Unexpected behavior with localhost and readtimeout

[fredrikekre]

Over in JuliaPackaging/PkgServer.jl#115 there are problems connecting to a server with the combination of localhost and readtimeout.

Looking at the code I found two things:

1. localhost is hardcoded to ipv4, but only with readtimeout=0:

   HTTP.jl/src/ConnectionPool.jl

   Line 653 in a469ac6

   tcp = Sockets.connect(host == "localhost" ? ip"127.0.0.1" : Sockets.getalladdrinfo(host)[1], p)

   while the other code path uses getalladdrinfo("localhost")[1]:

   HTTP.jl/src/ConnectionPool.jl

   Line 659 in a469ac6

   Sockets.connect!(tcp, Sockets.getalladdrinfo(host)[1], p)

   so if getalladdrinfo("localhost")[1] is the ipv6 address HTTP can't connect.
2. HTTP.jl seems to never care about getaddrinfo(host)[2:end].

I suggest that HTTP.jl should loop over getalladdrinfo(host) in both code paths. That is what curl seems to do for example (even with --retry=no which is the default).

Related: #511, #512, #428

CC: @staticfloat