From 350a196ded323ea94e0da46234be90e7e071c7f6 Mon Sep 17 00:00:00 2001
From: Attila Kovacs <attipaci@gmail.com>
Date: Sun, 5 Jan 2025 22:25:04 +0100
Subject: [PATCH] Only DB0 for clusters

---
 src/redisx-cluster.c |  6 ++++--
 src/redisx.c         | 10 ++++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/redisx-cluster.c b/src/redisx-cluster.c
index ea246ab..ac429e6 100644
--- a/src/redisx-cluster.c
+++ b/src/redisx-cluster.c
@@ -190,11 +190,13 @@ static RedisShard *rClusterDiscoverAsync(Redis *redis, int *n_shards) {
       }
 
       for(m = 0; m < s->n_servers; s++) {
+        Redis *r;
         RESP **node = (RESP **) desc[2]->value;
 
-        s->redis[m] = redisxInit((char *) node[0]->value);
+        r = s->redis[m] = redisxInit((char *) node[0]->value);
         redisxSetPort(s->redis[m], node[1]->n);
-        rCopyConfig(&((RedisPrivate *) redis->priv)->config, s->redis[m]);
+        rCopyConfig(&((RedisPrivate *) redis->priv)->config, r);
+        redisxSelectDB(r, 0); // Only DB 0 is allowed for clusters.
       }
     }
   }
diff --git a/src/redisx.c b/src/redisx.c
index c24039c..699ab94 100644
--- a/src/redisx.c
+++ b/src/redisx.c
@@ -443,13 +443,19 @@ int redisxSelectDB(Redis *redis, int idx) {
 
   prop_error(fn, rConfigLock(redis));
   p = (RedisPrivate *) redis->priv;
+
+  if(p->cluster && idx) {
+    rConfigUnlock(redis);
+    return x_error(X_SIZE_INVALID, EINVAL, fn, "cannot set non-zero db index %d for cluster", idx);
+  }
+
   dbIdx = p->config.dbIndex;
   rConfigUnlock(redis);
 
   if(dbIdx == idx) return X_SUCCESS;
 
-  if(idx) redisxAddConnectHook(redis, rAffirmDB);
-  else redisxRemoveConnectHook(redis, rAffirmDB);
+  if(idx) redisxAddConnectHook(redis, rAffirmDB);   // Use SELECT to switch to non-zero DB
+  else redisxRemoveConnectHook(redis, rAffirmDB);   // Don't use SELECT for DB 0 (cluster safe)
 
   if(!redisxIsConnected(redis)) return X_SUCCESS;