Fix sending compound messages corruption when including messages larger than 64KB

net.go

@@ -800,11 +800,17 @@ func (m *Memberlist) sendMsg(a Address, msg []byte) error {
 	msgs = append(msgs, msg)
 	msgs = append(msgs, extra...)
 
-	// Create a compound message
-	compound := makeCompoundMessage(msgs)
+	// Create one or more compound messages.
+	compounds := makeCompoundMessages(msgs)
 
-	// Send the message
-	return m.rawSendMsgPacket(a, nil, compound.Bytes())
+	// Send the messages.
+	for _, compound := range compounds {
+		if err := m.rawSendMsgPacket(a, nil, compound.Bytes()); err != nil {
+			return err
+		}
+	}
+
+	return nil
 }
 
 // rawSendMsgPacket is used to send message via packet to another host without

util.go

@@ -154,11 +154,37 @@ OUTER:
 
 // makeCompoundMessages takes a list of messages and packs
 // them into one or multiple messages based on the limitations
-// of compound messages (255 messages each).
+// of compound messages (255 messages each, 64KB max message size).
+//
+// The input msgs can be modified in-place.
 func makeCompoundMessages(msgs [][]byte) []*bytes.Buffer {
-	const maxMsgs = 255
+	const (
+		maxMsgs      = math.MaxUint8
+		maxMsgLength = math.MaxUint16
+	)
+
+	// Optimistically assume there will be no big message.
 	bufs := make([]*bytes.Buffer, 0, (len(msgs)+(maxMsgs-1))/maxMsgs)
 
+	// Do not add to a compound message any message bigger than the max message length
+	// we can store.
+	r, w := 0, 0
+	for r < len(msgs) {
+		if len(msgs[r]) <= maxMsgLength {
+			// Keep it.
+			msgs[w] = msgs[r]
+			r++
+			w++
+			continue
+		}
+
+		// This message is a large one, so we send it alone.
+		bufs = append(bufs, bytes.NewBuffer(msgs[r]))
+		r++
+	}
+	msgs = msgs[:w]
+
+	// Group remaining messages in compound message(s).
 	for ; len(msgs) > maxMsgs; msgs = msgs[maxMsgs:] {
 		bufs = append(bufs, makeCompoundMessage(msgs[:maxMsgs]))
 	}

util_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -384,3 +385,137 @@ func TestCompressDecompressPayload(t *testing.T) {
 		t.Fatalf("bad payload: %v", decomp)
 	}
 }
+
+func TestMakeCompoundMessages(t *testing.T) {
+	const (
+		smallMsgSeqNo         = uint32(1)
+		smallMsgPayloadLength = 1
+		bigMsgSeqNo           = uint32(2)
+		bigMsgPayloadLength   = 70000
+	)
+
+	// Generate some fixtures.
+	smallMessages := make([][]byte, 300)
+	for i := 0; i < len(smallMessages); i++ {
+		msg := &ackResp{SeqNo: smallMsgSeqNo, Payload: []byte{byte(i)}}
+		encoded, err := encode(ackRespMsg, msg)
+		require.NoError(t, err)
+
+		smallMessages[i] = encoded.Bytes()
+	}
+
+	bigMessages := make([][]byte, 3)
+	for i := 0; i < len(bigMessages); i++ {
+		payload := []byte{bigMsgPayloadLength - 1: byte(i)}
+		require.Len(t, payload, bigMsgPayloadLength)
+
+		msg := &ackResp{SeqNo: bigMsgSeqNo, Payload: payload}
+		encoded, err := encode(ackRespMsg, msg)
+		require.NoError(t, err)
+
+		bigMessages[i] = encoded.Bytes()
+	}
+
+	tests := map[string]struct {
+		input    [][]byte
+		expected [][]byte
+	}{
+		"no input": {
+			input:    [][]byte{},
+			expected: [][]byte{},
+		},
+		"one small message": {
+			input:    smallMessages[0:1],
+			expected: [][]byte{makeCompoundMessage(smallMessages[0:1]).Bytes()},
+		},
+		"few small messages": {
+			input:    smallMessages[0:3],
+			expected: [][]byte{makeCompoundMessage(smallMessages[0:3]).Bytes()},
+		},
+		"many small messages (more than 255)": {
+			input: smallMessages[0:300],
+			expected: [][]byte{
+				makeCompoundMessage(smallMessages[0:255]).Bytes(),
+				makeCompoundMessage(smallMessages[255:300]).Bytes(),
+			},
+		},
+		"one big message": {
+			input:    bigMessages[0:1],
+			expected: bigMessages[0:1],
+		},
+		"few big messages": {
+			input:    bigMessages[0:3],
+			expected: bigMessages[0:3],
+		},
+		"mix of many small and big messages": {
+			input: func() [][]byte {
+				var out [][]byte
+
+				out = append(out, bigMessages[0])
+				out = append(out, smallMessages[0:20]...)
+				out = append(out, bigMessages[1])
+				out = append(out, smallMessages[20:260]...)
+				out = append(out, bigMessages[2])
+				out = append(out, smallMessages[260:300]...)
+
+				return out
+			}(),
+			expected: [][]byte{
+				bigMessages[0],
+				bigMessages[1],
+				bigMessages[2],
+				makeCompoundMessage(smallMessages[0:255]).Bytes(),
+				makeCompoundMessage(smallMessages[255:300]).Bytes(),
+			},
+		},
+	}
+
+	for testName, testData := range tests {
+		t.Run(testName, func(t *testing.T) {
+			actual := makeCompoundMessages(testData.input)
+
+			// Get the actual []byte of each message.
+			actualBytes := make([][]byte, 0, len(actual))
+			for _, data := range actual {
+				actualBytes = append(actualBytes, data.Bytes())
+			}
+
+			assert.Equal(t, testData.expected, actualBytes)
+
+			// Ensure we can successfully decode every message.
+			for i := 0; i < len(actual); i++ {
+				msg := actualBytes[i]
+				typ := messageType(msg[0])
+
+				switch typ {
+				case ackRespMsg:
+					var got ackResp
+					require.NoError(t, decode(msg[1:], &got))
+
+					if got.SeqNo == smallMsgSeqNo {
+						assert.Len(t, got.Payload, smallMsgPayloadLength)
+					} else if got.SeqNo == bigMsgSeqNo {
+						assert.Len(t, got.Payload, bigMsgPayloadLength)
+					} else {
+						require.Fail(t, "unexpected seq no")
+					}
+				case compoundMsg:
+					trunc, parts, err := decodeCompoundMessage(msg[1:])
+					require.NoError(t, err)
+					require.Equal(t, 0, trunc)
+
+					for _, part := range parts {
+						require.Equal(t, ackRespMsg, messageType(part[0]))
+
+						var got ackResp
+						require.NoError(t, decode(part[1:], &got))
+						assert.Equal(t, smallMsgSeqNo, got.SeqNo)
+						assert.Len(t, got.Payload, smallMsgPayloadLength)
+					}
+				default:
+					require.Fail(t, "unexpected message")
+				}
+			}
+		})
+	}
+}