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

jenkins/__init__.py

@@ -513,6 +513,7 @@ class Jenkins(object):
         headers = response.headers
         if (headers.get('content-length') is None and
                 headers.get('transfer-encoding') is None and
+                headers.get('location') is None and
                 (response.content is None or len(response.content) <= 0)):
             # response body should only exist if one of these is provided
             raise EmptyResponseException(
@@ -1274,6 +1275,12 @@ class Jenkins(object):
         '''
         response = self.jenkins_request(requests.Request(
             'POST', self.build_job_url(name, parameters, token)))
+
+        if 'Location' not in response.headers:
+            raise EmptyResponseException(
+                "Header 'Location' not found in "
+                "response from server[%s]" % self.server)
+
         location = response.headers['Location']
         # location is a queue item, eg. "http://jenkins/queue/item/25/"
         if location.endswith('/'):

tests/helper.py

@@ -78,14 +78,15 @@ class NullServer(socketserver.TCPServer):
             *args, **kwargs)
 
 
-def build_response_mock(status_code, json_body=None, headers=None, **kwargs):
+def build_response_mock(status_code, json_body=None, headers=None,
+                        add_content_length=True, **kwargs):
     real_response = requests.Response()
     real_response.status_code = status_code
 
     text = None
     if json_body is not None:
         text = json.dumps(json_body)
-        if headers is not {}:
+        if add_content_length and headers is not {}:
             real_response.headers['content-length'] = len(text)
 
     if headers is not None:

tests/jobs/test_build.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from mock import patch
 
+import jenkins
 from six.moves.urllib.parse import quote
 from tests.helper import build_response_mock
 from tests.jobs.base import JenkinsJobsTestBase
@@ -19,6 +20,49 @@ class JenkinsBuildJobTest(JenkinsJobsTestBase):
                          self.make_url(quote(u'job/Test Jøb/build'.encode('utf8'))))
         self.assertEqual(queue_id, 25)
 
+    @patch('jenkins.requests.Session.send', autospec=True)
+    def test_assert_no_location(self, session_send_mock):
+        session_send_mock.return_value = build_response_mock(302, {})
+
+        with self.assertRaises(jenkins.EmptyResponseException) as context_mgr:
+            self.j.build_job(u'Test Job')
+
+        self.assertEqual(
+            str(context_mgr.exception),
+            "Header 'Location' not found in response from server[{0}]".format(
+                self.make_url('')))
+
+    @patch.object(jenkins.Jenkins, 'maybe_add_crumb')
+    @patch('jenkins.requests.Session.send', autospec=True)
+    def test_simple_no_content_lenght(self, session_send_mock,
+                                      maybe_add_crumb_mock):
+        maybe_add_crumb_mock.return_value = None
+        session_send_mock.return_value = build_response_mock(
+            201, None, add_content_length=False,
+            headers={'Location': self.make_url('/queue/item/25/')})
+
+        queue_id = self.j.build_job(u'Test Job')
+
+        self.assertEqual(session_send_mock.call_args[0][1].url,
+                         self.make_url('job/Test%20Job/build'))
+        self.assertEqual(queue_id, 25)
+
+    @patch.object(jenkins.Jenkins, 'maybe_add_crumb')
+    @patch('jenkins.requests.Session.send', autospec=True)
+    def test_assert_no_content_lenght_no_location(self, session_send_mock,
+                                                  maybe_add_crumb_mock):
+        maybe_add_crumb_mock.return_value = None
+        session_send_mock.return_value = build_response_mock(
+            201, None, add_content_length=False)
+
+        with self.assertRaises(jenkins.EmptyResponseException) as context_mgr:
+            self.j.build_job(u'Test Job')
+
+        self.assertEqual(
+            str(context_mgr.exception),
+            'Error communicating with server[{0}]: empty response'.format(
+                self.make_url('')))
+
     @patch('jenkins.requests.Session.send', autospec=True)
     def test_in_folder(self, session_send_mock):
         session_send_mock.return_value = build_response_mock(