feat: add support for S3 storage backend (#1080)

Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

backend/internal/storage/filesystem.go

@@ -0,0 +1,193 @@
+package storage
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/google/uuid"
+)
+
+type filesystemStorage struct {
+	root             *os.Root
+	absoluteRootPath string
+}
+
+func NewFilesystemStorage(rootPath string) (FileStorage, error) {
+	if err := os.MkdirAll(rootPath, 0700); err != nil {
+		return nil, fmt.Errorf("failed to create root directory '%s': %w", rootPath, err)
+	}
+	root, err := os.OpenRoot(rootPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open root directory '%s': %w", rootPath, err)
+	}
+
+	absoluteRootPath, err := filepath.Abs(rootPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get absolute path of root directory '%s': %w", rootPath, err)
+	}
+
+	return &filesystemStorage{root: root, absoluteRootPath: absoluteRootPath}, err
+}
+
+func (s *filesystemStorage) Type() string {
+	return TypeFileSystem
+}
+
+func (s *filesystemStorage) Save(_ context.Context, path string, data io.Reader) error {
+	path = filepath.FromSlash(path)
+
+	if err := s.root.MkdirAll(filepath.Dir(path), 0700); err != nil {
+		return fmt.Errorf("failed to create directories for path '%s': %w", path, err)
+	}
+
+	// Our strategy is to save to a separate file and then rename it to override the original file
+	tmpName := path + "." + uuid.NewString() + "-tmp"
+
+	// Write to the temporary file
+	tmpFile, err := s.root.Create(tmpName)
+	if err != nil {
+		return fmt.Errorf("failed to open file '%s' for writing: %w", tmpName, err)
+	}
+
+	_, err = io.Copy(tmpFile, data)
+	if err != nil {
+		tmpFile.Close()
+		_ = s.root.Remove(tmpName)
+		return fmt.Errorf("failed to write temporary file: %w", err)
+	}
+
+	if err = tmpFile.Close(); err != nil {
+		_ = s.root.Remove(tmpName)
+		return fmt.Errorf("failed to close temporary file: %w", err)
+	}
+
+	// Rename to the final file, which overrides existing files
+	// This is an atomic operation
+	if err = s.root.Rename(tmpName, path); err != nil {
+		_ = s.root.Remove(tmpName)
+		return fmt.Errorf("failed to move temporary file: %w", err)
+	}
+
+	return nil
+}
+
+func (s *filesystemStorage) Open(_ context.Context, path string) (io.ReadCloser, int64, error) {
+	path = filepath.FromSlash(path)
+
+	file, err := s.root.Open(path)
+	if err != nil {
+		return nil, 0, err
+	}
+	info, err := file.Stat()
+	if err != nil {
+		file.Close()
+		return nil, 0, err
+	}
+	return file, info.Size(), nil
+}
+
+func (s *filesystemStorage) Delete(_ context.Context, path string) error {
+	path = filepath.FromSlash(path)
+
+	err := s.root.Remove(path)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return err
+	}
+	return nil
+}
+
+func (s *filesystemStorage) DeleteAll(_ context.Context, path string) error {
+	path = filepath.FromSlash(path)
+
+	// If "/", "." or "" is requested, we delete all contents of the root.
+	if path == "" || path == "/" || path == "." {
+		dir, err := s.root.Open(".")
+		if err != nil {
+			return fmt.Errorf("failed to open root directory: %w", err)
+		}
+		defer dir.Close()
+
+		entries, err := dir.ReadDir(-1)
+		if err != nil {
+			return fmt.Errorf("failed to list root directory: %w", err)
+		}
+		for _, entry := range entries {
+			if err := s.root.RemoveAll(entry.Name()); err != nil {
+				return fmt.Errorf("failed to delete '%s': %w", entry.Name(), err)
+			}
+		}
+		return nil
+	}
+
+	return s.root.RemoveAll(path)
+}
+func (s *filesystemStorage) List(_ context.Context, path string) ([]ObjectInfo, error) {
+	path = filepath.FromSlash(path)
+
+	dir, err := s.root.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer dir.Close()
+
+	entries, err := dir.ReadDir(-1)
+	if err != nil {
+		return nil, err
+	}
+
+	objects := make([]ObjectInfo, 0, len(entries))
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		info, err := entry.Info()
+		if err != nil {
+			return nil, err
+		}
+		objects = append(objects, ObjectInfo{
+			Path:    filepath.Join(path, entry.Name()),
+			Size:    info.Size(),
+			ModTime: info.ModTime(),
+		})
+	}
+	return objects, nil
+}
+func (s *filesystemStorage) Walk(_ context.Context, root string, fn func(ObjectInfo) error) error {
+	root = filepath.FromSlash(root)
+
+	fullPath := filepath.Clean(filepath.Join(s.absoluteRootPath, root))
+
+	// As we can't use os.Root here, we manually ensure that the fullPath is within the root directory
+	sep := string(filepath.Separator)
+	if !strings.HasPrefix(fullPath+sep, s.absoluteRootPath+sep) {
+		return fmt.Errorf("invalid root path: %s", root)
+	}
+
+	return filepath.WalkDir(fullPath, func(full string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			return nil
+		}
+		rel, err := filepath.Rel(s.absoluteRootPath, full)
+		if err != nil {
+			return err
+		}
+		info, err := d.Info()
+		if err != nil {
+			return err
+		}
+		return fn(ObjectInfo{
+			Path:    filepath.ToSlash(rel),
+			Size:    info.Size(),
+			ModTime: info.ModTime(),
+		})
+	})
+}