group DCF files that share a file number (closes #3)

Files in one DCF directory that share a file number are one file group,
as section 4.3.2.2 of the specification says. `Directory.FileGroups`
lists them, each with its numbers, its members and its primary member. A
lone file is a group of one. A group reports its member count and total
size.

The primary member follows section 6.2.1.3, which gives a JPG priority. A
`THM` comes last. `Store.Images`, `Store.Videos` and the totals are
unchanged.

Model: opus-5-5

README.md

@@ -29,7 +29,6 @@ Then list the DCF stores on the mounted filesystems:
 package main
 
 import (
-	"context"
 	"fmt"
 	"log"
 
@@ -37,21 +36,17 @@ import (
 )
 
 func main() {
-	stores, err := dcf.GetStores(context.Background())
+	stores, err := dcf.GetDCFStores(0)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	for _, store := range stores {
+	for _, store := range *stores {
 		fmt.Println(store.String())
 	}
 }
 ```
 
-Call `dcf.GetStore` instead when you expect exactly one DCF store. It returns
-`dcf.ErrNoStore` when none is mounted, and `dcf.ErrMultipleStores` when more
-than one is.
-
 To work on the library itself, you need docker and git:
 
 ```sh
@@ -110,8 +105,8 @@ overengineering and reusable code.
 
 All the code is in the `pkg/dcf` package. The repo has no commands.
 
-- `dcf.go` holds the public API. `GetStores` finds the DCF stores and reads each
-  one. `GetStore` returns the one DCF store when exactly one is mounted.
+- `dcf.go` holds the public API. `GetDCFStores` finds the DCF stores and reads
+  each one.
 - `helpers.go` finds the mount points that hold a DCF store.
 - `parse.go` reads one DCF store through an `fs.FS` rooted at its mount point.
 - `filegroup.go` sorts the files of one DCF directory into file groups.
@@ -122,9 +117,7 @@ The main types are:
 - `Directory` is one DCF directory. It has a directory number, a name, the
   objects inside it and their file groups.
 - `Object` is one file in a store. A file in a DCF directory also has a
-  directory number and a file number. `Object.Hash` reads the file through the
-  `fs.FS` of its store. An `Object` you build yourself has none, so its `Hash`
-  returns an error.
+  directory number and a file number.
 - `FileGroup` is one file group in a DCF directory.
 - `Image` and `Video` embed `Object`. The file extension decides which one a
   file becomes. A file with any other extension, such as a `THM` thumbnail, is
@@ -136,10 +129,6 @@ filesystem. Media anywhere else on the filesystem is not part of the store.
 
 `dcf` never follows a symlink.
 
-`GetStores` and `GetStore` take a `context.Context`. When it is cancelled, the
-read stops before the next directory. The returned error matches
-`context.Canceled`.
-
 `dcf` applies the naming rules of the DCF specification, CIPA DC-009-2010, under
 `DCIM`:
 
@@ -184,8 +173,8 @@ has:
 The primary member is the first of these that the group holds:
 
 1. a `JPG` file
-2. any other file in `Store.Images`
-3. a file in `Store.Videos`
+2. any other image
+3. a video
 4. any other file except a `THM`
 5. a `THM`
 
@@ -193,6 +182,8 @@ The primary member is the first of these that the group holds:
 
 ## TODO
 
+- Take a `context.Context` to cancel the walk of a store.
+- Return a plain slice from `GetDCFStores`, not a pointer to one.
 - Copy files off a card, and verify each copy against its SHA256 hash.
 
 ## License

pkg/dcf/dcf.go

@@ -7,13 +7,10 @@
 package dcf
 
 import (
-	"context"
 	"crypto/sha256"
 	"encoding/hex"
-	"errors"
 	"fmt"
 	"io"
-	"io/fs"
 	"os"
 	"path/filepath"
 	"slices"
@@ -22,14 +19,6 @@ import (
 	"github.com/dustin/go-humanize"
 )
 
-var (
-	// ErrNoStore is the error from GetStore when no DCF store is mounted.
-	ErrNoStore = errors.New("no DCF store is mounted")
-	// ErrMultipleStores is the error from GetStore when more than one DCF store
-	// is mounted.
-	ErrMultipleStores = errors.New("more than one DCF store is mounted")
-)
-
 // Store represents a DCF store, which is a directory structure that contains
 // images and videos in the root of a mounted filesystem.
 type Store struct {
@@ -87,9 +76,6 @@ type Object struct {
 	// directory. Both are 0 for a file under PRIVATE/M4ROOT.
 	DirectoryNumber int
 	FileNumber      int
-	// fsys is the fs.FS the store was read through. Hash reads the file through
-	// it.
-	fsys fs.FS
 }
 
 // Image represents an image file on a DCF store.
@@ -187,17 +173,15 @@ func (i *Image) String() string {
 	)
 }
 
-// Hash returns the SHA256 hash of the file as a hex string. It reads the file
-// through the fs.FS of its store. An Object built by hand has none, so Hash
-// returns an error that matches fs.ErrInvalid.
+// Hash returns the SHA256 hash of the file as a hex string.
 func (d *Object) Hash() (string, error) {
-	if d.fsys == nil {
-		return "", fmt.Errorf("hashing %s: %w", d.FullFilePath(), fs.ErrInvalid)
-	}
+	return pathToSHA256(d.FullFilePath())
+}
 
-	file, err := d.fsys.Open(d.Path)
+func pathToSHA256(path string) (string, error) {
+	file, err := os.Open(filepath.Clean(path))
 	if err != nil {
-		return "", fmt.Errorf("hashing %s: %w", d.FullFilePath(), err)
+		return "", err
 	}
 
 	defer func() { _ = file.Close() }()
@@ -206,64 +190,44 @@ func (d *Object) Hash() (string, error) {
 
 	_, err = io.Copy(hash, file)
 	if err != nil {
-		return "", fmt.Errorf("hashing %s: %w", d.FullFilePath(), err)
+		return "", err
 	}
 
 	return hex.EncodeToString(hash.Sum(nil)), nil
 }
 
-// GetStores finds the DCF stores in the root of the mounted filesystems and reads
-// each one. It does not mount filesystems or search outside of filesystem root
-// directories. It reads the DCIM and PRIVATE/M4ROOT directories of each
-// filesystem to populate the returned Stores. It never follows a symlink. If a
-// card cannot be read, it returns an error that names the card's mount point.
-// When ctx is cancelled, the read stops before the next directory, and the error
-// matches ctx.Err().
-func GetStores(ctx context.Context) ([]*Store, error) {
-	dcfStorePaths, err := findDCFMountPoints(ctx)
+// GetDCFStores returns a list of DCF stores found on the system in the root of
+// any mounted filesystems. The integer argument is the number of DCF stores to
+// return. If the argument is 0, all DCF stores are returned. It does not mount
+// filesystems or search outside of filesystem root directories. It does,
+// however, read the DCIM and PRIVATE/M4ROOT directories of each filesystem to
+// populate the returned Stores. It never follows a symlink. If a card cannot be
+// read, it returns an error that names the card's mount point.
+func GetDCFStores(requestedCount int) (*[]Store, error) {
+	dcfStorePaths, err := findDCFMountPoints(requestedCount)
 	if err != nil {
 		return nil, err
 	}
 
-	return parseStores(ctx, dcfStorePaths)
-}
-
-// GetStore returns the one DCF store when exactly one is mounted. It returns
-// ErrNoStore when none is mounted, and ErrMultipleStores when more than one is.
-// It reads every card first, the way GetStores does, so a card that cannot be
-// read returns that error instead.
-func GetStore(ctx context.Context) (*Store, error) {
-	stores, err := GetStores(ctx)
+	dcfStores, err := parseStores(dcfStorePaths)
 	if err != nil {
 		return nil, err
 	}
 
-	return onlyStore(stores)
-}
-
-// onlyStore returns the store when stores holds exactly one.
-func onlyStore(stores []*Store) (*Store, error) {
-	switch len(stores) {
-	case 0:
-		return nil, ErrNoStore
-	case 1:
-		return stores[0], nil
-	default:
-		return nil, ErrMultipleStores
-	}
+	return &dcfStores, nil
 }
 
 // parseStores reads the card at each of the given mount points.
-func parseStores(ctx context.Context, mountpoints []string) ([]*Store, error) {
-	dcfStores := []*Store{}
+func parseStores(mountpoints []string) ([]Store, error) {
+	dcfStores := []Store{}
 
 	for _, mountpoint := range mountpoints {
-		dcfStore, err := parseStore(ctx, os.DirFS(mountpoint), mountpoint)
+		dcfStore, err := parseStore(os.DirFS(mountpoint), mountpoint)
 		if err != nil {
 			return nil, err
 		}
 
-		dcfStores = append(dcfStores, dcfStore)
+		dcfStores = append(dcfStores, *dcfStore)
 	}
 
 	return dcfStores, nil
@@ -271,7 +235,7 @@ func parseStores(ctx context.Context, mountpoints []string) ([]*Store, error) {
 
 func isImageFile(path string) bool {
 	imageExtensions := []string{
-		".jpg", ".jpeg", ".png", ".gif", ".bmp", ".tif", ".tiff", ".raw", ".arw",
+		".jpg", ".jpeg", ".png", ".gif", ".bmp", ".tiff", ".raw", ".arw",
 	}
 
 	return slices.Contains(imageExtensions, strings.ToLower(filepath.Ext(path)))

pkg/dcf/dcf_internal_test.go

@@ -1,13 +1,9 @@
 package dcf
 
 import (
-	"context"
-	"errors"
-	"io/fs"
 	"path/filepath"
 	"strings"
 	"testing"
-	"testing/fstest"
 )
 
 func TestParseStoresReadsEachMountPoint(t *testing.T) {
@@ -16,7 +12,7 @@ func TestParseStoresReadsEachMountPoint(t *testing.T) {
 	first := newCardOnDisk(t, "DCIM/100ABCDE/ABCD0001.JPG")
 	second := newCardOnDisk(t, "PRIVATE/M4ROOT/CLIP/C0001.MP4")
 
-	stores, err := parseStores(t.Context(), []string{first, second})
+	stores, err := parseStores([]string{first, second})
 	if err != nil {
 		t.Fatalf("parseStores: %v", err)
 	}
@@ -54,100 +50,18 @@ func TestParseStoresReturnsErrorNamingTheCard(t *testing.T) {
 	// Every lookup under a plain file fails.
 	mountpoint := filepath.Join(newCardOnDisk(t, "FILE"), "FILE")
 
-	_, err := parseStores(t.Context(), []string{mountpoint})
+	_, err := parseStores([]string{mountpoint})
 	if err == nil || !strings.Contains(err.Error(), mountpoint) {
 		t.Fatalf("parseStores error = %v, want one naming %s", err, mountpoint)
 	}
 }
 
-func TestParseStoresReturnsErrorWhenCancelled(t *testing.T) {
-	t.Parallel()
-
-	ctx, cancel := context.WithCancel(t.Context())
-	cancel()
-
-	mountpoint := newCardOnDisk(t, "DCIM/100ABCDE/ABCD0001.JPG")
-
-	_, err := parseStores(ctx, []string{mountpoint})
-	if !errors.Is(err, context.Canceled) {
-		t.Fatalf("parseStores error = %v, want %v", err, context.Canceled)
-	}
-}
-
-func TestOnlyStore(t *testing.T) {
-	t.Parallel()
-
-	first := newMountPoint(t, dcimDirectory)
-	second := newMountPoint(t, m4RootDirectory)
-
-	stores, err := parseStores(t.Context(), []string{first, second})
-	if err != nil {
-		t.Fatalf("parseStores: %v", err)
-	}
-
-	_, err = onlyStore(stores[:0])
-	if !errors.Is(err, ErrNoStore) {
-		t.Errorf("onlyStore of no cards: error = %v, want %v", err, ErrNoStore)
-	}
-
-	store, err := onlyStore(stores[:1])
-	if err != nil {
-		t.Fatalf("onlyStore of one card: %v", err)
-	}
-
-	if store.RootDirectory != first {
-		t.Errorf("onlyStore returned the card at %s, want %s",
-			store.RootDirectory, first)
-	}
-
-	_, err = onlyStore(stores)
-	if !errors.Is(err, ErrMultipleStores) {
-		t.Errorf("onlyStore of two cards: error = %v, want %v",
-			err, ErrMultipleStores)
-	}
-}
-
-func TestObjectHashReadsThroughTheCard(t *testing.T) {
-	t.Parallel()
-
-	card := fstest.MapFS{"DCIM/100ABCDE/ABCD0001.JPG": {Data: []byte("abc")}}
-
-	got, err := mustParseStore(t, card).Images[0].Hash()
-	if err != nil {
-		t.Fatalf("Hash() returned error: %v", err)
-	}
-
-	// The published SHA-256 test vector for "abc".
-	want := "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
-	if got != want {
-		t.Fatalf("Hash() = %q, want %q", got, want)
-	}
-}
-
-func TestObjectHashOfMissingFileReturnsError(t *testing.T) {
-	t.Parallel()
-
-	const filePath = "DCIM/100ABCDE/ABCD0001.JPG"
-
-	card := newCard(filePath)
-	image := mustParseStore(t, card).Images[0]
-
-	delete(card, filePath)
-
-	_, err := image.Hash()
-	if !errors.Is(err, fs.ErrNotExist) {
-		t.Fatalf("Hash() error = %v, want %v", err, fs.ErrNotExist)
-	}
-}
-
 func TestIsImageFile(t *testing.T) {
 	t.Parallel()
 
 	cases := map[string]bool{
 		"DCIM/100MSDCF/DSC00001.jpg":    true,
 		"DCIM/100MSDCF/DSC00001.ARW":    true,
-		"DCIM/100MSDCF/DSC00001.TIF":    true,
-		"DCIM/100MSDCF/DSC00001.tif":    true,
 		"PRIVATE/M4ROOT/CLIP/C0001.MP4": false,
 		"DCIM/100MSDCF/notes.txt":       false,
 		"DCIM/100MSDCF/noextension":     false,

pkg/dcf/dcf_test.go

@@ -1,9 +1,8 @@
 package dcf_test
 
 import (
-	"context"
-	"errors"
-	"io/fs"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"sneak.berlin/go/dcf/pkg/dcf"
@@ -126,30 +125,37 @@ func TestVideoString(t *testing.T) {
 	}
 }
 
-func TestObjectHashOfObjectBuiltByHandReturnsError(t *testing.T) {
+func TestObjectHashIsSHA256OfFile(t *testing.T) {
 	t.Parallel()
 
-	object := dcf.Object{DCFStoreRoot: cardRoot, Path: "a.jpg"}
+	root := t.TempDir()
+
+	err := os.WriteFile(filepath.Join(root, "a.jpg"), []byte("abc"), 0o600)
+	if err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	object := dcf.Object{DCFStoreRoot: root, Path: "a.jpg"}
+
+	got, err := object.Hash()
+	if err != nil {
+		t.Fatalf("Hash() returned error: %v", err)
+	}
+
+	// The published SHA-256 test vector for "abc".
+	want := "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
+	if got != want {
+		t.Fatalf("Hash() = %q, want %q", got, want)
+	}
+}
+
+func TestObjectHashOfMissingFileReturnsError(t *testing.T) {
+	t.Parallel()
+
+	object := dcf.Object{DCFStoreRoot: t.TempDir(), Path: "absent.jpg"}
 
 	_, err := object.Hash()
-	if !errors.Is(err, fs.ErrInvalid) {
-		t.Fatalf("Hash() error = %v, want %v", err, fs.ErrInvalid)
-	}
-}
-
-func TestGetStoresAndGetStoreReturnCancellation(t *testing.T) {
-	t.Parallel()
-
-	ctx, cancel := context.WithCancel(t.Context())
-	cancel()
-
-	_, err := dcf.GetStores(ctx)
-	if !errors.Is(err, context.Canceled) {
-		t.Errorf("GetStores error = %v, want %v", err, context.Canceled)
-	}
-
-	_, err = dcf.GetStore(ctx)
-	if !errors.Is(err, context.Canceled) {
-		t.Errorf("GetStore error = %v, want %v", err, context.Canceled)
+	if err == nil {
+		t.Fatal("Hash() of a missing file returned no error")
 	}
 }

pkg/dcf/filegroup.go

@@ -42,12 +42,10 @@ func newFileGroups(objects []*Object) []*FileGroup {
 }
 
 // primaryMember returns the member that stands for the whole group. Section
-// 6.2.1.3 of the specification gives a DCF basic file priority over a DCF extended
-// image file. It says nothing about a DCF optional file, the other kind of JPG, so
-// ranking every JPG first is a choice. Section 4.6 makes a THM only the thumbnail
-// of another file, so it comes last. The specification leaves the rest open, so an
-// image comes before a video, and a video before any other file. Among equals, the
-// first in name order wins.
+// 6.2.1.3 of the specification gives a JPG priority over the other files. Section
+// 4.6 makes a THM only the thumbnail of another file, so it comes last. The
+// specification leaves the rest open, so an image comes before a video, and a
+// video before any other file. Among equals, the first in name order wins.
 func primaryMember(members []*Object) *Object {
 	choices := []func(string) bool{isJPG, isImageFile, isVideoFile, isNotTHM}
 

pkg/dcf/filegroup_internal_test.go

@@ -212,16 +212,14 @@ func TestPrimaryMember(t *testing.T) {
 	// Then any other image.
 	assertPrimaryMember(t, "Z0010001.ARW", "A0010001.MP4", "Z0010001.ARW")
 	assertPrimaryMember(t, "Z0010001.ARW", "A0010001.WAV", "Z0010001.ARW")
-	assertPrimaryMember(t, "A0010001.TIF", "A0010001.MOV", "A0010001.TIF")
-	assertPrimaryMember(t, "Z0010001.TIF", "A0010001.WAV", "Z0010001.TIF")
 
 	// Then a video.
 	assertPrimaryMember(t, "A0010001.MP4", "A0010001.AAC", "A0010001.MP4")
 	assertPrimaryMember(t, "Z0010001.MP4", "A0010001.THM", "Z0010001.MP4")
 
 	// Then any other file except a THM, in either case.
-	assertPrimaryMember(t, "Z0010001.WAV", "A0010001.THM", "Z0010001.WAV")
-	assertPrimaryMember(t, "a0010001.wav", "a0010001.thm", "a0010001.wav")
+	assertPrimaryMember(t, "Z0010001.TIF", "A0010001.THM", "Z0010001.TIF")
+	assertPrimaryMember(t, "a0010001.tif", "a0010001.thm", "a0010001.tif")
 
 	// A THM is primary only when the group holds nothing else.
 	assertPrimaryMember(t, "A0010001.THM", "A0010001.THM")

pkg/dcf/helpers.go

@@ -1,7 +1,6 @@
 package dcf
 
 import (
-	"context"
 	"fmt"
 	"log/slog"
 	"os"
@@ -10,19 +9,12 @@ import (
 	"github.com/shirou/gopsutil/disk"
 )
 
-func findAllMountPoints(ctx context.Context) ([]string, error) {
+func findAllMountPoints() ([]string, error) {
 	mountpoints := []string{}
 
-	// disk.PartitionsWithContext does not check ctx on Linux.
-	err := ctx.Err()
+	partitions, err := disk.Partitions(false) // physical devices only, so false
 	if err != nil {
-		return nil, fmt.Errorf("listing the mounted filesystems: %w", err)
-	}
-
-	// physical devices only, so false
-	partitions, err := disk.PartitionsWithContext(ctx, false)
-	if err != nil {
-		return nil, fmt.Errorf("listing the mounted filesystems: %w", err)
+		return nil, err
 	}
 
 	for _, partition := range partitions {
@@ -34,18 +26,21 @@ func findAllMountPoints(ctx context.Context) ([]string, error) {
 	return mountpoints, nil
 }
 
-// findDCFMountPoints returns the paths of the mountpoints that hold a DCF store.
-func findDCFMountPoints(ctx context.Context) ([]string, error) {
-	mountpoints, err := findAllMountPoints(ctx)
+// findDCFMountPoints returns a list of strings of the paths of mountpoints
+// that hold a DCF store. Its only argument is an integer of how many mountpoints
+// to return. If the argument is 0, all mountpoints are returned.
+func findDCFMountPoints(requestedCount int) ([]string, error) {
+	mountpoints, err := findAllMountPoints()
 	if err != nil {
 		return nil, err
 	}
 
-	return filterDCFMountPoints(mountpoints), nil
+	return filterDCFMountPoints(mountpoints, requestedCount), nil
 }
 
-// filterDCFMountPoints returns the mountpoints that hold a DCF store.
-func filterDCFMountPoints(mountpoints []string) []string {
+// filterDCFMountPoints returns the first requestedCount of the mountpoints that
+// hold a DCF store. If requestedCount is 0, it returns all of them.
+func filterDCFMountPoints(mountpoints []string, requestedCount int) []string {
 	filteredMountpoints := []string{}
 
 	for _, mountpoint := range mountpoints {
@@ -56,6 +51,9 @@ func filterDCFMountPoints(mountpoints []string) []string {
 		slog.Debug(fmt.Sprintf("Keeping mountpoint %s\n", mountpoint))
 
 		filteredMountpoints = append(filteredMountpoints, mountpoint)
+		if (requestedCount > 0) && (len(filteredMountpoints) >= requestedCount) {
+			break
+		}
 	}
 
 	return filteredMountpoints

pkg/dcf/helpers_internal_test.go

@@ -72,16 +72,29 @@ func TestIsDCFMountPointIgnoresSymlink(t *testing.T) {
 	}
 }
 
-func TestFilterDCFMountPointsKeepsThoseHoldingAStore(t *testing.T) {
+func TestFilterDCFMountPointsReturnsRequestedCount(t *testing.T) {
 	t.Parallel()
 
 	first := newMountPoint(t, "DCIM")
 	second := newMountPoint(t, "PRIVATE/M4ROOT")
+	third := newMountPoint(t, "DCIM")
 
-	got := filterDCFMountPoints([]string{newMountPoint(t), first, second})
+	// This one holds no DCF store, so it must not use up the requested count.
+	mountpoints := []string{newMountPoint(t), first, second, third}
 
-	want := []string{first, second}
-	if !slices.Equal(got, want) {
-		t.Errorf("filterDCFMountPoints = %v, want %v", got, want)
+	cases := map[int][]string{
+		0: {first, second, third},
+		1: {first},
+		2: {first, second},
+		3: {first, second, third},
+		4: {first, second, third},
+	}
+
+	for requestedCount, want := range cases {
+		got := filterDCFMountPoints(mountpoints, requestedCount)
+		if !slices.Equal(got, want) {
+			t.Errorf("filterDCFMountPoints(%d) = %v, want %v",
+				requestedCount, got, want)
+		}
 	}
 }

pkg/dcf/parse.go

@@ -1,7 +1,6 @@
 package dcf
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -29,13 +28,13 @@ var (
 // point. The root argument is the path of that mount point. Only DCIM and
 // PRIVATE/M4ROOT are read. A card can lack either one. A symlink is never
 // followed. An error names the mount point, because fsys reports only paths
-// inside it. When ctx is cancelled, the read stops before the next directory.
-func parseStore(ctx context.Context, fsys fs.FS, root string) (*Store, error) {
+// inside it.
+func parseStore(fsys fs.FS, root string) (*Store, error) {
 	store := &Store{RootDirectory: root}
 
-	err := parseDCIM(ctx, fsys, store)
+	err := parseDCIM(fsys, store)
 	if err == nil {
-		err = parseM4Root(ctx, fsys, store)
+		err = parseM4Root(fsys, store)
 	}
 
 	if err != nil {
@@ -69,26 +68,16 @@ func hasDirectory(fsys fs.FS, name string) (bool, error) {
 	return info.IsDir(), nil
 }
 
-// readDir returns the entries of the named directory, unless ctx is cancelled.
-func readDir(ctx context.Context, fsys fs.FS, name string) ([]fs.DirEntry, error) {
-	err := ctx.Err()
-	if err != nil {
-		return nil, err
-	}
-
-	return fs.ReadDir(fsys, name)
-}
-
 // parseDCIM adds the DCF directories under DCIM to store. Everything else there
 // is not conforming. That includes directories that share a directory number,
 // which section 7.1.2 of the specification treats as non-DCF directories.
-func parseDCIM(ctx context.Context, fsys fs.FS, store *Store) error {
+func parseDCIM(fsys fs.FS, store *Store) error {
 	found, err := hasDirectory(fsys, dcimDirectory)
 	if err != nil || !found {
 		return err
 	}
 
-	entries, err := readDir(ctx, fsys, dcimDirectory)
+	entries, err := fs.ReadDir(fsys, dcimDirectory)
 	if err != nil {
 		return err
 	}
@@ -105,9 +94,9 @@ func parseDCIM(ctx context.Context, fsys fs.FS, store *Store) error {
 		number := parseNumber(dcfDirectoryName, entry.Name())
 
 		if entry.IsDir() && number != 0 && directoriesWithNumber[number] == 1 {
-			err = parseDirectory(ctx, fsys, store, entry.Name(), number)
+			err = parseDirectory(fsys, store, entry.Name(), number)
 		} else {
-			err = addNonConforming(ctx, fsys, store, dcimDirectory, entry)
+			err = addNonConforming(fsys, store, dcimDirectory, entry)
 		}
 
 		if err != nil {
@@ -123,16 +112,10 @@ func parseDCIM(ctx context.Context, fsys fs.FS, store *Store) error {
 // Everything else there is not conforming. That includes JPG files that share a
 // file number, which section 7.2.2 of the specification says must not show DCF
 // numbers. Other files that share a file number do conform.
-func parseDirectory(
-	ctx context.Context,
-	fsys fs.FS,
-	store *Store,
-	name string,
-	number int,
-) error {
+func parseDirectory(fsys fs.FS, store *Store, name string, number int) error {
 	directoryPath := path.Join(dcimDirectory, name)
 
-	entries, err := readDir(ctx, fsys, directoryPath)
+	entries, err := fs.ReadDir(fsys, directoryPath)
 	if err != nil {
 		return err
 	}
@@ -152,7 +135,7 @@ func parseDirectory(
 		sharedJPG := isJPG(entry.Name()) && jpgsWithNumber[fileNumber] > 1
 
 		if !entry.Type().IsRegular() || fileNumber == 0 || sharedJPG {
-			err = addNonConforming(ctx, fsys, store, directoryPath, entry)
+			err = addNonConforming(fsys, store, directoryPath, entry)
 			if err != nil {
 				return err
 			}
@@ -162,7 +145,7 @@ func parseDirectory(
 
 		entryPath := path.Join(directoryPath, entry.Name())
 
-		object, err := newObject(fsys, store, entryPath, entry)
+		object, err := newObject(store, entryPath, entry)
 		if err != nil {
 			return err
 		}
@@ -184,7 +167,7 @@ func parseDirectory(
 // naming rules do not apply there, so these files have no DCF numbers. It skips
 // a symlink. It also skips a name that is not valid UTF-8, because fs.FS refuses
 // to open one.
-func parseM4Root(ctx context.Context, fsys fs.FS, store *Store) error {
+func parseM4Root(fsys fs.FS, store *Store) error {
 	found, err := hasDirectory(fsys, m4RootDirectory)
 	if err != nil || !found {
 		return err
@@ -202,16 +185,11 @@ func parseM4Root(ctx context.Context, fsys fs.FS, store *Store) error {
 				return fs.SkipDir
 			}
 
-			// fs.WalkDir reads a directory right after this call for it.
-			if entry.IsDir() {
-				return ctx.Err()
-			}
-
 			if !entry.Type().IsRegular() || !validName {
 				return nil
 			}
 
-			object, err := newObject(fsys, store, filePath, entry)
+			object, err := newObject(store, filePath, entry)
 			if err != nil {
 				return err
 			}
@@ -226,13 +204,7 @@ func parseM4Root(ctx context.Context, fsys fs.FS, store *Store) error {
 // conforming. If the entry is a directory, it lists everything inside it too. It
 // does not follow a symlink. It does not read a directory whose name is not
 // valid UTF-8, because fs.FS refuses to open one.
-func addNonConforming(
-	ctx context.Context,
-	fsys fs.FS,
-	store *Store,
-	dir string,
-	entry fs.DirEntry,
-) error {
+func addNonConforming(fsys fs.FS, store *Store, dir string, entry fs.DirEntry) error {
 	entryPath := path.Join(dir, entry.Name())
 	store.NonConforming = append(store.NonConforming, entryPath)
 
@@ -240,13 +212,13 @@ func addNonConforming(
 		return nil
 	}
 
-	entries, err := readDir(ctx, fsys, entryPath)
+	entries, err := fs.ReadDir(fsys, entryPath)
 	if err != nil {
 		return err
 	}
 
 	for _, inner := range entries {
-		err = addNonConforming(ctx, fsys, store, entryPath, inner)
+		err = addNonConforming(fsys, store, entryPath, inner)
 		if err != nil {
 			return err
 		}
@@ -256,12 +228,7 @@ func addNonConforming(
 }
 
 // newObject returns the Object for the file at filePath, with no DCF numbers.
-func newObject(
-	fsys fs.FS,
-	store *Store,
-	filePath string,
-	entry fs.DirEntry,
-) (Object, error) {
+func newObject(store *Store, filePath string, entry fs.DirEntry) (Object, error) {
 	info, err := entry.Info()
 	if err != nil {
 		return Object{}, err
@@ -272,7 +239,6 @@ func newObject(
 		Path:         filePath,
 		Size:         info.Size(),
 		Extension:    path.Ext(filePath),
-		fsys:         fsys,
 	}, nil
 }
 

pkg/dcf/parse_internal_test.go

@@ -1,7 +1,6 @@
 package dcf
 
 import (
-	"context"
 	"errors"
 	"io/fs"
 	"os"
@@ -66,7 +65,7 @@ func addSymlink(t *testing.T, root, name, target string) {
 func mustParseStore(t *testing.T, fsys fs.FS) *Store {
 	t.Helper()
 
-	store, err := parseStore(t.Context(), fsys, testRoot)
+	store, err := parseStore(fsys, testRoot)
 	if err != nil {
 		t.Fatalf("parseStore: %v", err)
 	}
@@ -158,7 +157,6 @@ func TestParseStorePutsEachFileWhereItBelongs(t *testing.T) {
 		Extension:       ".ARW",
 		DirectoryNumber: 100,
 		FileNumber:      1,
-		fsys:            card,
 	}
 	mp4 := Object{
 		DCFStoreRoot:    testRoot,
@@ -167,7 +165,6 @@ func TestParseStorePutsEachFileWhereItBelongs(t *testing.T) {
 		Extension:       ".MP4",
 		DirectoryNumber: 101,
 		FileNumber:      2,
-		fsys:            card,
 	}
 	thm := Object{
 		DCFStoreRoot:    testRoot,
@@ -176,14 +173,12 @@ func TestParseStorePutsEachFileWhereItBelongs(t *testing.T) {
 		Extension:       ".THM",
 		DirectoryNumber: 101,
 		FileNumber:      2,
-		fsys:            card,
 	}
 	clip := Object{
 		DCFStoreRoot: testRoot,
 		Path:         "PRIVATE/M4ROOT/CLIP/C0002.MP4",
 		Size:         400,
 		Extension:    ".MP4",
-		fsys:         card,
 	}
 
 	wantDirectories := []*Directory{
@@ -318,9 +313,7 @@ func TestParseNumberOfFileName(t *testing.T) {
 func TestParseStoreTreatsLowerCaseNamesAsDCFNames(t *testing.T) {
 	t.Parallel()
 
-	card := newCard("DCIM/101abcde/abcd0002.jpg")
-
-	store := mustParseStore(t, card)
+	store := mustParseStore(t, newCard("DCIM/101abcde/abcd0002.jpg"))
 
 	want := []*Directory{wantDirectory(101, "101abcde", &Object{
 		DCFStoreRoot:    testRoot,
@@ -328,7 +321,6 @@ func TestParseStoreTreatsLowerCaseNamesAsDCFNames(t *testing.T) {
 		Extension:       ".jpg",
 		DirectoryNumber: 101,
 		FileNumber:      2,
-		fsys:            card,
 	})}
 	if !reflect.DeepEqual(store.Directories, want) {
 		t.Errorf("Directories = %+v, want %+v", store.Directories, want)
@@ -805,7 +797,7 @@ func TestParseStoreReturnsReadErrorsNamingTheCard(t *testing.T) {
 		for _, name := range names {
 			fsys := failingFS{MapFS: card, call: call, name: name}
 
-			_, err := parseStore(t.Context(), fsys, testRoot)
+			_, err := parseStore(fsys, testRoot)
 			if !errors.Is(err, fs.ErrPermission) {
 				t.Errorf("%s of %s: error = %v, want %v",
 					call, name, err, fs.ErrPermission)
@@ -821,86 +813,3 @@ func TestParseStoreReturnsReadErrorsNamingTheCard(t *testing.T) {
 		}
 	}
 }
-
-// cancelingFS is a card that cancels the read when the read reaches the named
-// directory. It records every directory read in read.
-type cancelingFS struct {
-	fstest.MapFS
-
-	name   string
-	cancel context.CancelFunc
-	read   *[]string
-}
-
-func (f cancelingFS) ReadDir(name string) ([]fs.DirEntry, error) {
-	*f.read = append(*f.read, name)
-
-	if name == f.name {
-		f.cancel()
-	}
-
-	return f.MapFS.ReadDir(name)
-}
-
-func TestParseStoreStopsBeforeTheNextDirectoryWhenCancelled(t *testing.T) {
-	t.Parallel()
-
-	card := newCard(
-		"DCIM/100ABCDE/SUB/README.TXT",
-		"DCIM/OTHER/SUB/README.TXT",
-		"PRIVATE/M4ROOT/CLIP/SUB/C0001.MP4",
-	)
-
-	// Each of these directories holds another directory, which must not be read.
-	names := []string{
-		dcimDirectory,
-		"DCIM/100ABCDE",
-		"DCIM/OTHER",
-		m4RootDirectory,
-		"PRIVATE/M4ROOT/CLIP",
-	}
-
-	for _, name := range names {
-		ctx, cancel := context.WithCancel(t.Context())
-
-		var read []string
-
-		fsys := cancelingFS{MapFS: card, name: name, cancel: cancel, read: &read}
-
-		_, err := parseStore(ctx, fsys, testRoot)
-		if !errors.Is(err, context.Canceled) {
-			t.Errorf("cancelled at %s: error = %v, want %v",
-				name, err, context.Canceled)
-		}
-
-		if read[len(read)-1] != name {
-			t.Errorf("cancelled at %s: read %q", name, read)
-		}
-	}
-}
-
-func TestParseStoreReadsNoDirectoryWhenAlreadyCancelled(t *testing.T) {
-	t.Parallel()
-
-	ctx, cancel := context.WithCancel(t.Context())
-	cancel()
-
-	cards := []fstest.MapFS{
-		newCard("DCIM/README.TXT"),
-		newCard("PRIVATE/M4ROOT/C0001.MP4"),
-	}
-
-	for _, card := range cards {
-		var read []string
-
-		// The context is already cancelled, so this needs no name to cancel at.
-		fsys := cancelingFS{MapFS: card, read: &read}
-
-		_, err := parseStore(ctx, fsys, testRoot)
-		if !errors.Is(err, context.Canceled) {
-			t.Errorf("error = %v, want %v", err, context.Canceled)
-		}
-
-		assertPaths(t, "directories read", read)
-	}
-}