From 8d2a27af7d1d23119da66585d71f7b1e60fde3d3 Mon Sep 17 00:00:00 2001
From: Steve Simpson <steve.simpson@grafana.com>
Date: Thu, 8 Jul 2021 15:51:22 +0200
Subject: [PATCH] Fix for compound messages containing >255 messages.

---
 memberlist_test.go |  6 +++---
 state.go           | 10 ++++++----
 util.go            | 17 +++++++++++++++++
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/memberlist_test.go b/memberlist_test.go
index 70b5d780c..6a1eb70a0 100644
--- a/memberlist_test.go
+++ b/memberlist_test.go
@@ -1200,9 +1200,9 @@ func TestMemberlist_UserData(t *testing.T) {
 
 	bindPort := m1.config.BindPort
 
-	bcasts := [][]byte{
-		[]byte("test"),
-		[]byte("foobar"),
+	bcasts := make([][]byte, 256)
+	for i := range bcasts {
+		bcasts[i] = []byte(fmt.Sprintf("%d", i))
 	}
 
 	// Create a second node
diff --git a/state.go b/state.go
index 5e4f7fdd7..95e6ddc48 100644
--- a/state.go
+++ b/state.go
@@ -606,10 +606,12 @@ func (m *Memberlist) gossip() {
 				m.logger.Printf("[ERR] memberlist: Failed to send gossip to %s: %s", addr, err)
 			}
 		} else {
-			// Otherwise create and send a compound message
-			compound := makeCompoundMessage(msgs)
-			if err := m.rawSendMsgPacket(node.FullAddress(), &node, compound.Bytes()); err != nil {
-				m.logger.Printf("[ERR] memberlist: Failed to send gossip to %s: %s", addr, err)
+			// Otherwise create and send one or more compound messages
+			compounds := makeCompoundMessages(msgs)
+			for _, compound := range compounds {
+				if err := m.rawSendMsgPacket(node.FullAddress(), &node, compound.Bytes()); err != nil {
+					m.logger.Printf("[ERR] memberlist: Failed to send gossip to %s: %s", addr, err)
+				}
 			}
 		}
 	}
diff --git a/util.go b/util.go
index 16a7d36d0..96d2c6b8f 100644
--- a/util.go
+++ b/util.go
@@ -152,6 +152,23 @@ OUTER:
 	return kNodes
 }
 
+// makeCompoundMessages takes a list of messages and packs
+// them into one or multiple messages based on the limitations
+// of compound messages (255 messages each).
+func makeCompoundMessages(msgs [][]byte) []*bytes.Buffer {
+	const maxMsgs = 255
+	bufs := make([]*bytes.Buffer, 0, (len(msgs)+(maxMsgs-1))/maxMsgs)
+
+	for ; len(msgs) > maxMsgs; msgs = msgs[maxMsgs:] {
+		bufs = append(bufs, makeCompoundMessage(msgs[:maxMsgs]))
+	}
+	if len(msgs) > 0 {
+		bufs = append(bufs, makeCompoundMessage(msgs))
+	}
+
+	return bufs
+}
+
 // makeCompoundMessage takes a list of messages and generates
 // a single compound message containing all of them
 func makeCompoundMessage(msgs [][]byte) *bytes.Buffer {