fix(redis): do not cache ASK redirection in slot table

Author: wayslog

src/brpc/redis_cluster.cpp

@@ -431,7 +431,11 @@ bool RedisClusterChannel::ExecuteSingleCommand(const std::vector<std::string>& a
             next_endpoint = redirect.endpoint;
             GetOrCreateChannel(next_endpoint);
         }
-        if (redirect.slot >= 0 && static_cast<size_t>(redirect.slot) < _slot_to_endpoint.size() &&
+        // ASK is a temporary redirection during slot migration and should not
+        // overwrite the stable slot map. Only persist MOVED target.
+        if (!redirect.asking &&
+            redirect.slot >= 0 &&
+            static_cast<size_t>(redirect.slot) < _slot_to_endpoint.size() &&
             !redirect.endpoint.empty()) {
             BAIDU_SCOPED_LOCK(_mutex);
             _slot_to_endpoint[redirect.slot] = redirect.endpoint;

test/brpc_redis_cluster_unittest.cpp

@@ -581,6 +581,32 @@ TEST_F(RedisClusterChannelTest, ask_redirection) {
     ASSERT_EQ("ask-value", resp.reply(0).data());
 }
 
+TEST_F(RedisClusterChannelTest, ask_redirection_does_not_override_slot_cache) {
+    brpc::RedisClusterChannel channel;
+    InitChannel(&channel);
+
+    _meta->enable_ask = true;
+    _meta->ask_from = 0;
+    _meta->ask_to = 1;
+    _meta->ask_key = FindKeyForNode(0);
+    {
+        BAIDU_SCOPED_LOCK(_node[1].mutex);
+        _node[1].kv[_meta->ask_key] = "ask-value";
+    }
+
+    for (int i = 0; i < 5; ++i) {
+        brpc::RedisRequest req;
+        brpc::RedisResponse resp;
+        brpc::Controller cntl;
+        ASSERT_TRUE(req.AddCommand("get %s", _meta->ask_key.c_str()));
+        channel.CallMethod(NULL, &cntl, &req, &resp, NULL);
+        ASSERT_FALSE(cntl.Failed()) << cntl.ErrorText();
+        ASSERT_EQ(1, resp.reply_size());
+        ASSERT_TRUE(resp.reply(0).is_string());
+        ASSERT_EQ("ask-value", resp.reply(0).data());
+    }
+}
+
 TEST_F(RedisClusterChannelTest, cluster_nodes_fallback) {
     _meta->fail_slots = true;
     brpc::RedisClusterChannel channel;