fix(resolve): release cancelled previews and preserve task ownership

internal/protocol/http/fetcher.go

@@ -418,6 +418,16 @@ func (f *Fetcher) updateMaxConnTime(d time.Duration) {
 }
 
 func (f *Fetcher) Resolve(req *base.Request) error {
+	return f.ResolveContext(context.Background(), req)
+}
+
+// ResolveContext cancels the initial request while waiting for headers. Once
+// Resolve has returned, the retained response belongs to the fetcher and its
+// existing Pause/Close lifecycle controls the body and prefetch.
+func (f *Fetcher) ResolveContext(ctx context.Context, req *base.Request) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
 	if err := base.ParseReqExtra[fhttp.ReqExtra](req); err != nil {
 		return err
 	}
@@ -429,6 +439,8 @@ func (f *Fetcher) Resolve(req *base.Request) error {
 	// This allows the response to be reused for downloading (important for one-time URLs)
 	// The body outlives Resolve, so the read timeout gets its own cancel func.
 	reqCtx, reqCancel := context.WithCancel(context.Background())
+	stopCancel := context.AfterFunc(ctx, reqCancel)
+	defer stopCancel()
 	httpReq, err := f.buildRequest(reqCtx, req)
 	if err != nil {
 		reqCancel()

pkg/api/resolve_release_test.go

@@ -0,0 +1,36 @@
+package api
+
+import (
+	"net/http"
+	"path/filepath"
+	"testing"
+
+	"github.com/GopeedLab/gopeed/pkg/base"
+	"github.com/GopeedLab/gopeed/pkg/download"
+	restmodel "github.com/GopeedLab/gopeed/pkg/rest/model"
+)
+
+func TestCancelledTorrentPreviewCanBeResolvedAgain(t *testing.T) {
+	d := download.NewDownloader(&download.DownloaderConfig{StorageDir: t.TempDir(), TempDir: t.TempDir()})
+	if err := d.Setup(); err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+	service, err := NewService(d)
+	if err != nil {
+		t.Fatal(err)
+	}
+	path, err := filepath.Abs("../../internal/protocol/bt/testdata/test.torrent")
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := &restmodel.ResolveTask{Req: &base.Request{URL: path}}
+	first := serviceTestRequest[*download.ResolveResult](t, service, http.MethodPost, "/api/v1/resolve", req)
+	serviceTestRequest[any](t, service, http.MethodDelete, "/api/v1/resolve/"+first.ID, nil)
+	// Release is idempotent, including an old window disposing after Create.
+	serviceTestRequest[any](t, service, http.MethodDelete, "/api/v1/resolve/"+first.ID, nil)
+	second := serviceTestRequest[*download.ResolveResult](t, service, http.MethodPost, "/api/v1/resolve", req)
+	if second.Res.Hash != first.Res.Hash {
+		t.Fatalf("different torrent after release: %v", second)
+	}
+}

pkg/api/service.go

@@ -51,6 +51,7 @@ func NewService(downloader *download.Downloader) (*Service, error) {
 	service.routes = []RouteSpec{
 		newRoute(http.MethodGet, "/api/v1/info", service.info),
 		newRoute(http.MethodPost, "/api/v1/resolve", service.resolve),
+		newRoute(http.MethodDelete, "/api/v1/resolve/{id}", service.releaseResolve),
 		newRoute(http.MethodPost, "/api/v1/tasks", service.createTask),
 		newRoute(http.MethodPost, "/api/v1/tasks/batch", service.createTaskBatch),
 		newRoute(http.MethodPatch, "/api/v1/tasks/{id}", service.patchTask),
@@ -143,13 +144,20 @@ func (s *Service) resolve(ctx *Context) *Response {
 	if response := decodeRequest(ctx.Body, &request); response != nil {
 		return response
 	}
-	result, err := s.Downloader.Resolve(request.Req)
+	result, err := s.Downloader.ResolveWithID(request.ID, request.Req)
 	if err != nil {
 		return newErrorResponse(err.Error())
 	}
 	return newOKResponse(result)
 }
 
+func (s *Service) releaseResolve(ctx *Context) *Response {
+	if err := s.Downloader.ReleaseResolve(ctx.PathParam("id")); err != nil {
+		return newErrorResponse(err.Error())
+	}
+	return newOKResponse(nil)
+}
+
 func (s *Service) createTask(ctx *Context) *Response {
 	var request restmodel.CreateTask
 	if response := decodeRequest(ctx.Body, &request); response != nil {

pkg/download/downloader.go

@@ -116,6 +116,7 @@ type Downloader struct {
 
 	cfg            *DownloaderConfig
 	fetcherCache   map[string]fetcher.Fetcher
+	resolveStates  map[string]*resolveState
 	storage        Storage
 	tasks          []*Task
 	waitTasks      []*Task
@@ -153,6 +154,7 @@ func NewDownloader(cfg *DownloaderConfig) *Downloader {
 		cancelBackground: cancelBackground,
 		cfg:              cfg,
 		fetcherCache:     make(map[string]fetcher.Fetcher),
+		resolveStates:    make(map[string]*resolveState),
 		waitTasks:        make([]*Task, 0),
 		groups:           make(map[string]*TaskGroup),
 		creatingGroups:   make(map[string]struct{}),
@@ -559,42 +561,156 @@ func ensureResourceRequestRawURLs(parentReq *base.Request, res *base.Resource) {
 	}
 }
 
-func (d *Downloader) Resolve(req *base.Request) (rr *ResolveResult, err error) {
-	rrId, err := gonanoid.New()
-	if err != nil {
-		return
-	}
-	ensureRequestRawURL(req)
+// resolveState owns a Fetcher until Create transfers it to a task.
+// State transitions are protected by fetcherMapLock; closeOnce serializes cleanup.
+type contextResolver interface {
+	ResolveContext(context.Context, *base.Request) error
+}
 
+type resolveState struct {
+	ctx       context.Context
+	cancel    context.CancelFunc
+	fetcher   fetcher.Fetcher
+	cancelled bool
+	resolved  bool
+	claimed   bool
+	closeOnce sync.Once
+	closeErr  error
+}
+
+func (s *resolveState) close(f fetcher.Fetcher) error {
+	if f == nil {
+		return nil
+	}
+	s.closeOnce.Do(func() { s.closeErr = f.Close() })
+	return s.closeErr
+}
+
+func (d *Downloader) Resolve(req *base.Request) (*ResolveResult, error) {
+	return d.ResolveWithID("", req)
+}
+
+// ResolveWithID lets a preview cancel before metadata is available. Clients
+// that do not supply an ID retain the server-generated resource ID behavior.
+func (d *Downloader) ResolveWithID(id string, req *base.Request) (rr *ResolveResult, err error) {
+	if id == "" {
+		id, err = gonanoid.New()
+		if err != nil {
+			return nil, err
+		}
+	}
+	if req == nil {
+		return nil, errors.New("resolve request is required")
+	}
+	resolveCtx, cancel := context.WithCancel(d.backgroundCtx)
+	defer cancel()
+	state := &resolveState{ctx: resolveCtx, cancel: cancel}
+	d.fetcherMapLock.Lock()
+	if d.closed.Load() {
+		d.fetcherMapLock.Unlock()
+		return nil, errors.New("downloader is closed")
+	}
+	if d.resolveStates[id] != nil || d.fetcherCache[id] != nil {
+		d.fetcherMapLock.Unlock()
+		return nil, errors.New("resource id is already in use")
+	}
+	d.resolveStates[id] = state
+	d.fetcherMapLock.Unlock()
+	defer func() {
+		if err != nil || state.fetcher == nil {
+			d.fetcherMapLock.Lock()
+			if d.resolveStates[id] == state {
+				delete(d.resolveStates, id)
+			}
+			d.fetcherMapLock.Unlock()
+			_ = state.close(state.fetcher)
+		}
+	}()
+	ensureRequestRawURL(req)
 	res, err := d.triggerOnResolve(req)
 	if err != nil {
-		return
+		return nil, err
 	}
 	if res != nil && len(res.Files) > 0 {
-		rr = &ResolveResult{
-			Res:                  res,
-			SuggestedDownloadDir: d.suggestedDownloadDir(res),
-		}
-		return
+		return &ResolveResult{Res: res, SuggestedDownloadDir: d.suggestedDownloadDir(res)}, nil
 	}
-
-	fetcher, err := d.buildFetcher(req.URL)
+	f, err := d.buildFetcher(req.URL)
 	if err != nil {
-		return
-	}
-	err = fetcher.Resolve(req)
-	if err != nil {
-		return
+		return nil, err
 	}
 	d.fetcherMapLock.Lock()
-	d.fetcherCache[rrId] = fetcher
+	state.fetcher = f
+	cancelled := state.cancelled || d.closed.Load()
 	d.fetcherMapLock.Unlock()
-	rr = &ResolveResult{
-		ID:                   rrId,
-		Res:                  fetcher.Meta().Res,
-		SuggestedDownloadDir: d.suggestedDownloadDir(fetcher.Meta().Res),
+	if cancelled {
+		return nil, errors.New("resource resolution cancelled")
+	}
+	if resolver, ok := f.(contextResolver); ok {
+		err = resolver.ResolveContext(state.ctx, req)
+	} else {
+		err = f.Resolve(req)
+	}
+	if err != nil {
+		return nil, err
+	}
+	d.fetcherMapLock.Lock()
+	defer d.fetcherMapLock.Unlock()
+	if state.cancelled || d.closed.Load() {
+		return nil, errors.New("resource resolution cancelled")
+	}
+	state.resolved = true
+	d.fetcherCache[id] = f
+	return &ResolveResult{ID: id, Res: f.Meta().Res, SuggestedDownloadDir: d.suggestedDownloadDir(f.Meta().Res)}, nil
+}
+
+// ReleaseResolve is idempotent. A resource already transferred to a task is
+// never closed by a late preview cancellation.
+func (d *Downloader) ReleaseResolve(id string) error {
+	d.fetcherMapLock.Lock()
+	state := d.resolveStates[id]
+	f := d.fetcherCache[id]
+	delete(d.fetcherCache, id)
+	delete(d.resolveStates, id)
+	if state != nil {
+		state.cancelled = true
+		state.cancel()
+		if state.claimed {
+			f = nil
+		} else {
+			f = state.fetcher
+			if _, cancellable := f.(contextResolver); cancellable && !state.resolved {
+				// Resolve owns unpublished response/prefetch state. Its context
+				// cancels the request; the returning resolver closes it once
+				// publication has stopped, including a racing response.
+				f = nil
+			}
+		}
+	}
+	d.fetcherMapLock.Unlock()
+	if state != nil {
+		return state.close(f)
+	}
+	if f != nil {
+		return f.Close()
+	}
+	return nil
+}
+
+func (d *Downloader) closeResolvedResources() {
+	d.fetcherMapLock.Lock()
+	ids := make(map[string]struct{}, len(d.resolveStates)+len(d.fetcherCache))
+	for id := range d.resolveStates {
+		ids[id] = struct{}{}
+	}
+	for id := range d.fetcherCache {
+		ids[id] = struct{}{}
+	}
+	d.fetcherMapLock.Unlock()
+	for id := range ids {
+		if err := d.ReleaseResolve(id); err != nil {
+			d.Logger.Warn().Err(err).Msg("close resolved resource failed")
+		}
 	}
-	return
 }
 
 func (d *Downloader) notifyRunning() {
@@ -868,18 +984,34 @@ func (d *Downloader) CreateWithOptions(rrId string, opts *base.Options) (string,
 func (d *Downloader) createResolved(rrId string, opts *base.Options, groupID string) (taskId string, err error) {
 	d.fetcherMapLock.Lock()
 	fetcher, ok := d.fetcherCache[rrId]
+	state := d.resolveStates[rrId]
+	if ok && state != nil {
+		state.claimed = true
+	}
 	delete(d.fetcherCache, rrId)
 	d.fetcherMapLock.Unlock()
 	if !ok {
 		return "", errors.New("invalid resource id")
 	}
-	// Only one creator may use a resolved fetcher. Failed creation makes it
-	// available again; a persisted task consumes it even if starting fails.
+	// Failed creation returns ownership to the preview unless it was cancelled.
 	defer func() {
-		if taskId == "" {
-			d.fetcherMapLock.Lock()
+		d.fetcherMapLock.Lock()
+		cancelled := d.closed.Load() || (state != nil && state.cancelled)
+		if taskId == "" && !cancelled {
 			d.fetcherCache[rrId] = fetcher
-			d.fetcherMapLock.Unlock()
+			if state != nil {
+				state.claimed = false
+			}
+		} else if d.resolveStates[rrId] == state {
+			delete(d.resolveStates, rrId)
+		}
+		d.fetcherMapLock.Unlock()
+		if taskId == "" && cancelled {
+			if state != nil {
+				_ = state.close(fetcher)
+			} else {
+				_ = fetcher.Close()
+			}
 		}
 	}()
 	if opts == nil {
@@ -1562,6 +1694,7 @@ func (d *Downloader) Close() error {
 		return nil
 	}
 	d.cancelBackground()
+	d.closeResolvedResources()
 	d.waitForExtensionGit()
 	if d.protocolJobs != nil {
 		d.protocolJobs.close()

pkg/download/resolve_lifecycle_test.go

@@ -0,0 +1,224 @@
+package download
+
+import (
+	"errors"
+	"fmt"
+	"github.com/GopeedLab/gopeed/internal/fetcher"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/GopeedLab/gopeed/pkg/base"
+)
+
+func TestReleaseResolveCancelsPendingHTTPHeaders(t *testing.T) {
+	entered := make(chan struct{})
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { close(entered); <-r.Context().Done() }))
+	defer server.Close()
+	d := NewDownloader(&DownloaderConfig{Storage: NewMemStorage(), StorageDir: t.TempDir(), TempDir: t.TempDir()})
+	if err := d.Setup(); err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+	done := make(chan error, 1)
+	go func() {
+		_, err := d.ResolveWithID("pending-http", &base.Request{URL: server.URL + "/file"})
+		done <- err
+	}()
+	select {
+	case <-entered:
+	case <-time.After(time.Second):
+		t.Fatal("request did not start")
+	}
+	if err := d.ReleaseResolve("pending-http"); err != nil {
+		t.Fatal(err)
+	}
+	select {
+	case err := <-done:
+		if err == nil {
+			t.Fatal("cancelled Resolve succeeded")
+		}
+	case <-time.After(300 * time.Millisecond):
+		server.CloseClientConnections()
+		t.Fatal("ReleaseResolve did not cancel the request waiting for headers")
+	}
+	if len(d.fetcherCache) != 0 || len(d.resolveStates) != 0 {
+		t.Fatal("cancelled operation retained resources")
+	}
+}
+func TestReleaseResolveAfterCreateDoesNotCloseTask(t *testing.T) {
+	d := NewDownloader(&DownloaderConfig{Storage: NewMemStorage(), StorageDir: t.TempDir(), TempDir: t.TempDir(), FetchManagers: nil})
+	if err := d.Setup(); err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+	d.cfg.MaxRunning = 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { w.Write([]byte("ok")) }))
+	defer server.Close()
+	rr, err := d.Resolve(&base.Request{URL: server.URL})
+	if err != nil {
+		t.Fatal(err)
+	}
+	id, err := d.CreateWithOptions(rr.ID, &base.Options{Path: t.TempDir()})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := d.ReleaseResolve(rr.ID); err != nil {
+		t.Fatal(err)
+	}
+	task := d.GetTask(id)
+	if task == nil {
+		t.Fatal("late release removed task")
+	}
+	if err := d.doStart(task); err != nil {
+		t.Fatal(err)
+	}
+	waitForTaskStatus(t, d, id, base.DownloadStatusDone, 3*time.Second)
+}
+func TestResolveRejectsClosedDownloader(t *testing.T) {
+	d := NewDownloader(&DownloaderConfig{StorageDir: t.TempDir(), TempDir: t.TempDir()})
+	if err := d.Setup(); err != nil {
+		t.Fatal(err)
+	}
+	d.Close()
+	if _, err := d.ResolveWithID("closed", &base.Request{URL: "http://127.0.0.1/"}); err == nil {
+		t.Fatalf("closed downloader accepted Resolve: %v", err)
+	}
+}
+
+func TestReleaseResolveCancelsPendingMagnetMetadata(t *testing.T) {
+	d := NewDownloader(&DownloaderConfig{Storage: NewMemStorage(), StorageDir: t.TempDir(), TempDir: t.TempDir()})
+	if err := d.Setup(); err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+	done := make(chan error, 1)
+	go func() {
+		_, err := d.ResolveWithID("pending-magnet", &base.Request{URL: "magnet:?xt=urn:btih:0123456789abcdef0123456789abcdef01234567"})
+		done <- err
+	}()
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		d.fetcherMapLock.Lock()
+		state := d.resolveStates["pending-magnet"]
+		ready := state != nil && state.fetcher != nil
+		d.fetcherMapLock.Unlock()
+		if ready {
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("magnet resolve did not start")
+		}
+		time.Sleep(time.Millisecond)
+	}
+	if err := d.ReleaseResolve("pending-magnet"); err != nil {
+		t.Fatal(err)
+	}
+	select {
+	case err := <-done:
+		if err == nil {
+			t.Fatal("cancelled magnet Resolve succeeded")
+		}
+	case <-time.After(time.Second):
+		t.Fatal("cancelled magnet remained in metadata wait")
+	}
+	if len(d.fetcherCache) != 0 || len(d.resolveStates) != 0 {
+		t.Fatal("cancelled magnet retained its resource")
+	}
+}
+func TestCloseDrainsResolvedPreviewCache(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { w.Write([]byte("ok")) }))
+	defer server.Close()
+	d := NewDownloader(&DownloaderConfig{Storage: NewMemStorage(), StorageDir: t.TempDir(), TempDir: t.TempDir()})
+	if err := d.Setup(); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := d.Resolve(&base.Request{URL: server.URL}); err != nil {
+		t.Fatal(err)
+	}
+	if err := d.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if len(d.fetcherCache) != 0 || len(d.resolveStates) != 0 {
+		t.Fatal("shutdown retained preview resources")
+	}
+}
+
+type cancelledCreationFetcher struct {
+	fetcher.Fetcher
+	entered chan struct{}
+	release chan struct{}
+	err     error
+}
+
+func (f *cancelledCreationFetcher) Patch(*base.Request, *base.Options) error {
+	close(f.entered)
+	<-f.release
+	return f.err
+}
+func TestReleaseResolveDuringCreationTransfersOrClosesOwnership(t *testing.T) {
+	for _, fail := range []bool{false, true} {
+		t.Run(fmt.Sprintf("fail=%v", fail), func(t *testing.T) {
+			d := NewDownloader(&DownloaderConfig{StorageDir: t.TempDir(), TempDir: t.TempDir()})
+			if err := d.Setup(); err != nil {
+				t.Fatal(err)
+			}
+			defer d.Close()
+			d.cfg.MaxRunning = 0
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { w.Write([]byte("ok")) }))
+			defer server.Close()
+			rr, err := d.Resolve(&base.Request{URL: server.URL})
+			if err != nil {
+				t.Fatal(err)
+			}
+			f := &cancelledCreationFetcher{Fetcher: d.fetcherCache[rr.ID], entered: make(chan struct{}), release: make(chan struct{})}
+			if fail {
+				f.err = errors.New("creation failed")
+			}
+			d.fetcherMapLock.Lock()
+			d.fetcherCache[rr.ID] = f
+			d.fetcherMapLock.Unlock()
+			done := make(chan struct{})
+			var id string
+			var createErr error
+			go func() {
+				defer close(done)
+				id, createErr = d.CreateWithOptions(rr.ID, &base.Options{Path: t.TempDir(), Size: 2})
+			}()
+			select {
+			case <-f.entered:
+			case <-time.After(time.Second):
+				t.Fatal("creation did not claim resource")
+			}
+			if err := d.ReleaseResolve(rr.ID); err != nil {
+				t.Fatal(err)
+			}
+			close(f.release)
+			select {
+			case <-done:
+			case <-time.After(time.Second):
+				t.Fatal("creation did not return")
+			}
+			if len(d.fetcherCache) != 0 || len(d.resolveStates) != 0 {
+				t.Fatal("cancelled creation returned ownership to preview cache")
+			}
+			if fail {
+				if createErr == nil {
+					t.Fatal("expected creation failure")
+				}
+				return
+			}
+			if createErr != nil {
+				t.Fatal(createErr)
+			}
+			// The protocol manager persists its concrete Fetcher type.
+			task := d.GetTask(id)
+			task.fetcher = f.Fetcher
+			if err := d.doStart(task); err != nil {
+				t.Fatal(err)
+			}
+			waitForTaskStatus(t, d, id, base.DownloadStatusDone, 3*time.Second)
+		})
+	}
+}

pkg/rest/api.go

@@ -24,7 +24,7 @@ func Info(w http.ResponseWriter, r *http.Request) {
 func Resolve(w http.ResponseWriter, r *http.Request) {
 	var req model.ResolveTask
 	if ReadJson(r, w, &req) {
-		rr, err := Downloader.Resolve(req.Req)
+		rr, err := Downloader.ResolveWithID(req.ID, req.Req)
 		if err != nil {
 			WriteJson(w, model.NewErrorResult(err.Error()))
 			return

pkg/rest/model/task.go

@@ -3,6 +3,7 @@ package model
 import "github.com/GopeedLab/gopeed/pkg/base"
 
 type ResolveTask struct {
+	ID  string        `json:"id,omitempty"`
 	Req *base.Request `json:"req"`
 }
 

ui/flutter/lib/api/api.dart

@@ -81,6 +81,9 @@ Future<ResolveResult> resolve(ResolveTask resolveTask) {
   );
 }
 
+Future<void> releaseResolve(String id) =>
+    _parse<void>(() => _request('api/v1/resolve/${Uri.encodeComponent(id)}', method: 'DELETE'), null);
+
 Future<String> createTask(CreateTask createTask) {
   return _parse<String>(() => _request('api/v1/tasks', method: 'POST', data: createTask), (data) => data as String);
 }

ui/flutter/lib/api/model/resolve_task.dart

@@ -8,7 +8,10 @@ part 'resolve_task.g.dart';
 class ResolveTask {
   Request? req;
 
-  ResolveTask({this.req});
+  @JsonKey(includeIfNull: false)
+  String? id;
+
+  ResolveTask({this.req, this.id});
 
   factory ResolveTask.fromJson(Map<String, dynamic> json) => _$ResolveTaskFromJson(json);
   Map<String, dynamic> toJson() => _$ResolveTaskToJson(this);

ui/flutter/lib/api/model/resolve_task.g.dart

@@ -10,7 +10,8 @@ ResolveTask _$ResolveTaskFromJson(Map<String, dynamic> json) => ResolveTask(
   req: json['req'] == null
       ? null
       : Request.fromJson(json['req'] as Map<String, dynamic>),
+  id: json['id'] as String?,
 );
 
 Map<String, dynamic> _$ResolveTaskToJson(ResolveTask instance) =>
-    <String, dynamic>{'req': ?instance.req};
+    <String, dynamic>{'req': ?instance.req, 'id': ?instance.id};

ui/flutter/lib/core/capabilities/app_capabilities.dart

@@ -93,6 +93,10 @@ void _bindGopeed(CapabilityRegistry registry, _ConfigStore configStore) {
       (p) => api.getMirrorCandidates(p['provider'] as String, p['url'] as String),
     )
     ..bind(GopeedMethods.resolve, api.resolve)
+    ..bind(GopeedMethods.releaseResolve, (id) async {
+      await api.releaseResolve(id);
+      return const RpcUnit();
+    })
     ..bind(GopeedMethods.createTask, api.createTask)
     ..bind(GopeedMethods.createTaskBatch, api.createTaskBatch)
     ..bind(GopeedMethods.patchTask, (params) async {

ui/flutter/lib/core/capabilities/gopeed_capability.dart

@@ -16,6 +16,7 @@ abstract final class GopeedMethods {
   static const triggerProtocolJob = RpcMethod<Map<String, dynamic>, RpcUnit>('gopeed.protocol.job.trigger');
   static const getMirrorCandidates = RpcMethod<Map<String, dynamic>, List<String>>('gopeed.mirrors.candidates');
   static const resolve = RpcMethod<ResolveTask, ResolveResult>('gopeed.resolve');
+  static const releaseResolve = RpcMethod<String, RpcUnit>('gopeed.releaseResolve');
   static const createTask = RpcMethod<CreateTask, String>('gopeed.task.create');
   static const createTaskBatch = RpcMethod<CreateTaskBatch, CreateTaskBatchResult>('gopeed.task.createBatch');
   static const patchTask = RpcMethod<Map<String, dynamic>, RpcUnit>('gopeed.task.patch');
@@ -50,6 +51,7 @@ class GopeedService {
   Future<List<String>> getMirrorCandidates(String provider, String url) =>
       _invoker.invoke(GopeedMethods.getMirrorCandidates, {'provider': provider, 'url': url});
   Future<ResolveResult> resolve(ResolveTask request) => _invoker.invoke(GopeedMethods.resolve, request);
+  Future<void> releaseResolve(String id) async => _invoker.invoke(GopeedMethods.releaseResolve, id);
 
   Future<String> createTask(CreateTask request) => _invoker.invoke(GopeedMethods.createTask, request);
 

ui/flutter/lib/features/tasks/application/pending_download.dart

@@ -1,3 +1,5 @@
+import 'dart:developer' as developer;
+import 'package:uuid/uuid.dart';
 import 'package:path/path.dart' as path;
 
 import '../../../api/model/create_task_batch.dart';
@@ -16,6 +18,8 @@ class PendingDownload {
   final Request request;
   final Options options;
   ResolveResult? result;
+  String? _resolveID;
+  bool _cancelled = false;
   String? resolveError;
   String? createError;
   final Set<int> selected = {};
@@ -50,11 +54,16 @@ class PendingDownload {
   bool get hasSelection => !created && result != null && selected.isNotEmpty;
 
   Future<void> resolve(GopeedService service) async {
-    if (result != null || resolving) return;
+    if (_cancelled || result != null || resolving) return;
     resolving = true;
     resolveError = null;
     try {
-      result = await service.resolve(ResolveTask(req: request));
+      _resolveID = const Uuid().v4();
+      result = await service.resolve(ResolveTask(req: request, id: _resolveID));
+      if (_cancelled) {
+        await _release(service, result!.id);
+        return;
+      }
       selected.addAll(List.generate(files.isEmpty ? 1 : files.length, (index) => index));
     } catch (error) {
       resolveError = error.toString();
@@ -63,6 +72,23 @@ class PendingDownload {
     }
   }
 
+  /// Stop an outstanding preview and release any resource it already owns.
+  /// A response arriving after cancellation is released by resolve() as well.
+  Future<void> cancel(GopeedService service) async {
+    if (_cancelled || created) return;
+    _cancelled = true;
+    await _release(service, result?.id.isNotEmpty == true ? result!.id : _resolveID);
+  }
+
+  Future<void> _release(GopeedService service, String? id) async {
+    if (id == null || id.isEmpty) return;
+    try {
+      await service.releaseResolve(id);
+    } catch (error, stack) {
+      developer.log('Failed to release resolved resource', name: 'gopeed.resolve', error: error, stackTrace: stack);
+    }
+  }
+
   List<CreateTaskBatchItem> creationItems() {
     final indexes = selected.toList()..sort();
     if (result!.id.isNotEmpty || files.isEmpty) {

ui/flutter/lib/features/tasks/presentation/widgets/resolve_download_dialog.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:shadcn_flutter/shadcn_flutter.dart';
 import 'package:flutter/widgets.dart' as flutter show Flexible;
 
@@ -49,6 +51,7 @@ class _ResolveDownloadsDialogState extends State<_ResolveDownloadsDialog> {
   @override
   void dispose() {
     _cancelled = true;
+    _releasePreviews();
     super.dispose();
   }
 
@@ -64,8 +67,15 @@ class _ResolveDownloadsDialogState extends State<_ResolveDownloadsDialog> {
     }
   }
 
+  void _releasePreviews() {
+    for (final source in widget.sources) {
+      unawaited(source.cancel(widget.service));
+    }
+  }
+
   void _cancel() {
     _cancelled = true;
+    _releasePreviews();
     closeOverlay(context, false);
   }
 

ui/flutter/test/features/tasks/presentation/resolve_download_dialog_test.dart

@@ -64,6 +64,81 @@ Future<void> open(
 }
 
 void main() {
+  testWidgets('cancel releases a ready preview resource', (tester) async {
+    final released = <String>[];
+    final registry = CapabilityRegistry(createAppCapabilityCodecs())
+      ..bind(GopeedMethods.resolve, (_) => resolved('ready-rid'))
+      ..bind(const RpcMethod<String, RpcUnit>('gopeed.releaseResolve'), (id) {
+        released.add(id);
+        return const RpcUnit();
+      });
+    await open(tester, [pending('torrent')], registry);
+    await tester.pumpAndSettle();
+    await tester.tap(find.byKey(const ValueKey('resolve-cancel-button')));
+    await tester.pumpAndSettle();
+    expect(released, contains('ready-rid'));
+  });
+
+  testWidgets('cancel releases a late preview result', (tester) async {
+    final response = Completer<ResolveResult>();
+    final released = <String>[];
+    final registry = CapabilityRegistry(createAppCapabilityCodecs())
+      ..bind(GopeedMethods.resolve, (_) => response.future)
+      ..bind(const RpcMethod<String, RpcUnit>('gopeed.releaseResolve'), (id) {
+        released.add(id);
+        return const RpcUnit();
+      });
+    await open(tester, [pending('torrent')], registry);
+    await tester.tap(find.byKey(const ValueKey('resolve-close-button')));
+    await tester.pumpAndSettle();
+    response.complete(resolved('late-rid'));
+    await tester.pumpAndSettle();
+    expect(released, contains('late-rid'));
+  });
+
+  testWidgets('cancel sends the request ID before a preview completes', (tester) async {
+    final response = Completer<ResolveResult>();
+    final released = <String>[];
+    String? requestedID;
+    final registry = CapabilityRegistry(createAppCapabilityCodecs())
+      ..bind(GopeedMethods.resolve, (request) {
+        requestedID = request.id;
+        return response.future;
+      })
+      ..bind(GopeedMethods.releaseResolve, (id) {
+        released.add(id);
+        return const RpcUnit();
+      });
+    await open(tester, [pending('torrent')], registry);
+    await tester.tap(find.byKey(const ValueKey('resolve-close-button')));
+    await tester.pumpAndSettle();
+    expect(requestedID, isNotEmpty);
+    expect(released, contains(requestedID));
+    response.complete(
+      ResolveResult(
+        id: requestedID!,
+        res: Resource(files: [FileInfo(name: 'late.txt')]),
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(released.where((id) => id == requestedID), hasLength(2));
+  });
+
+  testWidgets('successful creation keeps task-owned resources', (tester) async {
+    final released = <String>[];
+    final registry = CapabilityRegistry(createAppCapabilityCodecs())
+      ..bind(GopeedMethods.resolve, (_) => resolved('task-owned'))
+      ..bind(GopeedMethods.createTaskBatch, (_) => CreateTaskBatchResult(taskIds: ['task']))
+      ..bind(GopeedMethods.releaseResolve, (id) {
+        released.add(id);
+        return const RpcUnit();
+      });
+    await open(tester, [pending('torrent')], registry);
+    await tester.pumpAndSettle();
+    await tester.tap(find.byKey(const ValueKey('resolve-create-button')));
+    await tester.pumpAndSettle();
+    expect(released, isEmpty);
+  });
   for (final width in [390.0, 700.0, 1024.0]) {
     testWidgets('file list fits and exposes ready selections at width $width', (tester) async {
       final registry = CapabilityRegistry(createAppCapabilityCodecs())