Add storage backends and safety checks

internal/storage/backend.go

@@ -0,0 +1,68 @@
+package storage
+
+import (
+	"context"
+	"errors"
+	"io"
+)
+
+type EntryType string
+
+const (
+	EntryTypeFile      EntryType = "file"
+	EntryTypeDirectory EntryType = "directory"
+	EntryTypeSymlink   EntryType = "symlink"
+	EntryTypeOther     EntryType = "other"
+)
+
+type Entry struct {
+	Path string
+	Type EntryType
+	Size int64
+}
+
+type Backend interface {
+	ReadFile(ctx context.Context, path string) ([]byte, error)
+	OpenReader(ctx context.Context, path string) (io.ReadCloser, error)
+	WriteFile(ctx context.Context, path string, data []byte, opts WriteOptions) (Entry, error)
+	WriteFrom(ctx context.Context, path string, r io.Reader, opts WriteOptions) (Entry, error)
+	Stat(ctx context.Context, path string) (Entry, error)
+	Walk(ctx context.Context, prefix string, opts WalkOptions, fn WalkFunc) error
+	HasAny(ctx context.Context, prefix string) (bool, error)
+	DeleteManagedBundle(ctx context.Context, bundlePath string, managedOutputPaths []string, opts DeleteOptions) error
+}
+
+type WalkOptions struct {
+	Recursive bool
+	Limit     int
+}
+
+type WalkFunc func(Entry) error
+
+var ErrStopWalk = errors.New("stop walk")
+
+type WriteOptions struct {
+	ContentType  string
+	Overwrite    bool
+	PreferAtomic bool
+	Size         int64
+	SizeKnown    bool
+}
+
+type DeleteOptions struct {
+	IgnoreMissing  bool
+	PruneEmptyDirs bool
+}
+
+func List(ctx context.Context, backend Backend, prefix string, opts WalkOptions) ([]Entry, error) {
+	var entries []Entry
+	err := backend.Walk(ctx, prefix, opts, func(entry Entry) error {
+		entries = append(entries, entry)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	SortEntries(entries)
+	return entries, nil
+}