Use hash of test ID to pick Gerrit ports in tests

This eliminates need for 127.* IPs mapped to loopback interface (which
is true only for Linux) and makes test site generation even more
predictable (name of site dir for a test is the same on any machine).

Hash function used is md5(test_id) % 10000 which is enough for now. This
function is checked for collisions before every run in tox.ini, so if
someone happens to add test that will cause a collision, it'll be
immediately visible. Hash function can be changed to anything else that
maps test ID string to a number in [0,10000].

Change-Id: Ib05d9b489a80e4f55c84db2f8bea20b88e959649

git_review/tests/__init__.py

@@ -13,9 +13,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import hashlib
 import os
 import shutil
 import stat
+import struct
 import sys
 
 if sys.version < '3':
@@ -41,6 +43,20 @@ WAR_URL = 'http://tarballs.openstack.org/' \
 GOLDEN_SITE_VER = '4'
 
 
+# NOTE(yorik-sar): This function needs to be a perfect hash function for
+# existing test IDs. This is verified by running check_test_id_hashes script
+# prior to running tests. Note that this doesn't imply any cryptographic
+# requirements for underlying algorithm, so we can use weak hash here.
+# Range of results for this function is limited by port numbers selection
+# in _pick_gerrit_port_and_dir method (it can't be greater than 10000 now).
+def _hash_test_id(test_id):
+    if not isinstance(test_id, bytes):
+        test_id = test_id.encode('utf-8')
+    hash_ = hashlib.md5(test_id).digest()
+    num = struct.unpack("=I", hash_[:4])[0]
+    return num % 10000
+
+
 class GerritHelpers(object):
 
     def _dir(self, base, *args):
@@ -143,7 +159,6 @@ class GerritHelpers(object):
 class BaseGitReviewTestCase(testtools.TestCase, GerritHelpers):
     """Base class for the git-review tests."""
 
-    _test_counter = 0
     _remote = 'gerrit'
 
     @property
@@ -158,7 +173,6 @@ class BaseGitReviewTestCase(testtools.TestCase, GerritHelpers):
         """
         super(BaseGitReviewTestCase, self).setUp()
         self.useFixture(fixtures.Timeout(2 * 60, True))
-        BaseGitReviewTestCase._test_counter += 1
 
         # ensures git-review command runs in local mode (for functional tests)
         self.useFixture(
@@ -326,9 +340,13 @@ class BaseGitReviewTestCase(testtools.TestCase, GerritHelpers):
         self._run_git('config', 'gitreview.username', 'test_user')
 
     def _pick_gerrit_port_and_dir(self):
-        pid = os.getpid()
-        host = '127.%s.%s.%s' % (self._test_counter, pid >> 8, pid & 255)
-        return host, 29418, host, 8080, self._dir('gerrit', 'site-' + host)
+        hash_ = _hash_test_id(self.id())
+        host = '127.0.0.1'
+        return (
+            host, 12000 + hash_,  # avoid 11211 that is memcached port on CI
+            host, 22000 + hash_,  # avoid ephemeral ports at 32678+
+            self._dir('gerrit', 'site-' + str(hash_)),
+        )
 
     def _create_gitreview_file(self, **kwargs):
         cfg = ('[gerrit]\n'

git_review/tests/check_test_id_hashes.py

@@ -0,0 +1,57 @@
+# Copyright (c) 2013 Mirantis Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import sys
+
+from git_review import tests
+from git_review.tests import utils
+
+
+def list_test_ids(argv):
+    res = utils.run_cmd(sys.executable, '-m', 'testtools.run', *argv[1:])
+    return res.split('\n')
+
+
+def find_collisions(test_ids):
+    hashes = {}
+    for test_id in test_ids:
+        hash_ = tests._hash_test_id(test_id)
+        if hash_ in hashes:
+            return (hashes[hash_], test_id)
+        hashes[hash_] = test_id
+    return None
+
+
+def main(argv):
+    test_ids = list_test_ids(argv)
+    if not test_ids:
+        print("No tests found, check command line arguments", file=sys.stderr)
+        return 1
+    collision = find_collisions(test_ids)
+    if collision is None:
+        return 0
+    print(
+        "Found a collision for test ids hash function: %s and %s\n"
+        "You should change _hash_test_id function in"
+        " git_review/tests/__init__.py module to fit new set of test ids."
+        % collision,
+        file=sys.stderr,
+    )
+    return 2
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))

tox.ini

@@ -7,6 +7,7 @@ setenv =
     VIRTUAL_ENV={envdir}
 
 commands =
+  python -m git_review.tests.check_test_id_hashes discover --list
   python -m git_review.tests.prepare
   python setup.py testr --slowest --testr-args='--concurrency=2 {posargs}'