From 2e5181ef28ff0db00cca013ba7986456bd1d32d0 Mon Sep 17 00:00:00 2001
From: Josh Hershberg <yehoshua@redis.com>
Date: Sun, 5 Nov 2023 10:47:57 +0200
Subject: [PATCH] Cluster refactor: Add failover cmd support to cluster api

The failover command is up until now not supported
in cluster mode. This commit allows a cluster
implementation to support the command. The legacy
clustering implementation still does not support
this command.

Signed-off-by: Josh Hershberg <yehoshua@redis.com>
---
 src/cluster.h        |  2 ++
 src/cluster_legacy.c | 26 +++++++++++++++++++++-----
 src/replication.c    | 12 +++++++-----
 3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/src/cluster.h b/src/cluster.h
index 9f6e482f4..8b8feb24e 100644
--- a/src/cluster.h
+++ b/src/cluster.h
@@ -96,6 +96,8 @@ char* clusterNodeHostname(clusterNode *node);
 const char *getPreferredEndpoint(clusterNode *n);
 void migrateCommand(client *c);
 long long getReplOffset(clusterNode *node);
+int clusterAllowFailoverCmd(client *c);
+void clusterPromoteSelfToMaster(void);
 
 char **clusterDebugCommandHelp(void);
 ConnectionType *connTypeOfCluster(void);
diff --git a/src/cluster_legacy.c b/src/cluster_legacy.c
index 0fd8b0a20..72ab7428a 100644
--- a/src/cluster_legacy.c
+++ b/src/cluster_legacy.c
@@ -6400,11 +6400,27 @@ long long getReplOffset(clusterNode *node) {
 }
 
 const char *getPreferredEndpoint(clusterNode *n) {
-    char* hostname = clusterNodeHostname(n);
-    switch(server.cluster_preferred_endpoint_type) {
-        case CLUSTER_ENDPOINT_TYPE_IP: return clusterNodeIp(n);
-        case CLUSTER_ENDPOINT_TYPE_HOSTNAME: return (hostname != NULL && hostname[0] != '\0') ? hostname : "?";
-        case CLUSTER_ENDPOINT_TYPE_UNKNOWN_ENDPOINT: return "";
+    char *hostname = clusterNodeHostname(n);
+    switch (server.cluster_preferred_endpoint_type) {
+        case CLUSTER_ENDPOINT_TYPE_IP:
+            return clusterNodeIp(n);
+        case CLUSTER_ENDPOINT_TYPE_HOSTNAME:
+            return (hostname != NULL && hostname[0] != '\0') ? hostname : "?";
+        case CLUSTER_ENDPOINT_TYPE_UNKNOWN_ENDPOINT:
+            return "";
     }
     return "unknown";
 }
+
+int clusterAllowFailoverCmd(client *c) {
+    if (!server.cluster_enabled) {
+        return 1;
+    }
+    addReplyError(c,"FAILOVER not allowed in cluster mode. "
+                    "Use CLUSTER FAILOVER command instead.");
+    return 0;
+}
+
+void clusterPromoteSelfToMaster(void) {
+    replicationUnsetMaster();
+}
diff --git a/src/replication.c b/src/replication.c
index e64251663..e4b7c42e1 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -951,7 +951,11 @@ void syncCommand(client *c) {
         }
 
         if (!strcasecmp(c->argv[1]->ptr,server.replid)) {
-            replicationUnsetMaster();
+            if (server.cluster_enabled) {
+                clusterPromoteSelfToMaster();
+            } else {
+                replicationUnsetMaster();
+            }
             sds client = catClientInfoString(sdsempty(),c);
             serverLog(LL_NOTICE,
                 "MASTER MODE enabled (failover request from '%s')",client);
@@ -4061,12 +4065,10 @@ void abortFailover(const char *err) {
  * will attempt forever and must be manually aborted.
  */
 void failoverCommand(client *c) {
-    if (server.cluster_enabled) {
-        addReplyError(c,"FAILOVER not allowed in cluster mode. "
-                        "Use CLUSTER FAILOVER command instead.");
+    if (!clusterAllowFailoverCmd(c)) {
         return;
     }
-    
+
     /* Handle special case for abort */
     if ((c->argc == 2) && !strcasecmp(c->argv[1]->ptr,"abort")) {
         if (server.failover_state == NO_FAILOVER) {