1 files changed, 82 insertions, 0 deletions
diff --git a/app/finders/repositories/commits_with_trailer_finder.rb b/app/finders/repositories/commits_with_trailer_finder.rb
new file mode 100644
index 00000000000..4bd643c345b
--- /dev/null
+++ b/app/finders/repositories/commits_with_trailer_finder.rb
@@ -0,0 +1,82 @@
+# frozen_string_literal: true
+
+module Repositories
+  # Finder for obtaining commits between two refs, with a Git trailer set.
+  class CommitsWithTrailerFinder
+    # The maximum number of commits to retrieve per page.
+    #
+    # This value is arbitrarily chosen. Lowering it means more Gitaly calls, but
+    # less data being loaded into memory at once. Increasing it has the opposite
+    # effect.
+    #
+    # This amount is based around the number of commits that usually go in a
+    # GitLab release. Some examples for GitLab's own releases:
+    #
+    # * 13.6.0: 4636 commits
+    # * 13.5.0: 5912 commits
+    # * 13.4.0: 5541 commits
+    #
+    # Using this limit should result in most (very large) projects only needing
+    # 5-10 Gitaly calls, while keeping memory usage at a reasonable amount.
+    COMMITS_PER_PAGE = 1024
+
+    # The `project` argument specifies the project for which to obtain the
+    # commits.
+    #
+    # The `from` and `to` arguments specify the range of commits to include. The
+    # commit specified in `from` won't be included itself. The commit specified
+    # in `to` _is_ included.
+    #
+    # The `per_page` argument specifies how many commits are retrieved in a single
+    # Gitaly API call.
+    def initialize(project:, from:, to:, per_page: COMMITS_PER_PAGE)
+      @project = project
+      @from = from
+      @to = to
+      @per_page = per_page
+    end
+
+    # Fetches all commits that have the given trailer set.
+    #
+    # The commits are yielded to the supplied block in batches. This allows
+    # other code to process these commits in batches too, instead of first
+    # having to load all commits into memory.
+    #
+    # Example:
+    #
+    #     CommitsWithTrailerFinder.new(...).each_page('Signed-off-by') do |commits|
+    #       commits.each do |commit|
+    #         ...
+    #       end
+    #     end
+    def each_page(trailer)
+      return to_enum(__method__, trailer) unless block_given?
+
+      offset = 0
+      response = fetch_commits
+
+      while response.any?
+        commits = []
+
+        response.each do |commit|
+          commits.push(commit) if commit.trailers.key?(trailer)
+        end
+
+        yield commits
+
+        offset += response.length
+        response = fetch_commits(offset)
+      end
+    end
+
+    private
+
+    def fetch_commits(offset = 0)
+      range = "#{@from}..#{@to}"
+
+      @project
+        .repository
+        .commits(range, limit: @per_page, offset: offset, trailers: true)
+    end
+  end
+end