1 files changed, 75 insertions, 0 deletions
diff --git a/lib/gitlab/ci/trace/remote_checksum.rb b/lib/gitlab/ci/trace/remote_checksum.rb
new file mode 100644
index 00000000000..d57f3888ec0
--- /dev/null
+++ b/lib/gitlab/ci/trace/remote_checksum.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    class Trace
+      ##
+      # RemoteChecksum class is responsible for fetching the MD5 checksum of
+      # an uploaded build trace.
+      #
+      class RemoteChecksum
+        include Gitlab::Utils::StrongMemoize
+
+        def initialize(trace_artifact)
+          @trace_artifact = trace_artifact
+        end
+
+        def md5_checksum
+          strong_memoize(:md5_checksum) do
+            fetch_md5_checksum
+          end
+        end
+
+        private
+
+        attr_reader :trace_artifact
+        delegate :aws?, :google?, to: :object_store_config, prefix: :provider
+
+        def fetch_md5_checksum
+          return unless Feature.enabled?(:ci_archived_build_trace_checksum, trace_artifact.project, default_enabled: :yaml)
+          return unless object_store_config.enabled?
+          return if trace_artifact.local_store?
+
+          remote_checksum_value
+        end
+
+        def remote_checksum_value
+          strong_memoize(:remote_checksum_value) do
+            if provider_google?
+              checksum_from_google
+            elsif provider_aws?
+              checksum_from_aws
+            end
+          end
+        end
+
+        def object_store_config
+          strong_memoize(:object_store_config) do
+            trace_artifact.file.class.object_store_config
+          end
+        end
+
+        def checksum_from_google
+          content_md5 = upload_attributes.fetch(:content_md5)
+
+          Base64
+            .decode64(content_md5)
+            .unpack1('H*')
+        end
+
+        def checksum_from_aws
+          upload_attributes.fetch(:etag)
+        end
+
+        # Carrierwave caches attributes for the local file and does not replace
+        # them with the ones from object store after the upload completes.
+        # We need to force it to fetch them directly from the object store.
+        def upload_attributes
+          strong_memoize(:upload_attributes) do
+            ::Ci::JobArtifact.find(trace_artifact.id).file.file.attributes
+          end
+        end
+      end
+    end
+  end
+end