Fix: fix callback missing when metadata request failed (@aiquestion, #…

…3625)

* Fix: fix callback missing when metadata request failed

* Update comment

* Update CHANGELOG.md

Co-authored-by: Magnus Edenhill <magnus@edenhill.se>

CHANGELOG.md

@@ -84,6 +84,9 @@ librdkafka v1.9.0 is a feature release:
    to connect to (#3705).
  * Millisecond timeouts (`timeout_ms`) in various APIs, such as `rd_kafka_poll()`,
    was limited to roughly 36 hours before wrapping. (#3034)
+ * If a metadata request triggered by `rd_kafka_metadata()` or consumer group rebalancing
+   encountered a non-retriable error it would not be propagated to the caller and thus
+   cause a stall or timeout, this has now been fixed. (@aiquestion, #3625)
 
 
 ### Consumer fixes

src/rdkafka_request.c

@@ -1841,6 +1841,13 @@ static void rd_kafka_handle_Metadata(rd_kafka_t *rk,
                            rd_kafka_err2str(err),
                            (int)(request->rkbuf_ts_sent / 1000),
                            rd_kafka_actions2str(actions));
+                /* Respond back to caller on non-retriable errors */
+                if (rko && rko->rko_replyq.q) {
+                        rko->rko_err           = err;
+                        rko->rko_u.metadata.md = NULL;
+                        rd_kafka_replyq_enq(&rko->rko_replyq, rko, 0);
+                        rko = NULL;
+                }
         }