navidrome/scanner/walk_dir_tree_test.go

package scanner

import (
	"context"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"testing/fstest"

	"github.com/navidrome/navidrome/conf"
	"github.com/navidrome/navidrome/conf/configtest"
	"github.com/navidrome/navidrome/core/storage"
	"github.com/navidrome/navidrome/model"
	"github.com/navidrome/navidrome/tests"
	. "github.com/onsi/ginkgo/v2"
	. "github.com/onsi/gomega"
	"golang.org/x/sync/errgroup"
)

var _ = Describe("walk_dir_tree", func() {
	Describe("walkDirTree", func() {
		var (
			fsys storage.MusicFS
			job  *scanJob
			ctx  context.Context
		)

		Context("full library", func() {
			BeforeEach(func() {
				DeferCleanup(configtest.SetupConfig())
				ctx = GinkgoT().Context()
				fsys = &mockMusicFS{
					FS: fstest.MapFS{
						"root/a/.ndignore":       {Data: []byte("ignored/*")},
						"root/a/f1.mp3":          {},
						"root/a/f2.mp3":          {},
						"root/a/ignored/bad.mp3": {},
						"root/b/cover.jpg":       {},
						"root/c/f3":              {},
						"root/d":                 {},
						"root/d/.ndignore":       {},
						"root/d/f1.mp3":          {},
						"root/d/f2.mp3":          {},
						"root/d/f3.mp3":          {},
						"root/e/original/f1.mp3": {},
						"root/e/symlink":         {Mode: fs.ModeSymlink, Data: []byte("original")},
						"root/f/realsong.mp3":    {Data: []byte("AUDIO")},
						"root/f/legit.mp3":       {Mode: fs.ModeSymlink, Data: []byte("realsong.mp3")},
						"root/f/secret":          {Data: []byte("TOPSECRET")},
						"root/f/evil.mp3":        {Mode: fs.ModeSymlink, Data: []byte("secret")},
						"root/g/.Hack Sign Original Soundtrack/track.mp3": {},
						"root/h/.hidden.mp3":                              {},
						"root/i/.git/config":                              {},
						"root/i/.streams/stream.mp3":                      {},
					},
				}
				job = &scanJob{
					fs:  fsys,
					lib: model.Library{Path: "/music"},
				}
			})

			// Helper function to call walkDirTree and collect folders from the results channel
			getFolders := func() map[string]*folderEntry {
				results, err := walkDirTree(ctx, job)
				Expect(err).ToNot(HaveOccurred())

				folders := map[string]*folderEntry{}
				g := errgroup.Group{}
				g.Go(func() error {
					for folder := range results {
						folders[folder.path] = folder
					}
					return nil
				})
				_ = g.Wait()
				return folders
			}

			DescribeTable("symlink handling",
				func(followSymlinks bool, expectedFolderCount int) {
					conf.Server.Scanner.FollowSymlinks = followSymlinks
					folders := getFolders()

					Expect(folders).To(HaveLen(expectedFolderCount + 2)) // +2 for `.` and `root`

					// Basic folder structure checks
					Expect(folders["root/a"].audioFiles).To(SatisfyAll(
						HaveLen(2),
						HaveKey("f1.mp3"),
						HaveKey("f2.mp3"),
					))
					Expect(folders["root/a"].imageFiles).To(BeEmpty())
					Expect(folders["root/b"].audioFiles).To(BeEmpty())
					Expect(folders["root/b"].imageFiles).To(SatisfyAll(
						HaveLen(1),
						HaveKey("cover.jpg"),
					))
					Expect(folders["root/c"].audioFiles).To(BeEmpty())
					Expect(folders["root/c"].imageFiles).To(BeEmpty())
					Expect(folders).ToNot(HaveKey("root/d"))

					// By default (Scanner.IgnoreDotFolders == true), dot-prefixed
					// folders are skipped, dot-prefixed files are not indexed, and
					// the special ignoredDirs (.git, .streams) are never traversed.
					Expect(folders).ToNot(HaveKey("root/g/.Hack Sign Original Soundtrack"))
					Expect(folders["root/h"].audioFiles).To(BeEmpty())
					Expect(folders).ToNot(HaveKey("root/i/.git"))
					Expect(folders).ToNot(HaveKey("root/i/.streams"))

					// Symlink specific checks
					if followSymlinks {
						Expect(folders["root/e/symlink"].audioFiles).To(HaveLen(1))
						Expect(folders["root/f"].audioFiles).To(HaveKey("legit.mp3"))
						Expect(folders["root/f"].audioFiles).To(HaveKey("realsong.mp3"))
						Expect(folders["root/f"].audioFiles).ToNot(HaveKey("evil.mp3"))
					} else {
						Expect(folders).ToNot(HaveKey("root/e/symlink"))
						Expect(folders["root/f"].audioFiles).To(HaveKey("realsong.mp3"))
						Expect(folders["root/f"].audioFiles).ToNot(HaveKey("legit.mp3"))
						Expect(folders["root/f"].audioFiles).ToNot(HaveKey("evil.mp3"))
					}
				},
				Entry("with symlinks enabled", true, 11),
				Entry("with symlinks disabled", false, 10),
			)

			DescribeTable("dot-prefixed folders with IgnoreDotFolders disabled",
				func(followSymlinks bool) {
					conf.Server.Scanner.FollowSymlinks = followSymlinks
					conf.Server.Scanner.IgnoreDotFolders = false
					folders := getFolders()

					// Dot-prefixed album folders are now traversed and indexed
					Expect(folders["root/g/.Hack Sign Original Soundtrack"].audioFiles).To(SatisfyAll(
						HaveLen(1),
						HaveKey("track.mp3"),
					))

					// Dot-prefixed files are still ignored, even with the flag off
					Expect(folders["root/h"].audioFiles).To(BeEmpty())

					// Special ignoredDirs remain blocked regardless of the flag
					Expect(folders).ToNot(HaveKey("root/i/.git"))
					Expect(folders).ToNot(HaveKey("root/i/.streams"))
				},
				Entry("with symlinks enabled", true),
				Entry("with symlinks disabled", false),
			)
		})

		Context("with target folders", func() {
			BeforeEach(func() {
				DeferCleanup(configtest.SetupConfig())
				ctx = GinkgoT().Context()
				fsys = &mockMusicFS{
					FS: fstest.MapFS{
						"Artist/Album1/track1.mp3":      {},
						"Artist/Album1/track2.mp3":      {},
						"Artist/Album2/track1.mp3":      {},
						"Artist/Album2/track2.mp3":      {},
						"Artist/Album2/Sub/track3.mp3":  {},
						"OtherArtist/Album3/track1.mp3": {},
					},
				}
				job = &scanJob{
					fs:  fsys,
					lib: model.Library{Path: "/music"},
				}
			})

			It("should recursively walk all subdirectories of target folders", func() {
				results, err := walkDirTree(ctx, job, "Artist")
				Expect(err).ToNot(HaveOccurred())

				folders := map[string]*folderEntry{}
				g := errgroup.Group{}
				g.Go(func() error {
					for folder := range results {
						folders[folder.path] = folder
					}
					return nil
				})
				_ = g.Wait()

				// Should include the target folder and all its descendants
				Expect(folders).To(SatisfyAll(
					HaveKey("Artist"),
					HaveKey("Artist/Album1"),
					HaveKey("Artist/Album2"),
					HaveKey("Artist/Album2/Sub"),
				))

				// Should not include folders outside the target
				Expect(folders).ToNot(HaveKey("OtherArtist"))
				Expect(folders).ToNot(HaveKey("OtherArtist/Album3"))

				// Verify audio files are present
				Expect(folders["Artist/Album1"].audioFiles).To(HaveLen(2))
				Expect(folders["Artist/Album2"].audioFiles).To(HaveLen(2))
				Expect(folders["Artist/Album2/Sub"].audioFiles).To(HaveLen(1))
			})

			It("should handle multiple target folders", func() {
				results, err := walkDirTree(ctx, job, "Artist/Album1", "OtherArtist")
				Expect(err).ToNot(HaveOccurred())

				folders := map[string]*folderEntry{}
				g := errgroup.Group{}
				g.Go(func() error {
					for folder := range results {
						folders[folder.path] = folder
					}
					return nil
				})
				_ = g.Wait()

				// Should include both target folders and their descendants
				Expect(folders).To(SatisfyAll(
					HaveKey("Artist/Album1"),
					HaveKey("OtherArtist"),
					HaveKey("OtherArtist/Album3"),
				))

				// Should not include other folders
				Expect(folders).ToNot(HaveKey("Artist"))
				Expect(folders).ToNot(HaveKey("Artist/Album2"))
				Expect(folders).ToNot(HaveKey("Artist/Album2/Sub"))
			})

			It("should skip non-existent target folders and preserve them in lastUpdates", func() {
				// Setup job with lastUpdates for both existing and non-existing folders
				job.lastUpdates = map[string]model.FolderUpdateInfo{
					model.FolderID(job.lib, "Artist/Album1"):             {},
					model.FolderID(job.lib, "NonExistent/DeletedFolder"): {},
					model.FolderID(job.lib, "OtherArtist/Album3"):        {},
				}

				// Try to scan existing folder and non-existing folder
				results, err := walkDirTree(ctx, job, "Artist/Album1", "NonExistent/DeletedFolder")
				Expect(err).ToNot(HaveOccurred())

				// Collect results
				folders := map[string]struct{}{}
				for folder := range results {
					folders[folder.path] = struct{}{}
				}

				// Should only include the existing folder
				Expect(folders).To(HaveKey("Artist/Album1"))
				Expect(folders).ToNot(HaveKey("NonExistent/DeletedFolder"))

				// The non-existent folder should still be in lastUpdates (not removed by popLastUpdate)
				Expect(job.lastUpdates).To(HaveKey(model.FolderID(job.lib, "NonExistent/DeletedFolder")))

				// The existing folder should have been removed from lastUpdates
				Expect(job.lastUpdates).ToNot(HaveKey(model.FolderID(job.lib, "Artist/Album1")))

				// Folders not in targets should remain in lastUpdates
				Expect(job.lastUpdates).To(HaveKey(model.FolderID(job.lib, "OtherArtist/Album3")))
			})
		})
	})

	Describe("helper functions", func() {
		dir, _ := os.Getwd()
		fsys := os.DirFS(dir)
		baseDir := filepath.Join("tests", "fixtures")

		Describe("isDirOrSymlinkToDir", func() {
			BeforeEach(func() {
				DeferCleanup(configtest.SetupConfig())
			})

			Context("with symlinks enabled", func() {
				BeforeEach(func() {
					tests.SkipOnWindows("symlink semantics")
					conf.Server.Scanner.FollowSymlinks = true
				})

				DescribeTable("returns expected result",
					func(dirName string, expected bool) {
						dirEntry := getDirEntry("tests/fixtures", dirName)
						Expect(isDirOrSymlinkToDir(fsys, baseDir, dirEntry)).To(Equal(expected))
					},
					Entry("normal dir", "empty_folder", true),
					Entry("symlink to dir", "symlink2dir", true),
					Entry("regular file", "test.mp3", false),
					Entry("symlink to file", "symlink", false),
				)
			})

			Context("with symlinks disabled", func() {
				BeforeEach(func() {
					conf.Server.Scanner.FollowSymlinks = false
				})

				DescribeTable("returns expected result",
					func(dirName string, expected bool) {
						dirEntry := getDirEntry("tests/fixtures", dirName)
						Expect(isDirOrSymlinkToDir(fsys, baseDir, dirEntry)).To(Equal(expected))
					},
					Entry("normal dir", "empty_folder", true),
					Entry("symlink to dir", "symlink2dir", false),
					Entry("regular file", "test.mp3", false),
					Entry("symlink to file", "symlink", false),
				)
			})
		})

		Describe("resolveEntryName", func() {
			var fsys fs.FS
			BeforeEach(func() {
				DeferCleanup(configtest.SetupConfig())
				fsys = fstest.MapFS{
					"dir/real.mp3":   {Data: []byte("AUDIO")},
					"dir/mid.mp3":    {Mode: fs.ModeSymlink, Data: []byte("real.mp3")},
					"dir/chain.mp3":  {Mode: fs.ModeSymlink, Data: []byte("mid.mp3")},
					"dir/audio.mp3":  {Mode: fs.ModeSymlink, Data: []byte("real.mp3")},
					"dir/evil.mp3":   {Mode: fs.ModeSymlink, Data: []byte("../outside/passwd")},
					"dir/loop1.mp3":  {Mode: fs.ModeSymlink, Data: []byte("loop2.mp3")},
					"dir/loop2.mp3":  {Mode: fs.ModeSymlink, Data: []byte("loop1.mp3")},
					"dir/dangle.mp3": {Mode: fs.ModeSymlink, Data: []byte("missing.mp3")},
				}
			})

			resolve := func(name string) (string, bool) {
				entries, err := fs.ReadDir(fsys, "dir")
				Expect(err).ToNot(HaveOccurred())
				for _, e := range entries {
					if e.Name() == name {
						return resolveEntryName(GinkgoT().Context(), fsys, "dir", e)
					}
				}
				Fail("entry not found: " + name)
				return "", false
			}

			Context("with symlinks enabled", func() {
				BeforeEach(func() { conf.Server.Scanner.FollowSymlinks = true })

				It("returns the entry name for a plain file", func() {
					name, ok := resolve("real.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("real.mp3"))
				})
				It("resolves a direct symlink to its audio target name", func() {
					name, ok := resolve("audio.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("real.mp3"))
				})
				It("resolves a symlink CHAIN to the final target name", func() {
					name, ok := resolve("chain.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("real.mp3"))
				})
				It("resolves a symlink to a non-audio target name (so caller can reject it)", func() {
					name, ok := resolve("evil.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("passwd"))
				})
				It("rejects a symlink loop", func() {
					_, ok := resolve("loop1.mp3")
					Expect(ok).To(BeFalse())
				})
			})

			Context("with symlinks disabled", func() {
				BeforeEach(func() { conf.Server.Scanner.FollowSymlinks = false })

				It("returns the entry name for a plain file", func() {
					name, ok := resolve("real.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("real.mp3"))
				})
				It("skips any file symlink", func() {
					_, ok := resolve("audio.mp3")
					Expect(ok).To(BeFalse())
				})
			})
		})

		Describe("symlink chain (real fs)", func() {
			BeforeEach(func() {
				tests.SkipOnWindows("symlink semantics")
				DeferCleanup(configtest.SetupConfig())
			})

			classify := func(fsys fs.FS, dirPath, name string) (string, bool) {
				entries, err := fs.ReadDir(fsys, dirPath)
				Expect(err).ToNot(HaveOccurred())
				for _, e := range entries {
					if e.Name() == name {
						return resolveEntryName(GinkgoT().Context(), fsys, dirPath, e)
					}
				}
				Fail("entry not found: " + name)
				return "", false
			}

			Context("committed 3-level fixtures", func() {
				// tests.Init chdirs to the repo root, so the committed fixtures are at "tests/fixtures".
				var fsys fs.FS
				BeforeEach(func() {
					conf.Server.Scanner.FollowSymlinks = true
					wd, err := os.Getwd()
					Expect(err).ToNot(HaveOccurred())
					fsys = os.DirFS(wd)
				})

				It("keeps a 3-level chain that resolves to real audio", func() {
					name, ok := classify(fsys, "tests/fixtures/symlink_chain", "level3.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("test.mp3"))
					Expect(model.IsAudioFile(name)).To(BeTrue())
				})

				It("rejects a 3-level chain that resolves to a non-audio file", func() {
					name, ok := classify(fsys, "tests/fixtures/symlink_chain", "evil3.mp3")
					Expect(ok).To(BeTrue())
					Expect(name).To(Equal("index.html"))
					Expect(model.IsAudioFile(name)).To(BeFalse())
				})

				It("skips the chain entirely when FollowSymlinks is disabled", func() {
					conf.Server.Scanner.FollowSymlinks = false
					_, ok := classify(fsys, "tests/fixtures/symlink_chain", "level3.mp3")
					Expect(ok).To(BeFalse())
					_, ok = classify(fsys, "tests/fixtures/symlink_chain", "evil3.mp3")
					Expect(ok).To(BeFalse())
				})
			})

			// Regression for #5752: the production localFS must resolve file symlinks.
			// It wraps os.DirFS behind the fs.FS interface, so fs.ReadLink-based
			// resolution is not available and full OS-level resolution is required.
			Context("production local storage FS", func() {
				var libRoot string
				var musicFS storage.MusicFS

				BeforeEach(func() {
					conf.Server.Scanner.FollowSymlinks = true

					// Reproduces the reported layout: a "pool" with the real files and a
					// library containing only symlinks into the pool.
					base := GinkgoT().TempDir()
					pool := filepath.Join(base, "pool")
					libRoot = filepath.Join(base, "userlib")
					Expect(os.MkdirAll(pool, 0755)).To(Succeed())
					Expect(os.MkdirAll(libRoot, 0755)).To(Succeed())
					Expect(os.WriteFile(filepath.Join(pool, "real.mp3"), []byte("AUDIO"), 0600)).To(Succeed())
					Expect(os.WriteFile(filepath.Join(pool, "secrets.txt"), []byte("TOPSECRET"), 0600)).To(Succeed())
					// mid.wav lives OUTSIDE the library and has an audio name, but points at a
					// non-audio file. A chain through it must be classified by the FINAL target.
					Expect(os.Symlink(filepath.Join(pool, "secrets.txt"), filepath.Join(pool, "mid.wav"))).To(Succeed())

					Expect(os.Symlink("../pool/real.mp3", filepath.Join(libRoot, "relative.mp3"))).To(Succeed())
					Expect(os.Symlink(filepath.Join(pool, "real.mp3"), filepath.Join(libRoot, "absolute.mp3"))).To(Succeed())
					Expect(os.Symlink(filepath.Join(pool, "mid.wav"), filepath.Join(libRoot, "evil.wav"))).To(Succeed())
					Expect(os.Symlink(filepath.Join(pool, "missing.mp3"), filepath.Join(libRoot, "broken.mp3"))).To(Succeed())

					u, err := storage.LocalPathToURL(libRoot)
					Expect(err).ToNot(HaveOccurred())
					s, err := storage.For(u.String())
					Expect(err).ToNot(HaveOccurred())
					musicFS, err = s.FS()
					Expect(err).ToNot(HaveOccurred())
				})

				walkRoot := func() *folderEntry {
					job := &scanJob{fs: musicFS, lib: model.Library{Path: libRoot}}
					results, err := walkDirTree(GinkgoT().Context(), job)
					Expect(err).ToNot(HaveOccurred())
					var root *folderEntry
					for folder := range results {
						if folder.path == "." {
							root = folder
						}
					}
					Expect(root).ToNot(BeNil())
					return root
				}

				It("imports symlinks to out-of-library audio files", func() {
					root := walkRoot()
					Expect(root.audioFiles).To(HaveKey("relative.mp3"))
					Expect(root.audioFiles).To(HaveKey("absolute.mp3"))
				})

				It("rejects a chain that ends in a non-audio file, even through an audio-named intermediate", func() {
					root := walkRoot()
					Expect(root.audioFiles).ToNot(HaveKey("evil.wav"))
				})

				It("skips broken symlinks", func() {
					root := walkRoot()
					Expect(root.audioFiles).ToNot(HaveKey("broken.mp3"))
				})

				It("skips all file symlinks when FollowSymlinks is disabled", func() {
					conf.Server.Scanner.FollowSymlinks = false
					root := walkRoot()
					Expect(root.audioFiles).To(BeEmpty())
				})
			})

			Context("out-of-tree escape (temp dir)", func() {
				var root string
				BeforeEach(func() {
					conf.Server.Scanner.FollowSymlinks = true
					root = GinkgoT().TempDir()
					outside := GinkgoT().TempDir()
					Expect(os.WriteFile(filepath.Join(outside, "passwd"), []byte("TOPSECRET"), 0600)).To(Succeed())
					Expect(os.WriteFile(filepath.Join(outside, "real.flac"), []byte("AUDIO"), 0600)).To(Succeed())
					Expect(os.WriteFile(filepath.Join(root, "song.mp3"), []byte("AUDIO"), 0600)).To(Succeed())
					// evil.mp3 escapes to a non-audio target; legit.flac is a valid out-of-tree audio symlink.
					Expect(os.Symlink(filepath.Join(outside, "passwd"), filepath.Join(root, "evil.mp3"))).To(Succeed())
					Expect(os.Symlink(filepath.Join(outside, "real.flac"), filepath.Join(root, "legit.flac"))).To(Succeed())
				})

				It("rejects the absolute-path escape but keeps legit out-of-tree audio", func() {
					fsys := os.DirFS(root)

					name, ok := classify(fsys, ".", "song.mp3")
					Expect(ok).To(BeTrue())
					Expect(model.IsAudioFile(name)).To(BeTrue())

					name, ok = classify(fsys, ".", "legit.flac")
					Expect(ok).To(BeTrue())
					Expect(model.IsAudioFile(name)).To(BeTrue())

					name, ok = classify(fsys, ".", "evil.mp3")
					Expect(ok).To(BeTrue())
					Expect(model.IsAudioFile(name)).To(BeFalse())
				})

				It("skips all file symlinks when FollowSymlinks is disabled", func() {
					conf.Server.Scanner.FollowSymlinks = false
					fsys := os.DirFS(root)
					entries, err := fs.ReadDir(fsys, ".")
					Expect(err).ToNot(HaveOccurred())
					for _, e := range entries {
						_, ok := resolveEntryName(GinkgoT().Context(), fsys, ".", e)
						if e.Type()&fs.ModeSymlink != 0 {
							Expect(ok).To(BeFalse(), e.Name())
						} else {
							Expect(ok).To(BeTrue(), e.Name())
						}
					}
				})
			})
		})

		Describe("isDirIgnored", func() {
			DescribeTable("returns expected result",
				func(dirName string, expected bool) {
					Expect(isDirIgnored(dirName)).To(Equal(expected))
				},
				Entry("normal dir", "empty_folder", false),
				Entry("dot-prefixed album dir", ".Hack Sign Original Soundtrack", false),
				Entry("git dir", ".git", true),
				Entry("streams dir", ".streams", true),
				Entry("dir starting with ellipsis", "...unhidden_folder", false),
				Entry("recycle bin", "$Recycle.Bin", true),
				Entry("snapshot dir", "#snapshot", true),
			)
		})

		Describe("isIgnoredEntry", func() {
			BeforeEach(func() {
				DeferCleanup(configtest.SetupConfig())
			})

			DescribeTable("with IgnoreDotFolders enabled (default)",
				func(name string, isDir, expected bool) {
					conf.Server.Scanner.IgnoreDotFolders = true
					Expect(isIgnoredEntry(name, isDir)).To(Equal(expected))
				},
				Entry("normal dir", "Album", true, false),
				Entry("normal file", "track.mp3", false, false),
				Entry("dot folder", ".Hack Sign Original Soundtrack", true, true),
				Entry("dot file", ".hidden.mp3", false, true),
				Entry("blocklisted dir", ".git", true, true),
				Entry("ellipsis dir", "...unhidden", true, false),
			)

			DescribeTable("with IgnoreDotFolders disabled",
				func(name string, isDir, expected bool) {
					conf.Server.Scanner.IgnoreDotFolders = false
					Expect(isIgnoredEntry(name, isDir)).To(Equal(expected))
				},
				Entry("normal dir", "Album", true, false),
				Entry("normal file", "track.mp3", false, false),
				Entry("dot folder is allowed", ".Hack Sign Original Soundtrack", true, false),
				Entry("dot file is still ignored", ".hidden.mp3", false, true),
				Entry("blocklisted dir still ignored", ".git", true, true),
			)
		})

		Describe("isDotEntry", func() {
			DescribeTable("returns expected result",
				func(name string, expected bool) {
					Expect(isDotEntry(name)).To(Equal(expected))
				},
				Entry("dot folder", ".Hidden", true),
				Entry("dot file", ".hidden.mp3", true),
				Entry("current dir", ".", false),
				Entry("parent dir", "..", false),
				Entry("two leading dots", "..foo", false),
				Entry("ellipsis", "...unhidden", false),
				Entry("normal name", "Album", false),
			)
		})

		Describe("fullReadDir", func() {
			var (
				fsys fakeFS
				ctx  context.Context
			)

			BeforeEach(func() {
				ctx = GinkgoT().Context()
				fsys = fakeFS{MapFS: fstest.MapFS{
					"root/a/f1": {},
					"root/b/f2": {},
					"root/c/f3": {},
				}}
			})

			DescribeTable("reading directory entries",
				func(failOn string, expectedErr error, expectedNames []string) {
					fsys.failOn = failOn
					fsys.err = expectedErr
					dir, _ := fsys.Open("root")
					entries := fullReadDir(ctx, dir.(fs.ReadDirFile))
					Expect(entries).To(HaveLen(len(expectedNames)))
					for i, name := range expectedNames {
						Expect(entries[i].Name()).To(Equal(name))
					}
				},
				Entry("reads all entries", "", nil, []string{"a", "b", "c"}),
				Entry("skips entries with permission error", "b", nil, []string{"a", "c"}),
				Entry("aborts on fs.ErrNotExist", "", fs.ErrNotExist, []string{}),
			)
		})
	})
})

type fakeFS struct {
	fstest.MapFS
	failOn string
	err    error
}

func (f *fakeFS) Open(name string) (fs.File, error) {
	dir, err := f.MapFS.Open(name)
	return &fakeDirFile{File: dir, fail: f.failOn, err: f.err}, err
}

type fakeDirFile struct {
	fs.File
	entries []fs.DirEntry
	pos     int
	fail    string
	err     error
}

// Only works with n == -1
func (fd *fakeDirFile) ReadDir(int) ([]fs.DirEntry, error) {
	if fd.err != nil {
		return nil, fd.err
	}
	if fd.entries == nil {
		fd.entries, _ = fd.File.(fs.ReadDirFile).ReadDir(-1)
	}
	var dirs []fs.DirEntry
	for {
		if fd.pos >= len(fd.entries) {
			break
		}
		e := fd.entries[fd.pos]
		fd.pos++
		if e.Name() == fd.fail {
			return dirs, &fs.PathError{Op: "lstat", Path: e.Name(), Err: fs.ErrPermission}
		}
		dirs = append(dirs, e)
	}
	return dirs, nil
}

func getDirEntry(baseDir, name string) os.DirEntry {
	dirEntries, _ := os.ReadDir(baseDir)
	for _, entry := range dirEntries {
		if entry.Name() == name {
			return entry
		}
	}
	panic(fmt.Sprintf("Could not find %s in %s", name, baseDir))
}

// mockMusicFS is a mock implementation of the MusicFS interface that supports symlinks
type mockMusicFS struct {
	storage.MusicFS
	fs.FS
}

// Open resolves symlinks
func (m *mockMusicFS) Open(name string) (fs.File, error) {
	f, err := m.FS.Open(name)
	if err != nil {
		return nil, err
	}

	info, err := f.Stat()
	if err != nil {
		f.Close()
		return nil, err
	}

	if info.Mode()&fs.ModeSymlink != 0 {
		// For symlinks, read the target path from the Data field
		target := string(m.FS.(fstest.MapFS)[name].Data)
		f.Close()
		return m.FS.Open(target)
	}

	return f, nil
}

// Stat uses Open to resolve symlinks
func (m *mockMusicFS) Stat(name string) (fs.FileInfo, error) {
	f, err := m.Open(name)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return f.Stat()
}

// ReadDir uses Open to resolve symlinks
func (m *mockMusicFS) ReadDir(name string) ([]fs.DirEntry, error) {
	f, err := m.Open(name)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	if dirFile, ok := f.(fs.ReadDirFile); ok {
		return dirFile.ReadDir(-1)
	}
	return nil, fmt.Errorf("not a directory")
}

// ReadLink returns the target of the named symbolic link (implements fs.ReadLinkFS).
func (m *mockMusicFS) ReadLink(name string) (string, error) {
	mapFS := m.FS.(fstest.MapFS)
	entry, ok := mapFS[name]
	if !ok {
		return "", &fs.PathError{Op: "readlink", Path: name, Err: fs.ErrNotExist}
	}
	if entry.Mode&fs.ModeSymlink == 0 {
		return "", &fs.PathError{Op: "readlink", Path: name, Err: fmt.Errorf("not a symlink")}
	}
	return string(entry.Data), nil
}

// Lstat returns FileInfo for the named file without following symlinks (implements fs.ReadLinkFS).
func (m *mockMusicFS) Lstat(name string) (fs.FileInfo, error) {
	mapFS := m.FS.(fstest.MapFS)
	if _, ok := mapFS[name]; !ok {
		return nil, &fs.PathError{Op: "lstat", Path: name, Err: fs.ErrNotExist}
	}
	f, err := m.FS.Open(name)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return f.Stat()
}