When proxy protocol is used and --skip-name-resolve is not set,
thd_set_peer_addr() is called twice per connection: once for the real TCP peer (in check_connection),
and again for the proxied address (in handle_proxy_header).
Each call invokes ip_to_hostname(), which allocates a hostname string
(unless loopback connection is used) and stores it as
thd->main_security_ctx.host. That code missed to free previously
allocated hostname, which results into memory leak.
This is now fixed. Also added debug-only test to mysql_client_test, which
fakes DNS and IP resolution the same way some perfschema tests do, to
emulate remote TCP connection in MTR.
fcd3f81e08