PSYNC: More robust handling of unexpected reply to PSYNC.

src/replication.c

@@ -956,6 +956,14 @@ int slaveTryPartialResynchronization(int fd) {
         if (!runid || !offset || (offset-runid-1) != REDIS_RUN_ID_SIZE) {
             redisLog(REDIS_WARNING,
                 "Master replied with wrong +FULLRESYNC syntax.");
+            sdsfree(reply);
+            /* This is an unexpected condition, actually the +FULLRESYNC
+             * reply means that the master supports PSYNC, but the reply
+             * format seems wrong. To stay safe we blank the master
+             * runid to make sure next PSYNCs will fail, and return
+             * NOT_SUPPORTED to the caller to use SYNC instead. */
+            memset(server.repl_master_runid,0,REDIS_RUN_ID_SIZE+1);
+            return PSYNC_NOT_SUPPORTED;
         } else {
             memcpy(server.repl_master_runid, runid, offset-runid-1);
             server.repl_master_runid[REDIS_RUN_ID_SIZE] = '\0';