fix: check kafka reachability without involving spec topic

e2e_test/sink/kafka/create_sink.slt

@@ -10,7 +10,7 @@ create table t_kafka (
     v_timestamp timestamp
 );
 
-statement error failed to fetch metadata from kafka
+statement error cannot connect to kafka broker
 create sink sink_non_exist_broker from t_kafka with (
     connector = 'kafka',
     properties.bootstrap.server = 'make no sense',

src/connector/src/sink/kafka.rs

@@ -335,12 +335,17 @@ impl Sink for KafkaSink {
         // Try Kafka connection.
         // There is no such interface for kafka producer to validate a connection
         // use enumerator to validate broker reachability and existence of topic
-        let mut ticker = KafkaSplitEnumerator::new(
+        let check = KafkaSplitEnumerator::new(
             KafkaProperties::from(self.config.clone()),
             Arc::new(SourceEnumeratorContext::default()),
         )
         .await?;
-        _ = ticker.list_splits().await?;
+        if !check.check_reachability().await {
+            return Err(SinkError::Config(anyhow!(
+                "cannot connect to kafka broker ({})",
+                self.config.common.brokers
+            )));
+        }
         Ok(())
     }
 }

src/connector/src/source/kafka/enumerator/client.rs

@@ -342,6 +342,13 @@ impl KafkaSplitEnumerator {
             .set(offset);
     }
 
+    pub async fn check_reachability(&self) -> bool {
+        self.client
+            .fetch_metadata(None, self.sync_call_timeout)
+            .await
+            .is_ok()
+    }
+
     async fn fetch_topic_partition(&self) -> anyhow::Result<Vec<i32>> {
         // for now, we only support one topic
         let metadata = self