Closes #3247: Added support for command 'SELECT CONNECTION_ID()' in order to support 'mycli' client

lib/ProxySQL_Admin.cpp

@@ -4014,6 +4014,39 @@ void admin_session_handler(MySQL_Session *sess, void *_pa, PtrSize_t *pkt) {
 		goto __run_query;
 	}
 
+	// trivial implementation for 'connection_id()' to support 'mycli'. See #3247
+	if (!strncasecmp("select connection_id()", query_no_space, strlen("select connection_id()"))) {
+		char buf[32];
+		// 'connection_id()' is always forced to be '0'
+		sprintf(buf, "%lu", static_cast<unsigned long>(0));
+		uint16_t setStatus = 0;
+		MySQL_Data_Stream* myds=sess->client_myds;
+		MySQL_Protocol* myprot=&sess->client_myds->myprot;
+		myds->DSS=STATE_QUERY_SENT_DS;
+		int sid = 1;
+		myprot->generate_pkt_column_count(true,NULL,NULL,sid,1);
+		sid++;
+		myprot->generate_pkt_field(
+			true, NULL, NULL, sid, (char *)"", (char *)"", (char *)"",
+			(char *)"CONNECTION_ID()", (char *)"", 63, 31, MYSQL_TYPE_LONGLONG, 161, 0, false, 0, NULL
+		);
+		sid++;
+		myds->DSS=STATE_COLUMN_DEFINITION;
+		myprot->generate_pkt_EOF(true,NULL,NULL,sid,0, setStatus); sid++;
+		char **p=(char **)malloc(sizeof(char*)*1);
+		unsigned long *l=(unsigned long *)malloc(sizeof(unsigned long *)*1);
+		l[0]=strlen(buf);;
+		p[0]=buf;
+		myprot->generate_pkt_row(true,NULL,NULL,sid,1,l,p); sid++;
+		myds->DSS=STATE_ROW;
+		myprot->generate_pkt_EOF(true,NULL,NULL,sid,0, setStatus); sid++;
+		myds->DSS=STATE_SLEEP;
+		run_query=false;
+		free(l);
+		free(p);
+		goto __run_query;
+	}
+
 	if (query_no_space_length==SELECT_DB_USER_LEN) {
 		if (!strncasecmp(SELECT_DB_USER, query_no_space, query_no_space_length)) {
 			l_free(query_length,query);