/media_streamer_test.go | 37 ++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/core/stream/media_streamer.go b/core/stream/media_streamer.go
index 84fa84321..da605fb8e 100644
--- a/core/stream/media_streamer.go
+++ b/core/stream/media_streamer.go
@@ -92,6 +92,11 @@ func (ms *mediaStreamer) NewStream(ctx context.Context, mf *model.MediaFile, req
 		return s, nil
 	}
 
+	// Acquire throttle slot before accessing cache (which may spawn ffmpeg on miss)
+	if err := ms.throttle.Acquire(ctx); err != nil {
+		return nil, err
+	}
+
 	job := &streamJob{
 		ms:         ms,
 		mf:         mf,
@@ -105,12 +110,19 @@ func (ms *mediaStreamer) NewStream(ctx context.Context, mf *model.MediaFile, req
 	}
 	r, err := ms.cache.Get(ctx, job)
 	if err != nil {
+		ms.throttle.Release()
 		log.Error(ctx, "Error accessing transcoding cache", "id", mf.ID, err)
 		return nil, err
 	}
 	cached = r.Cached
-
-	s.ReadCloser = r
+	if cached {
+		// Cache hit — no ffmpeg process running, release the slot immediately
+		ms.throttle.Release()
+		s.ReadCloser = r
+	} else {
+		// Cache miss — slot released when stream is closed
+		s.ReadCloser = &releaseOnClose{ReadCloser: r, release: ms.throttle.Release}
+	}
 	s.Seeker = r.Seeker
 
 	log.Debug(ctx, "Streaming TRANSCODED file", "id", mf.ID, "path", filePath,
diff --git a/core/stream/media_streamer_test.go b/core/stream/media_streamer_test.go
index c7c7268fd..a5380324b 100644
--- a/core/stream/media_streamer_test.go
+++ b/core/stream/media_streamer_test.go
@@ -73,4 +73,41 @@ var _ = Describe("MediaStreamer", func() {
 			Expect(s.Seekable()).To(BeTrue())
 		})
 	})
+
+	Context("NewStream with throttle", func() {
+		var mf *model.MediaFile
+		BeforeEach(func() {
+			var err error
+			mf, err = ds.MediaFile(ctx).Get("123")
+			Expect(err).ToNot(HaveOccurred())
+		})
+
+		It("returns ErrTranscodingBusy when throttle rejects", func() {
+			throttle := stream.NewTranscodingThrottle(1, 1, 50*time.Millisecond)
+			Expect(throttle.Acquire(context.Background())).To(Succeed())
+
+			testCache := stream.NewTranscodingCache()
+			Eventually(func() bool { return testCache.Available(context.TODO()) }).Should(BeTrue())
+			throttledStreamer := stream.NewMediaStreamer(ds, ffmpeg, testCache, throttle)
+
+			_, err := throttledStreamer.NewStream(ctx, mf, stream.Request{Format: "mp3", BitRate: 64})
+			Expect(err).To(MatchError(stream.ErrTranscodingBusy))
+			throttle.Release()
+		})
+
+		It("does not throttle raw/direct-play requests", func() {
+			throttle := stream.NewTranscodingThrottle(1, 1, 50*time.Millisecond)
+			Expect(throttle.Acquire(context.Background())).To(Succeed())
+
+			testCache := stream.NewTranscodingCache()
+			Eventually(func() bool { return testCache.Available(context.TODO()) }).Should(BeTrue())
+			throttledStreamer := stream.NewMediaStreamer(ds, ffmpeg, testCache, throttle)
+
+			s, err := throttledStreamer.NewStream(ctx, mf, stream.Request{Format: "raw"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(s).ToNot(BeNil())
+			_ = s.Close()
+			throttle.Release()
+		})
+	})
 })