Force fetch metadata from object store

Sometimes the metadata is outdated and contains values for the local
file. Because we're interested in the metadata from object store we need
to burst that cache and force fetch it directly from the store.

lib/gitlab/ci/trace/remote_checksum.rb

@@ -50,16 +50,23 @@ module Gitlab
         end
 
         def checksum_from_google
-          Base64.decode64(upload_attributes[:content_md5].to_s).unpack1('H*')
+          content_md5 = upload_attributes.fetch(:content_md5)
+
+          Base64
+            .decode64(content_md5)
+            .unpack1('H*')
         end
 
         def checksum_from_aws
-          upload_attributes[:etag]
+          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
-            trace_artifact.file.file.attributes
+            ::Ci::JobArtifact.find(trace_artifact.id).file.file.attributes
           end
         end
       end

spec/lib/gitlab/ci/trace/remote_checksum_spec.rb

@@ -43,18 +43,30 @@ RSpec.describe Gitlab::Ci::Trace::RemoteChecksum do
         end
 
         context 'with Google as provider' do
-          let(:metadata) {{ content_md5: base64checksum }}
-
           before do
+            spy_file = spy(:file)
             expect(fetcher).to receive(:provider_google?) { true }
             expect(fetcher).not_to receive(:provider_aws?) { false }
+            allow(spy_file).to receive(:attributes).and_return(metadata)
 
-            allow(trace_artifact.file.file)
-              .to receive(:attributes)
-              .and_return(metadata)
+            allow_next_found_instance_of(Ci::JobArtifact) do |trace_artifact|
+              allow(trace_artifact.file).to receive(:file) { spy_file }
+            end
           end
 
-          it { is_expected.to eq(checksum) }
+          context 'when the response does not include :content_md5' do
+            let(:metadata) {{}}
+
+            it 'raises an exception' do
+              expect { subject }.to raise_error KeyError, /content_md5/
+            end
+          end
+
+          context 'when the response include :content_md5' do
+            let(:metadata) {{ content_md5: base64checksum }}
+
+            it { is_expected.to eq(checksum) }
+          end
         end
 
         context 'with unsupported providers' do