Big changes

server/internal/api/images.go

@@ -1,12 +1,16 @@
 package api
 
 import (
+	"context"
 	"errors"
 	"io"
+	"log/slog"
+	"net"
 	"net/http"
 	"net/url"
 	"strconv"
 	"strings"
+	"syscall"
 
 	"github.com/ponzischeme89/memby/server/internal/sonarr"
 	"github.com/ponzischeme89/memby/server/internal/store"
@@ -43,6 +47,9 @@ func (s *Server) handleImage(w http.ResponseWriter, r *http.Request, sess store.
 			params.Set(key, v)
 		}
 	}
+	if writeNotModifiedForTag(w, r, params.Get("tag")) {
+		return
+	}
 
 	resp, err := s.emby.ImageResponse(r.Context(), credentials(sess), itemID, imageType, params)
 	if err != nil {
@@ -61,14 +68,14 @@ func (s *Server) handleImage(w http.ResponseWriter, r *http.Request, sess store.
 	// stay conservative.
 	if params.Get("tag") != "" {
 		w.Header().Set("Cache-Control", "private, max-age=31536000, immutable")
+		w.Header().Set("ETag", imageETag(params.Get("tag")))
 	} else {
 		w.Header().Set("Cache-Control", "private, max-age=3600")
 	}
 
 	w.WriteHeader(http.StatusOK)
-	if _, err := io.Copy(w, resp.Body); err != nil {
-		s.log.Warn("image copy failed", "error", err)
-	}
+	copyImage(w, r, resp.Body, s.log,
+		"source", "emby", "item_id", itemID, "image_type", imageType)
 }
 
 func (s *Server) handleSonarrImage(w http.ResponseWriter, r *http.Request, itemID, imageType string) {
@@ -111,7 +118,71 @@ func (s *Server) handleSonarrImage(w http.ResponseWriter, r *http.Request, itemI
 	}
 	w.Header().Set("Cache-Control", "private, max-age=3600")
 	w.WriteHeader(http.StatusOK)
-	if _, err := io.Copy(w, resp.Body); err != nil {
-		s.log.Warn("sonarr image copy failed", "error", err)
+	copyImage(w, r, resp.Body, s.log,
+		"source", "sonarr", "item_id", itemID, "image_type", imageType)
+}
+
+func copyImage(
+	w io.Writer,
+	r *http.Request,
+	body io.Reader,
+	log *slog.Logger,
+	attributes ...any,
+) {
+	written, err := io.Copy(w, body)
+	if err == nil {
+		return
 	}
+	if expectedClientDisconnect(r, err) {
+		// Image loaders cancel work aggressively as cards leave the viewport. That is a
+		// successful resource-saving decision by the TV, not an unhealthy gateway.
+		return
+	}
+	fields := append([]any{"bytes_written", written, "error", err}, attributes...)
+	log.Warn("image stream interrupted", fields...)
+}
+
+func expectedClientDisconnect(r *http.Request, err error) bool {
+	if r.Context().Err() != nil ||
+		errors.Is(err, context.Canceled) ||
+		errors.Is(err, net.ErrClosed) ||
+		errors.Is(err, syscall.EPIPE) ||
+		errors.Is(err, syscall.ECONNRESET) {
+		return true
+	}
+	message := strings.ToLower(err.Error())
+	for _, fragment := range []string{
+		"broken pipe",
+		"connection reset by peer",
+		"client disconnected",
+		"request canceled",
+		"request cancelled",
+		"stream closed",
+	} {
+		if strings.Contains(message, fragment) {
+			return true
+		}
+	}
+	return false
+}
+
+func writeNotModifiedForTag(w http.ResponseWriter, r *http.Request, tag string) bool {
+	if tag == "" {
+		return false
+	}
+	etag := imageETag(tag)
+	w.Header().Set("ETag", etag)
+	w.Header().Set("Cache-Control", "private, max-age=31536000, immutable")
+	for _, candidate := range strings.Split(r.Header.Get("If-None-Match"), ",") {
+		if strings.TrimSpace(candidate) == etag || strings.TrimSpace(candidate) == "*" {
+			w.WriteHeader(http.StatusNotModified)
+			return true
+		}
+	}
+	return false
+}
+
+func imageETag(tag string) string {
+	// Emby image tags are normally hex, but quote defensively for a valid HTTP entity tag.
+	return `"` + strings.NewReplacer(`\`, "", `"`, "").Replace(tag) + `"`
 }