fix(podcast): address second round of CodeRabbit feedback

- Create the episode file only after a 200 response so failed downloads
  don't leave empty files behind
- Reuse the existing StreamID as the MediaFile ID on re-download instead of
  inserting duplicate tracks
- Link mobile podcast list rows to the channel show page
- Ignore stale getPodcasts responses and clear episodes when the channel
  changes in PodcastShow

core/podcasts/podcasts.go

@@ -348,13 +348,6 @@ func (s *podcastService) doDownload(ctx context.Context, ep *model.PodcastEpisod
 	}
 
 	dest := filepath.Join(dir, ep.ID+"."+suffix)
-	f, err := os.Create(dest)
-	if err != nil {
-		s.setEpisodeError(ctx, ep, err)
-		return
-	}
-	defer f.Close()
-
 	if err := validateURL(ep.EnclosureURL); err != nil {
 		s.setEpisodeError(ctx, ep, fmt.Errorf("invalid enclosure URL: %w", err))
 		return
@@ -380,6 +373,15 @@ func (s *podcastService) doDownload(ctx context.Context, ep *model.PodcastEpisod
 		return
 	}
 
+	// Create the file only once we have a 200 response, so failed requests
+	// don't leave empty files behind.
+	f, err := os.Create(dest)
+	if err != nil {
+		s.setEpisodeError(ctx, ep, err)
+		return
+	}
+	defer f.Close()
+
 	// Use Content-Length as total size when RSS feed didn't provide it
 	if resp.ContentLength > 0 && ep.Size == 0 {
 		ep.Size = resp.ContentLength
@@ -407,8 +409,14 @@ func (s *podcastService) doDownload(ctx context.Context, ep *model.PodcastEpisod
 		now := time.Now()
 		tags := model.Tags{}
 		tags.Add("genre", "Podcast")
+		// Reuse the existing MediaFile on re-download so Put updates it instead of
+		// leaving a duplicate track behind.
+		mfID := ep.StreamID
+		if mfID == "" {
+			mfID = id.NewRandom()
+		}
 		mf := &model.MediaFile{
-			ID:          id.NewRandom(),
+			ID:          mfID,
 			LibraryID:   libID,
 			Path:        relPath,
 			Title:       ep.Title,

core/podcasts/podcasts_test.go

@@ -179,6 +179,21 @@ var _ = Describe("PodcastService", func() {
 			Expect(found).To(BeTrue())
 		})
 
+		It("reuses the existing StreamID's MediaFile on re-download", func() {
+			_ = svc.DownloadEpisode(ctx, "ep-1")
+			Eventually(func() model.PodcastStatus {
+				return episodeRepo.Data["ep-1"].Status
+			}, "3s").Should(Equal(model.PodcastStatusCompleted))
+			first := episodeRepo.Data["ep-1"].StreamID
+			Expect(first).ToNot(BeEmpty())
+
+			_ = svc.DownloadEpisode(ctx, "ep-1")
+			Eventually(func() model.PodcastStatus {
+				return episodeRepo.Data["ep-1"].Status
+			}, "3s").Should(Equal(model.PodcastStatusCompleted))
+			Expect(episodeRepo.Data["ep-1"].StreamID).To(Equal(first))
+		})
+
 		It("records the file path after download", func() {
 			_ = svc.DownloadEpisode(ctx, "ep-1")
 			expectedPath := filepath.Join(conf.Server.DataFolder.String(), "podcasts", "ch-1", "ep-1.mp3")
@@ -236,6 +251,22 @@ var _ = Describe("PodcastService", func() {
 		BeforeEach(func() {
 			channelRepo.Data["ch-1"] = &model.PodcastChannel{ID: "ch-1", Title: "Test Channel"}
 		})
+		It("does not leave an empty file behind when the request fails", func() {
+			episodeRepo.Data["ep-bad"] = &model.PodcastEpisode{
+				ID:           "ep-bad",
+				ChannelID:    "ch-1",
+				EnclosureURL: "http://localhost:0/no-such.mp3",
+				Suffix:       "mp3",
+				Status:       model.PodcastStatusNew,
+			}
+			_ = svc.DownloadEpisode(ctx, "ep-bad")
+			Eventually(func() model.PodcastStatus {
+				return episodeRepo.Data["ep-bad"].Status
+			}, "3s").Should(Equal(model.PodcastStatusError))
+			dest := filepath.Join(conf.Server.DataFolder.String(), "podcasts", "ch-1", "ep-bad.mp3")
+			_, err := os.Stat(dest)
+			Expect(os.IsNotExist(err)).To(BeTrue())
+		})
 		It("sets status to error when download fails", func() {
 			episodeRepo.Data["ep-bad"] = &model.PodcastEpisode{
 				ID:           "ep-bad",

ui/src/podcast/PodcastList.jsx

@@ -179,6 +179,7 @@ const PodcastList = ({ permissions, ...props }) => {
     >
       {isXsmall ? (
         <SimpleList
+          linkType="show"
           leftAvatar={(r) => <CoverArtField record={r} />}
           primaryText={(r) => r.title}
           secondaryText={(r) => r.url}

ui/src/podcast/PodcastShow.jsx

@@ -1,4 +1,4 @@
-import React, { useEffect, useState } from 'react'
+import React, { useEffect, useRef, useState } from 'react'
 import {
   Card,
   CardContent,
@@ -110,11 +110,17 @@ const PodcastShow = (props) => {
   const { record } = useShowController(props)
   const [episodes, setEpisodes] = useState([])
 
+  // Incremented on every load and on channel change; responses from a
+  // superseded request are ignored so they can't overwrite the current channel.
+  const requestGen = useRef(0)
+
   const loadEpisodes = () => {
     if (!record?.id) return
+    const gen = ++requestGen.current
     subsonic
       .getPodcasts(record.id, true)
       .then((res) => {
+        if (gen !== requestGen.current) return
         const channels = res?.json?.['subsonic-response']?.podcasts?.channel || []
         const ch = channels.find((c) => c.id === record.id)
         setEpisodes(ch?.episode || [])
@@ -122,7 +128,13 @@ const PodcastShow = (props) => {
       .catch(() => {})
   }
 
-  useEffect(loadEpisodes, [record?.id])
+  useEffect(() => {
+    setEpisodes([]) // don't show the previous channel's episodes
+    loadEpisodes()
+    return () => {
+      requestGen.current++
+    }
+  }, [record?.id])
 
   // Stay subscribed to SSE progress while the view is mounted: a download
   // started from here may not be flagged 'downloading' yet when we refresh.