Introduce different repo types (git and gitiles)

recipe_engine/fetch.py

Index: recipe_engine/fetch.py
diff --git a/recipe_engine/fetch.py b/recipe_engine/fetch.py
index e67c137c183d837b6c8bc4e952b07db7e519dbfd..e237b7948b59fcff0f652fd59db053cd206349b0 100644
--- a/recipe_engine/fetch.py
+++ b/recipe_engine/fetch.py
@@ -49,89 +49,97 @@ def _run_git(checkout_dir, *args):
   return subprocess42.check_output(cmd)
 
 
-def ensure_git_checkout(repo, revision, checkout_dir, allow_fetch):
-  """Fetches given |repo| at |revision| to |checkout_dir| using git.
-
-  Network operations are performed only if |allow_fetch| is True.
-  """
-  logging.info('Freshening repository %s in %s', repo, checkout_dir)
-
-  if not os.path.isdir(checkout_dir):
-    if not allow_fetch:
-      raise FetchNotAllowedError(
-          'need to clone %s but fetch not allowed' % repo)
-    _run_git(None, 'clone', '-q', repo, checkout_dir)
-  elif not os.path.isdir(os.path.join(checkout_dir, '.git')):
-    raise UncleanFilesystemError(
-        '%s exists but is not a git repo' % checkout_dir)
-
-  actual_origin = _run_git(checkout_dir, 'config', 'remote.origin.url').strip()
-  if actual_origin != repo:
-    raise UncleanFilesystemError(
-        ('workdir %r exists but uses a different origin url %r '
-         'than requested %r') % (checkout_dir, actual_origin, repo))
-
-  try:
-    _run_git(checkout_dir, 'rev-parse', '-q', '--verify',
-             '%s^{commit}' % revision)
-  except subprocess42.CalledProcessError:
+class Backend(object):
+  def checkout(self, repo, revision, checkout_dir, allow_fetch):
+    """Checks out given |repo| at |revision| to |checkout_dir|.
+
+    Network operations are performed only if |allow_fetch| is True.
+    """
+    raise NotImplementedError()
+
+
+class GitBackend(Backend):
+  """GitBackend uses a local git checkout."""
+
+  def checkout(self, repo, revision, checkout_dir, allow_fetch):
+    logging.info('Freshening repository %s in %s', repo, checkout_dir)
+
+    if not os.path.isdir(checkout_dir):
+      if not allow_fetch:
+        raise FetchNotAllowedError(
+            'need to clone %s but fetch not allowed' % repo)
+      _run_git(None, 'clone', '-q', repo, checkout_dir)
+    elif not os.path.isdir(os.path.join(checkout_dir, '.git')):
+      raise UncleanFilesystemError(
+          '%s exists but is not a git repo' % checkout_dir)
+
+    actual_origin = _run_git(
+        checkout_dir, 'config', 'remote.origin.url').strip()
+    if actual_origin != repo:
+      raise UncleanFilesystemError(
+          ('workdir %r exists but uses a different origin url %r '
+           'than requested %r') % (checkout_dir, actual_origin, repo))
+
+    try:
+      _run_git(checkout_dir, 'rev-parse', '-q', '--verify',
+               '%s^{commit}' % revision)
+    except subprocess42.CalledProcessError:
+      if not allow_fetch:
+        raise FetchNotAllowedError(
+            'need to fetch %s but fetch not allowed' % repo)
+      _run_git(checkout_dir, 'fetch')
+    _run_git(checkout_dir, 'reset', '-q', '--hard', revision)
+
+
+class GitilesBackend(Backend):
+  """GitilesBackend uses a repo served by Gitiles."""
+
+  def checkout(self, repo, revision, checkout_dir, allow_fetch):
+    logging.info('Freshening repository %s in %s', repo, checkout_dir)
+
+    # TODO(phajdan.jr): implement caching.
     if not allow_fetch:
       raise FetchNotAllowedError(
-          'need to fetch %s but fetch not allowed' % repo)
-    _run_git(checkout_dir, 'fetch')
-  _run_git(checkout_dir, 'reset', '-q', '--hard', revision)
-
-
-def ensure_gitiles_checkout(repo, revision, checkout_dir, allow_fetch):
-  """Fetches given |repo| at |revision| to |checkout_dir| using gitiles.
-
-  Network operations are performed only if |allow_fetch| is True.
-  """
-  logging.info('Freshening repository %s in %s', repo, checkout_dir)
-
-  # TODO(phajdan.jr): implement caching.
-  if not allow_fetch:
-    raise FetchNotAllowedError(
-        'need to download %s from gitiles but fetch not allowed' % repo)
-
-  rev_url = '%s/+/%s?format=JSON' % (repo, requests.utils.quote(revision))
-  logging.info('fetching %s', rev_url)
-  rev_raw = requests.get(rev_url).text
-  if not rev_raw.startswith(')]}\'\n'):
-    raise FetchError('Unexpected gitiles response: %s' % rev_raw)
-  rev_json = json.loads(rev_raw.split('\n', 1)[1])
-  orig_revision = revision
-  revision = rev_json['commit']
-  logging.info('resolved %s to %s', orig_revision, revision)
-
-  shutil.rmtree(checkout_dir, ignore_errors=True)
-
-  recipes_cfg_url = '%s/+/%s/infra/config/recipes.cfg?format=TEXT' % (
-      repo, requests.utils.quote(revision))
-  logging.info('fetching %s' % recipes_cfg_url)
-  recipes_cfg_request = requests.get(recipes_cfg_url)
-  recipes_cfg_text = base64.b64decode(recipes_cfg_request.text)
-  recipes_cfg_proto = package_pb2.Package()
-  text_format.Merge(recipes_cfg_text, recipes_cfg_proto)
-  recipes_path_rel = recipes_cfg_proto.recipes_path
-
-  # Re-create recipes.cfg in |checkout_dir| so that the repo's recipes.py
-  # can look it up.
-  recipes_cfg_path = os.path.join(
-      checkout_dir, 'infra', 'config', 'recipes.cfg')
-  os.makedirs(os.path.dirname(recipes_cfg_path))
-  with open(recipes_cfg_path, 'w') as f:
-    f.write(recipes_cfg_text)
-
-  recipes_path = os.path.join(checkout_dir, recipes_path_rel)
-  os.makedirs(recipes_path)
-
-  archive_url = '%s/+archive/%s/%s.tar.gz' % (
-      repo, requests.utils.quote(revision), recipes_path_rel)
-  logging.info('fetching %s' % archive_url)
-  archive_request = requests.get(archive_url)
-  with tempfile.NamedTemporaryFile() as f:
-    f.write(archive_request.content)
-    f.flush()
-    with tarfile.open(f.name) as archive_tarfile:
-      archive_tarfile.extractall(recipes_path)
+          'need to download %s from gitiles but fetch not allowed' % repo)
+
+    rev_url = '%s/+/%s?format=JSON' % (repo, requests.utils.quote(revision))
+    logging.info('fetching %s', rev_url)
+    rev_raw = requests.get(rev_url).text
+    if not rev_raw.startswith(')]}\'\n'):
+      raise FetchError('Unexpected gitiles response: %s' % rev_raw)
+    rev_json = json.loads(rev_raw.split('\n', 1)[1])
+    orig_revision = revision
+    revision = rev_json['commit']
+    logging.info('resolved %s to %s', orig_revision, revision)
+
+    shutil.rmtree(checkout_dir, ignore_errors=True)
+
+    recipes_cfg_url = '%s/+/%s/infra/config/recipes.cfg?format=TEXT' % (
+        repo, requests.utils.quote(revision))
+    logging.info('fetching %s' % recipes_cfg_url)
+    recipes_cfg_request = requests.get(recipes_cfg_url)
+    recipes_cfg_text = base64.b64decode(recipes_cfg_request.text)
+    recipes_cfg_proto = package_pb2.Package()
+    text_format.Merge(recipes_cfg_text, recipes_cfg_proto)
+    recipes_path_rel = recipes_cfg_proto.recipes_path
+
+    # Re-create recipes.cfg in |checkout_dir| so that the repo's recipes.py
+    # can look it up.
+    recipes_cfg_path = os.path.join(
+        checkout_dir, 'infra', 'config', 'recipes.cfg')
+    os.makedirs(os.path.dirname(recipes_cfg_path))
+    with open(recipes_cfg_path, 'w') as f:
+      f.write(recipes_cfg_text)
+
+    recipes_path = os.path.join(checkout_dir, recipes_path_rel)
+    os.makedirs(recipes_path)
+
+    archive_url = '%s/+archive/%s/%s.tar.gz' % (
+        repo, requests.utils.quote(revision), recipes_path_rel)
+    logging.info('fetching %s' % archive_url)
+    archive_request = requests.get(archive_url)
+    with tempfile.NamedTemporaryFile() as f:
+      f.write(archive_request.content)
+      f.flush()
+      with tarfile.open(f.name) as archive_tarfile:
+        archive_tarfile.extractall(recipes_path)