Sanity-check gossip messages

router/gossip_channel.go

@@ -148,11 +148,18 @@ func (c *GossipChannel) gcSenders(connections ConnectionSet) {
 	}
 }
 
+// We have seen a couple of failures which suggest a >128GB slice was encountered.
+// 100MB should be enough for anyone.
+const maxFeasibleMessageLen = 100 * 1024 * 1024
+
 func (c *GossipChannel) sendDown(conn Connection, data GossipData) {
 	sender, found := c.senders[conn]
 	if !found {
 		sender = NewGossipSender(func(pending GossipData) {
 			for _, msg := range pending.Encode() {
+				if len(msg) > maxFeasibleMessageLen {
+					panic(fmt.Sprintf("Gossip message too large: len=%d bytes; on channel '%s' from %+v", len(msg), c.name, pending))
+				}
 				protocolMsg := ProtocolMsg{ProtocolGossip, GobEncode(c.name, c.ourself.Name, msg)}
 				conn.(ProtocolSender).SendProtocolMsg(protocolMsg)
 			}