Backport Gitlab::Git::Checksum to CE

lib/gitlab/git/checksum.rb

+module Gitlab
+  module Git
+    class Checksum
+      include Gitlab::Git::Popen
+
+      EMPTY_REPOSITORY_CHECKSUM = '0000000000000000000000000000000000000000'.freeze
+
+      Failure = Class.new(StandardError)
+
+      attr_reader :path, :relative_path, :storage, :storage_path
+
+      def initialize(storage, relative_path)
+        @storage       = storage
+        @storage_path  = Gitlab.config.repositories.storages[storage].legacy_disk_path
+        @relative_path = "#{relative_path}.git"
+        @path          = File.join(storage_path, @relative_path)
+      end
+
+      def calculate
+        unless repository_exists?
+          failure!(Gitlab::Git::Repository::NoRepository, 'No repository for such path')
+        end
+
+        calculate_checksum_by_shelling_out
+      end
+
+      private
+
+      def repository_exists?
+        raw_repository.exists?
+      end
+
+      def calculate_checksum_by_shelling_out
+        args = %W(--git-dir=#{path} show-ref --heads --tags)
+        output, status = run_git(args)
+
+        if status&.zero?
+          refs = output.split("\n")
+
+          result = refs.inject(nil) do |checksum, ref|
+            value = Digest::SHA1.hexdigest(ref).hex
+
+            if checksum.nil?
+              value
+            else
+              checksum ^ value
+            end
+          end
+
+          result.to_s(16)
+        else
+          # Empty repositories return with a non-zero status and an empty output.
+          if output&.empty?
+            EMPTY_REPOSITORY_CHECKSUM
+          else
+            failure!(Gitlab::Git::Checksum::Failure, output)
+          end
+        end
+      end
+
+      def failure!(klass, message)
+        Gitlab::GitLogger.error("'git show-ref --heads --tags' in #{path}: #{message}")
+
+        raise klass.new("Could not calculate the checksum for #{path}: #{message}")
+      end
+
+      def circuit_breaker
+        @circuit_breaker ||= Gitlab::Git::Storage::CircuitBreaker.for_storage(storage)
+      end
+
+      def raw_repository
+        Gitlab::Git::Repository.new(storage, relative_path, nil)
+      end
+
+      def run_git(args)
+        circuit_breaker.perform do
+          popen([Gitlab.config.git.bin_path, *args], path)
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/git/checksum_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Git::Checksum, seed_helper: true do
+  let(:storage) { 'default' }
+
+  it 'raises Gitlab::Git::Repository::NoRepository when there is no repo' do
+    checksum = described_class.new(storage, 'nonexistent-repo')
+
+    expect { checksum.calculate }.to raise_error Gitlab::Git::Repository::NoRepository
+  end
+
+  it 'pretends that checksum is 000000... when the repo is empty' do
+    FileUtils.rm_rf(File.join(SEED_STORAGE_PATH, 'empty-repo.git'))
+
+    system(git_env, *%W(#{Gitlab.config.git.bin_path} init --bare empty-repo.git),
+           chdir: SEED_STORAGE_PATH,
+           out:   '/dev/null',
+           err:   '/dev/null')
+
+    checksum = described_class.new(storage, 'empty-repo')
+
+    expect(checksum.calculate).to eq '0000000000000000000000000000000000000000'
+  end
+
+  it 'raises Gitlab::Git::Repository::Failure when shelling out to git return non-zero status' do
+    checksum = described_class.new(storage, 'gitlab-git-test')
+
+    allow(checksum).to receive(:popen).and_return(['output', nil])
+
+    expect { checksum.calculate }.to raise_error Gitlab::Git::Checksum::Failure
+  end
+
+  it 'calculates the checksum when there is a repo' do
+    checksum = described_class.new(storage, 'gitlab-git-test')
+
+    expect(checksum.calculate).to eq '54f21be4c32c02f6788d72207fa03ad3bce725e4'
+  end
+end