feat(core): persist tasks and recover them after restart

core/core.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/charmbracelet/log"
 	"github.com/krau/SaveAny-Bot/config"
+	"github.com/krau/SaveAny-Bot/database"
 	"github.com/krau/SaveAny-Bot/pkg/enums/tasktype"
 	"github.com/krau/SaveAny-Bot/pkg/queue"
 	"github.com/krau/SaveAny-Bot/pkg/taskevent"
@@ -45,6 +46,9 @@ func worker(ctx context.Context, qe *queue.TaskQueue[Executable], semaphore chan
 		exe := qtask.Data
 		taskCtx := qtask.Context()
 		logger.Infof("Processing task: %s", exe.TaskID())
+		if err := database.UpdateTaskStatus(taskCtx, exe.TaskID(), database.TaskStatusRunning, ""); err != nil {
+			logger.Errorf("Failed to mark task %s as running: %v", exe.TaskID(), err)
+		}
 		taskevent.Emit(taskCtx, taskevent.Event{TaskID: exe.TaskID(), Phase: taskevent.PhaseStart})
 		if err := ExecCommandString(taskCtx, execHooks.TaskBeforeStart); err != nil {
 			logger.Errorf("Failed to execute before start hook for task %s: %v", exe.TaskID(), err)
@@ -70,6 +74,9 @@ func worker(ctx context.Context, qe *queue.TaskQueue[Executable], semaphore chan
 		}
 		taskevent.Emit(taskCtx, taskevent.Event{TaskID: exe.TaskID(), Phase: taskevent.PhaseDone, Err: err})
 		qe.Done(qtask.ID)
+		if err := database.DeleteTask(ctx, exe.TaskID()); err != nil {
+			logger.Errorf("Failed to delete persisted task %s: %v", exe.TaskID(), err)
+		}
 		<-semaphore
 	}
 }
@@ -92,12 +99,21 @@ func Close() {
 }
 
 func AddTask(ctx context.Context, task Executable) error {
+	if err := persistTask(ctx, task); err != nil {
+		log.FromContext(ctx).Errorf("Failed to persist task %s: %v", task.TaskID(), err)
+	}
 	return initQueue().Add(queue.NewTask(ctx, task.TaskID(), task.Title(), task))
 }
 
 func CancelTask(ctx context.Context, id string) error {
 	err := queueInstance.CancelTask(id)
-	return err
+	if err != nil {
+		return err
+	}
+	if err := database.DeleteTask(ctx, id); err != nil {
+		log.FromContext(ctx).Errorf("Failed to delete persisted task %s: %v", id, err)
+	}
+	return nil
 }
 
 func GetLength(ctx context.Context) int {

core/persist.go

@@ -0,0 +1,114 @@
+package core
+
+import (
+	"context"
+	"sync"
+
+	"github.com/charmbracelet/log"
+	"github.com/gotd/td/telegram/downloader"
+
+	"github.com/krau/SaveAny-Bot/database"
+	"github.com/krau/SaveAny-Bot/pkg/enums/tasktype"
+)
+
+// TaskCodec serializes and rebuilds a task from its persisted payload.
+// Task types without a registered codec are dropped with a warning on
+// recovery instead of being silently re-enqueued.
+type TaskCodec interface {
+	Marshal(task Executable) ([]byte, error)
+	Unmarshal(payload []byte) (Executable, error)
+}
+
+var (
+	taskCodecsMu sync.RWMutex
+	taskCodecs   = make(map[tasktype.TaskType]TaskCodec)
+
+	dlerMu       sync.RWMutex
+	dlerProvider func() downloader.Client
+)
+
+func RegisterTaskCodec(t tasktype.TaskType, codec TaskCodec) {
+	taskCodecsMu.Lock()
+	defer taskCodecsMu.Unlock()
+	taskCodecs[t] = codec
+}
+
+func TaskCodecFor(t tasktype.TaskType) (TaskCodec, bool) {
+	taskCodecsMu.RLock()
+	defer taskCodecsMu.RUnlock()
+	codec, ok := taskCodecs[t]
+	return codec, ok
+}
+
+// SetDownloaderProvider registers the download client factory used to
+// rebuild tfile.TGFile values when recovering tasks.
+func SetDownloaderProvider(f func() downloader.Client) {
+	dlerMu.Lock()
+	defer dlerMu.Unlock()
+	dlerProvider = f
+}
+
+// DownloaderClient returns the registered download client, or nil.
+func DownloaderClient() downloader.Client {
+	dlerMu.RLock()
+	defer dlerMu.RUnlock()
+	if dlerProvider == nil {
+		return nil
+	}
+	return dlerProvider()
+}
+
+func persistTask(ctx context.Context, task Executable) error {
+	codec, ok := TaskCodecFor(task.Type())
+	if !ok {
+		return nil
+	}
+	payload, err := codec.Marshal(task)
+	if err != nil {
+		return err
+	}
+	return database.UpsertTask(ctx, &database.Task{
+		ID:      task.TaskID(),
+		Type:    string(task.Type()),
+		Payload: payload,
+		Status:  string(database.TaskStatusQueued),
+	})
+}
+
+// RecoverTasks re-enqueues tasks that were unfinished when the process last
+// exited. Must be called after storages are loaded and before Run. Tasks of
+// types without a registered codec are dropped with a warning.
+func RecoverTasks(ctx context.Context) {
+	logger := log.FromContext(ctx)
+	tasks, err := database.GetUnfinishedTasks(ctx)
+	if err != nil {
+		logger.Errorf("Failed to load unfinished tasks: %v", err)
+		return
+	}
+	for _, t := range tasks {
+		codec, ok := TaskCodecFor(tasktype.TaskType(t.Type))
+		if !ok {
+			logger.Warnf("Dropping unrecoverable task %s (type %s): no codec registered", t.ID, t.Type)
+			if err := database.DeleteTask(ctx, t.ID); err != nil {
+				logger.Errorf("Failed to delete task %s: %v", t.ID, err)
+			}
+			continue
+		}
+		task, err := codec.Unmarshal(t.Payload)
+		if err != nil {
+			logger.Errorf("Dropping task %s: failed to rebuild: %v", t.ID, err)
+			if err := database.DeleteTask(ctx, t.ID); err != nil {
+				logger.Errorf("Failed to delete task %s: %v", t.ID, err)
+			}
+			continue
+		}
+		if err := AddTask(ctx, task); err != nil {
+			logger.Errorf("Dropping task %s: failed to re-enqueue: %v", t.ID, err)
+			if err := database.DeleteTask(ctx, t.ID); err != nil {
+				logger.Errorf("Failed to delete task %s: %v", t.ID, err)
+			}
+			continue
+		}
+		logger.Infof("Recovered task %s (%s)", t.ID, t.Type)
+	}
+}

core/persist_test.go

@@ -0,0 +1,124 @@
+package core
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/krau/SaveAny-Bot/config"
+	"github.com/krau/SaveAny-Bot/database"
+	"github.com/krau/SaveAny-Bot/pkg/enums/tasktype"
+)
+
+const testRecoverType = tasktype.TaskType("test-recover")
+
+type stubTask struct {
+	id string
+}
+
+func (s *stubTask) Type() tasktype.TaskType       { return testRecoverType }
+func (s *stubTask) Title() string                 { return s.id }
+func (s *stubTask) TaskID() string                { return s.id }
+func (s *stubTask) Execute(context.Context) error { return nil }
+
+type stubCodec struct{}
+
+func (stubCodec) Marshal(task Executable) ([]byte, error) {
+	return []byte(task.TaskID()), nil
+}
+
+func (stubCodec) Unmarshal(payload []byte) (Executable, error) {
+	if len(payload) == 0 {
+		return nil, fmt.Errorf("empty payload")
+	}
+	return &stubTask{id: string(payload)}, nil
+}
+
+func initRecoveryEnv(t *testing.T) context.Context {
+	t.Helper()
+	dir := t.TempDir()
+	cfgPath := filepath.Join(dir, "config.toml")
+	content := fmt.Sprintf("[db]\npath = %q\n", filepath.Join(dir, "test.db"))
+	if err := os.WriteFile(cfgPath, []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := config.Init(context.Background(), cfgPath); err != nil {
+		t.Fatalf("config init: %v", err)
+	}
+	database.Init(context.Background())
+	RegisterTaskCodec(testRecoverType, stubCodec{})
+	return context.Background()
+}
+
+func TestRecoverTasksReenqueuesAndDropsUnknown(t *testing.T) {
+	ctx := initRecoveryEnv(t)
+
+	if err := database.CreateTask(ctx, &database.Task{
+		ID: "rec-1", Type: string(testRecoverType), Payload: []byte("rec-1"), Status: string(database.TaskStatusQueued),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := database.CreateTask(ctx, &database.Task{
+		ID: "rec-2", Type: string(testRecoverType), Payload: []byte("rec-2"), Status: string(database.TaskStatusRunning),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := database.CreateTask(ctx, &database.Task{
+		ID: "drop-1", Type: "unregistered", Payload: nil, Status: string(database.TaskStatusQueued),
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	RecoverTasks(ctx)
+
+	ids := map[string]bool{}
+	for _, info := range GetQueuedTasks(ctx) {
+		ids[info.ID] = true
+	}
+	if !ids["rec-1"] || !ids["rec-2"] {
+		t.Fatalf("recovered task ids = %v, want rec-1 and rec-2", ids)
+	}
+
+	unfinished, err := database.GetUnfinishedTasks(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(unfinished) != 2 {
+		t.Fatalf("unfinished rows = %d, want 2", len(unfinished))
+	}
+	for _, task := range unfinished {
+		if task.ID == "drop-1" {
+			t.Fatalf("unregistered task record was not dropped")
+		}
+		if task.Status != string(database.TaskStatusQueued) {
+			t.Fatalf("recovered task status = %s, want queued", task.Status)
+		}
+	}
+}
+
+func TestRecoverTasksDropsInvalidPayload(t *testing.T) {
+	ctx := initRecoveryEnv(t)
+
+	if err := database.CreateTask(ctx, &database.Task{
+		ID: "bad-1", Type: string(testRecoverType), Payload: nil, Status: string(database.TaskStatusQueued),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	RecoverTasks(ctx)
+
+	// bad-1 must not be enqueued nor remain in the database.
+	for _, info := range GetQueuedTasks(ctx) {
+		if info.ID == "bad-1" {
+			t.Fatalf("task with invalid payload was enqueued")
+		}
+	}
+	count, err := database.CountUnfinishedTasks(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if count != 0 {
+		t.Fatalf("unfinished rows = %d, want 0", count)
+	}
+}

core/tasks/batchtfile/codec.go

@@ -0,0 +1,106 @@
+package batchtfile
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"path/filepath"
+
+	"github.com/krau/SaveAny-Bot/config"
+	"github.com/krau/SaveAny-Bot/core"
+	"github.com/krau/SaveAny-Bot/pkg/enums/tasktype"
+	tfilepkg "github.com/krau/SaveAny-Bot/pkg/tfile"
+	"github.com/krau/SaveAny-Bot/storage"
+)
+
+type elementPayload struct {
+	ID              string               `json:"id"`
+	Storage         string               `json:"storage"`
+	Path            string               `json:"path"`
+	File            tfilepkg.FilePayload `json:"file"`
+	SourceGroupKey  string               `json:"source_group_key"`
+	SourceCaption   string               `json:"source_caption"`
+	PreserveCaption bool                 `json:"preserve_caption"`
+}
+
+type taskPayload struct {
+	ID           string           `json:"id"`
+	Elements     []elementPayload `json:"elements"`
+	ChatID       int64            `json:"chat_id"`
+	MessageID    int              `json:"message_id"`
+	IgnoreErrors bool             `json:"ignore_errors"`
+}
+
+type taskCodec struct{}
+
+func init() {
+	core.RegisterTaskCodec(tasktype.TaskTypeTgfiles, taskCodec{})
+}
+
+func (taskCodec) Marshal(task core.Executable) ([]byte, error) {
+	t, ok := task.(*Task)
+	if !ok {
+		return nil, fmt.Errorf("unexpected task type %T", task)
+	}
+	p := taskPayload{
+		ID:           t.ID,
+		IgnoreErrors: t.IgnoreErrors,
+	}
+	for _, elem := range t.elems {
+		filePayload, ok := tfilepkg.FilePayloadOf(elem.File)
+		if !ok {
+			return nil, fmt.Errorf("file %T is not serializable", elem.File)
+		}
+		p.Elements = append(p.Elements, elementPayload{
+			ID:              elem.ID,
+			Storage:         elem.Storage.Name(),
+			Path:            elem.Path,
+			File:            filePayload,
+			SourceGroupKey:  elem.sourceGroupKey,
+			SourceCaption:   elem.sourceCaption,
+			PreserveCaption: elem.preserveCaption,
+		})
+	}
+	if progress, ok := t.Progress.(*Progress); ok {
+		p.ChatID = progress.ChatID
+		p.MessageID = progress.MessageID
+	}
+	return json.Marshal(p)
+}
+
+func (taskCodec) Unmarshal(data []byte) (core.Executable, error) {
+	var p taskPayload
+	if err := json.Unmarshal(data, &p); err != nil {
+		return nil, fmt.Errorf("invalid task payload: %w", err)
+	}
+	dler := core.DownloaderClient()
+	if dler == nil {
+		return nil, fmt.Errorf("no downloader client available")
+	}
+	elems := make([]TaskElement, 0, len(p.Elements))
+	for _, ep := range p.Elements {
+		stor, err := storage.GetStorageByName(context.Background(), ep.Storage)
+		if err != nil {
+			return nil, fmt.Errorf("storage %q: %w", ep.Storage, err)
+		}
+		localPath, err := filepath.Abs(filepath.Join(config.C().Temp.BasePath, fmt.Sprintf("%s_%s", ep.ID, ep.File.Name)))
+		if err != nil {
+			return nil, fmt.Errorf("failed to build cache path: %w", err)
+		}
+		elems = append(elems, TaskElement{
+			ID:              ep.ID,
+			Storage:         stor,
+			Path:            ep.Path,
+			File:            tfilepkg.FileFromPayload(ep.File, dler),
+			localPath:       localPath,
+			sourceGroupKey:  ep.SourceGroupKey,
+			sourceCaption:   ep.SourceCaption,
+			preserveCaption: ep.PreserveCaption,
+		})
+	}
+	var progress ProgressTracker
+	if p.ChatID != 0 {
+		progress = NewProgressTracker(p.MessageID, p.ChatID)
+	}
+	return NewBatchTGFileTask(p.ID, context.Background(), elems, progress, p.IgnoreErrors), nil
+}

core/tasks/batchtfile/execute.go

@@ -134,7 +134,12 @@ func (t *Task) processElements(ctx context.Context, elems []*TaskElement) error
 }
 
 func (t *Task) processBatch(ctx context.Context, group executionGroup) error {
+	// Cache files are kept on failure so a later restart can resume upload.
+	uploaded := false
 	defer func() {
+		if !uploaded {
+			return
+		}
 		for _, elem := range group.elems {
 			if err := os.Remove(elem.localPath); err != nil && !os.IsNotExist(err) {
 				log.FromContext(ctx).Warnf("Failed to cleanup batch cache file %s: %v", elem.localPath, err)
@@ -219,7 +224,11 @@ func (t *Task) processBatch(ctx context.Context, group executionGroup) error {
 	for index, item := range items {
 		t.recordDownloadComplete(successElems[index].ID, item.Size)
 	}
-	return t.saveBatchItems(ctx, successElems, items)
+	err := t.saveBatchItems(ctx, successElems, items)
+	if err == nil {
+		uploaded = true
+	}
+	return err
 }
 
 func (t *Task) saveBatchItems(ctx context.Context, successElems []*TaskElement, items []storagetypes.BatchItem) error {
@@ -289,34 +298,10 @@ func (t *Task) unmarkProcessing(id string) {
 func (t *Task) downloadElement(ctx context.Context, elem *TaskElement) error {
 	logger := log.FromContext(ctx).WithPrefix(fmt.Sprintf("file[%s]", elem.File.Name()))
 	logger.Info("Starting file download")
-	localFile, err := fsutil.CreateFile(elem.localPath)
-	if err != nil {
-		t.markItemFailed(elem.ID, FailureStageCache, err)
+	if err := t.downloadToCache(ctx, elem); err != nil {
+		t.markItemFailed(elem.ID, FailureStageDownload, err)
 		t.notifyStateChange(ctx)
-		return fmt.Errorf("failed to create local file: %w", err)
-	}
-	wrAt := ioutil.NewProgressWriterAt(localFile, func(n int) {
-		t.recordItemDownload(elem.ID, int64(n), time.Now())
-		downloaded := t.downloaded.Add(int64(n))
-		t.notifyProgress(ctx)
-		taskevent.Emit(ctx, taskevent.Event{
-			TaskID:          t.ID,
-			Phase:           taskevent.PhaseProgress,
-			TotalBytes:      t.totalSize,
-			DownloadedBytes: downloaded,
-		})
-	})
-	_, downloadErr := tdler.NewDownloader(elem.File).Parallel(ctx, wrAt)
-	closeErr := localFile.Close()
-	if downloadErr != nil {
-		t.markItemFailed(elem.ID, FailureStageDownload, downloadErr)
-		t.notifyStateChange(ctx)
-		return fmt.Errorf("failed to download file: %w", downloadErr)
-	}
-	if closeErr != nil {
-		t.markItemFailed(elem.ID, FailureStageCache, closeErr)
-		t.notifyStateChange(ctx)
-		return fmt.Errorf("failed to close cache file: %w", closeErr)
+		return fmt.Errorf("failed to download file: %w", err)
 	}
 	logger.Info("File downloaded successfully")
 	if path.Ext(elem.FileName()) == "" {
@@ -387,24 +372,15 @@ func (t *Task) processElement(ctx context.Context, elem TaskElement) error {
 		t.notifyStateChange(ctx)
 		return fmt.Errorf("failed to create local file: %w", err)
 	}
+	success := false
 	defer func() {
-		if err := localFile.CloseAndRemove(); err != nil {
-			logger.Errorf("Failed to close local file: %v", err)
+		if success {
+			if err := localFile.CloseAndRemove(); err != nil {
+				logger.Errorf("Failed to close local file: %v", err)
+			}
 		}
 	}()
-	wrAt := ioutil.NewProgressWriterAt(localFile, func(n int) {
-		t.recordItemDownload(elem.ID, int64(n), time.Now())
-		downloaded := t.downloaded.Add(int64(n))
-		t.notifyProgress(ctx)
-		taskevent.Emit(ctx, taskevent.Event{
-			TaskID:          t.ID,
-			Phase:           taskevent.PhaseProgress,
-			TotalBytes:      t.totalSize,
-			DownloadedBytes: downloaded,
-		})
-	})
-	_, err = tdler.NewDownloader(elem.File).Parallel(ctx, wrAt)
-	if err != nil {
+	if err := t.downloadToCache(ctx, &elem); err != nil {
 		t.markItemFailed(elem.ID, FailureStageDownload, err)
 		t.notifyStateChange(ctx)
 		return fmt.Errorf("failed to download file: %w", err)
@@ -460,6 +436,7 @@ func (t *Task) processElement(ctx context.Context, elem TaskElement) error {
 		onProgress(fileStat.Size(), fileStat.Size())
 		t.markItemCompleted(elem.ID)
 		t.notifyStateChange(vctx)
+		success = true
 	} else {
 		t.markItemFailed(elem.ID, lastFailureStage, err)
 		t.notifyStateChange(vctx)

core/tasks/tfile/codec.go

@@ -0,0 +1,85 @@
+package tfile
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"path/filepath"
+
+	"github.com/krau/SaveAny-Bot/config"
+	"github.com/krau/SaveAny-Bot/core"
+	"github.com/krau/SaveAny-Bot/pkg/enums/tasktype"
+	tfilepkg "github.com/krau/SaveAny-Bot/pkg/tfile"
+	"github.com/krau/SaveAny-Bot/storage"
+)
+
+type taskPayload struct {
+	ID        string               `json:"id"`
+	Storage   string               `json:"storage"`
+	Path      string               `json:"path"`
+	File      tfilepkg.FilePayload `json:"file"`
+	ChatID    int64                `json:"chat_id"`
+	MessageID int                  `json:"message_id"`
+}
+
+type taskCodec struct{}
+
+func init() {
+	core.RegisterTaskCodec(tasktype.TaskTypeTgfiles, taskCodec{})
+}
+
+func (taskCodec) Marshal(task core.Executable) ([]byte, error) {
+	t, ok := task.(*Task)
+	if !ok {
+		return nil, fmt.Errorf("unexpected task type %T", task)
+	}
+	filePayload, ok := tfilepkg.FilePayloadOf(t.File)
+	if !ok {
+		return nil, fmt.Errorf("file %T is not serializable", t.File)
+	}
+	p := taskPayload{
+		ID:      t.ID,
+		Storage: t.Storage.Name(),
+		Path:    t.Path,
+		File:    filePayload,
+	}
+	if progress, ok := t.Progress.(*Progress); ok {
+		p.ChatID = progress.ChatID
+		p.MessageID = progress.MessageID
+	}
+	return json.Marshal(p)
+}
+
+func (taskCodec) Unmarshal(data []byte) (core.Executable, error) {
+	var p taskPayload
+	if err := json.Unmarshal(data, &p); err != nil {
+		return nil, fmt.Errorf("invalid task payload: %w", err)
+	}
+	dler := core.DownloaderClient()
+	if dler == nil {
+		return nil, fmt.Errorf("no downloader client available")
+	}
+	file := tfilepkg.FileFromPayload(p.File, dler)
+	stor, err := storage.GetStorageByName(context.Background(), p.Storage)
+	if err != nil {
+		return nil, fmt.Errorf("storage %q: %w", p.Storage, err)
+	}
+	var progress ProgressTracker
+	if p.ChatID != 0 {
+		progress = NewProgressTrack(p.MessageID, p.ChatID)
+	}
+	localPath, err := filepath.Abs(filepath.Join(config.C().Temp.BasePath, fmt.Sprintf("%s_%s", p.ID, file.Name())))
+	if err != nil {
+		return nil, fmt.Errorf("failed to build cache path: %w", err)
+	}
+	return &Task{
+		ID:        p.ID,
+		Ctx:       context.Background(),
+		File:      file,
+		Storage:   stor,
+		Path:      p.Path,
+		Progress:  progress,
+		stream:    false, // recovered tasks always download to cache first
+		localPath: localPath,
+	}, nil
+}

core/tasks/tfile/execute.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/charmbracelet/log"
 	"github.com/duke-git/lancet/v2/retry"
-	"github.com/krau/SaveAny-Bot/common/tdler"
 	"github.com/krau/SaveAny-Bot/common/utils/fsutil"
 	"github.com/krau/SaveAny-Bot/common/utils/ioutil"
 	"github.com/krau/SaveAny-Bot/config"
@@ -19,8 +18,13 @@ import (
 	"github.com/krau/SaveAny-Bot/storage"
 )
 
-func (t *Task) Execute(ctx context.Context) error {
+func (t *Task) Execute(ctx context.Context) (err error) {
 	logger := log.FromContext(ctx).WithPrefix(fmt.Sprintf("file[%s]", t.File.Name()))
+	defer func() {
+		if t.Progress != nil {
+			t.Progress.OnDone(ctx, t, err)
+		}
+	}()
 	if t.Progress != nil {
 		t.Progress.OnStart(ctx, t)
 	}
@@ -29,35 +33,16 @@ func (t *Task) Execute(ctx context.Context) error {
 	}
 
 	logger.Info("Starting file download")
-	localFile, err := fsutil.CreateFile(t.localPath)
-	if err != nil {
-		return fmt.Errorf("failed to create local file: %w", err)
-	}
-	defer func() {
-		if err := localFile.CloseAndRemove(); err != nil {
-			logger.Errorf("Failed to close local file: %v", err)
-		}
-	}()
-	wrAt := newWriterAt(ctx, localFile, t.Progress, t)
-
-	defer func() {
-		if t.Progress != nil {
-			t.Progress.OnDone(ctx, t, err)
-		}
-	}()
-	_, err = tdler.NewDownloader(t.File).Parallel(ctx, wrAt)
-	if err != nil {
+	if err := t.download(ctx); err != nil {
 		return fmt.Errorf("failed to download file: %w", err)
 	}
-	logger.Infof("File downloaded successfully")
 	if path.Ext(t.File.Name()) == "" {
 		ext := fsutil.DetectFileExt(t.localPath)
 		if ext != "" {
 			t.Path = t.Path + ext
 		}
 	}
-	var fileStat os.FileInfo
-	fileStat, err = os.Stat(t.localPath)
+	fileStat, err := os.Stat(t.localPath)
 	if err != nil {
 		return fmt.Errorf("failed to get file stat: %w", err)
 	}
@@ -97,6 +82,10 @@ func (t *Task) Execute(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("failed to save file after retries: %w", err)
 	}
+	// Cache file is kept on failure so a later restart can resume upload.
+	if err := os.Remove(t.localPath); err != nil {
+		logger.Errorf("Failed to remove cache file: %v", err)
+	}
 	return nil
 }
 

core/tasks/transfer/codec.go

@@ -0,0 +1,92 @@
+package transfer
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/krau/SaveAny-Bot/core"
+	"github.com/krau/SaveAny-Bot/pkg/enums/tasktype"
+	"github.com/krau/SaveAny-Bot/pkg/storagetypes"
+	"github.com/krau/SaveAny-Bot/storage"
+)
+
+type elementPayload struct {
+	ID            string                `json:"id"`
+	SourceStorage string                `json:"source_storage"`
+	SourcePath    string                `json:"source_path"`
+	FileInfo      storagetypes.FileInfo `json:"file_info"`
+	TargetStorage string                `json:"target_storage"`
+	TargetPath    string                `json:"target_path"`
+}
+
+type taskPayload struct {
+	ID           string           `json:"id"`
+	Elements     []elementPayload `json:"elements"`
+	ChatID       int64            `json:"chat_id"`
+	MessageID    int              `json:"message_id"`
+	IgnoreErrors bool             `json:"ignore_errors"`
+}
+
+type taskCodec struct{}
+
+func init() {
+	core.RegisterTaskCodec(tasktype.TaskTypeTransfer, taskCodec{})
+}
+
+func (taskCodec) Marshal(task core.Executable) ([]byte, error) {
+	t, ok := task.(*Task)
+	if !ok {
+		return nil, fmt.Errorf("unexpected task type %T", task)
+	}
+	p := taskPayload{
+		ID:           t.ID,
+		IgnoreErrors: t.IgnoreErrors,
+	}
+	for _, elem := range t.elems {
+		p.Elements = append(p.Elements, elementPayload{
+			ID:            elem.ID,
+			SourceStorage: elem.SourceStorage.Name(),
+			SourcePath:    elem.SourcePath,
+			FileInfo:      elem.FileInfo,
+			TargetStorage: elem.TargetStorage.Name(),
+			TargetPath:    elem.TargetPath,
+		})
+	}
+	if progress, ok := t.Progress.(*Progress); ok {
+		p.ChatID = progress.ChatID
+		p.MessageID = progress.MessageID
+	}
+	return json.Marshal(p)
+}
+
+func (taskCodec) Unmarshal(data []byte) (core.Executable, error) {
+	var p taskPayload
+	if err := json.Unmarshal(data, &p); err != nil {
+		return nil, fmt.Errorf("invalid task payload: %w", err)
+	}
+	elems := make([]TaskElement, 0, len(p.Elements))
+	for _, ep := range p.Elements {
+		source, err := storage.GetStorageByName(context.Background(), ep.SourceStorage)
+		if err != nil {
+			return nil, fmt.Errorf("source storage %q: %w", ep.SourceStorage, err)
+		}
+		target, err := storage.GetStorageByName(context.Background(), ep.TargetStorage)
+		if err != nil {
+			return nil, fmt.Errorf("target storage %q: %w", ep.TargetStorage, err)
+		}
+		elems = append(elems, TaskElement{
+			ID:            ep.ID,
+			SourceStorage: source,
+			SourcePath:    ep.SourcePath,
+			FileInfo:      ep.FileInfo,
+			TargetStorage: target,
+			TargetPath:    ep.TargetPath,
+		})
+	}
+	var progress ProgressTracker
+	if p.ChatID != 0 {
+		progress = NewProgressTracker(p.MessageID, p.ChatID)
+	}
+	return NewTransferTask(p.ID, context.Background(), elems, progress, p.IgnoreErrors), nil
+}