[gerrit_util] Factor out SSOHelper

Add a layer of abstraction/isolation for general organization.

Also, this logic needs to be used in Git setup too, not just Gerrit
authentication.

Bug: b/348024314
Change-Id: Ie1310a9b8e71c05c72a4b987dcbff76b70c67945
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5645906
Commit-Queue: Allen Li <ayatane@chromium.org>
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>

gerrit_util.py

@@ -11,7 +11,6 @@ from __future__ import annotations
 
 import base64
 import contextlib
-import functools
 import http.cookiejar
 import json
 import logging
@@ -149,6 +148,29 @@ def _QueryString(params, first_param=None):
     return '+'.join(q)
 
 
+class SSOHelper(object):
+    """SSOHelper finds a Google-internal SSO helper."""
+
+    _sso_cmd: Optional[str] = None
+
+    def find_cmd(self) -> str:
+        """Returns the cached command-line to invoke git-remote-sso.
+
+        If git-remote-sso is not in $PATH, returns None.
+        """
+        if self._sso_cmd is not None:
+            return self._sso_cmd
+        cmd = shutil.which('git-remote-sso')
+        if cmd is None:
+            cmd = ''
+        self._sso_cmd = cmd
+        return cmd
+
+
+# Global instance
+ssoHelper = SSOHelper()
+
+
 class Authenticator(object):
     """Base authenticator class for authenticator implementations to subclass."""
 
@@ -234,16 +256,6 @@ class SSOAuthenticator(Authenticator):
     # Overridden in tests.
     _timeout_secs = 5
 
-    # Tri-state cache for sso helper command:
-    #   * None - no lookup yet
-    #   * () - lookup was performed, but no binary was found.
-    #   * non-empty tuple - lookup was performed, and this is the command to
-    #     run.
-    #
-    # NOTE: Tests directly assign to this to substitute a helper process that
-    # can exercise other aspects of SSOAuthenticator.
-    _sso_cmd: Optional[Tuple[str, ...]] = None
-
     @dataclass
     class SSOInfo:
         proxy: httplib2.ProxyInfo
@@ -260,19 +272,14 @@ class SSOAuthenticator(Authenticator):
 
         If git-remote-sso is not in $PATH, returns ().
         """
-        cmd = cls._sso_cmd
-        if cmd is None:
-            pth = shutil.which('git-remote-sso')
-            if pth is None:
-                cmd = ()
-            else:
-                cmd = (
-                    pth,
+        cmd = ssoHelper.find_cmd()
+        if not cmd:
+            return ()
+        return (
+            cmd,
             '-print_config',
             'sso://*.git.corp.google.com',
         )
-            cls._sso_cmd = cmd
-        return cmd
 
     @classmethod
     def is_applicable(cls) -> bool:

tests/gerrit_util_test.py

@@ -599,7 +599,6 @@ class SSOAuthenticatorTest(unittest.TestCase):
         return super().setUpClass()
 
     def setUp(self) -> None:
-        gerrit_util.SSOAuthenticator._sso_cmd = None
         gerrit_util.SSOAuthenticator._sso_info = None
         gerrit_util.SSOAuthenticator._testing_load_expired_cookies = True
         gerrit_util.SSOAuthenticator._timeout_secs = self._original_timeout_secs
@@ -607,7 +606,6 @@ class SSOAuthenticatorTest(unittest.TestCase):
         return super().setUp()
 
     def tearDown(self) -> None:
-        gerrit_util.SSOAuthenticator._sso_cmd = None
         gerrit_util.SSOAuthenticator._sso_info = None
         gerrit_util.SSOAuthenticator._testing_load_expired_cookies = False
         gerrit_util.SSOAuthenticator._timeout_secs = self._original_timeout_secs
@@ -619,24 +617,19 @@ class SSOAuthenticatorTest(unittest.TestCase):
         # Here _testMethodName would be a string like "testCmdAssemblyFound"
         return base / self._testMethodName
 
-    @mock.patch('shutil.which', return_value='/fake/git-remote-sso')
+    @mock.patch('gerrit_util.ssoHelper.find_cmd',
+                return_value='/fake/git-remote-sso')
     def testCmdAssemblyFound(self, _):
         self.assertEqual(self.sso._resolve_sso_cmd(),
                          ('/fake/git-remote-sso', '-print_config',
                           'sso://*.git.corp.google.com'))
         self.assertTrue(self.sso.is_applicable())
 
-    @mock.patch('shutil.which', return_value=None)
+    @mock.patch('gerrit_util.ssoHelper.find_cmd', return_value=None)
     def testCmdAssemblyNotFound(self, _):
         self.assertEqual(self.sso._resolve_sso_cmd(), ())
         self.assertFalse(self.sso.is_applicable())
 
-    @mock.patch('shutil.which', return_value='/fake/git-remote-sso')
-    def testCmdAssemblyCached(self, which):
-        self.sso._resolve_sso_cmd()
-        self.sso._resolve_sso_cmd()
-        self.assertEqual(which.called, 1)
-
     def testParseConfigOK(self):
         parsed = self.sso._parse_config(
             textwrap.dedent(f'''
@@ -696,5 +689,26 @@ class SSOAuthenticatorTest(unittest.TestCase):
             self.sso._get_sso_info()
 
 
+class SSOHelperTest(unittest.TestCase):
+
+    def setUp(self) -> None:
+        self.sso = gerrit_util.SSOHelper()
+        return super().setUp()
+
+    @mock.patch('shutil.which', return_value='/fake/git-remote-sso')
+    def testFindCmd(self, _):
+        self.assertEqual(self.sso.find_cmd(), '/fake/git-remote-sso')
+
+    @mock.patch('shutil.which', return_value=None)
+    def testFindCmdMissing(self, _):
+        self.assertEqual(self.sso.find_cmd(), '')
+
+    @mock.patch('shutil.which', return_value='/fake/git-remote-sso')
+    def testFindCmdCached(self, which):
+        self.sso.find_cmd()
+        self.sso.find_cmd()
+        self.assertEqual(which.called, 1)
+
+
 if __name__ == '__main__':
     unittest.main()