optimize packetization of DATA_BLOCKED frames (#4845)

DATA_BLOCKED frames should be sent in the same as the STREAM frames that
resulted in the connection becoming blocked on connection flow control.
If there's not enough space left in that packet, the DATA_BLOCKED frame
is sent in the next packet.

integrationtests/self/packetization_test.go

@@ -129,16 +129,33 @@ func TestACKBundling(t *testing.T) {
 }
 
 func TestStreamDataBlocked(t *testing.T) {
+	testConnAndStreamDataBlocked(t, true, false)
+}
+
+func TestConnDataBlocked(t *testing.T) {
+	testConnAndStreamDataBlocked(t, false, true)
+}
+
+func testConnAndStreamDataBlocked(t *testing.T, limitStream, limitConn bool) {
 	const window = 100
 	const numBatches = 3
+
+	initialStreamWindow := uint64(quicvarint.Max)
+	initialConnWindow := uint64(quicvarint.Max)
+	if limitStream {
+		initialStreamWindow = window
+	}
+	if limitConn {
+		initialConnWindow = window
+	}
 	rtt := scaleDuration(5 * time.Millisecond)
 
 	ln, err := quic.Listen(
 		newUPDConnLocalhost(t),
 		getTLSConfig(),
 		getQuicConfig(&quic.Config{
-			InitialStreamReceiveWindow:     window,
-			InitialConnectionReceiveWindow: quicvarint.Max,
+			InitialStreamReceiveWindow:     initialStreamWindow,
+			InitialConnectionReceiveWindow: initialConnWindow,
 		}),
 	)
 	require.NoError(t, err)
@@ -214,6 +231,9 @@ func TestStreamDataBlocked(t *testing.T) {
 			case *logging.StreamDataBlockedFrame:
 				streamDataBlockedFrames = append(streamDataBlockedFrames, *frame)
 				blockedOffset = frame.MaximumStreamData
+			case *logging.DataBlockedFrame:
+				dataBlockedFrames = append(dataBlockedFrames, *frame)
+				blockedOffset = frame.MaximumData
 			case *logging.StreamFrame:
 				// the STREAM frame is always packed last
 				if frame.Offset+frame.Length == blockedOffset {
@@ -223,15 +243,29 @@ func TestStreamDataBlocked(t *testing.T) {
 		}
 	}
 
-	assert.Len(t, streamDataBlockedFrames, numBatches)
-	for i, f := range streamDataBlockedFrames {
-		assert.Equal(t, str.StreamID(), f.StreamID)
+	var expectedBlockOffsets []protocol.ByteCount
+	for i := 0; i < numBatches; i++ {
 		var offset protocol.ByteCount
 		for _, s := range windowSizes[:i+1] {
 			offset += s
 		}
-		assert.Equal(t, offset, f.MaximumStreamData)
+		expectedBlockOffsets = append(expectedBlockOffsets, offset)
 	}
-	assert.Empty(t, dataBlockedFrames)
+
 	assert.Equal(t, numBatches, bundledCounter)
+	if limitStream {
+		assert.Empty(t, dataBlockedFrames)
+		assert.Len(t, streamDataBlockedFrames, numBatches)
+		for i, f := range streamDataBlockedFrames {
+			assert.Equal(t, str.StreamID(), f.StreamID)
+			assert.Equal(t, expectedBlockOffsets[i], f.MaximumStreamData)
+		}
+	}
+	if limitConn {
+		assert.Empty(t, streamDataBlockedFrames)
+		assert.Len(t, dataBlockedFrames, numBatches)
+		for i, f := range dataBlockedFrames {
+			assert.Equal(t, expectedBlockOffsets[i], f.MaximumData)
+		}
+	}
 }