Add atomic account registration and local media

medialocal/store.go

@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: MPL-2.0
+
+// Package medialocal stores prepared media in a private content-addressed
+// filesystem tree.
+package medialocal
+
+import (
+	"context"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"time"
+
+	"gamertan.com/web/media"
+)
+
+type Store struct {
+	root string
+	now  func() time.Time
+}
+
+type Options struct {
+	Now func() time.Time
+}
+
+func Open(root string, options Options) (*Store, error) {
+	absolute, err := filepath.Abs(root)
+	if err != nil || filepath.Clean(absolute) != absolute {
+		return nil, errors.New("medialocal: root must be a clean absolute path")
+	}
+	if err = secureDirectory(absolute, true); err != nil {
+		return nil, err
+	}
+	resolved, err := filepath.EvalSymlinks(absolute)
+	if err != nil {
+		return nil, fmt.Errorf("medialocal: resolve root: %w", err)
+	}
+	if options.Now == nil {
+		options.Now = time.Now
+	}
+	return &Store{root: resolved, now: options.Now}, nil
+}
+
+func (store *Store) Put(ctx context.Context, prepared media.Prepared) (media.Object, error) {
+	if err := ctx.Err(); err != nil {
+		return media.Object{}, err
+	}
+	if len(prepared.Data) == 0 || !media.ValidKey(prepared.Key()) || sha256.Sum256(prepared.Data) != prepared.Digest {
+		return media.Object{}, media.ErrInvalidMedia
+	}
+	shard, target := store.objectPath(prepared.Key())
+	if err := secureDirectory(shard, true); err != nil {
+		return media.Object{}, err
+	}
+	if object, ok, err := inspect(target, prepared.MediaType); err != nil {
+		return media.Object{}, err
+	} else if ok {
+		if object.Size != int64(len(prepared.Data)) {
+			return media.Object{}, errors.New("medialocal: existing digest has an unexpected size")
+		}
+		return object, nil
+	}
+	temporary, err := os.CreateTemp(shard, ".upload-*")
+	if err != nil {
+		return media.Object{}, fmt.Errorf("medialocal: create temporary object: %w", err)
+	}
+	temporaryName := temporary.Name()
+	defer os.Remove(temporaryName)
+	if err = temporary.Chmod(0o640); err == nil {
+		_, err = temporary.Write(prepared.Data)
+	}
+	if err == nil {
+		err = temporary.Sync()
+	}
+	if closeErr := temporary.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		return media.Object{}, fmt.Errorf("medialocal: write object: %w", err)
+	}
+	if err = os.Link(temporaryName, target); err != nil {
+		if errors.Is(err, os.ErrExist) {
+			object, ok, inspectErr := inspect(target, prepared.MediaType)
+			if inspectErr != nil {
+				return media.Object{}, inspectErr
+			}
+			if ok && object.Size == int64(len(prepared.Data)) {
+				return object, nil
+			}
+		}
+		return media.Object{}, fmt.Errorf("medialocal: commit object: %w", err)
+	}
+	return media.Object{Key: prepared.Key(), Size: int64(len(prepared.Data)), MediaType: prepared.MediaType, CreatedAt: store.now().UTC()}, nil
+}
+
+func (store *Store) Open(ctx context.Context, key string) (io.ReadCloser, media.Object, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, media.Object{}, err
+	}
+	if !media.ValidKey(key) {
+		return nil, media.Object{}, media.ErrNotFound
+	}
+	shard, target := store.objectPath(key)
+	if err := secureDirectory(shard, false); err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil, media.Object{}, media.ErrNotFound
+		}
+		return nil, media.Object{}, err
+	}
+	before, err := os.Lstat(target)
+	if errors.Is(err, os.ErrNotExist) {
+		return nil, media.Object{}, media.ErrNotFound
+	}
+	if err != nil || !before.Mode().IsRegular() || before.Mode()&os.ModeSymlink != 0 {
+		return nil, media.Object{}, errors.New("medialocal: object is not a regular file")
+	}
+	file, err := os.Open(target)
+	if err != nil {
+		return nil, media.Object{}, err
+	}
+	after, err := file.Stat()
+	if err != nil || !os.SameFile(before, after) {
+		file.Close()
+		return nil, media.Object{}, errors.New("medialocal: object changed while opening")
+	}
+	return file, media.Object{Key: key, Size: after.Size(), CreatedAt: after.ModTime().UTC()}, nil
+}
+
+func (store *Store) Delete(ctx context.Context, key string) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	if !media.ValidKey(key) {
+		return media.ErrNotFound
+	}
+	_, target := store.objectPath(key)
+	info, err := os.Lstat(target)
+	if errors.Is(err, os.ErrNotExist) {
+		return media.ErrNotFound
+	}
+	if err != nil || !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 {
+		return errors.New("medialocal: refusing to delete a non-regular object")
+	}
+	if err = os.Remove(target); errors.Is(err, os.ErrNotExist) {
+		return media.ErrNotFound
+	}
+	return err
+}
+
+func (store *Store) objectPath(key string) (string, string) {
+	shard := filepath.Join(store.root, key[:2])
+	return shard, filepath.Join(shard, key)
+}
+
+func secureDirectory(path string, create bool) error {
+	info, err := os.Lstat(path)
+	if errors.Is(err, os.ErrNotExist) && create {
+		if err = os.MkdirAll(path, 0o750); err != nil {
+			return fmt.Errorf("medialocal: create directory: %w", err)
+		}
+		info, err = os.Lstat(path)
+	}
+	if err != nil {
+		return err
+	}
+	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
+		return errors.New("medialocal: storage directory must not be a symlink")
+	}
+	return nil
+}
+
+func inspect(path, mediaType string) (media.Object, bool, error) {
+	info, err := os.Lstat(path)
+	if errors.Is(err, os.ErrNotExist) {
+		return media.Object{}, false, nil
+	}
+	if err != nil {
+		return media.Object{}, false, err
+	}
+	if !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 {
+		return media.Object{}, false, errors.New("medialocal: existing object is not a regular file")
+	}
+	return media.Object{Key: filepath.Base(path), Size: info.Size(), MediaType: mediaType, CreatedAt: info.ModTime().UTC()}, true, nil
+}