Intercept LISTEN command and return "not supported" #5109

ProxySQL currently does not support PostgreSQL's LISTEN command.
When clients attempt to use it, we now intercept the command and return
an appropriate "not supported" response instead of passing it through.

This behavior is implemented for both:
- Simple query flow
- Extended (prepared) query flow

lib/PgSQL_Session.cpp

@@ -760,6 +760,21 @@ void PgSQL_Session::generate_proxysql_internal_session_json(json& j) {
 
 bool PgSQL_Session::handler_special_queries(PtrSize_t* pkt, bool* lock_hostgroup) {
 
+	if ((pkt->size >= 7 + 5) && (strncasecmp("LISTEN ", (const char*)pkt->ptr + 5, 7) == 0)) {
+		client_myds->DSS = STATE_QUERY_SENT_NET;
+		proxy_warning("LISTEN command is not supported\n");
+		client_myds->myprot.generate_error_packet(true, true, "LISTEN is not supported",
+			PGSQL_ERROR_CODES::ERRCODE_FEATURE_NOT_SUPPORTED, false, true);
+		if (mirror == false) {
+			RequestEnd(NULL, true);
+		} else {
+			client_myds->DSS = STATE_SLEEP;
+			status = WAITING_CLIENT_DATA;
+		}
+		l_free(pkt->size, pkt->ptr);
+		return true;
+	}
+
 	if (pkt->size > (5 + 18) && strncasecmp((char*)"PROXYSQL INTERNAL ", (char*)pkt->ptr + 5, 18) == 0) {
 		return_proxysql_internal(pkt);
 		return true;
@@ -837,7 +852,7 @@ bool PgSQL_Session::handler_special_queries(PtrSize_t* pkt, bool* lock_hostgroup
 		l_free(pkt->size, pkt->ptr);
 
 		return true;
-	}*/
+	}
 
 	// 'LOAD DATA LOCAL INFILE' is unsupported. We report an specific error to inform clients about this fact. For more context see #833.
 	if ((pkt->size >= 22 + 5) && (strncasecmp((char*)"LOAD DATA LOCAL INFILE", (char*)pkt->ptr + 5, 22) == 0)) {
@@ -869,7 +884,7 @@ bool PgSQL_Session::handler_special_queries(PtrSize_t* pkt, bool* lock_hostgroup
 				);
 			}
 		}
-	}
+	}*/
 
 	return false;
 }
@@ -5532,6 +5547,15 @@ int PgSQL_Session::handle_post_sync_parse_message(PgSQL_Parse_Message* parse_msg
 	CurrentQuery.begin((unsigned char*)parse_data.query_string, strlen(parse_data.query_string) + 1, false);
 	// parse_msg memory will be freed in pgsql_real_query.end(), if message is sent to backend server
 	// CurrentQuery.stmt_client_name may briefly become a dangling pointer until CurrentQuery.end() is invoked
+
+	// check for LISTEN command
+	const char* query_to_check = (CurrentQuery.get_digest_text() ? CurrentQuery.get_digest_text() : parse_data.query_string);
+	if (query_to_check && (strncasecmp("LISTEN ", query_to_check, 7) == 0)) {
+		proxy_warning("LISTEN command is not supported\n");
+		handle_post_sync_error(PGSQL_ERROR_CODES::ERRCODE_FEATURE_NOT_SUPPORTED, "LISTEN is not supported", false);
+		return 2;
+	}
+
 	extended_query_info.stmt_client_name = parse_data.stmt_name;
 
 	if (extended_query_exec_qp) {