Ensure RepositoryLinkFilter handles Gitaly failures gracefully

We do this by setting all paths to `:blob` type if we get either
`GRPC::Unavailable` or `GRPC::DeadlineExceeded` when calling
`GitalyClient`. This is acceptable because all files existing in a
repository can be viewed in "blob" mode, although if Gitaly is down we
won't be able to fetch the object anyways.

changelogs/unreleased/196883-repository-link-grpc-graceful-failure.yml

+---
+title: Ensure RepositoryLinkFilter handles Gitaly failures gracefully
+merge_request: 26531
+author:
+type: performance

lib/banzai/filter/repository_link_filter.rb

@@ -80,6 +80,13 @@ module Banzai
         end
 
         Gitlab::GitalyClient::BlobService.new(repository).get_blob_types(revision_paths, 1)
+      rescue GRPC::Unavailable, GRPC::DeadlineExceeded => e
+        # Handle Gitaly connection issues gracefully
+        Gitlab::ErrorTracking.track_exception(e, project_id: project.id)
+        # Return all links as blob types
+        paths.collect do |path|
+          [path, :blob]
+        end
       end
 
       def get_uri(html_attr)

spec/lib/banzai/filter/repository_link_filter_spec.rb

@@ -149,6 +149,34 @@ describe Banzai::Filter::RepositoryLinkFilter do
   end
 
   shared_examples :valid_repository do
+    it 'handles Gitaly unavailable exceptions gracefully' do
+      allow_next_instance_of(Gitlab::GitalyClient::BlobService) do |blob_service|
+        allow(blob_service).to receive(:get_blob_types).and_raise(GRPC::Unavailable)
+      end
+
+      expect(Gitlab::ErrorTracking).to receive(:track_exception).with(
+        an_instance_of(GRPC::Unavailable), project_id: project.id
+      )
+      doc = ""
+      expect { doc = filter(link('doc/api/README.md')) }.not_to raise_error
+      expect(doc.at_css('a')['href'])
+          .to eq "/#{project_path}/-/blob/#{ref}/doc/api/README.md"
+    end
+
+    it 'handles Gitaly timeout exceptions gracefully' do
+      allow_next_instance_of(Gitlab::GitalyClient::BlobService) do |blob_service|
+        allow(blob_service).to receive(:get_blob_types).and_raise(GRPC::DeadlineExceeded)
+      end
+
+      expect(Gitlab::ErrorTracking).to receive(:track_exception).with(
+        an_instance_of(GRPC::DeadlineExceeded), project_id: project.id
+      )
+      doc = ""
+      expect { doc = filter(link('doc/api/README.md')) }.not_to raise_error
+      expect(doc.at_css('a')['href'])
+          .to eq "/#{project_path}/-/blob/#{ref}/doc/api/README.md"
+    end
+
     it 'rebuilds absolute URL for a file in the repo' do
       doc = filter(link('/doc/api/README.md'))
       expect(doc.at_css('a')['href'])