git_command: set GIT_HTTP_USER_AGENT on all requests

We've been setting the User-Agent header when making connections
from repo itself, but not when running git (as the latter will set
up User-Agent itself).  Our Gerrit/Git admins say it'll be helpful
if we pass through the repo version settings even when running git.

We currently set GIT_HTTP_USER_AGENT and not GIT_USER_AGENT as it's
unclear if the extended form works over all protocols.  We can wait
for a user request.

Bug: https://crbug.com/gerrit/11144
Change-Id: I21d293f49534058dbc23225152451df26c5b7bef
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/239233
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: David Pursehouse <dpursehouse@collab.net>

git_command.py

@@ -134,6 +134,7 @@ class UserAgent(object):
 
   _os = None
   _repo_ua = None
+  _git_ua = None
 
   @property
   def os(self):
@@ -165,6 +166,17 @@ class UserAgent(object):
 
     return self._repo_ua
 
+  @property
+  def git(self):
+    """The UA when running git."""
+    if self._git_ua is None:
+      self._git_ua = 'git/%s (%s) git-repo/%s' % (
+          git.version_tuple().full,
+          self.os,
+          RepoSourceVersion())
+
+    return self._git_ua
+
 user_agent = UserAgent()
 
 def git_require(min_version, fail=False, msg=''):
@@ -214,6 +226,7 @@ class GitCommand(object):
     if 'GIT_ALLOW_PROTOCOL' not in env:
       _setenv(env, 'GIT_ALLOW_PROTOCOL',
               'file:git:http:https:ssh:persistent-http:persistent-https:sso:rpc')
+    _setenv(env, 'GIT_HTTP_USER_AGENT', user_agent.git)
 
     if project:
       if not cwd:

tests/test_git_command.py

@@ -68,3 +68,11 @@ class UserAgentUnitTest(unittest.TestCase):
     # the general form.
     m = re.match(r'^git-repo/[^ ]+ ([^ ]+) git/[^ ]+ Python/[0-9.]+', ua)
     self.assertIsNotNone(m)
+
+  def test_smoke_git(self):
+    """Make sure git UA returns something useful."""
+    ua = git_command.user_agent.git
+    # We can't dive too deep because of OS/tool differences, but we can check
+    # the general form.
+    m = re.match(r'^git/[^ ]+ ([^ ]+) git-repo/[^ ]+', ua)
+    self.assertIsNotNone(m)