As discussed in #41570, UNIX systems often cache the contents of
/etc/resolv.conf, which can cause lookup failures to persist even after
a network connection becomes available. This patch modifies lookup_host
to force a reload of the nameserver entries following a lookup failure.
This is in line with what many C programs already do (see #41570 for
details). On systems with nscd, this should not be necessary, but not
all systems run nscd.
Introduces an std linkage dependency on libresolv on macOS/iOS (which
also makes it necessary to update run-make/tools.mk).
Fixes#41570.
Depends on rust-lang/libc#585.
These methods enable socket reads without side-effects. That is,
repeated calls to peek() return identical data. This is accomplished
by providing the POSIX flag MSG_PEEK to the underlying socket read
operations.
This also moves the current implementation of recv_from out of the
platform-independent sys_common and into respective sys/windows and
sys/unix implementations. This allows for more platform-dependent
implementations.
