[jira] [Created] (PROTON-2474) proton with cyrus-sasl queries DNS for short hostname

["Ken Dreyer (Jira)" <ji...@apache.org>]

Ken Dreyer created PROTON-2474:
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             Summary: proton with cyrus-sasl queries DNS for short hostname
                 Key: PROTON-2474
                 URL: https://issues.apache.org/jira/browse/PROTON-2474
             Project: Qpid Proton
          Issue Type: New Feature
          Components: python-binding
    Affects Versions: proton-c-0.35.0
            Reporter: Ken Dreyer


My python-qpid-proton 0.35.0 client hangs for about four seconds on every new connection operation to my broker. The problem is that the client tries to look up its own hostname's A and AAAA DNS records before completing the SASL exchange (and my DNS server takes a while for missing records.)

*Steps to reproduce:*
 # Set up a CentOS 8 or 9 host.
 # Install cyrus-sasl-devel
 # Install python-qpid-proton. Ensure it's dynamically linked to cyrus-sasl ({{{}/lib64/libsasl2.so.3{}}}).
 # Ensure the unqualified (short) hostname from the "{{{}hostname{}}}" command is not present in {{{}/etc/hosts{}}}.
 # Connect to a broker with ANONYMOUS SASL and no SSL.

*Actual results:*
Immediately after Proton receives the {{sasl.mechanisms}} message, but before Proton sends the {{sasl.init}} / {{sasl.outcome}} AMQP messages, it makes two DNS queries (A and AAAA) for my host's unqualified hostname.

The AAAA request takes a while to answer (3.5 seconds). This makes makes the {{pn_transport_push()}} call hang here:
{noformat}
-> exec(cmd, globals, locals)
  <string>(1)<module>()
  /home/vagrant/dns.py(51)<module>()
-> Container(HelloWorld()).run()
  /usr/lib64/python3.6/site-packages/proton/_reactor.py(180)run()
-> while self.process():
  /usr/lib64/python3.6/site-packages/proton/_reactor.py(245)process()
-> event.dispatch(self._global_handler)
  /usr/lib64/python3.6/site-packages/proton/_events.py(162)dispatch()
-> _dispatch(handler, type.method, self)
  /usr/lib64/python3.6/site-packages/proton/_events.py(125)_dispatch()
-> handler.on_unhandled(method, *args)
  /usr/lib64/python3.6/site-packages/proton/_reactor.py(876)on_unhandled()
-> event.dispatch(self.base)
  /usr/lib64/python3.6/site-packages/proton/_events.py(162)dispatch()
-> _dispatch(handler, type.method, self)
  /usr/lib64/python3.6/site-packages/proton/_events.py(123)_dispatch()
-> m(*args)
  /usr/lib64/python3.6/site-packages/proton/_handlers.py(1241)on_selectable_readable()
-> n = t.push(b)
  /usr/lib64/python3.6/site-packages/proton/_transport.py(304)push()
-> n = self._check(pn_transport_push(self._impl, binary))
{noformat}
*Expected Results:*

proton with cyrus-sasl should behave the same way it does without cyrus-sasl: it should authenticate quickly, without looking up the IP address of its own short hostname.

*Extra information:*

This only happens when I build against cyrus-sasl-devel. When I do not have cyrus-sasl-devel available, then the package from PyPI does not link against cyrus-sasl, and there is no DNS request. (The qpid-proton package in EPEL is built against cyrus-sasl, and that  is where I discovered this bug.)

If the client can resolve its unqualified (short) hostname to an IP, then there is no delay. For example, if my Proton client's hostname is myclient.example.com, I can fix the delay by adding the following entry to /etc/hosts:
{noformat}
127.0.0.1   myclient localhost
{noformat}
or by ensuring my DNS server will immediately return A or AAAA records for the unqualified "myclient" name.



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