fix: make sure GetBlocks() channel is closed on session close

This commit was moved from ipfs/go-bitswap@994279b

Author: dirkmc

bitswap/getter/getter.go

@@ -61,40 +61,56 @@ func SyncGetBlock(p context.Context, k cid.Cid, gb GetBlocksFunc) (blocks.Block,
 type WantFunc func(context.Context, []cid.Cid)
 
 // AsyncGetBlocks take a set of block cids, a pubsub channel for incoming
-// blocks, a want function, and a close function,
-// and returns a channel of incoming blocks.
-func AsyncGetBlocks(ctx context.Context, keys []cid.Cid, notif notifications.PubSub, want WantFunc, cwants func([]cid.Cid)) (<-chan blocks.Block, error) {
+// blocks, a want function, and a close function, and returns a channel of
+// incoming blocks.
+func AsyncGetBlocks(ctx context.Context, sessctx context.Context, keys []cid.Cid, notif notifications.PubSub,
+	want WantFunc, cwants func([]cid.Cid)) (<-chan blocks.Block, error) {
+
+	// If there are no keys supplied, just return a closed channel
 	if len(keys) == 0 {
 		out := make(chan blocks.Block)
 		close(out)
 		return out, nil
 	}
 
+	// Use a PubSub notifier to listen for incoming blocks for each key
 	remaining := cid.NewSet()
 	promise := notif.Subscribe(ctx, keys...)
 	for _, k := range keys {
 		log.Event(ctx, "Bitswap.GetBlockRequest.Start", k)
 		remaining.Add(k)
 	}
 
+	// Send the want request for the keys to the network
 	want(ctx, keys)
 
 	out := make(chan blocks.Block)
-	go handleIncoming(ctx, remaining, promise, out, cwants)
+	go handleIncoming(ctx, sessctx, remaining, promise, out, cwants)
 	return out, nil
 }
 
-func handleIncoming(ctx context.Context, remaining *cid.Set, in <-chan blocks.Block, out chan blocks.Block, cfun func([]cid.Cid)) {
+// Listens for incoming blocks, passing them to the out channel.
+// If the context is cancelled or the incoming channel closes, calls cfun with
+// any keys corresponding to blocks that were never received.
+func handleIncoming(ctx context.Context, sessctx context.Context, remaining *cid.Set,
+	in <-chan blocks.Block, out chan blocks.Block, cfun func([]cid.Cid)) {
+
 	ctx, cancel := context.WithCancel(ctx)
+
+	// Clean up before exiting this function, and call the cancel function on
+	// any remaining keys
 	defer func() {
 		cancel()
 		close(out)
 		// can't just defer this call on its own, arguments are resolved *when* the defer is created
 		cfun(remaining.Keys())
 	}()
+
 	for {
 		select {
 		case blk, ok := <-in:
+			// If the channel is closed, we're done (note that PubSub closes
+			// the channel once all the keys have been received)
 			if !ok {
 				return
 			}
@@ -104,9 +120,13 @@ func handleIncoming(ctx context.Context, remaining *cid.Set, in <-chan blocks.Bl
 			case out <- blk:
 			case <-ctx.Done():
 				return
+			case <-sessctx.Done():
+				return
 			}
 		case <-ctx.Done():
 			return
+		case <-sessctx.Done():
+			return
 		}
 	}
 }

bitswap/notifications/notifications.go

@@ -60,8 +60,8 @@ func (ps *impl) Shutdown() {
 }
 
 // Subscribe returns a channel of blocks for the given |keys|. |blockChannel|
-// is closed if the |ctx| times out or is cancelled, or after sending len(keys)
-// blocks.
+// is closed if the |ctx| times out or is cancelled, or after receiving the blocks
+// corresponding to |keys|.
 func (ps *impl) Subscribe(ctx context.Context, keys ...cid.Cid) <-chan blocks.Block {
 
 	blocksCh := make(chan blocks.Block, len(keys))
@@ -82,6 +82,8 @@ func (ps *impl) Subscribe(ctx context.Context, keys ...cid.Cid) <-chan blocks.Bl
 	default:
 	}
 
+	// AddSubOnceEach listens for each key in the list, and closes the channel
+	// once all keys have been received
 	ps.wrapped.AddSubOnceEach(valuesCh, toStrings(keys)...)
 	go func() {
 		defer func() {

bitswap/session/session.go

@@ -182,7 +182,8 @@ func (s *Session) GetBlock(parent context.Context, k cid.Cid) (blocks.Block, err
 // guaranteed on the returned blocks.
 func (s *Session) GetBlocks(ctx context.Context, keys []cid.Cid) (<-chan blocks.Block, error) {
 	ctx = logging.ContextWithLoggable(ctx, s.uuid)
-	return bsgetter.AsyncGetBlocks(ctx, keys, s.notif,
+
+	return bsgetter.AsyncGetBlocks(ctx, s.ctx, keys, s.notif,
 		func(ctx context.Context, keys []cid.Cid) {
 			select {
 			case s.newReqs <- keys:

bitswap/session/session_test.go

@@ -416,3 +416,45 @@ func TestSessionFailingToGetFirstBlock(t *testing.T) {
 		t.Fatal("Did not rebroadcast to find more peers")
 	}
 }
+
+func TestSessionCtxCancelClosesGetBlocksChannel(t *testing.T) {
+	wantReqs := make(chan wantReq, 1)
+	cancelReqs := make(chan wantReq, 1)
+	fwm := &fakeWantManager{wantReqs, cancelReqs}
+	fpm := &fakePeerManager{}
+	frs := &fakeRequestSplitter{}
+	notif := notifications.New()
+	defer notif.Shutdown()
+	id := testutil.GenerateSessionID()
+
+	// Create a new session with its own context
+	sessctx, sesscancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	session := New(sessctx, id, fwm, fpm, frs, notif, time.Second, delay.Fixed(time.Minute))
+
+	timerCtx, timerCancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	defer timerCancel()
+
+	// Request a block with a new context
+	blockGenerator := blocksutil.NewBlockGenerator()
+	blks := blockGenerator.Blocks(1)
+	getctx, getcancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer getcancel()
+
+	getBlocksCh, err := session.GetBlocks(getctx, []cid.Cid{blks[0].Cid()})
+	if err != nil {
+		t.Fatal("error getting blocks")
+	}
+
+	// Cancel the session context
+	sesscancel()
+
+	// Expect the GetBlocks() channel to be closed
+	select {
+	case _, ok := <-getBlocksCh:
+		if ok {
+			t.Fatal("expected channel to be closed but was not closed")
+		}
+	case <-timerCtx.Done():
+		t.Fatal("expected channel to be closed before timeout")
+	}
+}