Fix finding wiki pages when they have invalidly-encoded content

Fixes #43715

GITALY_SERVER_VERSION

-0.99.0
+0.100.0

changelogs/unreleased/fix-wiki-find-page-invalid-encoding.yml

+---
+title: Fix finding wiki pages when they have invalidly-encoded content
+merge_request: 18856
+author:
+type: fixed

config/initializers/gollum.rb

@@ -7,6 +7,20 @@ module Gollum
 end
 require "gollum-lib"
 
+module Gollum
+  class Page
+    def text_data(encoding = nil)
+      data = if raw_data.respond_to?(:encoding)
+               raw_data.force_encoding(encoding || Encoding::UTF_8)
+             else
+               raw_data
+             end
+
+      Gitlab::EncodingHelper.encode!(data)
+    end
+  end
+end
+
 Rails.application.configure do
   config.after_initialize do
     Gollum::Page.per_page = Kaminari.config.default_per_page

spec/models/project_wiki_spec.rb

@@ -159,6 +159,17 @@ describe ProjectWiki do
           expect(page.title).to eq("autre pagé")
         end
       end
+
+      context 'pages with invalidly-encoded content' do
+        before do
+          create_page("encoding is fun", "f\xFCr".b)
+        end
+
+        it "can find the page" do
+          page = subject.find_page("encoding is fun")
+          expect(page.content).to eq("fr")
+        end
+      end
     end
 
     context 'when Gitaly wiki_find_page is enabled' do