feat(radio): back off long on permanent ICY errors

Dead stream URLs (4xx) and stations without icy-metaint retried
every 30s for the whole session; classify them permanent and
retry every 10 minutes instead.

Signed-off-by: hiyukoim <11803292+hiyukoim@users.noreply.github.com>

core/radio/metadata_manager.go

@@ -19,6 +19,29 @@ var (
 // keep an ICY reader connected to the station forever.
 const defaultSessionTTL = 10 * time.Minute
 
+// permanentRetryDelay is used instead of the regular backoff when the reader
+// reports a permanent error (dead URL, station without ICY metadata), so we
+// do not hammer a stream that will never yield titles.
+const permanentRetryDelay = 10 * time.Minute
+
+type permanentError struct{ err error }
+
+func (e *permanentError) Error() string { return e.err.Error() }
+func (e *permanentError) Unwrap() error { return e.err }
+
+// MarkPermanent wraps err so the retry loop switches to permanentRetryDelay.
+func MarkPermanent(err error) error {
+	if err == nil {
+		return nil
+	}
+	return &permanentError{err: err}
+}
+
+func isPermanent(err error) bool {
+	var p *permanentError
+	return errors.As(err, &p)
+}
+
 type Station struct {
 	ID        string
 	StreamURL string
@@ -229,6 +252,9 @@ func (m *MetadataManager) runReader(reader *activeReader) {
 		}
 
 		delay := m.backoff(attempt)
+		if isPermanent(err) && delay < permanentRetryDelay {
+			delay = permanentRetryDelay
+		}
 		if delay <= 0 {
 			continue
 		}

core/radio/metadata_manager_test.go

@@ -155,6 +155,25 @@ var _ = Describe("MetadataManager", func() {
 		Expect(manager.Start(context.Background(), "session-1", Station{ID: "rd-1", StreamURL: ""})).To(MatchError(ErrInvalidStation))
 	})
 
+	It("backs off for a long time on permanent reader errors", func() {
+		reader.err = MarkPermanent(errors.New("missing icy metadata interval"))
+		slow := NewMetadataManager(
+			reader.Read,
+			publisher.Publish,
+			WithRetryBackoff(func(int) time.Duration { return time.Millisecond }),
+		)
+
+		Expect(slow.Start(context.Background(), "session-1", Station{
+			ID:        "rd-1",
+			StreamURL: "https://stream.example.test/radio",
+		})).To(Succeed())
+
+		Eventually(reader.StartCount).Should(Equal(1))
+		// Regular backoff is 1ms; the permanent error must stretch it, so no
+		// second attempt happens within the observation window.
+		Consistently(reader.StartCount, 300*time.Millisecond, 20*time.Millisecond).Should(Equal(1))
+	})
+
 	It("expires sessions that are never refreshed", func() {
 		expiring := NewMetadataManager(
 			reader.Read,

core/radio/provider.go

@@ -2,6 +2,7 @@ package radio
 
 import (
 	"context"
+	"errors"
 	"net"
 	"net/http"
 	"time"
@@ -26,6 +27,22 @@ var icyHTTPClient = &http.Client{
 
 func NewMetadataManagerService(publisher TitlePublisher) *MetadataManager {
 	return NewMetadataManager(func(ctx context.Context, streamURL string, handleTitle func(string)) error {
-		return icy.ReadHTTPStreamTitles(ctx, icyHTTPClient, streamURL, handleTitle)
+		return classifyICYError(icy.ReadHTTPStreamTitles(ctx, icyHTTPClient, streamURL, handleTitle))
 	}, publisher)
 }
+
+// classifyICYError marks errors that a retry will not fix — a stream without
+// ICY metadata or a client-error HTTP status — so the reader backs off for
+// much longer instead of hammering the station.
+func classifyICYError(err error) error {
+	if errors.Is(err, icy.ErrMissingMetaInt) {
+		return MarkPermanent(err)
+	}
+	var statusErr *icy.ResponseStatusError
+	if errors.As(err, &statusErr) &&
+		statusErr.StatusCode >= 400 && statusErr.StatusCode < 500 &&
+		statusErr.StatusCode != http.StatusRequestTimeout && statusErr.StatusCode != http.StatusTooManyRequests {
+		return MarkPermanent(err)
+	}
+	return err
+}