To avoid the function call overhead described by jch, instead of calling tr_sessionIsUTPEnabled() and tr_sessionIsDHTEnabled(), we test for WITH_UTP to be defined and test the tr_session.isUTPEnabled and tr_session.isDHTEnabled flags directly.
Previously we allocated a 4096 character buffer each time; now we allocate it on the stack. It seems all the distros and OS flavors that Transmission runs on have multi-MB default stack sizes, so a hardwired 4K array should be safe.
This is a little overlapping since the utp code can be closed more-or-less immediately, but the udp manager needs to stay open in order to process the udp tracker connection requests before sending out event=stopped. Moreover DNS resolver can be shut down after the UDP tracker is shutdown.
The EV_READ callback allocates a buffer, but then returns without freeing it if recvfrom() returns <= 0. This commit inverts the logic to avoid returning until the buffer's been free()d.
Since we're using a single UDP socket to implement multiple uTP sockets,
and since we're not always timely in servicing an incoming UDP packet,
it's important to use a large receive buffer. The send buffer is probably
less critical, we increase it nonetheless.
There's no need to test for DHT/uTP being enabled in tr-udp. The DHT
will silently discard any packets directed at the wrong session (see the
beginning of dhtCallback). As to uTP, we need to grok uTP packets
to close any remaining connections after we disabled uTP, so it's better
to participate in uTP, just reject any incoming connections.
This adds code to participate in the UTP protocol, but without doing anything
useful yet -- we just shut down immediately any incoming connexion request.
Add code to honor the ipv6 bind address. Thanks to jch for saving me a little work by confirming the bug and pointing out where in the code the change needed to be made.
Jordan Lee