Fix stuck on processing GET request

memcached stuck on processing GET request when number of processed commands is
exceeded of batch_count.

How command processing looks like in memcached:

For each incoming connection memcached starts endless loop in function
memcached_loop() where it reads network data to buffer, parse commands from
buffer one by one, process commands and write answers to network socket.

What goes wrong:

In reproducer we have a sequence of two commands with SETQ (SETQ is the
same as SET command but confirmation is not required) and GET command
that should return a value set by one of the previous SETQ command.
Processing of both SETQ commands finished successfully and something
interesting happens when GET command in the incoming buffer and
batch_count is equal to it's max value equal to 20. After processing the
request with the second SETQ we process the return code from
con->cb.process_request() (that is actually is memcached_bin_process()).
Because processing finished successfully (rc != -1) and we are not
willing to close a connection we go out of these conditions and come to
a 'continue' and start loop from the beginning, where we do a network
read.

    rc = con->cb.process_request(con);
    ...
    if (rc == -1)
            memcached_loop_error(con);
    if (con->close_connection) {
            break;
    } else if (rc == 0 && ibuf_used(con->in) > 0 &&
               batch_count < con->cfg->batch_count) {
            goto next;
    }
    ...
    continue;

Author: ligurio

memcached/internal/memcached.c

@@ -208,6 +208,9 @@ memcached_loop(struct memcached_connection *con)
 			memcached_flush(con);
 		fiber_reschedule();
 		batch_count = 0;
+                if (ibuf_used(con->in) > 0) {
+                    goto next;
+                }
 		continue;
 	}
 	memcached_flush(con);