Centralize storage walk emission

internal/adapters/local/backend.go

@@ -161,31 +161,10 @@ func (b *Backend) Walk(ctx context.Context, prefix string, opts storage.WalkOpti
 		}
 		return b.translateError(storage.OpWalk, prefix, err)
 	}
-	visited := 0
-	emit := func(entry storage.Entry) error {
-		if err := ctx.Err(); err != nil {
-			return err
-		}
-		if opts.Limit > 0 && visited >= opts.Limit {
-			return storage.ErrStopWalk
-		}
-		visited++
-		if err := fn(entry); err != nil {
-			if errors.Is(err, storage.ErrStopWalk) {
-				return storage.ErrStopWalk
-			}
-			return storage.NewError(storage.OpWalk, backendName, entry.Path, storage.ErrUnknown, err)
-		}
-		return nil
-	}
+	emitter := storage.NewWalkEmitter(ctx, backendName, opts, fn)
 
 	if !info.IsDir() {
-		if err := emit(entryFromInfo(prefix, info)); errors.Is(err, storage.ErrStopWalk) {
-			return nil
-		} else if err != nil {
-			return err
-		}
-		return nil
+		return storage.FinishWalk(emitter.Emit(entryFromInfo(prefix, info)))
 	}
 
 	walkErr := filepath.WalkDir(nativePrefix, func(nativePath string, dirEntry fs.DirEntry, err error) error {
@@ -210,24 +189,13 @@ func (b *Backend) Walk(ctx context.Context, prefix string, opts storage.WalkOpti
 		if err != nil {
 			return b.translateError(storage.OpWalk, logicalPath, err)
 		}
-		return emit(entryFromInfo(logicalPath, info))
+		return emitter.Emit(entryFromInfo(logicalPath, info))
 	})
-	if errors.Is(walkErr, storage.ErrStopWalk) {
-		return nil
-	}
-	return walkErr
+	return storage.FinishWalk(walkErr)
 }
 
 func (b *Backend) HasAny(ctx context.Context, prefix string) (bool, error) {
-	found := false
-	err := b.Walk(ctx, prefix, storage.WalkOptions{Recursive: false, Limit: 1}, func(storage.Entry) error {
-		found = true
-		return storage.ErrStopWalk
-	})
-	if err != nil {
-		return false, err
-	}
-	return found, nil
+	return storage.HasAny(ctx, b, prefix)
 }
 
 func (b *Backend) DeleteManagedBundle(ctx context.Context, bundlePath string, managedOutputPaths []string, opts storage.DeleteOptions) error {

internal/adapters/s3/backend.go

@@ -183,55 +183,25 @@ func (b *Backend) Walk(ctx context.Context, logicalPrefix string, opts storage.W
 	if err := storage.ValidatePrefix(logicalPrefix); err != nil {
 		return err
 	}
-	visited := 0
-	emit := func(entry storage.Entry) error {
-		if err := ctx.Err(); err != nil {
-			return err
-		}
-		if opts.Limit > 0 && visited >= opts.Limit {
-			return storage.ErrStopWalk
-		}
-		visited++
-		if err := fn(entry); err != nil {
-			if errors.Is(err, storage.ErrStopWalk) {
-				return storage.ErrStopWalk
-			}
-			return storage.NewError(storage.OpWalk, BackendName, entry.Path, storage.ErrUnknown, err)
-		}
-		return nil
-	}
+	emitter := storage.NewWalkEmitter(ctx, BackendName, opts, fn)
 	if logicalPrefix != "" {
 		entry, err := b.Stat(ctx, logicalPrefix)
 		if err == nil {
-			if err := emit(entry); errors.Is(err, storage.ErrStopWalk) {
-				return nil
-			} else if err != nil {
-				return err
+			if err := emitter.Emit(entry); err != nil {
+				return storage.FinishWalk(err)
 			}
-			if opts.Limit > 0 && visited >= opts.Limit {
+			if emitter.LimitReached() {
 				return nil
 			}
 		} else if !storage.IsNotFound(err) {
 			return err
 		}
 	}
-	err := b.walkObjects(ctx, logicalPrefix, opts, emit)
-	if errors.Is(err, storage.ErrStopWalk) {
-		return nil
-	}
-	return err
+	return storage.FinishWalk(b.walkObjects(ctx, logicalPrefix, opts, emitter.Emit))
 }
 
 func (b *Backend) HasAny(ctx context.Context, logicalPrefix string) (bool, error) {
-	found := false
-	err := b.Walk(ctx, logicalPrefix, storage.WalkOptions{Recursive: false, Limit: 1}, func(storage.Entry) error {
-		found = true
-		return storage.ErrStopWalk
-	})
-	if err != nil {
-		return false, err
-	}
-	return found, nil
+	return storage.HasAny(ctx, b, logicalPrefix)
 }
 
 func (b *Backend) DeleteManagedBundle(ctx context.Context, bundlePath string, managedOutputPaths []string, opts storage.DeleteOptions) error {

internal/adapters/ssh/backend.go

@@ -209,51 +209,17 @@ func (b *Backend) Walk(ctx context.Context, prefix string, opts storage.WalkOpti
 		return b.translateError(storage.OpWalk, prefix, err)
 	}
 
-	visited := 0
-	emit := func(entry storage.Entry) error {
-		if err := ctx.Err(); err != nil {
-			return err
-		}
-		if opts.Limit > 0 && visited >= opts.Limit {
-			return storage.ErrStopWalk
-		}
-		visited++
-		if err := fn(entry); err != nil {
-			if errors.Is(err, storage.ErrStopWalk) {
-				return storage.ErrStopWalk
-			}
-			return storage.NewError(storage.OpWalk, BackendName, entry.Path, storage.ErrUnknown, err)
-		}
-		return nil
-	}
+	emitter := storage.NewWalkEmitter(ctx, BackendName, opts, fn)
 
 	if !info.IsDir() {
-		if err := emit(entryFromInfo(prefix, info)); errors.Is(err, storage.ErrStopWalk) {
-			return nil
-		} else if err != nil {
-			return err
-		}
-		return nil
+		return storage.FinishWalk(emitter.Emit(entryFromInfo(prefix, info)))
 	}
 
-	if err := b.walkDirectory(ctx, prefix, nativePrefix, opts, emit); errors.Is(err, storage.ErrStopWalk) {
-		return nil
-	} else if err != nil {
-		return err
-	}
-	return nil
+	return storage.FinishWalk(b.walkDirectory(ctx, prefix, nativePrefix, opts, emitter.Emit))
 }
 
 func (b *Backend) HasAny(ctx context.Context, prefix string) (bool, error) {
-	found := false
-	err := b.Walk(ctx, prefix, storage.WalkOptions{Recursive: false, Limit: 1}, func(storage.Entry) error {
-		found = true
-		return storage.ErrStopWalk
-	})
-	if err != nil {
-		return false, err
-	}
-	return found, nil
+	return storage.HasAny(ctx, b, prefix)
 }
 
 func (b *Backend) DeleteManagedBundle(ctx context.Context, bundlePath string, managedOutputPaths []string, opts storage.DeleteOptions) error {

internal/storage/walk.go

@@ -0,0 +1,63 @@
+package storage
+
+import (
+	"context"
+	"errors"
+)
+
+type WalkEmitter struct {
+	ctx     context.Context
+	backend string
+	opts    WalkOptions
+	fn      WalkFunc
+	count   int
+}
+
+func NewWalkEmitter(ctx context.Context, backend string, opts WalkOptions, fn WalkFunc) *WalkEmitter {
+	return &WalkEmitter{
+		ctx:     ctx,
+		backend: backend,
+		opts:    opts,
+		fn:      fn,
+	}
+}
+
+func (e *WalkEmitter) Emit(entry Entry) error {
+	if err := e.ctx.Err(); err != nil {
+		return err
+	}
+	if e.opts.Limit > 0 && e.count >= e.opts.Limit {
+		return ErrStopWalk
+	}
+	e.count++
+	if err := e.fn(entry); err != nil {
+		if errors.Is(err, ErrStopWalk) {
+			return ErrStopWalk
+		}
+		return NewError(OpWalk, e.backend, entry.Path, ErrUnknown, err)
+	}
+	return nil
+}
+
+func (e *WalkEmitter) LimitReached() bool {
+	return e.opts.Limit > 0 && e.count >= e.opts.Limit
+}
+
+func FinishWalk(err error) error {
+	if errors.Is(err, ErrStopWalk) {
+		return nil
+	}
+	return err
+}
+
+func HasAny(ctx context.Context, backend Backend, prefix string) (bool, error) {
+	found := false
+	err := backend.Walk(ctx, prefix, WalkOptions{Recursive: false, Limit: 1}, func(Entry) error {
+		found = true
+		return ErrStopWalk
+	})
+	if err != nil {
+		return false, err
+	}
+	return found, nil
+}

internal/storage/walk_test.go

@@ -0,0 +1,107 @@
+package storage
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestWalkEmitterHonorsLimit(t *testing.T) {
+	emitter := NewWalkEmitter(context.Background(), "test", WalkOptions{Limit: 2}, func(Entry) error {
+		return nil
+	})
+
+	if err := emitter.Emit(Entry{Path: "one"}); err != nil {
+		t.Fatalf("first Emit() error = %v", err)
+	}
+	if err := emitter.Emit(Entry{Path: "two"}); err != nil {
+		t.Fatalf("second Emit() error = %v", err)
+	}
+	if err := emitter.Emit(Entry{Path: "three"}); !errors.Is(err, ErrStopWalk) {
+		t.Fatalf("third Emit() error = %v, want ErrStopWalk", err)
+	}
+	if !emitter.LimitReached() {
+		t.Fatal("LimitReached() = false, want true")
+	}
+}
+
+func TestWalkEmitterStopsWithoutError(t *testing.T) {
+	emitter := NewWalkEmitter(context.Background(), "test", WalkOptions{}, func(Entry) error {
+		return ErrStopWalk
+	})
+
+	err := emitter.Emit(Entry{Path: "one"})
+	if !errors.Is(err, ErrStopWalk) {
+		t.Fatalf("Emit() error = %v, want ErrStopWalk", err)
+	}
+	if err := FinishWalk(err); err != nil {
+		t.Fatalf("FinishWalk() error = %v, want nil", err)
+	}
+}
+
+func TestWalkEmitterWrapsCallbackErrors(t *testing.T) {
+	callbackErr := errors.New("callback failed")
+	emitter := NewWalkEmitter(context.Background(), "test", WalkOptions{}, func(Entry) error {
+		return callbackErr
+	})
+
+	err := emitter.Emit(Entry{Path: "one"})
+	if !errors.Is(err, callbackErr) {
+		t.Fatalf("Emit() error = %v, want callback error", err)
+	}
+	var storageErr *Error
+	if !errors.As(err, &storageErr) {
+		t.Fatalf("Emit() error type = %T, want *Error", err)
+	}
+	if storageErr.Op != OpWalk || storageErr.Backend != "test" || storageErr.Path != "one" || storageErr.Kind != ErrUnknown {
+		t.Fatalf("wrapped error = %#v", storageErr)
+	}
+}
+
+func TestWalkEmitterHonorsContextCancellation(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	called := false
+	emitter := NewWalkEmitter(ctx, "test", WalkOptions{}, func(Entry) error {
+		called = true
+		return nil
+	})
+
+	err := emitter.Emit(Entry{Path: "one"})
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("Emit() error = %v, want context.Canceled", err)
+	}
+	if called {
+		t.Fatal("callback was called after context cancellation")
+	}
+}
+
+func TestHasAnyUsesNonRecursiveLimitOneWalk(t *testing.T) {
+	backend := &recordingBackend{}
+
+	found, err := HasAny(context.Background(), backend, "bundle")
+	if err != nil {
+		t.Fatalf("HasAny() error = %v", err)
+	}
+	if !found {
+		t.Fatal("HasAny() = false, want true")
+	}
+	if backend.prefix != "bundle" {
+		t.Fatalf("walk prefix = %q, want bundle", backend.prefix)
+	}
+	if backend.opts != (WalkOptions{Recursive: false, Limit: 1}) {
+		t.Fatalf("walk options = %#v, want non-recursive limit one", backend.opts)
+	}
+}
+
+type recordingBackend struct {
+	Backend
+	prefix string
+	opts   WalkOptions
+}
+
+func (b *recordingBackend) Walk(_ context.Context, prefix string, opts WalkOptions, fn WalkFunc) error {
+	b.prefix = prefix
+	b.opts = opts
+	return FinishWalk(fn(Entry{Path: "bundle/file.txt", Type: EntryTypeFile}))
+}