eth: fix snap sync cancellation

eth/downloader/downloader.go

@@ -346,7 +346,6 @@ func (d *Downloader) Synchronise(id string, head common.Hash, td *big.Int, mode
 	case nil, errBusy, errCanceled:
 		return err
 	}
-
 	if errors.Is(err, errInvalidChain) || errors.Is(err, errBadPeer) || errors.Is(err, errTimeout) ||
 		errors.Is(err, errStallingPeer) || errors.Is(err, errUnsyncedPeer) || errors.Is(err, errEmptyHeaderSet) ||
 		errors.Is(err, errPeersUnavailable) || errors.Is(err, errTooOld) || errors.Is(err, errInvalidAncestor) {
@@ -1764,7 +1763,7 @@ func (d *Downloader) processFastSyncContent() error {
 	}()
 
 	closeOnErr := func(s *stateSync) {
-		if err := s.Wait(); err != nil && err != errCancelStateFetch && err != errCanceled {
+		if err := s.Wait(); err != nil && err != errCancelStateFetch && err != errCanceled && err != snap.ErrCancelled {
 			d.queue.Close() // wake up Results
 		}
 	}

eth/protocols/snap/protocol.go

@@ -61,7 +61,6 @@ var (
 	errDecode         = errors.New("invalid message")
 	errInvalidMsgCode = errors.New("invalid message code")
 	errBadRequest     = errors.New("bad request")
-	errCancelled      = errors.New("sync cancelled")
 )
 
 // Packet represents a p2p message in the `snap` protocol.

eth/protocols/snap/sync.go

@@ -88,6 +88,10 @@ var (
 	requestTimeout = 10 * time.Second // TODO(karalabe): Make it dynamic ala fast-sync?
 )
 
+// ErrCancelled is returned from snap syncing if the operation was prematurely
+// terminated.
+var ErrCancelled = errors.New("sync cancelled")
+
 // accountRequest tracks a pending account range request to ensure responses are
 // to actual requests and to validate any security constraints.
 //
@@ -615,7 +619,7 @@ func (s *Syncer) Sync(root common.Hash, cancel chan struct{}) error {
 		case id := <-peerDrop:
 			s.revertRequests(id)
 		case <-cancel:
-			return errCancelled
+			return ErrCancelled
 
 		case req := <-s.accountReqFails:
 			s.revertAccountRequest(req)