bindwithrange() honours a range by setting IP_LOCAL_PORT_RANGE where it
exists, which leaves the kernel to pick a port inside it and skip the ones
still closing. Everywhere else it binds a port out of the range at random,
ten times, and lets the system choose when all ten are taken.
A port which carried a connection cannot be bound again until that close
completes - four minutes of it on Windows - so a window of fifty ports
shared by three services in one configuration can have too few left, and
the connection then binds outside the range and the case fails. The window
is five hundred ports there instead. The Linux one is unchanged: the
kernel picks from it and needs no room to spare.
tcppm and udppm forward a port each, so test both directions of each: a
request through the TCP mapper reaching its target, a datagram through the
UDP one coming back answered, and a mapper whose rules deny the client
answering nothing.
tlspr takes its destination from the name in the handshake, so point that
name at 127.0.0.1 with nsrecord and give the certificate the same name: the
name then both chooses where the request goes and is what the client checks.
dnspr answers from its cache, including the documented 0.0.0.0 record, which
is handed out as an address rather than withheld.
auto is asked to serve an HTTP proxy request, SOCKS4, SOCKS5 and a TLS
handshake on one port, and to make nothing of a request that is none of
them. Its protocols reach different places, so there are two origins.
The SOCKS UDP association was only checked for the port it binds. Send
datagrams through it as well, large and small, and check a second
association gets its own port - and that one bound inside an intport range
still relays.
A UDP service has no socket to connect to, so readiness is found by asking
until it answers rather than racing it.
The MITM case reached its origin by address, so it depended on the
certificate 3proxy spoofs carrying an IP alternative name. It does when the
upstream certificate is copied, which is what happens on Linux and macOS
but not on Windows, where the client then refused the connection. Point a
name at 127.0.0.1 with nsrecord instead, and check the chain rather than
the name: an intercepted certificate names the upstream host, not the one
that was asked for. The log assertions gain from it too, since the name is
better evidence than a port that the request was seen.
nsrecord needs nserver as well as nscache, and has to follow nscache, so
say that in the manual: the record goes into the table nscache allocates,
and the table is only consulted when nserver is set.
The port-range fallback was exercised with a range the same case had
already used, so on a busy machine it could fail to bind for the ordinary
reason rather than the one under test. Use privileged ports, which nothing
can take.
When a case fails, print what its servers wrote: the reason usually goes to
the server's stderr, which was captured and then thrown away.
