From 890de52b5c323cb0259b01def4f123ed333a1e76 Mon Sep 17 00:00:00 2001
From: VivekSainiEQ <vivek@eqalpha.com>
Date: Tue, 2 Nov 2021 17:43:17 +0000
Subject: [PATCH] Check that cluster connection is valid before setting write
 handler

Former-commit-id: 6a0a005ff2587c1c2647d3a077472b8bca38a074
---
 src/cluster.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/cluster.cpp b/src/cluster.cpp
index 4f1cc7710..29b27ac44 100644
--- a/src/cluster.cpp
+++ b/src/cluster.cpp
@@ -2447,7 +2447,10 @@ void clusterSendMessage(clusterLink *link, unsigned char *msg, size_t msglen) {
     if (sdslen(link->sndbuf) == 0 && msglen != 0)
     {
         aePostFunction(g_pserver->rgthreadvar[IDX_EVENT_LOOP_MAIN].el, [link] {
-            connSetWriteHandlerWithBarrier(link->conn, clusterWriteHandler, 1);
+            /* The connection could be timed out before this posted function executes (thanks to TCP keepalive).
+             * So check that the connection is still there before setting the write handler, otherwise you segfault */
+            if (link->conn != nullptr)
+                connSetWriteHandlerWithBarrier(link->conn, clusterWriteHandler, 1);
         });
     }