compiling with c-ares seems to break os x domain resolution?

I installed php 5.6 with homebrew on macOS 10.14 (mojave). One of its
dependencies is curl-openssl which is curl built with the following
configure flags:

--disable-debug
--disable-dependency-tracking
--disable-silent-rules
--prefix=#{prefix}
--enable-ares=#{Formula["c-ares"].opt_prefix}
--with-ca-bundle=#{etc}/openssl_at_1.1/cert.pem
--with-ca-path=#{etc}/openssl_at_1.1/certs
--with-gssapi
--with-libidn2
--with-libmetalink
--with-librtmp
--with-libssh2
--with-ssl=#{Formula["openssl_at_1.1"].opt_prefix}
--without-libpsl

When run in isolation, this build of cURL failed to resolve an internal
host using the VPN DNS.

$ /usr/local/opt/curl-openssl/bin/curl mydomain.com
curl: (6) Could not resolve: mydomain.com (Domain name not found)

The system cURL on the other hand works as expected and is built with the
following:

--enable-hidden-symbols
--enable-threaded-resolver
--with-gssapi
--with-ssl=/usr/local/libressl

This internal host is correctly resolved a browser. It cannot be resolved
using nslookup, host, or dig.

I solved my problem by uninstalling the homebrew curl and having php use
the system curl instead, but it begs the question why it broke in the first
place. I have read that macOS no longer uses /etc/resolv.conf and thought
perhaps that c-ares might rely on it exclusively? I can confirm that after
connecting to my corporate VPN, resolv.conf is unchanged.

#

# macOS Notice

#

# This file is not consulted for DNS hostname resolution, address

# resolution, or the DNS query routing mechanism used by most

# processes on this system.

#

# To view the DNS configuration used by this system, use:

# scutil --dns

#

# SEE ALSO

# dns-sd(1), scutil(8)

#

# This file is automatically generated.

#

domain home

nameserver 127.0.0.1

scutil on the other hand correctly lists my VPN DNS as a resolver:

$ scutil --dns

...

resolver #2

  search domain[0] : mydomain.com

  nameserver[0] : ...

  if_index : 12 (utun10)

  flags : Scoped, Request A records

  reach : 0x00000002 (Reachable)

Wondering if anyone can shed some light on how curl handles domain
resolution and why it would fail when built with c-ares?

Thanks,
Cole

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Received on 2020-01-16