build_job() is failing with "... empty response" exception when Jenkins is behind haproxy where disabled keep_alive

[Dennis Dmitriev]

Jenkins supports keep_alive http option, and when JenkinsClient:build_job() is called, normally the response contains the 'content-length' header, for example:

  ipdb> response.status_code
  201
  ipdb> response.headers
  {'Date': 'Mon, 04 Jun 2018 11:52:00 GMT', 'Content-Length': '0', 'Location': 'http://10.70.0.15:8081/queue/item/11/', 'X-Content-Type-Options': 'nosniff', 'Server': 'Jetty(9.4.z-SNAPSHOT)'}

But if Jenkins master is behind HAProxy with enabled 'option httpclose', which disables keep_alive, the response doesn't contain 'content-length' header:

  ipdb> response.status_code
  201
  ipdb> response.headers
  {'Date': 'Mon, 04 Jun 2018 11:55:36 GMT', 'Connection': 'close', 'Location': 'http://10.60.0.90:8081/queue/item/16/', 'X-Content-Type-Options': 'nosniff', 'Server': 'Jetty(9.4.z-SNAPSHOT)'}

Other fields that are checked in JenkisClient:_response_handler() are empty in both cases:
  ipdb> response.content
  ''
  ipdb> response.text
  u''

As the result: JenkinsClient raises an exception like:

  File ".../local/lib/python2.7/site-packages/jenkins/__init__.py", line 1280, in build_job
    'POST', self.build_job_url(name, parameters, token)))
  File ".../lib/python2.7/site-packages/jenkins/__init__.py", line 565, in jenkins_request
    self._request(req))
  File ".../lib/python2.7/site-packages/jenkins/__init__.py", line 523, in _response_handler
    "empty response" % self.server)
jenkins.EmptyResponseException: Error communicating with server[http://10.60.0.90:8081/]: empty response

However, the response is valid because the meaningful part of the response is the header 'Location'.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/572179

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/572179
Committed: https://git.openstack.org/cgit/openstack/python-jenkins/commit/?id=f420d6de01de4558a8f285deaedae58cbc4cb743
Submitter: Zuul
Branch: master

commit f420d6de01de4558a8f285deaedae58cbc4cb743
Author: Dennis Dmitriev <email address hidden>
Date: Mon Jun 4 21:02:20 2018 +0300

    Check for 'Location' header in the response

    If the keep_alive is not available because of using reverse
    proxy, the header 'Content-Lenght' may not be available,
    causing the exception:

     Error communicating with server[...]: empty response

    However, if 'Location' header is present, the response is valid.

    Add unit tests:
    - build_job must pass even if no 'content-lenght'
      in response header
    - build_job must fail if no 'location' in response header

    Change-Id: I4da6dd19f9d8302a76652a3686a9377f9a2503a6
    Closes-Bug:#1775047