Merge remote-tracking branch 'origin/fix/263-slskd-transfer-lifecycle' into batch/258-272

backend/download/candidate_shape_test.go

@@ -0,0 +1,248 @@
+package download
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// Multi-disc rips, single-track results and coverage counted in tracks
+// rather than files (#270).
+
+func TestParsePathReadsTheDiscFromItsFolder(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		path   string
+		disc   int
+		track  int
+		folder string
+	}{
+		{`\share\Pink Floyd - The Wall (1979)\CD2\03 Hey You.flac`, 2, 3, "The Wall"},
+		{`\share\The Wall\Disc 1\01 In The Flesh.flac`, 1, 1, "The Wall"},
+		{`\share\The Wall\[Disk-2]\01 Hey You.flac`, 2, 1, "The Wall"},
+		{`\share\The Wall\CD1 - Live\04 Mother.flac`, 1, 4, "The Wall"},
+		// The filename's own disc number is more specific than the folder.
+		{`\share\The Wall\CD1\2-05 Comfortably Numb.flac`, 2, 5, "The Wall"},
+		// Not a disc folder: a number is required.
+		{`\share\CDs\The Wall\01 In The Flesh.flac`, 0, 1, "The Wall"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.path, func(t *testing.T) {
+			t.Parallel()
+
+			got := ParsePath(tc.path)
+			if got.Disc != tc.disc || got.Track != tc.track || got.Folder != tc.folder {
+				t.Errorf(
+					"ParsePath = disc %d track %d folder %q, want %d %d %q",
+					got.Disc, got.Track, got.Folder, tc.disc, tc.track, tc.folder,
+				)
+			}
+		})
+	}
+}
+
+func TestAlbumDir(t *testing.T) {
+	t.Parallel()
+
+	cases := map[string]string{
+		`\share\Album\CD1\01 A.flac`:  "/share/Album",
+		`\share\Album\01 A.flac`:      "/share/Album",
+		`CD1\01 A.flac`:               "CD1",
+		`\share\CD Collection\01.mp3`: "/share/CD Collection",
+	}
+
+	for in, want := range cases {
+		if got := AlbumDir(in); got != want {
+			t.Errorf("AlbumDir(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+// One album shared as CD1/CD2 is one candidate, named after the album.
+func TestSlskdGroupsDiscFoldersIntoOneCandidate(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.responses = []slskdResponse{{
+		Username: "peer",
+		Files: []slskdFile{
+			{Filename: `\m\The Wall\CD1\01 In The Flesh.flac`, Size: 1},
+			{Filename: `\m\The Wall\CD1\02 The Thin Ice.flac`, Size: 1},
+			{Filename: `\m\The Wall\CD2\01 Hey You.flac`, Size: 1},
+			{Filename: `\m\The Wall\CD2\02 Is There Anybody Out There.flac`, Size: 1},
+		},
+	}}
+
+	s, _ := newStubSlskd(t, stub)
+
+	got, err := s.Search(context.Background(), Download{Query: "the wall"})
+	if err != nil {
+		t.Fatalf("Search: %v", err)
+	}
+
+	if len(got) != 1 {
+		t.Fatalf("got %d candidates, want the two discs as one", len(got))
+	}
+
+	if got[0].Title != "The Wall" || len(got[0].Files) != 4 {
+		t.Errorf(
+			"candidate = %q with %d files, want \"The Wall\" with 4",
+			got[0].Title, len(got[0].Files),
+		)
+	}
+}
+
+// A track search matches one file per folder, so a single-track request
+// must accept a one-file folder that an album request rightly drops.
+func TestSlskdKeepsASingleFileForATrackRequest(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.responses = []slskdResponse{{
+		Username: "peer",
+		Files: []slskdFile{
+			{Filename: `\m\OK Computer\02 Paranoid Android.flac`, Size: 1},
+		},
+	}}
+
+	s, _ := newStubSlskd(t, stub)
+
+	track, err := s.Search(context.Background(), Download{
+		RecordingMBID: "rec-1", Artist: "Radiohead", Album: "Paranoid Android",
+	})
+	if err != nil {
+		t.Fatalf("Search: %v", err)
+	}
+
+	if len(track) != 1 {
+		t.Errorf("track request: got %d candidates, want 1", len(track))
+	}
+
+	album, err := s.Search(context.Background(), Download{
+		ReleaseMBID: "rel-1", Artist: "Radiohead", Album: "OK Computer",
+	})
+	if err != nil {
+		t.Fatalf("Search: %v", err)
+	}
+
+	if len(album) != 0 {
+		t.Errorf("album request: got %d candidates, want the one-file folder dropped", len(album))
+	}
+}
+
+// Two discs with a file of the same name both reach staging, each under
+// its disc folder, where the importer reads the disc number from.
+func TestSlskdCollectKeepsDiscFolders(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	s, downloads := newStubSlskd(t, stub)
+
+	for _, disc := range []string{"CD1", "CD2"} {
+		dir := filepath.Join(downloads, disc)
+		if err := os.MkdirAll(dir, 0o750); err != nil {
+			t.Fatalf("mkdir: %v", err)
+		}
+
+		if err := os.WriteFile(
+			filepath.Join(dir, "01 Intro.flac"), []byte(disc), 0o600,
+		); err != nil {
+			t.Fatalf("write: %v", err)
+		}
+	}
+
+	dst := t.TempDir()
+
+	got, err := s.collect(Candidate{Files: []CandidateFile{
+		{Path: `\m\Album\CD1\01 Intro.flac`, IsAudio: true},
+		{Path: `\m\Album\CD2\01 Intro.flac`, IsAudio: true},
+	}}, dst)
+	if err != nil {
+		t.Fatalf("collect: %v", err)
+	}
+
+	if len(got.Files) != 2 {
+		t.Fatalf("collected %d files, want 2", len(got.Files))
+	}
+
+	for _, disc := range []string{"CD1", "CD2"} {
+		data, err := os.ReadFile(filepath.Join(dst, disc, "01 Intro.flac"))
+		if err != nil || string(data) != disc {
+			t.Errorf("%s's file missing or overwritten: %q, %v", disc, data, err)
+		}
+
+		if hint := ParsePath(filepath.Join(dst, disc, "01 Intro.flac")); hint.Disc == 0 {
+			t.Errorf("staged %s file lost its disc number", disc)
+		}
+	}
+}
+
+// A two-disc release whose discs both number from 01 aligns completely
+// once the disc comes from the folder; before, disc 2's 01 collided with
+// disc 1's.
+func TestMultiDiscCandidateAlignsEveryTrack(t *testing.T) {
+	t.Parallel()
+
+	dl := Download{
+		ReleaseMBID: "the-wall",
+		Artist:      "Pink Floyd",
+		Album:       "The Wall",
+		Expected: []ExpectedTrack{
+			{DiscNumber: 1, Position: 1, Title: "In the Flesh?"},
+			{DiscNumber: 1, Position: 2, Title: "The Thin Ice"},
+			{DiscNumber: 2, Position: 1, Title: "Hey You"},
+			{DiscNumber: 2, Position: 2, Title: "Is There Anybody Out There?"},
+		},
+	}
+
+	c := Candidate{
+		Title: "The Wall",
+		Files: []CandidateFile{
+			{Path: `\m\Pink Floyd - The Wall\CD1\01 In the Flesh.flac`, Size: 1},
+			{Path: `\m\Pink Floyd - The Wall\CD1\02 The Thin Ice.flac`, Size: 1},
+			{Path: `\m\Pink Floyd - The Wall\CD2\01 Hey You.flac`, Size: 1},
+			{Path: `\m\Pink Floyd - The Wall\CD2\02 Is There Anybody Out There.flac`, Size: 1},
+		},
+	}
+
+	got := Score(dl, c, 50, AutoDownloadPrefs{})
+
+	if got.Match.Completeness != 1 {
+		t.Errorf("completeness = %f, want 1", got.Match.Completeness)
+	}
+
+	if got.Match.AlbumFit < 0.99 {
+		t.Errorf("album fit = %f, want the album's own name to match", got.Match.AlbumFit)
+	}
+
+	if got.Match.Overall < minMatch {
+		t.Errorf("match = %f, want it to clear the auto-pick bar %f", got.Match.Overall, minMatch)
+	}
+}
+
+// Ten files against a ten-track album is not a complete album when only
+// three of them are its tracks.
+func TestCompletenessCountsTracksNotFiles(t *testing.T) {
+	t.Parallel()
+
+	dl := okComputer()
+
+	c := Candidate{Title: "OK Computer", Files: []CandidateFile{
+		{Path: `\m\Radiohead - OK Computer\Airbag.flac`, Size: 1},
+		{Path: `\m\Radiohead - OK Computer\Paranoid Android.flac`, Size: 1},
+		{Path: `\m\Radiohead - OK Computer\Exit Music (For a Film).flac`, Size: 1},
+		{Path: `\m\Radiohead - OK Computer\Creep.flac`, Size: 1},
+	}}
+
+	got := Score(dl, c, 50, AutoDownloadPrefs{})
+
+	if got.Match.Completeness > 0.76 {
+		t.Errorf(
+			"completeness = %f with 3 of 4 tracks present, want at most 0.75",
+			got.Match.Completeness,
+		)
+	}
+}

backend/download/concurrency_test.go

@@ -47,7 +47,7 @@ func grabAll(
 		go func() {
 			defer wg.Done()
 
-			f.manager.grab(ctx, dl, candidate, nil)
+			f.manager.grab(ctx, dl, candidate, nil, false)
 		}()
 	}
 
@@ -79,9 +79,9 @@ func TestConcurrencyForPrefersOverrideThenKind(t *testing.T) {
 		want int
 	}{
 		{
-			name: "slskd defaults to one",
+			name: "slskd defaults to a few peers",
 			cfg:  Config{Kind: KindSlskd},
-			want: 1,
+			want: 3,
 		},
 		{
 			name: "usenet defaults higher",
@@ -92,9 +92,9 @@ func TestConcurrencyForPrefersOverrideThenKind(t *testing.T) {
 			name: "explicit override wins",
 			cfg: Config{
 				Kind:     KindSlskd,
-				Settings: map[string]string{concurrencyKey: "3"},
+				Settings: map[string]string{concurrencyKey: "1"},
 			},
-			want: 3,
+			want: 1,
 		},
 		{
 			name: "nonsense override falls back",
@@ -102,7 +102,7 @@ func TestConcurrencyForPrefersOverrideThenKind(t *testing.T) {
 				Kind:     KindSlskd,
 				Settings: map[string]string{concurrencyKey: "not a number"},
 			},
-			want: 1,
+			want: 3,
 		},
 		{
 			name: "zero override falls back",
@@ -110,7 +110,7 @@ func TestConcurrencyForPrefersOverrideThenKind(t *testing.T) {
 				Kind:     KindSlskd,
 				Settings: map[string]string{concurrencyKey: "0"},
 			},
-			want: 1,
+			want: 3,
 		},
 		{
 			name: "unknown kind falls back to the global default",
@@ -126,9 +126,9 @@ func TestConcurrencyForPrefersOverrideThenKind(t *testing.T) {
 	}
 }
 
-// The reason the per-provider cap exists: a Soulseek daemon capped at
-// one transfer must serialize, even when the global cap would allow
-// more and the user has queued several albums at once.
+// The reason the per-provider cap exists: a daemon capped at one
+// transfer must serialize, even when the global cap would allow more and
+// the user has queued several albums at once.
 func TestPerProviderCapSerializesTransfers(t *testing.T) {
 	t.Parallel()
 
@@ -142,6 +142,7 @@ func TestPerProviderCapSerializesTransfers(t *testing.T) {
 		ID:       1,
 		Kind:     KindSlskd,
 		Priority: 50,
+		Settings: map[string]string{concurrencyKey: "1"},
 	}, slow)
 
 	// Three requests against the same one-at-a-time provider.
@@ -210,8 +211,8 @@ func TestSyncSemaphoresReplacesChangedLimits(t *testing.T) {
 	f.manager.installProvider(Config{ID: 1, Kind: KindSlskd}, nil)
 
 	first := f.manager.semaphoreFor(1)
-	if cap(first) != 1 {
-		t.Fatalf("slskd semaphore cap = %d, want 1", cap(first))
+	if want := kindConcurrency[KindSlskd]; cap(first) != want {
+		t.Fatalf("slskd semaphore cap = %d, want %d", cap(first), want)
 	}
 
 	// Same limit: the semaphore is kept, so in-flight accounting is not

backend/download/fallback_test.go

@@ -0,0 +1,261 @@
+package download
+
+import (
+	"context"
+	"errors"
+	"os"
+	"testing"
+)
+
+// A transfer that fails on one copy of an album is not a failed
+// download while another acceptable copy exists.  On Soulseek the usual
+// failure is one peer being offline, with several others offering the
+// same folder.
+
+var errPeerOffline = errors.New("peer went offline")
+
+func TestManagerFallsBackToTheNextCandidate(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+
+	// The failing source ranks first on priority, so the fallback is
+	// what reaches the one that works.
+	bad := fakeWithAlbum(1, "offline-peer", ".flac")
+	bad.GrabErr = errPeerOffline
+	good := fakeWithAlbum(2, "online-peer", ".flac")
+
+	f.manager.installProvider(Config{ID: 1, Priority: 90}, bad)
+	f.manager.installProvider(Config{ID: 2, Priority: 10}, good)
+
+	dl := fourTrackDownload()
+
+	if _, err := f.manager.Start(context.Background(), dl); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+
+	waitForDownloadState(t, f.store, dl.ID, StateComplete)
+
+	if bad.GrabCalls != 1 || good.GrabCalls != 1 {
+		t.Errorf(
+			"grabs: failing=%d working=%d, want 1 and 1",
+			bad.GrabCalls, good.GrabCalls,
+		)
+	}
+
+	// The abandoned attempt's staging goes with it; only a request that
+	// fails outright keeps its staging for inspection.
+	waitFor(t, func() bool {
+		entries, err := os.ReadDir(f.staging.Root())
+
+		return err == nil && len(entries) == 0
+	}, "the failed attempt's staging was never released")
+}
+
+// Falling back must not lower the bar.  A second choice outside the
+// user's guardrails is not a choice auto-pick may make, first or second.
+func TestManagerFallbackRespectsTheGuardrails(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+	f.manager.SetPreferences(AutoDownloadPrefs{MaxSizeMB: 50})
+
+	bad := fakeWithAlbum(1, "offline-peer", ".flac")
+	bad.GrabErr = errPeerOffline
+	bad.Candidates[0].TotalSize = 40 << 20
+
+	huge := fakeWithAlbum(2, "oversized", ".flac")
+	huge.Candidates[0].TotalSize = 900 << 20
+
+	f.manager.installProvider(Config{ID: 1, Priority: 90}, bad)
+	f.manager.installProvider(Config{ID: 2, Priority: 10}, huge)
+
+	dl := fourTrackDownload()
+
+	if _, err := f.manager.Start(context.Background(), dl); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+
+	waitForDownloadState(t, f.store, dl.ID, StateFailed)
+
+	if huge.GrabCalls != 0 {
+		t.Errorf("fell back to a candidate over the size ceiling")
+	}
+}
+
+// A copy the user picked by hand is the copy they asked for.  Quietly
+// substituting another is a decision they did not make.
+func TestManagerPickDoesNotFallBack(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+
+	bad := fakeWithAlbum(1, "offline-peer", ".flac")
+	bad.GrabErr = errPeerOffline
+	good := fakeWithAlbum(2, "online-peer", ".flac")
+
+	f.manager.installProvider(Config{ID: 1, Priority: 90}, bad)
+	f.manager.installProvider(Config{ID: 2, Priority: 10}, good)
+
+	// A ceiling below both copies parks the result set for the user.
+	f.manager.SetPreferences(AutoDownloadPrefs{MaxSizeMB: 1})
+
+	bad.Candidates[0].TotalSize = 30 << 20
+	good.Candidates[0].TotalSize = 30 << 20
+
+	dl := fourTrackDownload()
+
+	if _, err := f.manager.Start(context.Background(), dl); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+
+	if err := f.manager.Pick(
+		context.Background(), dl.ID, "offline-peer-cand",
+	); err != nil {
+		t.Fatalf("Pick: %v", err)
+	}
+
+	waitForDownloadState(t, f.store, dl.ID, StateFailed)
+
+	if good.GrabCalls != 0 {
+		t.Errorf("a hand-picked grab fell back to another candidate")
+	}
+}
+
+// Fallback is for surviving an offline peer or two, not for walking a
+// forty-peer list for six hours.
+func TestManagerFallbackIsBounded(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+
+	var providers []*FakeProvider
+
+	for i := int64(1); i <= maxGrabAttempts+2; i++ {
+		p := fakeWithAlbum(i, "peer-"+itoa(int(i)), ".flac")
+		p.GrabErr = errPeerOffline
+
+		f.manager.installProvider(Config{ID: i, Priority: 50}, p)
+		providers = append(providers, p)
+	}
+
+	dl := fourTrackDownload()
+
+	if _, err := f.manager.Start(context.Background(), dl); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+
+	waitForDownloadState(t, f.store, dl.ID, StateFailed)
+
+	grabs := 0
+	for _, p := range providers {
+		grabs += p.GrabCalls
+	}
+
+	if grabs != maxGrabAttempts {
+		t.Errorf("grabs = %d, want %d", grabs, maxGrabAttempts)
+	}
+}
+
+// The veto judges the best candidate *inside* the guardrails, so the
+// grab has to take that one — not the overall best, which may be the
+// very copy the user said not to take unattended.
+func TestManagerAutoPickTakesTheBestEligibleCandidate(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+	f.manager.SetPreferences(AutoDownloadPrefs{MaxSizeMB: 50})
+
+	huge := fakeWithAlbum(1, "oversized", ".flac")
+	huge.Candidates[0].TotalSize = 900 << 20
+
+	fits := fakeWithAlbum(2, "fits", ".flac")
+	fits.Candidates[0].TotalSize = 40 << 20
+
+	f.manager.installProvider(Config{ID: 1, Priority: 90}, huge)
+	f.manager.installProvider(Config{ID: 2, Priority: 10}, fits)
+
+	dl := fourTrackDownload()
+
+	ranked, err := f.manager.Start(context.Background(), dl)
+	if err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+
+	if ranked[0].ID != "oversized-cand" {
+		t.Fatalf("fixture: best overall is %s, want the oversized copy", ranked[0].ID)
+	}
+
+	waitForDownloadState(t, f.store, dl.ID, StateComplete)
+
+	if huge.GrabCalls != 0 || fits.GrabCalls != 1 {
+		t.Errorf(
+			"grabs: oversized=%d fits=%d, want 0 and 1",
+			huge.GrabCalls, fits.GrabCalls,
+		)
+	}
+}
+
+// On Soulseek a failure is the peer's, so every folder that peer offered
+// goes with it.  Elsewhere a failure is the release's, and one indexer's
+// other releases are still worth trying.
+func TestRuledOutBy(t *testing.T) {
+	t.Parallel()
+
+	failed := []Candidate{
+		{ID: "slskd:alice:Album", Kind: KindSlskd, ProviderID: 1, Origin: "alice"},
+		{ID: "tracker-1", Kind: KindProwlarr, ProviderID: 2, Origin: "indexer"},
+	}
+
+	cases := []struct {
+		name string
+		c    Candidate
+		want bool
+	}{
+		{
+			name: "the same candidate",
+			c:    Candidate{ID: "tracker-1", Kind: KindProwlarr, ProviderID: 2, Origin: "indexer"},
+			want: true,
+		},
+		{
+			name: "another folder from a failed peer",
+			c: Candidate{
+				ID:         "slskd:alice:Album (2)",
+				Kind:       KindSlskd,
+				ProviderID: 1,
+				Origin:     "alice",
+			},
+			want: true,
+		},
+		{
+			name: "another peer",
+			c:    Candidate{ID: "slskd:bob:Album", Kind: KindSlskd, ProviderID: 1, Origin: "bob"},
+			want: false,
+		},
+		{
+			name: "another release from the same indexer",
+			c:    Candidate{ID: "tracker-2", Kind: KindProwlarr, ProviderID: 2, Origin: "indexer"},
+			want: false,
+		},
+		{
+			name: "a peer of the same name on a different daemon",
+			c: Candidate{
+				ID:         "slskd:alice:Album",
+				Kind:       KindSlskd,
+				ProviderID: 3,
+				Origin:     "alice",
+			},
+			want: false,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := ruledOutBy(tc.c, failed); got != tc.want {
+				t.Errorf("ruledOutBy = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}

backend/download/keyedlock.go

@@ -0,0 +1,77 @@
+package download
+
+import (
+	"context"
+	"sync"
+)
+
+// keyedLock is a set of mutexes created on demand, one per key, that
+// honour a context while waiting.  An entry lives only while someone
+// holds or waits on it, so a key per Soulseek peer or per folder name
+// does not accumulate for the life of the process.
+type keyedLock[K comparable] struct {
+	mu   sync.Mutex
+	held map[K]*keyedEntry
+}
+
+type keyedEntry struct {
+	ch chan struct{}
+
+	// refs counts holders and waiters; the entry is dropped at zero.
+	refs int
+}
+
+// acquire blocks until k is free or ctx ends, and returns the function
+// that frees it.
+func (l *keyedLock[K]) acquire(ctx context.Context, k K) (func(), error) {
+	l.mu.Lock()
+
+	if l.held == nil {
+		l.held = map[K]*keyedEntry{}
+	}
+
+	e, ok := l.held[k]
+	if !ok {
+		e = &keyedEntry{ch: make(chan struct{}, 1)}
+		l.held[k] = e
+	}
+
+	e.refs++
+
+	l.mu.Unlock()
+
+	select {
+	case e.ch <- struct{}{}:
+	case <-ctx.Done():
+		l.drop(k, e)
+
+		return nil, ctx.Err()
+	}
+
+	var once sync.Once
+
+	return func() {
+		once.Do(func() {
+			<-e.ch
+			l.drop(k, e)
+		})
+	}, nil
+}
+
+func (l *keyedLock[K]) drop(k K, e *keyedEntry) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	e.refs--
+	if e.refs == 0 {
+		delete(l.held, k)
+	}
+}
+
+// size reports how many keys are held or awaited, for tests.
+func (l *keyedLock[K]) size() int {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	return len(l.held)
+}

backend/download/manager.go

@@ -59,13 +59,15 @@ const concurrencyKey = "maxConcurrent"
 // A single global cap is the wrong shape here: usenet and torrent
 // clients are built to run many transfers at once and are throttled by
 // bandwidth, while Soulseek transfers come from one person's home
-// upload slot.  Hitting the same peer with parallel requests gets you
-// queued behind everyone else at best and banned at worst, so slskd is
-// capped at one — the polite number, and the one that actually
-// completes fastest, because a Soulseek peer serves one file at a time
-// regardless of how many you ask for.
+// upload slot.  Politeness there is per *peer* — asking one user for two
+// folders at once gets you queued behind everyone else at best and
+// banned at worst — and the manager holds that line separately, one
+// grab per peer (peerLocks).  Two different users do not compete for
+// anyone's slot, so the daemon-wide number only bounds how many peers
+// are asked at once, and one slow peer no longer serialises every other
+// Soulseek download behind it.
 var kindConcurrency = map[Kind]int{
-	KindSlskd:       1,
+	KindSlskd:       3,
 	KindYtDlp:       2,
 	KindQBittorrent: 4,
 	KindSABnzbd:     4,
@@ -155,6 +157,11 @@ type Manager struct {
 	semMu   sync.Mutex
 	provSem map[int64]chan struct{}
 
+	// peerLocks holds one grab per Soulseek peer, taken before any
+	// slot: a grab waiting for a busy peer must not sit on a provider
+	// slot another peer could be using.
+	peerLocks keyedLock[peerKey]
+
 	// delegatePoll is how often delegating managers are asked for
 	// status.  A field rather than the constant so tests can drive the
 	// full delegate flow without sleeping through it.
@@ -577,12 +584,12 @@ func (m *Manager) Start(
 		))
 	}
 
-	if m.AutoPickable(dl, ranked) {
+	if pick, ok := autoPick(dl, ranked, m.preferences()); ok {
 		if job != nil {
 			job.Logf(jobs.LevelInfo, "Auto-selected best candidate")
 		}
 
-		go m.grab(context.WithoutCancel(ctx), dl, ranked[0], job)
+		go m.grab(context.WithoutCancel(ctx), dl, pick, job, true)
 
 		return ranked, nil
 	}
@@ -622,6 +629,13 @@ func (m *Manager) Attempt(
 		return false, veto, nil
 	}
 
+	pick, ok := autoPick(dl, ranked, m.preferences())
+	if !ok {
+		// Unreachable while autoPick and AutoPickVeto agree; kept so a
+		// future divergence refuses rather than grabbing blind.
+		return false, "no candidate clears the auto-download bar", nil
+	}
+
 	if err := m.store.CreateDownload(ctx, dl); err != nil {
 		return false, "", err
 	}
@@ -643,7 +657,7 @@ func (m *Manager) Attempt(
 		))
 	}
 
-	go m.grab(context.WithoutCancel(ctx), dl, ranked[0], job)
+	go m.grab(context.WithoutCancel(ctx), dl, pick, job, true)
 
 	return true, "", nil
 }
@@ -678,7 +692,7 @@ func (m *Manager) Pick(
 
 	job := m.startJob(dl)
 
-	go m.grab(context.WithoutCancel(ctx), dl, *chosen, job)
+	go m.grab(context.WithoutCancel(ctx), dl, *chosen, job, false)
 
 	return nil
 }
@@ -702,13 +716,20 @@ func (m *Manager) Cancel(ctx context.Context, downloadID string) error {
 	return nil
 }
 
-// grab drives one candidate all the way to the library.  It runs on its
+// grab drives one request all the way to the library.  It runs on its
 // own goroutine and owns the job from here on.
+//
+// When fallback is set and a candidate's transfer fails, the next
+// candidate that auto-pick would itself have accepted is tried in its
+// place (see nextCandidate).  It is set for the two unattended routes
+// and not for a candidate the user picked by hand: they chose that copy,
+// and quietly substituting another is a decision they did not make.
 func (m *Manager) grab(
 	ctx context.Context,
 	dl Download,
 	c Candidate,
 	job *jobs.Handle,
+	fallback bool,
 ) {
 	ctx, cancel := context.WithTimeout(ctx, grabTimeout)
 	defer cancel()
@@ -723,6 +744,99 @@ func (m *Manager) grab(
 		m.actMu.Unlock()
 	}()
 
+	var failed []Candidate
+
+	for {
+		out := m.attemptGrab(ctx, dl, c, job)
+		if out.err == nil {
+			m.finishGrab(ctx, dl, out.item, out.imported, job)
+
+			return
+		}
+
+		failed = append(failed, c)
+
+		next, ok := m.nextCandidate(ctx, dl, failed, out, fallback)
+		if !ok {
+			m.failDownload(ctx, job, dl.ID, out.err)
+
+			return
+		}
+
+		m.logger.Info(
+			"download candidate failed; trying the next",
+			"download", dl.ID,
+			"failed", c.ID,
+			"next", next.ID,
+			"error", out.err,
+		)
+
+		if job != nil {
+			job.Logf(jobs.LevelWarn, fmt.Sprintf(
+				"%s failed (%v); trying %s instead",
+				describeCandidate(c), out.err, describeCandidate(next),
+			))
+		}
+
+		// The failed attempt's staging holds at most a partial folder
+		// nobody is going to import, and the next attempt reserves its
+		// own.  Only the final failure keeps its staging for inspection.
+		if out.item.StagingDir != "" {
+			if err := m.staging.Release(out.item.StagingDir); err != nil {
+				m.logger.Warn("could not release staging dir", "error", err)
+			}
+		}
+
+		c = next
+	}
+}
+
+// maxGrabAttempts bounds how many candidates one request will try.  A
+// popular album can have dozens of peers; the point of falling back is
+// to survive the ordinary one or two that are offline, not to walk the
+// whole list for six hours.
+const maxGrabAttempts = 3
+
+// peerKey names one Soulseek user on one daemon.  The same username on
+// two daemons is two logins and two queues.
+type peerKey struct {
+	provider int64
+	peer     string
+}
+
+// peerKeyFor returns the peer a candidate is fetched from, when the
+// source is one where asking a peer for two things at once is rude.
+func peerKeyFor(c Candidate) (peerKey, bool) {
+	if c.Kind != KindSlskd || c.Origin == "" {
+		return peerKey{}, false
+	}
+
+	return peerKey{provider: c.ProviderID, peer: c.Origin}, true
+}
+
+// grabOutcome is how one candidate's attempt ended.
+type grabOutcome struct {
+	item     DownloadItem
+	imported ImportResult
+	err      error
+
+	// retryable reports whether another candidate might succeed where
+	// this one failed: the transfer failed, or delivered too little of
+	// the album.  Anything else — no staging space, no library root, a
+	// tag write failing — would fail the next candidate identically.
+	retryable bool
+}
+
+// attemptGrab takes one candidate through transfer and import.  It
+// records the item's own failure, but not the download's: whether the
+// download has failed is the caller's decision, since another candidate
+// may yet succeed.
+func (m *Manager) attemptGrab(
+	ctx context.Context,
+	dl Download,
+	c Candidate,
+	job *jobs.Handle,
+) grabOutcome {
 	// Who will move the bytes is decided before any slot is taken, so
 	// the transfer waits in its own provider's queue rather than in a
 	// global one.  A delegate takes no slot at all: the transfer is
@@ -731,21 +845,26 @@ func (m *Manager) grab(
 	// work against our budget.
 	plan, err := m.planTransfer(dl, c)
 	if err != nil {
-		m.failDownload(ctx, job, dl.ID, err)
-
-		return
+		return grabOutcome{err: err}
 	}
 
 	if !plan.delegated() {
+		if key, ok := peerKeyFor(c); ok {
+			release, err := m.peerLocks.acquire(ctx, key)
+			if err != nil {
+				return grabOutcome{err: err}
+			}
+
+			defer release()
+		}
+
 		provSem := m.semaphoreFor(plan.transportID)
 
 		select {
 		case provSem <- struct{}{}:
 			defer func() { <-provSem }()
 		case <-ctx.Done():
-			m.failDownload(ctx, job, dl.ID, ctx.Err())
-
-			return
+			return grabOutcome{err: ctx.Err()}
 		}
 
 		globalSem := m.globalSem()
@@ -754,9 +873,7 @@ func (m *Manager) grab(
 		case globalSem <- struct{}{}:
 			defer func() { <-globalSem }()
 		case <-ctx.Done():
-			m.failDownload(ctx, job, dl.ID, ctx.Err())
-
-			return
+			return grabOutcome{err: ctx.Err()}
 		}
 	}
 
@@ -771,24 +888,30 @@ func (m *Manager) grab(
 
 	dir, err := m.staging.Reserve(item.ID)
 	if err != nil {
-		m.failDownload(ctx, job, dl.ID, err)
-
-		return
+		return grabOutcome{err: err}
 	}
 
 	item.StagingDir = dir
 
 	if err := m.store.CreateItem(ctx, item); err != nil {
-		m.failDownload(ctx, job, dl.ID, err)
+		return grabOutcome{item: item, err: err}
+	}
 
-		return
+	fail := func(err error, retryable bool) grabOutcome {
+		if serr := m.store.SetItemState(
+			ctx, item.ID, StateFailed, err.Error(),
+		); serr != nil {
+			m.logger.Warn("could not record item failure", "error", serr)
+		}
+
+		return grabOutcome{item: item, err: err, retryable: retryable}
 	}
 
 	result, err := m.transfer(ctx, dl, item, plan, job)
 	if err != nil {
-		m.failItem(ctx, job, item, dl.ID, err)
-
-		return
+		// A delegate's failure is the external manager's verdict on the
+		// whole request, not on one copy of it.
+		return fail(err, !plan.delegated())
 	}
 
 	m.setStates(ctx, dl.ID, item.ID, StateImporting)
@@ -798,42 +921,116 @@ func (m *Manager) grab(
 		job.SetStages(importStages(2))
 	}
 
-	var imported ImportResult
-
 	if result.Delegated {
 		// The external manager already placed and tagged these files in
 		// its own library.  Moving them out from under a system that is
 		// still managing them would be worse than useless, so the files
 		// are recorded where they are and the library scan picks them
 		// up in place.
-		imported = ImportResult{Paths: result.Files}
-
 		if job != nil {
 			job.Logf(jobs.LevelInfo, fmt.Sprintf(
 				"External manager imported %d files; recording them in place",
 				len(result.Files),
 			))
 		}
-	} else {
-		opts := m.importOptions()
-		opts.WriteTags = true
 
-		opts.LibraryRoot, err = m.library.LibraryPath(dl.LibraryID)
-		if err != nil {
-			m.failItem(ctx, job, item, dl.ID,
-				fmt.Errorf("resolve library root: %w", err))
-
-			return
-		}
-
-		imported, err = m.importer.Import(ctx, dl, result, opts)
-		if err != nil {
-			m.failItem(ctx, job, item, dl.ID, err)
-
-			return
+		return grabOutcome{
+			item:     item,
+			imported: ImportResult{Paths: result.Files},
 		}
 	}
 
+	opts := m.importOptions()
+	opts.WriteTags = true
+
+	opts.LibraryRoot, err = m.library.LibraryPath(dl.LibraryID)
+	if err != nil {
+		return fail(fmt.Errorf("resolve library root: %w", err), false)
+	}
+
+	imported, err := m.importer.Import(ctx, dl, result, opts)
+	if err != nil {
+		return fail(err, errors.Is(err, ErrTooIncomplete))
+	}
+
+	return grabOutcome{item: item, imported: imported}
+}
+
+// nextCandidate picks the candidate to try after the ones in failed.
+//
+// It only ever offers a candidate auto-pick would have taken on its own
+// (autoAcceptable), so falling back cannot lower the bar an unattended
+// download is held to: the second choice has to clear the same gates
+// the first did.
+//
+// On Soulseek a failure belongs to the *peer* — offline, refusing, or
+// holding us in a queue — so every folder that peer offered is skipped
+// with it.  Elsewhere a failure belongs to the release, and only that
+// candidate is.
+func (m *Manager) nextCandidate(
+	ctx context.Context,
+	dl Download,
+	failed []Candidate,
+	out grabOutcome,
+	fallback bool,
+) (Candidate, bool) {
+	if !fallback || !out.retryable || ctx.Err() != nil ||
+		len(failed) >= maxGrabAttempts {
+		return Candidate{}, false
+	}
+
+	m.resMu.RLock()
+	ranked := m.results[dl.ID]
+	m.resMu.RUnlock()
+
+	prefs := m.preferences()
+
+	for _, c := range ranked {
+		if ruledOutBy(c, failed) || !autoAcceptable(dl, c, prefs) {
+			continue
+		}
+
+		return c, true
+	}
+
+	return Candidate{}, false
+}
+
+// ruledOutBy reports whether a failure among failed also rules out c.
+func ruledOutBy(c Candidate, failed []Candidate) bool {
+	for _, f := range failed {
+		if c.ID == f.ID && c.ProviderID == f.ProviderID {
+			return true
+		}
+
+		if c.Kind == KindSlskd && f.Kind == KindSlskd &&
+			c.ProviderID == f.ProviderID && c.Origin != "" &&
+			c.Origin == f.Origin {
+			return true
+		}
+	}
+
+	return false
+}
+
+// describeCandidate names a candidate for the job log.
+func describeCandidate(c Candidate) string {
+	if c.Origin != "" {
+		return fmt.Sprintf("%q from %s", c.Title, c.Origin)
+	}
+
+	return fmt.Sprintf("%q", c.Title)
+}
+
+// finishGrab records a successful import and retires what the request
+// was holding.
+func (m *Manager) finishGrab(
+	ctx context.Context,
+	dl Download,
+	item DownloadItem,
+	imported ImportResult,
+	job *jobs.Handle,
+) {
 	if err := m.store.SetItemImported(
 		ctx, item.ID, imported.Paths,
 	); err != nil {
@@ -1177,23 +1374,6 @@ func (m *Manager) failDownload(
 	}
 }
 
-// failItem records an item-level failure and fails its download.
-func (m *Manager) failItem(
-	ctx context.Context,
-	job *jobs.Handle,
-	item DownloadItem,
-	downloadID string,
-	err error,
-) {
-	if serr := m.store.SetItemState(
-		ctx, item.ID, StateFailed, err.Error(),
-	); serr != nil {
-		m.logger.Warn("could not record item failure", "error", serr)
-	}
-
-	m.failDownload(ctx, job, downloadID, err)
-}
-
 // startJob registers the request in the background jobs panel.
 func (m *Manager) startJob(dl Download) *jobs.Handle {
 	if m.jobsReg == nil {

backend/download/pathmatch.go

@@ -66,6 +66,14 @@ var (
 
 	// separatorPattern splits "Artist - Album" style folder names.
 	separatorPattern = regexp.MustCompile(`\s+[-–—]\s+`)
+
+	// discFolderPattern matches a directory that holds one disc of an
+	// album rather than the album: "CD1", "CD 2", "Disc 3", "Disk-1",
+	// "[Disc 2]", "CD1 - The Early Years".  A number is required, so a
+	// folder merely called "CDs" is not one.
+	discFolderPattern = regexp.MustCompile(
+		`(?i)^\s*[\[(]?\s*(?:cd|disc|disk)\s*[-_.#]?\s*(\d{1,2})\b`,
+	)
 )
 
 // FormatForPath returns the audio format implied by a path's extension,
@@ -94,16 +102,63 @@ type TrackHint struct {
 	Folder string
 }
 
+// discFolder reports whether a directory name is one disc of an album,
+// and which.
+func discFolder(name string) (int, bool) {
+	m := discFolderPattern.FindStringSubmatch(name)
+	if m == nil {
+		return 0, false
+	}
+
+	n, err := strconv.Atoi(m[1])
+	if err != nil || n == 0 {
+		return 0, false
+	}
+
+	return n, true
+}
+
+// AlbumDir is the directory that holds a file's *album*: its parent,
+// or its grandparent when the parent is a disc folder.
+//
+// Multi-disc rips are shared as `Album/CD1/…` and `Album/CD2/…`, and
+// grouping candidates by the immediate parent split one album into two
+// half-albums, each titled "CD1".  Neither could clear the completeness
+// or album-title bars, so a multi-disc release could not be auto-picked
+// at all.  A disc folder at the root has no album above it and is
+// returned as it is.
+func AlbumDir(p string) string {
+	dir := path.Dir(strings.ReplaceAll(p, `\`, "/"))
+
+	if _, ok := discFolder(path.Base(dir)); !ok {
+		return dir
+	}
+
+	parent := path.Dir(dir)
+	if parent == "." || parent == "/" || parent == "" {
+		return dir
+	}
+
+	return parent
+}
+
 // ParsePath extracts what it can from one candidate file path.
 func ParsePath(p string) TrackHint {
 	// Soulseek paths are Windows-style; normalize before splitting.
 	norm := strings.ReplaceAll(p, `\`, "/")
 	base := path.Base(norm)
-	folder := path.Base(path.Dir(norm))
 
 	name := strings.TrimSuffix(base, path.Ext(base))
 
-	hint := TrackHint{Folder: cleanAlbumName(folder)}
+	// The album's name is the album directory's, not a disc folder's,
+	// and the disc folder is where a multi-disc rip says which disc a
+	// file is on.  A disc number in the filename ("2-01 …") is more
+	// specific and overrides it below.
+	hint := TrackHint{Folder: cleanAlbumName(path.Base(AlbumDir(norm)))}
+
+	if disc, ok := discFolder(path.Base(path.Dir(norm))); ok {
+		hint.Disc = disc
+	}
 
 	if m := trackNumPattern.FindStringSubmatch(name); m != nil {
 		if m[1] != "" {
@@ -203,21 +258,72 @@ func AnnotateFiles(files []CandidateFile) []CandidateFile {
 
 // matchFiles aligns a candidate's audio files to the expected tracklist
 // and returns the per-file assignment plus the mean title similarity of
-// the aligned pairs.
+// the aligned pairs.  alignFiles is the same alignment with the
+// duration evidence as well.
+func matchFiles(
+	files []CandidateFile,
+	expected []ExpectedTrack,
+) ([]CandidateFile, float64) {
+	a := alignFiles(files, expected)
+
+	return a.files, a.titleFit
+}
+
+// alignment is what aligning a candidate to a tracklist found.
+type alignment struct {
+	files []CandidateFile
+
+	// titleFit is the mean title similarity over aligned pairs.
+	titleFit float64
+
+	// durationFit is the mean duration agreement over aligned pairs
+	// where both sides state a length, and timedPairs is how many such
+	// pairs there were.
+	durationFit float64
+	timedPairs  int
+	aligned     int
+}
+
+// durationAgreement scores how well a file's length matches the
+// expected track's, in 0..1.  Rips of the same master differ by a
+// second or two of silence; a different edit, a live take or a
+// truncated file differs by tens of seconds.
+func durationAgreement(got, want int64) float64 {
+	const (
+		exactMillis = 3_000
+		wrongMillis = 30_000
+	)
+
+	d := got - want
+	if d < 0 {
+		d = -d
+	}
+
+	switch {
+	case d <= exactMillis:
+		return 1
+	case d >= wrongMillis:
+		return 0
+	default:
+		return 1 - float64(d-exactMillis)/float64(wrongMillis-exactMillis)
+	}
+}
+
+// alignFiles aligns a candidate's audio files to the expected tracklist.
 //
 // Alignment is greedy by score rather than optimal: candidate folders
 // are small (a few dozen files at most) and the common cases — correct
 // track numbers, or clean "NN Title" names — are unambiguous, so the
 // extra machinery of Hungarian assignment buys nothing here.
-func matchFiles(
+func alignFiles(
 	files []CandidateFile,
 	expected []ExpectedTrack,
-) ([]CandidateFile, float64) {
+) alignment {
 	annotated := make([]CandidateFile, len(files))
 	copy(annotated, files)
 
 	if len(expected) == 0 {
-		return annotated, 0
+		return alignment{files: annotated}
 	}
 
 	hints := make([]TrackHint, len(annotated))
@@ -230,8 +336,19 @@ func matchFiles(
 	var (
 		total   float64
 		matched int
+
+		durTotal float64
+		timed    int
 	)
 
+	// timing adds a pair's duration evidence when both sides state one.
+	timing := func(f CandidateFile, e ExpectedTrack) {
+		if f.LengthMillis > 0 && e.LengthMillis > 0 {
+			durTotal += durationAgreement(f.LengthMillis, e.LengthMillis)
+			timed++
+		}
+	}
+
 	// Pass 1: trust explicit track numbers when they are unique and in
 	// range.  A folder that numbers its files correctly is the strong
 	// case, and title comparison only adds noise there.
@@ -250,6 +367,8 @@ func matchFiles(
 
 		total += autotag.TitleSimilarity(hints[i].Title, expected[idx].Title)
 		matched++
+
+		timing(annotated[i], expected[idx])
 	}
 
 	// Pass 2: title similarity for whatever is left.
@@ -284,13 +403,26 @@ func matchFiles(
 
 		total += bestSim
 		matched++
+
+		timing(annotated[i], expected[bestIdx])
 	}
 
 	if matched == 0 {
-		return annotated, 0
+		return alignment{files: annotated}
 	}
 
-	return annotated, total / float64(matched)
+	a := alignment{
+		files:      annotated,
+		titleFit:   total / float64(matched),
+		timedPairs: timed,
+		aligned:    matched,
+	}
+
+	if timed > 0 {
+		a.durationFit = durTotal / float64(timed)
+	}
+
+	return a
 }
 
 // indexForPosition finds the expected track at a disc/track position.

backend/download/peer_concurrency_test.go

@@ -0,0 +1,224 @@
+package download
+
+import (
+	"context"
+	"errors"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+)
+
+// Soulseek politeness is per peer, not per daemon (#272).
+
+func TestKeyedLockSerialisesOneKeyOnly(t *testing.T) {
+	t.Parallel()
+
+	var l keyedLock[string]
+
+	ctx := context.Background()
+
+	releaseA, err := l.acquire(ctx, "a")
+	if err != nil {
+		t.Fatalf("acquire a: %v", err)
+	}
+
+	// Another key is free while "a" is held.
+	releaseB, err := l.acquire(ctx, "b")
+	if err != nil {
+		t.Fatalf("acquire b: %v", err)
+	}
+
+	releaseB()
+
+	// The same key waits, and gives up with its context.
+	short, cancel := context.WithTimeout(ctx, 20*time.Millisecond)
+	defer cancel()
+
+	if _, err := l.acquire(short, "a"); !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("second acquire of a held key = %v, want the deadline", err)
+	}
+
+	releaseA()
+	releaseA() // Idempotent: a second call must not free someone else's hold.
+
+	if n := l.size(); n != 0 {
+		t.Errorf("%d keys left behind, want none once nobody holds or waits", n)
+	}
+}
+
+// grabEach runs one grab per candidate and returns a function that waits
+// for all of them; grabAll's reasons for waiting apply.
+func grabEach(t *testing.T, f managerFixture, cands []Candidate) func() {
+	t.Helper()
+
+	ctx := context.Background()
+
+	var wg sync.WaitGroup
+
+	for i, c := range cands {
+		dl := fourTrackDownload()
+		dl.ID = "dl-" + string(rune('a'+i))
+
+		if err := f.store.CreateDownload(ctx, dl); err != nil {
+			t.Fatalf("CreateDownload: %v", err)
+		}
+
+		wg.Add(1)
+
+		go func() {
+			defer wg.Done()
+
+			f.manager.grab(ctx, dl, c, nil, false)
+		}()
+	}
+
+	return func() {
+		done := make(chan struct{})
+
+		go func() {
+			wg.Wait()
+			close(done)
+		}()
+
+		select {
+		case <-done:
+		case <-time.After(5 * time.Second):
+			t.Error("transfers did not finish")
+		}
+	}
+}
+
+func slskdCandidates(p *FakeProvider, peers ...string) []Candidate {
+	out := make([]Candidate, 0, len(peers))
+
+	for i, peer := range peers {
+		c := p.Candidates[0]
+		c.ID = c.ID + "-" + itoa(i)
+		c.Kind = KindSlskd
+		c.ProviderID = 1
+		c.Origin = peer
+		out = append(out, c)
+	}
+
+	return out
+}
+
+// Three albums from one user are asked for one at a time, even though
+// the daemon would allow three transfers.
+func TestOnePeerIsAskedForOneThingAtATime(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+	f.manager.SetMaxConcurrent(4)
+
+	p := fakeWithAlbum(1, "slskd", ".flac")
+	p.GrabGate = make(chan struct{})
+
+	f.manager.installProvider(Config{ID: 1, Kind: KindSlskd, Priority: 50}, p)
+
+	wait := grabEach(t, f, slskdCandidates(p, "alice", "alice", "alice"))
+
+	waitFor(t, func() bool { return p.GrabCallCount() >= 1 }, "no grab started")
+	time.Sleep(150 * time.Millisecond)
+
+	if got := p.MaxParallelGrabs(); got != 1 {
+		t.Errorf("%d simultaneous grabs from one peer, want 1", got)
+	}
+
+	close(p.GrabGate)
+
+	waitFor(t, func() bool { return p.GrabCallCount() == 3 }, "queued grabs never ran")
+	wait()
+
+	if n := f.manager.peerLocks.size(); n != 0 {
+		t.Errorf("%d peer locks left behind", n)
+	}
+}
+
+// Different users run at once, up to the daemon's cap — the point of
+// the change: one slow peer no longer holds up every other.
+func TestDifferentPeersRunTogether(t *testing.T) {
+	t.Parallel()
+
+	f := newManagerFixture(t)
+	f.manager.SetMaxConcurrent(8)
+
+	p := fakeWithAlbum(1, "slskd", ".flac")
+	p.GrabGate = make(chan struct{})
+
+	f.manager.installProvider(Config{ID: 1, Kind: KindSlskd, Priority: 50}, p)
+
+	wait := grabEach(t, f, slskdCandidates(p, "alice", "bob", "carol", "dave"))
+
+	waitFor(
+		t,
+		func() bool { return p.MaxParallelGrabs() >= kindConcurrency[KindSlskd] },
+		"different peers were serialised",
+	)
+	time.Sleep(100 * time.Millisecond)
+
+	if got := p.MaxParallelGrabs(); got != kindConcurrency[KindSlskd] {
+		t.Errorf("%d simultaneous grabs, want the daemon cap %d", got, kindConcurrency[KindSlskd])
+	}
+
+	close(p.GrabGate)
+	wait()
+}
+
+func TestSlskdLocalFolders(t *testing.T) {
+	t.Parallel()
+
+	s := &slskd{downloadsPath: "/dl"}
+
+	got := s.localFolders(Candidate{Files: []CandidateFile{
+		{Path: `\m\The Wall\CD2\01 Hey You.flac`},
+		{Path: `\m\The Wall\CD1\01 In The Flesh.flac`},
+		{Path: `\m\The Wall\CD1\02 The Thin Ice.flac`},
+	}})
+
+	want := []string{filepath.Join("/dl", "CD1"), filepath.Join("/dl", "CD2")}
+	if len(got) != len(want) || got[0] != want[0] || got[1] != want[1] {
+		t.Errorf("localFolders = %q, want %q", got, want)
+	}
+}
+
+// Two peers' "Greatest Hits" land in one slskd directory, so the second
+// grab does not enqueue until the first has collected its files.
+func TestSlskdSameFolderNameWaits(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	s, downloads := newStubSlskd(t, stub)
+
+	c := Candidate{
+		Payload: map[string]string{"username": "bob"},
+		Files: []CandidateFile{
+			{Path: `\music\Greatest Hits\01 Intro.flac`, Size: 1, IsAudio: true},
+		},
+	}
+
+	release, err := lockSlskdFolders(
+		context.Background(), []string{filepath.Join(downloads, "Greatest Hits")},
+	)
+	if err != nil {
+		t.Fatalf("lock: %v", err)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+
+	if _, err := s.Grab(ctx, c, t.TempDir(), nil); !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("Grab = %v, want it to wait on the held folder", err)
+	}
+
+	release()
+
+	stub.mu.Lock()
+	posted := stub.posted
+	stub.mu.Unlock()
+
+	if posted {
+		t.Error("enqueued transfers into a folder another grab held")
+	}
+}

backend/download/provider.go

@@ -236,17 +236,18 @@ func Register(d Descriptor, c Constructor) {
 }
 
 // concurrencyField describes the per-provider transfer limit, with help
-// text explaining why the default is what it is — a user who raises
-// slskd from 1 to 8 and gets themselves queued behind every other
-// Soulseek user deserves to have been warned.
+// text explaining what the number means where it means something
+// unusual: on slskd it counts peers, since each peer is only ever asked
+// for one folder at a time whatever it is set to.
 func concurrencyField(k Kind) Field {
 	help := "Maximum simultaneous transfers from this client."
 
 	if k == KindSlskd {
-		help = "Maximum simultaneous transfers. Soulseek peers serve " +
-			"one file at a time and queue or ban clients that ask for " +
-			"more, so 1 is both the polite setting and usually the " +
-			"fastest."
+		help = "How many Soulseek users to download from at once. " +
+			"Each user is only ever asked for one album at a time, " +
+			"since peers queue or ban clients that ask for more; " +
+			"this bounds how many different users are asked in " +
+			"parallel."
 	}
 
 	return Field{

backend/download/provider_slskd.go

@@ -5,9 +5,12 @@ import (
 	"errors"
 	"fmt"
 	"log/slog"
+	"net/url"
 	"os"
 	"path"
 	"path/filepath"
+	"regexp"
+	"slices"
 	"strings"
 	"time"
 
@@ -69,12 +72,34 @@ const (
 	slskdTransferPoll = 3 * time.Second
 
 	// slskdMinFiles is the fewest audio files a folder needs before it
-	// is offered as a candidate.  Soulseek returns a lot of one-file
-	// noise for common queries.
+	// is offered as a candidate for an album.  Soulseek returns a lot of
+	// one-file noise for common queries.  A single-track request takes
+	// one (see minFilesFor).
 	slskdMinFiles = 2
 
 	// slskdHTTPTimeout bounds one API call.
 	slskdHTTPTimeout = 20 * time.Second
+
+	// millisPerSecond converts slskd's whole-second file lengths.
+	millisPerSecond = 1000
+
+	// slskdStallAfter is how long a grab may go without a byte arriving
+	// before the peer is given up on.  It is measured from enqueue, so
+	// it covers a peer that queues us and never starts as well as one
+	// that starts and stops.  Ten minutes is long enough for a short
+	// queue ahead of us to clear and short enough that one unresponsive
+	// peer does not hold slskd's single transfer slot for an evening.
+	slskdStallAfter = 10 * time.Minute
+
+	// slskdAbsentGrace is how long a requested file may be missing from
+	// slskd's transfer list before it is counted as failed.  slskd lists
+	// a transfer as soon as it accepts it, so a file still absent after
+	// a few polls was refused.
+	slskdAbsentGrace = 30 * time.Second
+
+	// slskdCancelTimeout bounds the cleanup that cancels abandoned
+	// transfers.
+	slskdCancelTimeout = 15 * time.Second
 )
 
 func init() {
@@ -134,6 +159,8 @@ type slskd struct {
 	searchPoll   time.Duration
 	searchWait   time.Duration
 	transferPoll time.Duration
+	stallAfter   time.Duration
+	absentGrace  time.Duration
 }
 
 // newSlskd builds the provider from config.
@@ -188,6 +215,8 @@ func newSlskd(
 		searchPoll:    slskdSearchPoll,
 		searchWait:    slskdSearchWait,
 		transferPoll:  slskdTransferPoll,
+		stallAfter:    slskdStallAfter,
+		absentGrace:   slskdAbsentGrace,
 	}, nil
 }
 
@@ -231,14 +260,13 @@ type slskdSearch struct {
 
 // slskdResponse is one peer's answer to a search.
 type slskdResponse struct {
-	Username           string      `json:"username"`
-	HasFreeUploadSlot  bool        `json:"hasFreeUploadSlot"`
-	QueueLength        int         `json:"queueLength"`
-	UploadSpeed        int64       `json:"uploadSpeed"`
-	Files              []slskdFile `json:"files"`
-	LockedFileCount    int         `json:"lockedFileCount"`
-	FileCount          int         `json:"fileCount"`
-	FreeUploadSlotFlag bool        `json:"freeUploadSlots"`
+	Username          string      `json:"username"`
+	HasFreeUploadSlot bool        `json:"hasFreeUploadSlot"`
+	QueueLength       int         `json:"queueLength"`
+	UploadSpeed       int64       `json:"uploadSpeed"`
+	Files             []slskdFile `json:"files"`
+	LockedFileCount   int         `json:"lockedFileCount"`
+	FileCount         int         `json:"fileCount"`
 }
 
 // slskdFile is one file a peer is offering.
@@ -246,7 +274,9 @@ type slskdFile struct {
 	Filename string `json:"filename"`
 	Size     int64  `json:"size"`
 	BitRate  int    `json:"bitRate"`
-	Length   int    `json:"length"`
+
+	// Length is the duration in whole seconds.
+	Length int `json:"length"`
 }
 
 // slskdTransfer is one download's state.
@@ -278,24 +308,89 @@ func (t slskdTransfer) done() (finished, ok bool) {
 // per-folder candidates.  A folder from one peer is the unit a user
 // actually wants: Soulseek has no album concept, but people organise
 // their shares by album directory.
+//
+// Up to two queries run at once — the request as written and a
+// normalised form of it (see slskdQueries) — and their candidates are
+// merged.  They run concurrently rather than as a fallback because the
+// manager gives a provider one search budget, and a Soulseek search
+// spends most of it waiting for peers to answer; a second query after
+// the first would not fit.
 func (s *slskd) Search(ctx context.Context, dl Download) ([]Candidate, error) {
+	queries := slskdQueries(dl)
+	if len(queries) == 0 {
+		return nil, nil
+	}
+
+	type found struct {
+		candidates []Candidate
+		err        error
+	}
+
+	results := make(chan found, len(queries))
+
+	for _, q := range queries {
+		go func(q string) {
+			c, err := s.searchOnce(ctx, q, minFilesFor(dl))
+			results <- found{candidates: c, err: err}
+		}(q)
+	}
+
+	var (
+		out      []Candidate
+		seen     = map[string]bool{}
+		firstErr error
+		answered int
+	)
+
+	for range queries {
+		r := <-results
+		if r.err != nil {
+			s.logger.Debug("slskd search failed", "error", r.err)
+
+			if firstErr == nil {
+				firstErr = r.err
+			}
+
+			continue
+		}
+
+		answered++
+
+		// The same peer's folder turns up under both queries; the ID is
+		// peer and folder, so it is the same candidate.
+		for _, c := range r.candidates {
+			if seen[c.ID] {
+				continue
+			}
+
+			seen[c.ID] = true
+
+			out = append(out, c)
+		}
+	}
+
+	if answered == 0 {
+		return nil, firstErr
+	}
+
+	return out, nil
+}
+
+// searchOnce runs one query to completion and returns its candidates.
+func (s *slskd) searchOnce(
+	ctx context.Context,
+	text string,
+	minFiles int,
+) ([]Candidate, error) {
 	// slskd's search endpoint deserializes id as a .NET Guid server-side,
 	// so it must be a dashed UUID — the app's own newID() (a plain hex
 	// string, used for request/item IDs elsewhere) is rejected with an
 	// HTTP 400 before any search happens.
 	searchID := uuid.NewString()
 
-	body := map[string]any{
-		"id":         searchID,
-		"searchText": dl.SearchText(),
-	}
-
-	if err := s.client.post(ctx, "/api/v0/searches", body, nil); err != nil {
-		return nil, err
-	}
-
-	search, err := s.awaitSearch(ctx, searchID)
-	if err != nil {
+	if err := s.client.post(
+		ctx, "/api/v0/searches", s.searchRequest(searchID, text, minFiles), nil,
+	); err != nil {
 		return nil, err
 	}
 
@@ -307,52 +402,222 @@ func (s *slskd) Search(ctx context.Context, dl Download) ([]Candidate, error) {
 		)
 	}()
 
-	return s.candidatesFrom(search), nil
+	if err := s.awaitSearch(ctx, searchID); err != nil {
+		return nil, err
+	}
+
+	responses, err := s.searchResponses(ctx, searchID)
+	if err != nil {
+		return nil, err
+	}
+
+	return s.candidatesFrom(responses, minFiles), nil
+}
+
+// searchRequest is the body that starts a search.
+//
+// Every option is stated rather than left to the daemon, because
+// slskd's defaults are its own and not ours.  Its search timeout in
+// particular has to finish inside our wait: a search that slskd is still
+// running when we stop polling is results we asked for and discarded.
+// The response and file limits are raised well above what a popular
+// album produces, and the peer filters let slskd drop answers this
+// provider would only score down to nothing — a folder too small to be
+// a candidate, a peer with a queue it will not reach today.
+func (s *slskd) searchRequest(id, text string, minFiles int) map[string]any {
+	const (
+		responseLimit          = 500
+		fileLimit              = 20_000
+		maximumPeerQueueLength = 100
+	)
+
+	// A tenth of the wait is left for the last poll and the responses
+	// fetch.
+	timeout := s.searchWait - s.searchWait/10
+
+	return map[string]any{
+		"id":                       id,
+		"searchText":               text,
+		"searchTimeout":            timeout.Milliseconds(),
+		"responseLimit":            responseLimit,
+		"fileLimit":                fileLimit,
+		"filterResponses":          true,
+		"minimumResponseFileCount": minFiles,
+		"maximumPeerQueueLength":   maximumPeerQueueLength,
+	}
+}
+
+// slskdQueries is what is searched for a request: the request's own
+// search text, and a normalised form of it when that differs.
+//
+// Soulseek matches every term against the file's full path, so each
+// extra word is a filter, and some words filter wrongly:
+//
+//   - edition qualifiers — "(Deluxe Edition)", "[2011 Remaster]" — are
+//     in the catalog's title and rarely in anyone's folder name;
+//   - punctuation splits a term oddly, and a term that starts with "-"
+//     is an *exclusion*, so an album called "-ism" searches for
+//     everything without it;
+//   - "Various Artists" is in no one's path for a compilation.
+//
+// A query the user typed is theirs and is searched exactly as written.
+func slskdQueries(dl Download) []string {
+	primary := strings.TrimSpace(dl.SearchText())
+	if primary == "" {
+		return nil
+	}
+
+	out := []string{primary}
+
+	if dl.Query != "" {
+		return out
+	}
+
+	artist := dl.Artist
+	if isVariousArtists(artist) {
+		artist = ""
+	}
+
+	normal := Download{
+		Artist: normalizeSearchTerms(artist),
+		Album:  normalizeSearchTerms(editionPattern.ReplaceAllString(dl.Album, " ")),
+	}
+
+	if alt := strings.TrimSpace(normal.SearchText()); alt != "" &&
+		!strings.EqualFold(alt, primary) {
+		out = append(out, alt)
+	}
+
+	return out
+}
+
+var (
+	// editionPattern finds an edition qualifier: a bracketed group that
+	// names an edition, or a trailing " - 2011 Remaster".
+	editionPattern = regexp.MustCompile(
+		`(?i)\s*[(\[][^)\]]*\b(?:deluxe|edition|remaster(?:ed)?|expanded|` +
+			`anniversary|bonus|explicit|reissue|special|collector'?s?|` +
+			`version|mono|stereo)\b[^)\]]*[)\]]` +
+			`|\s+-\s+(?:\d{4}\s+)?remaster(?:ed)?\b.*$`,
+	)
+
+	// nonWordPattern is everything that is not a letter or a digit.
+	nonWordPattern = regexp.MustCompile(`[^\p{L}\p{N}]+`)
+)
+
+// normalizeSearchTerms reduces text to plain words.
+func normalizeSearchTerms(s string) string {
+	return strings.Join(strings.Fields(nonWordPattern.ReplaceAllString(s, " ")), " ")
+}
+
+// isVariousArtists reports whether an artist credit is a compilation's
+// placeholder rather than an artist.
+func isVariousArtists(artist string) bool {
+	switch strings.ToLower(strings.TrimSpace(artist)) {
+	case "various artists", "various", "va":
+		return true
+	default:
+		return false
+	}
+}
+
+// minFilesFor is the fewest audio files a folder must offer to be a
+// candidate for this request.
+//
+// Soulseek answers a search with the files that match it, not with the
+// folders they sit in.  An album query matches every file in the album's
+// folder, because the folder name carries the terms; a *track* query
+// usually matches one file per folder.  The two-file floor that filters
+// out one-file noise for an album therefore filtered out every result
+// for a track, and a single-track request could never be served here.
+func minFilesFor(dl Download) int {
+	if dl.RecordingMBID != "" {
+		return 1
+	}
+
+	return slskdMinFiles
 }
 
 // awaitSearch polls until the search completes or the budget runs out.
 // A timeout is not an error: partial Soulseek results are normal and
 // often good enough.
-func (s *slskd) awaitSearch(
-	ctx context.Context,
-	searchID string,
-) (slskdSearch, error) {
+//
+// The poll asks for the search's state only.  It used to ask for every
+// response on every one-second tick, which for a popular album is the
+// same few thousand file entries serialised twenty times to be read
+// once; searchResponses fetches them once at the end.
+func (s *slskd) awaitSearch(ctx context.Context, searchID string) error {
 	deadline := time.Now().Add(s.searchWait)
 
-	var last slskdSearch
-
 	for time.Now().Before(deadline) {
 		select {
 		case <-ctx.Done():
-			return last, fmt.Errorf("%w: search cancelled", ErrSlskdTimeout)
+			return fmt.Errorf("%w: search cancelled", ErrSlskdTimeout)
 		case <-time.After(s.searchPoll):
 		}
 
 		var search slskdSearch
 
 		if err := s.client.get(
-			ctx,
-			"/api/v0/searches/"+searchID+"?includeResponses=true",
-			&search,
+			ctx, "/api/v0/searches/"+searchID, &search,
 		); err != nil {
-			return last, err
+			return err
 		}
 
-		last = search
-
 		if search.IsComplete {
-			return search, nil
+			return nil
 		}
 	}
 
-	return last, nil
+	return nil
 }
 
-// candidatesFrom groups a search's responses into candidates.
-func (s *slskd) candidatesFrom(search slskdSearch) []Candidate {
-	out := make([]Candidate, 0, len(search.Responses))
+// searchResponses fetches a search's responses once.
+//
+// `/searches/{id}/responses` is the endpoint for that; a daemon that
+// does not answer it is asked the older way, with the search itself
+// carrying its responses, so an older slskd degrades to the previous
+// behaviour rather than to no results at all.
+func (s *slskd) searchResponses(
+	ctx context.Context,
+	searchID string,
+) ([]slskdResponse, error) {
+	var responses []slskdResponse
 
-	for _, resp := range search.Responses {
+	err := s.client.get(
+		ctx, "/api/v0/searches/"+searchID+"/responses", &responses,
+	)
+	if err == nil {
+		return responses, nil
+	}
+
+	s.logger.Debug(
+		"slskd responses endpoint failed; asking with the search",
+		"error", err,
+	)
+
+	var search slskdSearch
+
+	if err := s.client.get(
+		ctx,
+		"/api/v0/searches/"+searchID+"?includeResponses=true",
+		&search,
+	); err != nil {
+		return nil, err
+	}
+
+	return search.Responses, nil
+}
+
+// candidatesFrom groups a search's responses into candidates, dropping
+// folders with fewer than minFiles audio files.
+func (s *slskd) candidatesFrom(
+	responses []slskdResponse,
+	minFiles int,
+) []Candidate {
+	out := make([]Candidate, 0, len(responses))
+
+	for _, resp := range responses {
 		for folder, files := range groupByFolder(resp.Files) {
 			audio := 0
 
@@ -372,12 +637,14 @@ func (s *slskd) candidatesFrom(search slskdSearch) []Candidate {
 					Format:  format,
 					Bitrate: f.BitRate,
 					IsAudio: isAudio,
+
+					LengthMillis: int64(f.Length) * millisPerSecond,
 				})
 
 				total += f.Size
 			}
 
-			if audio < slskdMinFiles {
+			if audio < minFiles {
 				continue
 			}
 
@@ -398,13 +665,15 @@ func (s *slskd) candidatesFrom(search slskdSearch) []Candidate {
 	return out
 }
 
-// groupByFolder buckets a peer's files by their containing directory.
+// groupByFolder buckets a peer's files by the album directory they sit
+// in — the containing directory, or the one above it for a disc folder
+// (see AlbumDir), so a multi-disc rip is one candidate and not two.
 func groupByFolder(files []slskdFile) map[string][]slskdFile {
 	out := map[string][]slskdFile{}
 
 	for _, f := range files {
-		norm := strings.ReplaceAll(f.Filename, `\`, "/")
-		out[path.Dir(norm)] = append(out[path.Dir(norm)], f)
+		dir := AlbumDir(f.Filename)
+		out[dir] = append(out[dir], f)
 	}
 
 	return out
@@ -418,7 +687,7 @@ func groupByFolder(files []slskdFile) map[string][]slskdFile {
 func peerHealth(r slskdResponse) float64 {
 	score := 0.35
 
-	if r.HasFreeUploadSlot || r.FreeUploadSlotFlag {
+	if r.HasFreeUploadSlot {
 		score += 0.4
 	}
 
@@ -467,6 +736,21 @@ func (s *slskd) Grab(
 		)
 	}
 
+	// slskd keeps finished transfers listed until someone removes them,
+	// and a transfer is matched to the request by filename.  A record
+	// left by an earlier attempt at the same file from the same peer
+	// would otherwise be read as this attempt's answer the moment the
+	// first poll came back — an old failure failing a transfer that has
+	// not started.  So what is already terminal is noted before enqueueing
+	// and ignored after.
+	release, err := lockSlskdFolders(ctx, s.localFolders(c))
+	if err != nil {
+		return Result{}, err
+	}
+	defer release()
+
+	stale := s.terminalTransferIDs(ctx, username)
+
 	wanted := make([]map[string]any, 0, len(c.Files))
 	for _, f := range c.Files {
 		wanted = append(wanted, map[string]any{
@@ -476,24 +760,122 @@ func (s *slskd) Grab(
 	}
 
 	if err := s.client.post(
-		ctx, "/api/v0/transfers/downloads/"+username, wanted, nil,
+		ctx, slskdDownloadsPath(username), wanted, nil,
 	); err != nil {
 		return Result{}, err
 	}
 
-	if err := s.awaitTransfers(ctx, username, c, onProgress); err != nil {
+	if err := s.awaitTransfers(
+		ctx, username, stale, c, onProgress,
+	); err != nil {
 		return Result{}, err
 	}
 
 	return s.collect(c, dst)
 }
 
+// slskdFolders serialises grabs that land in the same local folder.
+//
+// slskd names a download's directory after the remote *leaf* folder, so
+// two different albums both shared as "Greatest Hits" — or any two
+// multi-disc rips, whose leaves are "CD1" and "CD2" — are written into
+// one directory, and collect finds files by name there.  Run at once,
+// a file one peer never sent is filled by the other peer's file of the
+// same name.  One grab per peer made that impossible; several peers at
+// once makes it likely.  It is package-level and keyed on the full
+// path because two configured clients can share one daemon.
+var slskdFolders keyedLock[string]
+
+// localFolders returns the directories under downloadsPath a candidate's
+// files will be written to, sorted so every grab takes them in the same
+// order and two cannot each hold what the other waits for.
+func (s *slskd) localFolders(c Candidate) []string {
+	var out []string
+
+	for _, f := range c.Files {
+		norm := strings.ReplaceAll(f.Path, `\`, "/")
+		out = append(out, filepath.Join(s.downloadsPath, path.Base(path.Dir(norm))))
+	}
+
+	slices.Sort(out)
+
+	return slices.Compact(out)
+}
+
+// lockSlskdFolders takes every folder in order, releasing what it holds
+// if the context ends part way.
+func lockSlskdFolders(ctx context.Context, folders []string) (func(), error) {
+	releases := make([]func(), 0, len(folders))
+
+	releaseAll := func() {
+		for _, r := range slices.Backward(releases) {
+			r()
+		}
+	}
+
+	for _, f := range folders {
+		r, err := slskdFolders.acquire(ctx, f)
+		if err != nil {
+			releaseAll()
+
+			return nil, err
+		}
+
+		releases = append(releases, r)
+	}
+
+	return releaseAll, nil
+}
+
+// slskdDownloadsPath is the transfers endpoint for one peer.  Soulseek
+// usernames may contain spaces and punctuation, so the name is escaped
+// rather than spliced into the path.
+func slskdDownloadsPath(username string) string {
+	return "/api/v0/transfers/downloads/" + url.PathEscape(username)
+}
+
+// terminalTransferIDs returns the ids of this peer's transfers that are
+// already finished.  Best effort: slskd answers 404 for a peer it has no
+// transfers with, and any failure here means only that there is nothing
+// to ignore.
+func (s *slskd) terminalTransferIDs(
+	ctx context.Context,
+	username string,
+) map[string]bool {
+	transfers, err := s.transfersFor(ctx, username)
+	if err != nil {
+		return nil
+	}
+
+	out := make(map[string]bool, len(transfers))
+
+	for _, t := range transfers {
+		if finished, _ := t.done(); finished && t.ID != "" {
+			out[t.ID] = true
+		}
+	}
+
+	return out
+}
+
 // awaitTransfers polls until every requested file reaches a terminal
-// state.  Soulseek queues are measured in hours, so the only deadline
-// is the caller's context.
+// state, the transfer stalls, or the caller gives up.
+//
+// Soulseek queues are measured in hours, so there is no deadline on the
+// transfer as a whole — but there is one on *progress*.  slskd's
+// transfer limit is one, so a peer that holds us in its queue without
+// sending a byte is not only failing this download, it is holding every
+// other Soulseek download behind it.  After stallAfter with nothing
+// moving the peer is given up on, and the manager tries another.
+//
+// Whatever way this ends short of every file finishing, the transfers
+// still live in slskd are cancelled there.  Returning without doing so
+// leaves the daemon downloading into its own folder for a request
+// nobody is waiting on any more.
 func (s *slskd) awaitTransfers(
 	ctx context.Context,
 	username string,
+	stale map[string]bool,
 	c Candidate,
 	onProgress ProgressFunc,
 ) error {
@@ -502,9 +884,18 @@ func (s *slskd) awaitTransfers(
 		wanted[f.Path] = true
 	}
 
+	var (
+		started      = time.Now()
+		lastProgress = started
+		lastBytes    int64
+		live         []slskdTransfer
+	)
+
 	for {
 		select {
 		case <-ctx.Done():
+			s.cancelTransfers(username, live)
+
 			return fmt.Errorf("%w: transfer cancelled", ErrSlskdTimeout)
 		case <-time.After(s.transferPoll):
 		}
@@ -512,60 +903,177 @@ func (s *slskd) awaitTransfers(
 		transfers, err := s.transfersFor(ctx, username)
 		if err != nil {
 			// A blip talking to the daemon should not abandon a
-			// transfer that may be hours in.
+			// transfer that may be hours in — but a daemon that stays
+			// away is a stall like any other.
 			s.logger.Debug("slskd transfer poll failed", "error", err)
 
+			if time.Since(lastProgress) >= s.stallAfter {
+				s.cancelTransfers(username, live)
+
+				return fmt.Errorf(
+					"%w: slskd has not answered for %s: %w",
+					ErrSlskdTimeout, s.stallAfter, err,
+				)
+			}
+
 			continue
 		}
 
-		var (
-			done, failed int
-			current      int64
+		tally := tallyTransfers(
+			transfers, wanted, stale,
+			time.Since(started) >= s.absentGrace,
 		)
+		live = tally.live
 
-		for _, t := range transfers {
-			if !wanted[t.Filename] {
-				continue
-			}
-
-			current += t.BytesTransferred
-
-			finished, ok := t.done()
-			if !finished {
-				continue
-			}
-
-			if ok {
-				done++
-			} else {
-				failed++
-			}
+		if tally.bytes > lastBytes {
+			lastBytes = tally.bytes
+			lastProgress = time.Now()
 		}
 
 		if onProgress != nil {
 			onProgress(Progress{
-				Current: current,
+				Current: tally.bytes,
 				Total:   c.TotalSize,
 				Phase: fmt.Sprintf(
-					"Transferring from %s (%d/%d)", username, done, len(wanted),
+					"Transferring from %s (%d/%d)",
+					username, tally.done, len(wanted),
 				),
 			})
 		}
 
-		if done+failed < len(wanted) {
+		if tally.done+tally.failed >= len(wanted) {
+			// Some files failing is normal — a peer goes offline
+			// mid-folder.  Let the importer's completeness check decide
+			// whether what arrived is enough, rather than discarding it
+			// here.
+			if tally.done == 0 {
+				return fmt.Errorf(
+					"%w: all %d files failed",
+					ErrSlskdTransferFailed, tally.failed,
+				)
+			}
+
+			return nil
+		}
+
+		if time.Since(lastProgress) < s.stallAfter {
 			continue
 		}
 
-		// Some files failing is normal — a peer goes offline mid-folder.
-		// Let the importer's completeness check decide whether what
-		// arrived is enough, rather than discarding it here.
-		if done == 0 {
-			return fmt.Errorf(
-				"%w: all %d files failed", ErrSlskdTransferFailed, failed,
+		s.cancelTransfers(username, live)
+
+		// A folder that stalls on its last track is the same shape as
+		// one whose last track failed, and goes forward the same way.
+		if tally.done > 0 {
+			s.logger.Info(
+				"slskd transfer stalled; keeping what arrived",
+				"peer", username,
+				"done", tally.done,
+				"wanted", len(wanted),
 			)
+
+			return nil
 		}
 
-		return nil
+		return fmt.Errorf(
+			"%w: %s sent nothing in %s",
+			ErrSlskdTimeout, username, s.stallAfter,
+		)
+	}
+}
+
+// transferTally is one poll's reading of the files a grab asked for.
+type transferTally struct {
+	done, failed int
+	bytes        int64
+
+	// live are the requested transfers slskd is still working on,
+	// which are what has to be cancelled if the grab is abandoned.
+	live []slskdTransfer
+}
+
+// tallyTransfers reads a peer's transfer list against the files a grab
+// asked for.
+//
+// A requested file slskd does not list at all is one it never accepted
+// — refused at enqueue, or dropped — and it will never reach a terminal
+// state to be counted by.  Once absentExpired, such a file counts as
+// failed, or the grab would wait on it until the six-hour ceiling.
+func tallyTransfers(
+	transfers []slskdTransfer,
+	wanted map[string]bool,
+	stale map[string]bool,
+	absentExpired bool,
+) transferTally {
+	seen := make(map[string]slskdTransfer, len(wanted))
+
+	for _, t := range transfers {
+		if !wanted[t.Filename] || stale[t.ID] {
+			continue
+		}
+
+		seen[t.Filename] = t
+	}
+
+	var out transferTally
+
+	for name := range wanted {
+		t, ok := seen[name]
+		if !ok {
+			if absentExpired {
+				out.failed++
+			}
+
+			continue
+		}
+
+		out.bytes += t.BytesTransferred
+
+		finished, succeeded := t.done()
+
+		switch {
+		case !finished:
+			out.live = append(out.live, t)
+		case succeeded:
+			out.done++
+		default:
+			out.failed++
+		}
+	}
+
+	return out
+}
+
+// cancelTransfers asks slskd to cancel and forget transfers this grab
+// is abandoning.  It runs on a context of its own: the usual reason to
+// be here is that the caller's context has just been cancelled, and a
+// cleanup that inherited it would never be sent.
+func (s *slskd) cancelTransfers(username string, live []slskdTransfer) {
+	if len(live) == 0 {
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(
+		context.Background(), slskdCancelTimeout,
+	)
+	defer cancel()
+
+	for _, t := range live {
+		if t.ID == "" {
+			continue
+		}
+
+		endpoint := slskdDownloadsPath(username) + "/" +
+			url.PathEscape(t.ID) + "?remove=true"
+
+		if err := s.client.delete(ctx, endpoint); err != nil {
+			s.logger.Warn(
+				"could not cancel slskd transfer",
+				"peer", username,
+				"file", t.Filename,
+				"error", err,
+			)
+		}
 	}
 }
 
@@ -581,9 +1089,7 @@ func (s *slskd) transfersFor(
 		} `json:"directories"`
 	}
 
-	if err := s.client.get(
-		ctx, "/api/v0/transfers/downloads/"+username, &raw,
-	); err != nil {
+	if err := s.client.get(ctx, slskdDownloadsPath(username), &raw); err != nil {
 		return nil, err
 	}
 
@@ -616,7 +1122,13 @@ func (s *slskd) collect(c Candidate, dst string) (Result, error) {
 			continue
 		}
 
+		// A multi-disc candidate keeps its disc folders in staging.
+		// Flattened, disc 2's "01 Intro.flac" overwrites disc 1's, and
+		// the importer loses the folder it reads the disc number from.
 		target := filepath.Join(dst, base)
+		if _, ok := discFolder(folder); ok {
+			target = filepath.Join(dst, folder, base)
+		}
 
 		if err := movePath(src, target); err != nil {
 			return Result{}, fmt.Errorf("collect %s: %w", base, err)

backend/download/provider_slskd_test.go

@@ -31,11 +31,30 @@ type slskdStub struct {
 	transfers [][]slskdTransfer
 	pollCount int
 
+	// before is what the downloads endpoint reports until something is
+	// enqueued: records slskd already held from earlier attempts.
+	before []slskdTransfer
+
 	// enqueued records what was requested for download.
 	enqueued []map[string]any
+	posted   bool
+
+	// paths records the escaped path of every transfers call, and
+	// cancelled the escaped request URI of every DELETE.
+	paths     []string
+	cancelled []string
 
 	// unauthorized makes every call return 401.
 	unauthorized bool
+
+	// searches records every search request body, and searchGets the
+	// request URI of every search GET.
+	searches   []map[string]any
+	searchGets []string
+
+	// noResponsesEndpoint makes /searches/{id}/responses 404, as an
+	// older daemon would.
+	noResponsesEndpoint bool
 }
 
 func newSlskdStub(t *testing.T) *slskdStub {
@@ -57,6 +76,16 @@ func newSlskdStub(t *testing.T) *slskdStub {
 			return
 		}
 
+		var body map[string]any
+
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			t.Errorf("decode search body: %v", err)
+		}
+
+		s.mu.Lock()
+		s.searches = append(s.searches, body)
+		s.mu.Unlock()
+
 		w.WriteHeader(http.StatusCreated)
 	})
 
@@ -73,8 +102,26 @@ func newSlskdStub(t *testing.T) *slskdStub {
 
 		s.mu.Lock()
 		responses := s.responses
+		noEndpoint := s.noResponsesEndpoint
+		s.searchGets = append(s.searchGets, r.URL.RequestURI())
 		s.mu.Unlock()
 
+		if strings.HasSuffix(r.URL.Path, "/responses") {
+			if noEndpoint {
+				w.WriteHeader(http.StatusNotFound)
+
+				return
+			}
+
+			writeJSON(t, w, responses)
+
+			return
+		}
+
+		if r.URL.Query().Get("includeResponses") != "true" {
+			responses = nil
+		}
+
 		writeJSON(t, w, slskdSearch{
 			ID:         "search-1",
 			IsComplete: true,
@@ -87,7 +134,12 @@ func newSlskdStub(t *testing.T) *slskdStub {
 			return
 		}
 
-		if r.Method == http.MethodPost {
+		s.mu.Lock()
+		s.paths = append(s.paths, r.URL.EscapedPath())
+		s.mu.Unlock()
+
+		switch r.Method {
+		case http.MethodPost:
 			var body []map[string]any
 
 			if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
@@ -96,15 +148,35 @@ func newSlskdStub(t *testing.T) *slskdStub {
 
 			s.mu.Lock()
 			s.enqueued = body
+			s.posted = true
 			s.mu.Unlock()
 
 			w.WriteHeader(http.StatusCreated)
 
+			return
+		case http.MethodDelete:
+			s.mu.Lock()
+			s.cancelled = append(s.cancelled, r.URL.RequestURI())
+			s.mu.Unlock()
+
+			w.WriteHeader(http.StatusNoContent)
+
 			return
 		}
 
 		s.mu.Lock()
 
+		if !s.posted {
+			before := s.before
+			s.mu.Unlock()
+
+			writeJSON(t, w, map[string]any{
+				"directories": []map[string]any{{"files": before}},
+			})
+
+			return
+		}
+
 		idx := s.pollCount
 		if idx >= len(s.transfers) {
 			idx = len(s.transfers) - 1
@@ -191,6 +263,11 @@ func newStubSlskd(t *testing.T, stub *slskdStub) (*slskd, string) {
 	s.searchWait = 200 * time.Millisecond
 	s.transferPoll = time.Millisecond
 
+	// Long enough that no existing test trips them by accident; the
+	// tests about stalls and absences set their own.
+	s.stallAfter = time.Minute
+	s.absentGrace = time.Minute
+
 	return s, downloads
 }
 
@@ -565,3 +642,293 @@ func TestSlskdRequiresConfiguration(t *testing.T) {
 		})
 	}
 }
+
+// slskdAlbum is a two-file candidate from peer, with the files slskd
+// would have written already in place under downloads.
+func slskdAlbum(t *testing.T, downloads, peer string, arrived ...string) Candidate {
+	t.Helper()
+
+	folder := filepath.Join(downloads, "Album")
+	if err := os.MkdirAll(folder, 0o750); err != nil {
+		t.Fatalf("mkdir: %v", err)
+	}
+
+	for _, name := range arrived {
+		if err := os.WriteFile(
+			filepath.Join(folder, name), []byte("audio"), 0o600,
+		); err != nil {
+			t.Fatalf("write: %v", err)
+		}
+	}
+
+	return Candidate{
+		Files: []CandidateFile{
+			{Path: `\s\Album\01 A.flac`, Size: 500, IsAudio: true},
+			{Path: `\s\Album\02 B.flac`, Size: 500, IsAudio: true},
+		},
+		TotalSize: 1000,
+		Payload:   map[string]string{"username": peer},
+	}
+}
+
+// cancelledURIs returns what the stub was asked to cancel.
+func (s *slskdStub) cancelledURIs() []string {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	return append([]string(nil), s.cancelled...)
+}
+
+// A peer that queues us and never sends a byte is given up on, and the
+// queued transfers are cancelled in slskd rather than left to start
+// hours later for a request nobody is waiting on.
+func TestSlskdGrabGivesUpOnAStalledPeer(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.transfers = [][]slskdTransfer{{
+		{ID: "t1", Filename: `\s\Album\01 A.flac`, State: "Queued, Remotely"},
+		{ID: "t2", Filename: `\s\Album\02 B.flac`, State: "Queued, Remotely"},
+	}}
+
+	s, downloads := newStubSlskd(t, stub)
+	s.stallAfter = 30 * time.Millisecond
+
+	_, err := s.Grab(
+		context.Background(), slskdAlbum(t, downloads, "peer"), t.TempDir(), nil,
+	)
+	if !errors.Is(err, ErrSlskdTimeout) {
+		t.Fatalf("error = %v, want ErrSlskdTimeout", err)
+	}
+
+	got := stub.cancelledURIs()
+	if len(got) != 2 {
+		t.Fatalf("cancelled %v, want both queued transfers", got)
+	}
+
+	for _, uri := range got {
+		if !strings.HasSuffix(uri, "?remove=true") {
+			t.Errorf("cancel %s does not remove the record", uri)
+		}
+	}
+}
+
+// A folder that stalls on its last track goes forward with what
+// arrived, the same as one whose last track failed; the importer's
+// completeness check decides whether that is enough.
+func TestSlskdGrabKeepsWhatArrivedBeforeAStall(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.transfers = [][]slskdTransfer{{
+		{
+			ID: "t1", Filename: `\s\Album\01 A.flac`,
+			State: "Completed, Succeeded", BytesTransferred: 500,
+		},
+		{ID: "t2", Filename: `\s\Album\02 B.flac`, State: "Queued, Remotely"},
+	}}
+
+	s, downloads := newStubSlskd(t, stub)
+	s.stallAfter = 30 * time.Millisecond
+
+	got, err := s.Grab(
+		context.Background(),
+		slskdAlbum(t, downloads, "peer", "01 A.flac"),
+		t.TempDir(), nil,
+	)
+	if err != nil {
+		t.Fatalf("Grab: %v", err)
+	}
+
+	if len(got.Files) != 1 {
+		t.Errorf("collected %d files, want the 1 that arrived", len(got.Files))
+	}
+
+	if cancelled := stub.cancelledURIs(); len(cancelled) != 1 ||
+		!strings.Contains(cancelled[0], "/t2") {
+		t.Errorf("cancelled %v, want only the stalled t2", cancelled)
+	}
+}
+
+// Progress is what holds the stall timer off.  A transfer that keeps
+// moving bytes is never abandoned, however long it takes.
+func TestSlskdGrabWaitsOnATransferThatIsMoving(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+
+	for b := int64(1); b <= 100; b++ {
+		stub.transfers = append(stub.transfers, []slskdTransfer{
+			{ID: "t1", Filename: `\s\Album\01 A.flac`, State: "InProgress", BytesTransferred: b},
+			{ID: "t2", Filename: `\s\Album\02 B.flac`, State: "Queued, Remotely"},
+		})
+	}
+
+	stub.transfers = append(stub.transfers, []slskdTransfer{
+		{
+			ID:               "t1",
+			Filename:         `\s\Album\01 A.flac`,
+			State:            "Completed, Succeeded",
+			BytesTransferred: 500,
+		},
+		{
+			ID:               "t2",
+			Filename:         `\s\Album\02 B.flac`,
+			State:            "Completed, Succeeded",
+			BytesTransferred: 500,
+		},
+	})
+
+	s, downloads := newStubSlskd(t, stub)
+	// A hundred polls take several times the stall window; each one
+	// moves a byte.  The window is kept well above one poll so a
+	// descheduled test runner does not read as a stall.
+	s.transferPoll = 5 * time.Millisecond
+	s.stallAfter = 150 * time.Millisecond
+
+	got, err := s.Grab(
+		context.Background(),
+		slskdAlbum(t, downloads, "peer", "01 A.flac", "02 B.flac"),
+		t.TempDir(), nil,
+	)
+	if err != nil {
+		t.Fatalf("Grab: %v", err)
+	}
+
+	if len(got.Files) != 2 {
+		t.Errorf("collected %d files, want 2", len(got.Files))
+	}
+}
+
+// A file slskd never lists was refused at enqueue and will never reach
+// a terminal state.  It counts as failed once the grace period is up,
+// rather than being waited on until the six-hour ceiling.
+func TestSlskdGrabCountsAnUnlistedFileAsFailed(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.transfers = [][]slskdTransfer{{
+		{
+			ID: "t1", Filename: `\s\Album\01 A.flac`,
+			State: "Completed, Succeeded", BytesTransferred: 500,
+		},
+	}}
+
+	s, downloads := newStubSlskd(t, stub)
+	s.absentGrace = 20 * time.Millisecond
+
+	got, err := s.Grab(
+		context.Background(),
+		slskdAlbum(t, downloads, "peer", "01 A.flac"),
+		t.TempDir(), nil,
+	)
+	if err != nil {
+		t.Fatalf("Grab: %v", err)
+	}
+
+	if len(got.Files) != 1 {
+		t.Errorf("collected %d files, want 1", len(got.Files))
+	}
+}
+
+// A finished record left by an earlier attempt at the same file is not
+// this attempt's answer.  Without the snapshot it would fail the grab on
+// the first poll, before the new transfer had started.
+func TestSlskdGrabIgnoresAnEarlierAttemptsRecord(t *testing.T) {
+	t.Parallel()
+
+	stale := slskdTransfer{
+		ID: "old", Filename: `\s\Album\01 A.flac`, State: "Completed, Errored",
+	}
+
+	stub := newSlskdStub(t)
+	stub.before = []slskdTransfer{stale}
+	stub.transfers = [][]slskdTransfer{
+		{stale},
+		{
+			stale,
+			{
+				ID: "new", Filename: `\s\Album\01 A.flac`,
+				State: "Completed, Succeeded", BytesTransferred: 500,
+			},
+		},
+	}
+
+	s, downloads := newStubSlskd(t, stub)
+
+	c := slskdAlbum(t, downloads, "peer", "01 A.flac")
+	c.Files = c.Files[:1]
+
+	got, err := s.Grab(context.Background(), c, t.TempDir(), nil)
+	if err != nil {
+		t.Fatalf("Grab: %v", err)
+	}
+
+	if len(got.Files) != 1 {
+		t.Errorf("collected %d files, want 1", len(got.Files))
+	}
+}
+
+// Cancelling the download cancels the transfer in slskd too.  The
+// cleanup must not inherit the cancelled context, or it is never sent.
+func TestSlskdGrabCancelsTransfersWhenTheCallerGivesUp(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.transfers = [][]slskdTransfer{{
+		{ID: "t1", Filename: `\s\Album\01 A.flac`, State: "InProgress", BytesTransferred: 10},
+		{ID: "t2", Filename: `\s\Album\02 B.flac`, State: "Queued, Remotely"},
+	}}
+
+	s, downloads := newStubSlskd(t, stub)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancel()
+
+	_, err := s.Grab(ctx, slskdAlbum(t, downloads, "peer"), t.TempDir(), nil)
+	if !errors.Is(err, ErrSlskdTimeout) {
+		t.Fatalf("error = %v, want ErrSlskdTimeout", err)
+	}
+
+	if got := stub.cancelledURIs(); len(got) != 2 {
+		t.Errorf("cancelled %v, want both live transfers", got)
+	}
+}
+
+// Soulseek usernames carry spaces and punctuation; spliced raw into the
+// path, a name with a slash addresses a different endpoint entirely.
+func TestSlskdEscapesTheUsername(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.transfers = [][]slskdTransfer{{
+		{
+			ID: "t1", Filename: `\s\Album\01 A.flac`,
+			State: "Completed, Succeeded", BytesTransferred: 500,
+		},
+		{
+			ID: "t2", Filename: `\s\Album\02 B.flac`,
+			State: "Completed, Succeeded", BytesTransferred: 500,
+		},
+	}}
+
+	s, downloads := newStubSlskd(t, stub)
+
+	if _, err := s.Grab(
+		context.Background(),
+		slskdAlbum(t, downloads, "dj a/b", "01 A.flac", "02 B.flac"),
+		t.TempDir(), nil,
+	); err != nil {
+		t.Fatalf("Grab: %v", err)
+	}
+
+	stub.mu.Lock()
+	paths := append([]string(nil), stub.paths...)
+	stub.mu.Unlock()
+
+	for _, p := range paths {
+		if p != "/api/v0/transfers/downloads/dj%20a%2Fb" {
+			t.Errorf("transfers call went to %s", p)
+		}
+	}
+}

backend/download/rank.go

@@ -35,6 +35,15 @@ const (
 	weightArtistFit    = 0.12
 )
 
+// Match sub-weights when the candidate's durations are known.  Duration
+// takes its weight from title fit, the signal it corroborates: a title
+// says which song a file claims to be, a length says whether it is that
+// recording — the right edit, the whole file, not the live take.
+const (
+	timedWeightTitleFit    = 0.25
+	timedWeightDurationFit = 0.15
+)
+
 // Quality sub-weights.  Each set sums to 1.0.
 //
 // There are two of them because a stated preference changes what the
@@ -319,13 +328,13 @@ func Score(dl Download, c Candidate, priority int, prefs AutoDownloadPrefs) Cand
 
 	audio := c.AudioFiles()
 
-	matched, titleFit := matchFiles(audio, dl.Expected)
+	a := alignFiles(audio, dl.Expected)
 
 	// Write the alignment back so the picker can show which file maps
 	// to which track.
-	c.Files = mergeMatched(c.Files, matched)
+	c.Files = mergeMatched(c.Files, a.files)
 
-	c.Match = scoreMatch(dl, c, audio, titleFit)
+	c.Match = scoreMatch(dl, c, audio, a)
 	c.Quality = scoreQuality(
 		c, audio, priority, prefs, dl.runtimeMillis(),
 	)
@@ -340,14 +349,21 @@ func scoreMatch(
 	dl Download,
 	c Candidate,
 	audio []CandidateFile,
-	titleFit float64,
+	a alignment,
 ) MatchScore {
 	m := MatchScore{
-		Anchored: dl.Anchored(),
-		TitleFit: titleFit,
+		Anchored:    dl.Anchored(),
+		TitleFit:    a.titleFit,
+		DurationFit: a.durationFit,
+
+		// Durations count once at least half the aligned pairs state
+		// one; a single timed pair would be a coin toss carrying 15%.
+		DurationKnown: a.timedPairs > 0 && a.timedPairs*2 >= a.aligned,
 	}
 
-	m.Completeness = completeness(len(audio), len(dl.Expected))
+	m.Completeness = completeness(
+		alignedCount(c.Files), len(audio), len(dl.Expected),
+	)
 
 	// The candidate's own title, and the folder its files sit in, are
 	// two independent guesses at the album name.  Take the better one:
@@ -367,9 +383,16 @@ func scoreMatch(
 	// With no expected tracklist there is no title signal at all, so
 	// redistribute its weight onto the album/artist evidence rather
 	// than scoring every free-text result as half-wrong.
-	if len(dl.Expected) == 0 {
+	switch {
+	case len(dl.Expected) == 0:
 		m.Overall = 0.55*m.AlbumFit + 0.45*m.ArtistFit
-	} else {
+	case m.DurationKnown:
+		m.Overall = timedWeightTitleFit*m.TitleFit +
+			timedWeightDurationFit*m.DurationFit +
+			weightCompleteness*m.Completeness +
+			weightAlbumFit*m.AlbumFit +
+			weightArtistFit*m.ArtistFit
+	default:
 		m.Overall = weightTitleFit*m.TitleFit +
 			weightCompleteness*m.Completeness +
 			weightAlbumFit*m.AlbumFit +
@@ -415,30 +438,54 @@ func artistFit(want string, c Candidate) float64 {
 	return best
 }
 
-// completeness scores audio file count against the expected track
-// count.  Extra files are penalized far more gently than missing ones:
+// completeness scores how much of the expected tracklist a candidate
+// covers.  Extra files are penalized far more gently than missing ones:
 // a folder with bonus tracks or a stray intro is still the album, while
 // a folder missing half the tracks is not.
-func completeness(got, want int) float64 {
+//
+// **Coverage is counted in aligned tracks, not in files.**  It used to
+// be the audio file count, so any ten files scored full marks against
+// a ten-track album whether or not they were its tracks — and since
+// title fit is the mean over the files that *did* align, a folder where
+// three titles matched read as a near-perfect candidate on both counts.
+// `aligned` is how many files matchFiles assigned to an expected track;
+// `audio` still sets the penalty for extras, because a folder of thirty
+// files holding the ten wanted is a worse copy than one holding ten.
+func completeness(aligned, audio, want int) float64 {
 	if want == 0 {
-		if got > 0 {
+		if audio > 0 {
 			return 0.5
 		}
 
 		return 0
 	}
 
-	if got == 0 {
+	if aligned == 0 {
 		return 0
 	}
 
-	if got >= want {
-		extra := float64(got-want) / float64(want)
+	cover := float64(min(aligned, want)) / float64(want)
 
-		return math.Max(0.75, 1.0-0.25*extra)
+	if audio > want {
+		extra := float64(audio-want) / float64(want)
+		cover *= math.Max(0.75, 1.0-0.25*extra)
 	}
 
-	return float64(got) / float64(want)
+	return cover
+}
+
+// alignedCount is how many audio files were assigned to an expected
+// track.
+func alignedCount(files []CandidateFile) int {
+	n := 0
+
+	for _, f := range files {
+		if f.IsAudio && f.MatchedTo != 0 {
+			n++
+		}
+	}
+
+	return n
 }
 
 // scoreQuality answers whether this is a good copy.
@@ -735,6 +782,45 @@ func AutoPickVeto(
 	return ""
 }
 
+// autoAcceptable reports whether auto-pick may take this one candidate
+// without asking: the request is anchored to a tracklist, and the
+// candidate is inside the user's guardrails and clears the match and
+// quality bars.  It is AutoPickVeto's test applied to a single
+// candidate, which is what falling back to a second choice needs.
+func autoAcceptable(dl Download, c Candidate, prefs AutoDownloadPrefs) bool {
+	return dl.Anchored() &&
+		len(dl.Expected) > 0 &&
+		prefs.eligible(c, dl.runtimeMillis()) &&
+		c.Match.Overall >= minMatch &&
+		c.Quality.Overall >= minQuality
+}
+
+// autoPick returns the candidate auto-pick takes: the best-ranked one
+// it may take at all.
+//
+// That is not `ranked[0]`.  AutoPickVeto judges the best candidate
+// *inside* the guardrails, so when the overall best is outside them —
+// over the size ceiling, say — the veto passes on the strength of the
+// second, and grabbing the first would download exactly the copy the
+// user said not to take unattended.
+func autoPick(
+	dl Download,
+	ranked []Candidate,
+	prefs AutoDownloadPrefs,
+) (Candidate, bool) {
+	if AutoPickVeto(dl, ranked, prefs) != "" {
+		return Candidate{}, false
+	}
+
+	for _, c := range ranked {
+		if autoAcceptable(dl, c, prefs) {
+			return c, true
+		}
+	}
+
+	return Candidate{}, false
+}
+
 // mergeMatched copies MatchedTo assignments from the audio-only slice
 // back onto the full file list.
 func mergeMatched(all, matched []CandidateFile) []CandidateFile {

backend/download/rank_test.go

@@ -282,28 +282,32 @@ func TestCompleteness(t *testing.T) {
 
 	tests := []struct {
 		name     string
-		got      int
+		aligned  int
+		audio    int
 		want     int
 		minScore float64
 		maxScore float64
 	}{
-		{"exact", 10, 10, 1.0, 1.0},
-		{"half missing", 5, 10, 0.49, 0.51},
-		{"one bonus track", 11, 10, 0.95, 1.0},
-		{"double", 20, 10, 0.74, 0.76},
-		{"nothing", 0, 10, 0, 0},
-		{"no expectation", 5, 0, 0.5, 0.5},
+		{"exact", 10, 10, 10, 1.0, 1.0},
+		{"half missing", 5, 5, 10, 0.49, 0.51},
+		{"one bonus track", 10, 11, 10, 0.95, 1.0},
+		{"double", 10, 20, 10, 0.74, 0.76},
+		{"nothing", 0, 0, 10, 0, 0},
+		{"no expectation", 0, 5, 0, 0.5, 0.5},
+		// Ten files are not ten tracks: three that align are three.
+		{"right count, wrong tracks", 3, 10, 10, 0.29, 0.31},
+		{"files that align to nothing", 0, 10, 10, 0, 0},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
 
-			got := completeness(tt.got, tt.want)
+			got := completeness(tt.aligned, tt.audio, tt.want)
 			if got < tt.minScore || got > tt.maxScore {
 				t.Errorf(
-					"completeness(%d, %d) = %f, want in [%f, %f]",
-					tt.got, tt.want, got, tt.minScore, tt.maxScore,
+					"completeness(%d, %d, %d) = %f, want in [%f, %f]",
+					tt.aligned, tt.audio, tt.want, got, tt.minScore, tt.maxScore,
 				)
 			}
 		})

backend/download/search_recall_test.go

@@ -0,0 +1,238 @@
+package download
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+// What Soulseek is asked, how, and what is kept from the answer (#271).
+
+func TestSlskdQueries(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name string
+		dl   Download
+		want []string
+	}{
+		{
+			name: "a plain request is searched once",
+			dl:   Download{Artist: "Radiohead", Album: "OK Computer"},
+			want: []string{"Radiohead OK Computer"},
+		},
+		{
+			name: "an edition qualifier gets a second query without it",
+			dl:   Download{Artist: "Radiohead", Album: "OK Computer (Collector's Edition)"},
+			want: []string{
+				"Radiohead OK Computer (Collector's Edition)",
+				"Radiohead OK Computer",
+			},
+		},
+		{
+			name: "a trailing remaster note",
+			dl:   Download{Artist: "Pink Floyd", Album: "Animals - 2018 Remaster"},
+			want: []string{
+				"Pink Floyd Animals - 2018 Remaster",
+				"Pink Floyd Animals",
+			},
+		},
+		{
+			name: "a leading dash would be an exclusion",
+			dl:   Download{Artist: "Mocky", Album: "-ism"},
+			want: []string{"Mocky -ism", "Mocky ism"},
+		},
+		{
+			name: "a compilation is not searched by its placeholder artist",
+			dl:   Download{Artist: "Various Artists", Album: "Pulp Fiction"},
+			want: []string{"Various Artists Pulp Fiction", "Pulp Fiction"},
+		},
+		{
+			name: "what the user typed is searched as written",
+			dl:   Download{Query: "ok computer (deluxe)", Album: "OK Computer (Deluxe)"},
+			want: []string{"ok computer (deluxe)"},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			got := slskdQueries(tc.dl)
+			if strings.Join(got, "|") != strings.Join(tc.want, "|") {
+				t.Errorf("slskdQueries = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+// Both queries run, the options are stated rather than left to the
+// daemon's defaults, and a folder both queries found is one candidate.
+func TestSlskdSearchRunsBothQueriesAndMerges(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.responses = []slskdResponse{{
+		Username: "peer",
+		Files: []slskdFile{
+			{Filename: `\m\Radiohead - OK Computer\01 Airbag.flac`, Size: 1, Length: 284},
+			{Filename: `\m\Radiohead - OK Computer\02 Paranoid Android.flac`, Size: 1, Length: 383},
+		},
+	}}
+
+	s, _ := newStubSlskd(t, stub)
+
+	got, err := s.Search(context.Background(), Download{
+		ReleaseMBID: "rel", Artist: "Radiohead", Album: "OK Computer (Deluxe Edition)",
+	})
+	if err != nil {
+		t.Fatalf("Search: %v", err)
+	}
+
+	if len(got) != 1 {
+		t.Fatalf("got %d candidates, want the one folder once", len(got))
+	}
+
+	if got[0].Files[0].LengthMillis != 284_000 {
+		t.Errorf("length = %d ms, want 284000 from slskd's seconds", got[0].Files[0].LengthMillis)
+	}
+
+	stub.mu.Lock()
+	searches := append([]map[string]any(nil), stub.searches...)
+	gets := append([]string(nil), stub.searchGets...)
+	stub.mu.Unlock()
+
+	if len(searches) != 2 {
+		t.Fatalf("ran %d searches, want 2", len(searches))
+	}
+
+	for _, body := range searches {
+		for _, key := range []string{
+			"searchTimeout", "responseLimit", "fileLimit",
+			"minimumResponseFileCount", "maximumPeerQueueLength",
+		} {
+			if _, ok := body[key]; !ok {
+				t.Errorf("search %q does not state %s", body["searchText"], key)
+			}
+		}
+	}
+
+	// The responses are fetched once at the end, not with every poll.
+	for _, uri := range gets {
+		if strings.Contains(uri, "includeResponses") {
+			t.Errorf("poll %s asked for every response", uri)
+		}
+	}
+}
+
+// A daemon without the responses endpoint still returns results.
+func TestSlskdSearchFallsBackForAnOlderDaemon(t *testing.T) {
+	t.Parallel()
+
+	stub := newSlskdStub(t)
+	stub.noResponsesEndpoint = true
+	stub.responses = []slskdResponse{{
+		Username: "peer",
+		Files: []slskdFile{
+			{Filename: `\m\Album\01 A.flac`, Size: 1},
+			{Filename: `\m\Album\02 B.flac`, Size: 1},
+		},
+	}}
+
+	s, _ := newStubSlskd(t, stub)
+
+	got, err := s.Search(context.Background(), Download{Query: "album"})
+	if err != nil {
+		t.Fatalf("Search: %v", err)
+	}
+
+	if len(got) != 1 {
+		t.Errorf("got %d candidates, want 1 through the fallback", len(got))
+	}
+}
+
+func TestDurationAgreement(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		got, want int64
+		score     float64
+	}{
+		{300_000, 300_000, 1},
+		{301_500, 300_000, 1}, // a second of silence
+		{300_000, 316_500, 0.5},
+		{300_000, 345_000, 0}, // a different edit
+	}
+
+	for _, tc := range cases {
+		if got := durationAgreement(tc.got, tc.want); got < tc.score-0.01 || got > tc.score+0.01 {
+			t.Errorf("durationAgreement(%d, %d) = %f, want %f", tc.got, tc.want, got, tc.score)
+		}
+	}
+}
+
+// Two folders with the same track names are told apart by their
+// lengths: one is the album, the other a live record of the same songs.
+func TestDurationsSeparateTheRightRecording(t *testing.T) {
+	t.Parallel()
+
+	dl := okComputer()
+
+	timed := func(id string, lengths ...int64) Candidate {
+		c := candidateFor(id, allTitles(), ".flac", 30_000_000)
+		for i := range c.Files {
+			c.Files[i].LengthMillis = lengths[i]
+		}
+
+		return c
+	}
+
+	studio := timed("studio", trackMillis, trackMillis+1_000, trackMillis, trackMillis-500)
+	live := timed(
+		"live",
+		trackMillis+60_000,
+		trackMillis+75_000,
+		trackMillis+50_000,
+		trackMillis+90_000,
+	)
+
+	ranked := Rank(dl, []Candidate{live, studio}, nil, AutoDownloadPrefs{})
+
+	if ranked[0].ID != "studio" {
+		t.Fatalf("winner = %s, want the recording whose lengths match", ranked[0].ID)
+	}
+
+	if !ranked[0].Match.DurationKnown || ranked[0].Match.DurationFit < 0.99 {
+		t.Errorf(
+			"studio duration fit = %f known=%v",
+			ranked[0].Match.DurationFit,
+			ranked[0].Match.DurationKnown,
+		)
+	}
+
+	if ranked[1].Match.DurationFit != 0 {
+		t.Errorf("live duration fit = %f, want 0", ranked[1].Match.DurationFit)
+	}
+}
+
+// Without lengths the score is exactly what it was before durations
+// were read, so a provider that reports none is not penalised.
+func TestUnknownDurationsLeaveTheScoreAlone(t *testing.T) {
+	t.Parallel()
+
+	dl := okComputer()
+	c := Score(dl, candidateFor("c", allTitles(), ".flac", 30_000_000), 50, AutoDownloadPrefs{})
+
+	if c.Match.DurationKnown {
+		t.Fatal("no file states a length, yet durations are known")
+	}
+
+	want := weightTitleFit*c.Match.TitleFit +
+		weightCompleteness*c.Match.Completeness +
+		weightAlbumFit*c.Match.AlbumFit +
+		weightArtistFit*c.Match.ArtistFit
+
+	if c.Match.Overall != want {
+		t.Errorf("match = %f, want the untimed formula's %f", c.Match.Overall, want)
+	}
+}

backend/download/types.go

@@ -232,12 +232,17 @@ type Candidate struct {
 // results give paths and sizes but no tags, so Format and duration are
 // inferred from the path and size where possible.
 type CandidateFile struct {
-	Path      string `json:"path"`
-	Size      int64  `json:"size"`
-	Format    Format `json:"format"`
-	Bitrate   int    `json:"bitrate,omitempty"` // kbps, 0 when unknown
-	IsAudio   bool   `json:"isAudio"`
-	MatchedTo int    `json:"matchedTo,omitempty"` // expected track position
+	Path    string `json:"path"`
+	Size    int64  `json:"size"`
+	Format  Format `json:"format"`
+	Bitrate int    `json:"bitrate,omitempty"` // kbps, 0 when unknown
+	IsAudio bool   `json:"isAudio"`
+
+	// LengthMillis is the file's duration as the source reports it, or
+	// 0 when it does not.  Soulseek reports it for most audio files.
+	LengthMillis int64 `json:"lengthMillis,omitempty"`
+
+	MatchedTo int `json:"matchedTo,omitempty"` // expected track position
 }
 
 // Format is a normalized audio container/codec name.
@@ -286,7 +291,14 @@ type MatchScore struct {
 	TitleFit     float64 `json:"titleFit"`     // filenames vs expected titles
 	ArtistFit    float64 `json:"artistFit"`    // path/origin vs expected artist
 	AlbumFit     float64 `json:"albumFit"`     // folder name vs album title
-	Completeness float64 `json:"completeness"` // audio files vs expected count
+	Completeness float64 `json:"completeness"` // aligned tracks vs expected count
+
+	// DurationFit is how well the aligned files' lengths agree with the
+	// expected tracks', and DurationKnown whether enough of them stated
+	// a length for that to count.  When it does not, the score is the
+	// four text signals alone, exactly as before durations were read.
+	DurationFit   float64 `json:"durationFit"`
+	DurationKnown bool    `json:"durationKnown"`
 
 	// Anchored records whether an MBID drove this score.  Unanchored
 	// matches are capped, because there is nothing to be right about.

backend/library/coverart_storage_test.go

@@ -8,6 +8,7 @@ import (
 
 	"yellowjacket/backend/coverart"
 	"yellowjacket/backend/database/sql/sqlcgen"
+	"yellowjacket/internal/testfixtures"
 )
 
 // TestScan_StoresOnlyCoverTiers pins the size decision: a scan writes
@@ -26,10 +27,9 @@ func TestScan_StoresOnlyCoverTiers(t *testing.T) {
 
 	lib, db := setupTestLibrary(t)
 
-	root, err := filepath.Abs("../../test_data/music_library_test")
-	if err != nil {
-		t.Fatalf("resolve fixture path: %v", err)
-	}
+	// Load skips when the fixture library has not been generated, as
+	// every other fixture test does.
+	root := testfixtures.Load(t).Root()
 
 	library, err := db.Queries.CreateLibrary(lib.ctx, sqlcgen.CreateLibraryParams{
 		Name: "Fixtures",