Implement resumable download queue (T-301)

2026-07-16 19:49:06 +08:00
parent 2d302b731a
commit 8dad40f934
27 changed files with 5498 additions and 18 deletions
@@ -0,0 +1,354 @@
+package storage
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"sort"
+	"strings"
+	"sync"
+
+	"softbox.local/core/downloader"
+)
+
+const (
+	maxDownloadTaskDocumentBytes = 64 * 1024
+	maxDownloadTaskCount         = 4096
+)
+
+var ErrDownloadTaskLayoutUnsafe = errors.New("download task storage layout is unsafe")
+
+// DownloadTaskStore atomically persists download metadata below
+// downloads/tasks. Transfer bytes live separately below downloads/files.
+type DownloadTaskStore struct {
+	root string
+	mu   sync.Mutex
+}
+
+// NewDownloadTaskStore creates a strict JSON task store.
+func NewDownloadTaskStore(downloadsRoot string) *DownloadTaskStore {
+	return &DownloadTaskStore{root: downloadsRoot}
+}
+
+// Write validates and atomically replaces one task document.
+func (store *DownloadTaskStore) Write(task downloader.Task) error {
+	store.mu.Lock()
+	defer store.mu.Unlock()
+
+	if err := task.Validate(); err != nil {
+		return err
+	}
+	paths, err := store.ensureLayout(task.RequestID)
+	if err != nil {
+		return err
+	}
+	document, err := json.Marshal(task)
+	if err != nil {
+		return fmt.Errorf("encode download task: %w", err)
+	}
+	document = append(document, '\n')
+	if len(document) > maxDownloadTaskDocumentBytes {
+		return fmt.Errorf("%w: metadata is too large", downloader.ErrInvalidTask)
+	}
+	return replaceDownloadTaskFile(paths.TasksDir, paths.Metadata, paths.Backup, document)
+}
+
+// LoadAll reads every task, falling back to a backup only when its main file
+// is absent.
+func (store *DownloadTaskStore) LoadAll() ([]downloader.Task, error) {
+	store.mu.Lock()
+	defer store.mu.Unlock()
+
+	paths, err := store.ensureLayout("layout-probe")
+	if err != nil {
+		return nil, err
+	}
+	entries, err := os.ReadDir(paths.TasksDir)
+	if err != nil {
+		return nil, fmt.Errorf("read download task directory: %w", err)
+	}
+	requestIDs := make(map[string]struct{})
+	for _, entry := range entries {
+		name := entry.Name()
+		if strings.HasPrefix(name, ".download-task-") && strings.HasSuffix(name, ".tmp") {
+			continue
+		}
+		requestID, recognized := metadataRequestID(name)
+		if !recognized || !downloader.ValidRequestID(requestID) {
+			return nil, fmt.Errorf(
+				"%w: unexpected metadata entry %q",
+				ErrDownloadTaskLayoutUnsafe,
+				name,
+			)
+		}
+		info, infoErr := entry.Info()
+		if infoErr != nil {
+			return nil, fmt.Errorf("inspect download task entry: %w", infoErr)
+		}
+		if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
+			return nil, fmt.Errorf(
+				"%w: metadata entry is not regular",
+				ErrDownloadTaskLayoutUnsafe,
+			)
+		}
+		requestIDs[requestID] = struct{}{}
+	}
+	if len(requestIDs) > maxDownloadTaskCount {
+		return nil, fmt.Errorf("%w: too many tasks", downloader.ErrInvalidTask)
+	}
+	sortedIDs := make([]string, 0, len(requestIDs))
+	for requestID := range requestIDs {
+		sortedIDs = append(sortedIDs, requestID)
+	}
+	sort.Strings(sortedIDs)
+
+	tasks := make([]downloader.Task, 0, len(sortedIDs))
+	for _, requestID := range sortedIDs {
+		taskPaths, deriveErr := downloader.DeriveTaskPaths(store.root, requestID)
+		if deriveErr != nil {
+			return nil, deriveErr
+		}
+		document, readErr := readBoundedRegularFile(
+			taskPaths.Metadata,
+			maxDownloadTaskDocumentBytes,
+		)
+		if os.IsNotExist(readErr) {
+			document, readErr = readBoundedRegularFile(
+				taskPaths.Backup,
+				maxDownloadTaskDocumentBytes,
+			)
+		}
+		if readErr != nil {
+			return nil, readErr
+		}
+		task, decodeErr := decodeDownloadTask(document)
+		if decodeErr != nil {
+			return nil, decodeErr
+		}
+		if task.RequestID != requestID {
+			return nil, fmt.Errorf(
+				"%w: request_id does not match metadata filename",
+				downloader.ErrInvalidTask,
+			)
+		}
+		tasks = append(tasks, task)
+	}
+	return tasks, nil
+}
+
+// Delete removes the exact metadata and backup files for a request.
+func (store *DownloadTaskStore) Delete(requestID string) error {
+	store.mu.Lock()
+	defer store.mu.Unlock()
+
+	paths, err := downloader.DeriveTaskPaths(store.root, requestID)
+	if err != nil {
+		return err
+	}
+	for _, candidate := range []string{paths.Metadata, paths.Backup} {
+		info, inspectErr := os.Lstat(candidate)
+		if os.IsNotExist(inspectErr) {
+			continue
+		}
+		if inspectErr != nil {
+			return fmt.Errorf("inspect download task metadata: %w", inspectErr)
+		}
+		if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
+			return fmt.Errorf(
+				"%w: metadata is not a regular file",
+				ErrDownloadTaskLayoutUnsafe,
+			)
+		}
+		if removeErr := os.Remove(candidate); removeErr != nil {
+			return fmt.Errorf("remove download task metadata: %w", removeErr)
+		}
+	}
+	return nil
+}
+
+func (store *DownloadTaskStore) ensureLayout(requestID string) (downloader.TaskPaths, error) {
+	paths, err := downloader.DeriveTaskPaths(store.root, requestID)
+	if err != nil {
+		return downloader.TaskPaths{}, err
+	}
+	if err := os.MkdirAll(paths.Root, 0o700); err != nil {
+		return downloader.TaskPaths{}, fmt.Errorf("create downloads root: %w", err)
+	}
+	for _, directory := range []string{paths.Root, paths.TasksDir, paths.FilesDir} {
+		if err := os.Mkdir(directory, 0o700); err != nil && !os.IsExist(err) {
+			return downloader.TaskPaths{}, fmt.Errorf("create download directory: %w", err)
+		}
+		info, inspectErr := os.Lstat(directory)
+		if inspectErr != nil {
+			return downloader.TaskPaths{}, fmt.Errorf("inspect download directory: %w", inspectErr)
+		}
+		if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
+			return downloader.TaskPaths{}, fmt.Errorf(
+				"%w: managed path is not a real directory",
+				ErrDownloadTaskLayoutUnsafe,
+			)
+		}
+	}
+	return paths, nil
+}
+
+func metadataRequestID(name string) (string, bool) {
+	switch {
+	case strings.HasSuffix(name, ".json.backup"):
+		return strings.TrimSuffix(name, ".json.backup"), true
+	case strings.HasSuffix(name, ".json"):
+		return strings.TrimSuffix(name, ".json"), true
+	default:
+		return "", false
+	}
+}
+
+func decodeDownloadTask(document []byte) (downloader.Task, error) {
+	var task downloader.Task
+	decoder := json.NewDecoder(bytes.NewReader(document))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&task); err != nil {
+		return downloader.Task{}, fmt.Errorf("%w: decode: %v", downloader.ErrInvalidTask, err)
+	}
+	var extra any
+	if err := decoder.Decode(&extra); err != io.EOF {
+		if err == nil {
+			return downloader.Task{}, fmt.Errorf(
+				"%w: trailing JSON value",
+				downloader.ErrInvalidTask,
+			)
+		}
+		return downloader.Task{}, fmt.Errorf(
+			"%w: trailing data: %v",
+			downloader.ErrInvalidTask,
+			err,
+		)
+	}
+	if err := task.Validate(); err != nil {
+		return downloader.Task{}, err
+	}
+	return task, nil
+}
+
+func readBoundedRegularFile(filePath string, maximum int64) ([]byte, error) {
+	info, err := os.Lstat(filePath)
+	if err != nil {
+		return nil, err
+	}
+	if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
+		return nil, fmt.Errorf(
+			"%w: metadata is not a regular file",
+			ErrDownloadTaskLayoutUnsafe,
+		)
+	}
+	if info.Size() > maximum {
+		return nil, fmt.Errorf("%w: metadata is too large", downloader.ErrInvalidTask)
+	}
+	file, err := os.Open(filePath)
+	if err != nil {
+		return nil, fmt.Errorf("open download task metadata: %w", err)
+	}
+	defer file.Close()
+	document, err := io.ReadAll(io.LimitReader(file, maximum+1))
+	if err != nil {
+		return nil, fmt.Errorf("read download task metadata: %w", err)
+	}
+	if int64(len(document)) > maximum {
+		return nil, fmt.Errorf("%w: metadata is too large", downloader.ErrInvalidTask)
+	}
+	return document, nil
+}
+
+func replaceDownloadTaskFile(directory, target, backup string, document []byte) error {
+	temporary, err := os.CreateTemp(directory, ".download-task-*.tmp")
+	if err != nil {
+		return fmt.Errorf("create download task temp file: %w", err)
+	}
+	temporaryPath := temporary.Name()
+	defer os.Remove(temporaryPath)
+
+	if err := temporary.Chmod(0o600); err != nil {
+		temporary.Close()
+		return fmt.Errorf("protect download task temp file: %w", err)
+	}
+	if _, err := temporary.Write(document); err != nil {
+		temporary.Close()
+		return fmt.Errorf("write download task temp file: %w", err)
+	}
+	if err := temporary.Sync(); err != nil {
+		temporary.Close()
+		return fmt.Errorf("sync download task temp file: %w", err)
+	}
+	if err := temporary.Close(); err != nil {
+		return fmt.Errorf("close download task temp file: %w", err)
+	}
+
+	movedTarget := false
+	hadBackup := false
+	if info, inspectErr := os.Lstat(target); inspectErr == nil {
+		if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
+			return fmt.Errorf(
+				"%w: metadata target is not regular",
+				ErrDownloadTaskLayoutUnsafe,
+			)
+		}
+		if err := removeExactRegularFile(backup); err != nil {
+			return err
+		}
+		if err := os.Rename(target, backup); err != nil {
+			return fmt.Errorf("backup download task metadata: %w", err)
+		}
+		movedTarget = true
+	} else if !os.IsNotExist(inspectErr) {
+		return fmt.Errorf("inspect download task metadata: %w", inspectErr)
+	} else {
+		backupInfo, backupErr := os.Lstat(backup)
+		switch {
+		case backupErr == nil:
+			if backupInfo.Mode()&os.ModeSymlink != 0 || !backupInfo.Mode().IsRegular() {
+				return fmt.Errorf(
+					"%w: metadata backup is not regular",
+					ErrDownloadTaskLayoutUnsafe,
+				)
+			}
+			hadBackup = true
+		case !os.IsNotExist(backupErr):
+			return fmt.Errorf("inspect download task backup: %w", backupErr)
+		}
+	}
+	if err := os.Rename(temporaryPath, target); err != nil {
+		if movedTarget {
+			_ = os.Rename(backup, target)
+		}
+		return fmt.Errorf("activate download task metadata: %w", err)
+	}
+	if movedTarget || hadBackup {
+		if err := removeExactRegularFile(backup); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func removeExactRegularFile(filePath string) error {
+	info, err := os.Lstat(filePath)
+	if os.IsNotExist(err) {
+		return nil
+	}
+	if err != nil {
+		return fmt.Errorf("inspect download task backup: %w", err)
+	}
+	if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
+		return fmt.Errorf(
+			"%w: metadata backup is not regular",
+			ErrDownloadTaskLayoutUnsafe,
+		)
+	}
+	if err := os.Remove(filePath); err != nil {
+		return fmt.Errorf("remove download task backup: %w", err)
+	}
+	return nil
+}