access: Move access checks into standalone function

We're about to split up access checks into those which are specific to
references and those which are specific to all changed objects. This
requires some refactoring on our side where we not only iterate over all
changes separately, but also where we do another batched check for all
objects introduced via all changes at once.

To ease the transition, refactor the access checks into their own
function. This allows us to more easily handle timeouts across both
kinds of checks.

lib/gitlab/git_access.rb

@@ -334,18 +334,17 @@ module Gitlab
         # clear stale lock files.
         project.repository.clean_stale_repository_files if project.present?
 
+        check_access!
+      end
+    end
+
+    def check_access!
       # Iterate over all changes to find if user allowed all of them to be applied
       changes_list.each.with_index do |change, index|
-          first_change = index == 0
+        skip_lfs_integrity_check = index != 0
 
         # If user does not have access to make at least one change, cancel all
         # push by allowing the exception to bubble up
-          check_single_change_access(change, skip_lfs_integrity_check: !first_change)
-        end
-      end
-    end
-
-    def check_single_change_access(change, skip_lfs_integrity_check: false)
         Checks::ChangeAccess.new(
           change,
           user_access: user_access,
@@ -354,6 +353,7 @@ module Gitlab
           protocol: protocol,
           logger: logger
         ).validate!
+      end
     rescue Checks::TimedLogger::TimeoutError
       raise TimeoutError, logger.full_message
     end

lib/gitlab/git_access_snippet.rb

@@ -109,20 +109,18 @@ module Gitlab
       end
 
       check_size_before_push!
+      check_access!
+      check_push_size!
+    end
 
+    override :check_access!
+    def check_access!
       changes_list.each do |change|
         # If user does not have access to make at least one change, cancel all
         # push by allowing the exception to bubble up
-        check_single_change_access(change)
-      end
-
-      check_push_size!
-    end
-
-    override :check_single_change_access
-    def check_single_change_access(change, _skip_lfs_integrity_check: false)
         Checks::SnippetCheck.new(change, default_branch: snippet.default_branch, root_ref: snippet.repository.root_ref, logger: logger).validate!
         Checks::PushFileCountCheck.new(change, repository: repository, limit: Snippet.max_file_limit, logger: logger).validate!
+      end
     rescue Checks::TimedLogger::TimeoutError
       raise TimeoutError, logger.full_message
     end

spec/lib/gitlab/git_access_spec.rb

@@ -1006,7 +1006,7 @@ RSpec.describe Gitlab::GitAccess do
         expect { access.check('git-receive-pack', changes) }.not_to exceed_query_limit(control_count).with_threshold(2)
       end
 
-      it 'raises TimeoutError when #check_single_change_access raises a timeout error' do
+      it 'raises TimeoutError when #check_access! raises a timeout error' do
         message = "Push operation timed out\n\nTiming information for debugging purposes:\nRunning checks for ref: wow"
 
         expect_next_instance_of(Gitlab::Checks::ChangeAccess) do |check|