std::net::lookup_host repeats output

[nieksand]

Using std::net::lookup_host seems to duplicate each IP in the result set.

prompt> ./main rust-lang.org
V4(72.8.141.90:0)
V4(72.8.141.90:0)

prompt> ./main google.com | sort
V4(74.125.28.100:0)
V4(74.125.28.100:0)
V4(74.125.28.101:0)
V4(74.125.28.101:0)
V4(74.125.28.102:0)
V4(74.125.28.102:0)
V4(74.125.28.113:0)
V4(74.125.28.113:0)
V4(74.125.28.138:0)
V4(74.125.28.138:0)
V4(74.125.28.139:0)
V4(74.125.28.139:0)
V6([2607:f8b0:400e:c04::66]:0)
V6([2607:f8b0:400e:c04::66]:0)

The documentation snippet (https://doc.rust-lang.org/std/net/fn.lookup_host.html) is enough to reproduce.

I also have a simple gist here: https://gist.github.com/nieksand/9c42100be6dc52df3305

I'm using the latest Rust from master branch on MacOS X 10.9.5. I have not checked on other platforms. I see this for any hostname that I try, so I don't think it's a problem on the nameserver side.

Expected behavior is seeing each IP address listed only once.

[imron]

This is happening because the underlying call to getaddrinfo doesn't provide an addrinfo as a hint, and so the linked list of returned addrinfo structs contains addrinfo for both TCP and UDP protocols.

A simple fix would be to simply pass in a hint specifying only one protocol (e.g. TCP)

However I'm not sure how often you'll find a hostname that has UDP available but not TCP and vice versa, and whether or not it's worth capturing that with something like LookupHostUdp and LookupHostTcp.

[nieksand]

Requiring a hint argument specifying tcp vs udp makes sense to me.

[alexcrichton]

Fixed by #34700