Relativize absolute links to the instance on export

app/models/account/data_transfer/action_text/rich_text_record_set.rb

@@ -20,7 +20,7 @@ class Account::DataTransfer::ActionText::RichTextRecordSet < Account::DataTransf
     end
 
     def export_record(rich_text)
-      data = rich_text.as_json.merge("body" => convert_sgids_to_gids(rich_text.body))
+      data = rich_text.as_json.merge("body" => transform_body_for_export(rich_text.body))
       zip.add_file "data/action_text_rich_texts/#{rich_text.id}.json", data.to_json
     end
 
@@ -54,9 +54,14 @@ class Account::DataTransfer::ActionText::RichTextRecordSet < Account::DataTransf
       check_associations_dont_exist(data)
     end
 
-    def convert_sgids_to_gids(content)
+    def transform_body_for_export(content)
       return nil if content.blank?
 
+      html = convert_sgids_to_gids(content)
+      relativize_urls(html)
+    end
+
+    def convert_sgids_to_gids(content)
       content.send(:attachment_nodes).each do |node|
         sgid = SignedGlobalID.parse(node["sgid"], for: ::ActionText::Attachable::LOCATOR_NAME)
 
@@ -75,6 +80,25 @@ class Account::DataTransfer::ActionText::RichTextRecordSet < Account::DataTransf
       content.fragment.source.to_html
     end
 
+    def relativize_urls(html)
+      host = Rails.application.routes.default_url_options[:host]
+      return html unless host
+
+      fragment = Nokogiri::HTML.fragment(html)
+
+      fragment.css("a[href]").each do |link|
+        uri = URI.parse(link["href"]) rescue nil
+
+        if uri.respond_to?(:host) && uri.host == host
+          link["href"] = uri.path
+          link["href"] += "?#{uri.query}" if uri.query
+          link["href"] += "##{uri.fragment}" if uri.fragment
+        end
+      end
+
+      fragment.to_html
+    end
+
     def transform_body_for_import(body)
       return body if body.blank?
 
@@ -112,7 +136,7 @@ class Account::DataTransfer::ActionText::RichTextRecordSet < Account::DataTransf
         if match
           path = match.post_match.presence || "/"
           valid_path = Rails.application.routes.recognize_path(path) rescue nil
-          link["href"] = "#{account.slug}#{remaining_path}" if valid_path
+          link["href"] = "#{account.slug}#{path}" if valid_path
         end
       end
 

test/models/account/data_transfer/action_text/rich_text_record_set_test.rb

@@ -117,4 +117,57 @@ class Account::DataTransfer::ActionText::RichTextRecordSetTest < ActiveSupport::
 
     assert_equal html, result
   end
+
+  test "relativize_urls strips instance host from absolute URLs" do
+    with_default_url_host("fizzy.example.com") do
+      record_set = Account::DataTransfer::ActionText::RichTextRecordSet.new(accounts(:"37s"))
+
+      html = %(<p>See <a href="https://fizzy.example.com/123/cards/42">card</a></p>)
+      result = record_set.send(:relativize_urls, html)
+
+      assert_includes result, %(/123/cards/42)
+      assert_not_includes result, "fizzy.example.com"
+    end
+  end
+
+  test "relativize_urls preserves query and fragment" do
+    with_default_url_host("fizzy.example.com") do
+      record_set = Account::DataTransfer::ActionText::RichTextRecordSet.new(accounts(:"37s"))
+
+      html = %(<p><a href="https://fizzy.example.com/123/cards/42?tab=comments#comment_1">link</a></p>)
+      result = record_set.send(:relativize_urls, html)
+
+      assert_includes result, "/123/cards/42?tab=comments#comment_1"
+      assert_not_includes result, "fizzy.example.com"
+    end
+  end
+
+  test "relativize_urls leaves external URLs alone" do
+    with_default_url_host("fizzy.example.com") do
+      record_set = Account::DataTransfer::ActionText::RichTextRecordSet.new(accounts(:"37s"))
+
+      html = %(<p><a href="https://github.com/some/repo">link</a></p>)
+      result = record_set.send(:relativize_urls, html)
+
+      assert_includes result, "https://github.com/some/repo"
+    end
+  end
+
+  test "relativize_urls is a no-op when host is not configured" do
+    record_set = Account::DataTransfer::ActionText::RichTextRecordSet.new(accounts(:"37s"))
+
+    html = %(<p><a href="https://fizzy.example.com/123/cards/42">link</a></p>)
+    result = record_set.send(:relativize_urls, html)
+
+    assert_includes result, "https://fizzy.example.com/123/cards/42"
+  end
+
+  private
+    def with_default_url_host(host)
+      original = Rails.application.routes.default_url_options[:host]
+      Rails.application.routes.default_url_options[:host] = host
+      yield
+    ensure
+      Rails.application.routes.default_url_options[:host] = original
+    end
 end