Fix some link previews being incorrectly generated from other prior links (#16885)

* Add tests

* Fix some link previews being incorrectly generated from different prior links

PR #12403 added a cache to avoid redundant queries when the OEmbed endpoint can
be guessed from the URL. This caching mechanism is not perfectly correct as
there is no guarantee that all pages from a given domain share the same
OEmbed provider endpoint.

This PR prevents the FetchOEmbedService from caching OEmbed endpoint that
cannot be generalized by replacing a fully-qualified URL from the endpoint's
parameters, greatly reducing the number of incorrect cached generalizations.

1 files changed, 41 insertions, 0 deletions

diff --git a/spec/services/fetch_oembed_service_spec.rb b/spec/services/fetch_oembed_service_spec.rb
index a4262b040..88f0113ed 100644
--- a/spec/services/fetch_oembed_service_spec.rb
+++ b/spec/services/fetch_oembed_service_spec.rb
@@ -13,6 +13,32 @@ describe FetchOEmbedService, type: :service do
 
   describe 'discover_provider' do
     context 'when status code is 200 and MIME type is text/html' do
+      context 'when OEmbed endpoint contains URL as parameter' do
+        before do
+          stub_request(:get, 'https://www.youtube.com/watch?v=IPSbNdBmWKE').to_return(
+            status: 200,
+            headers: { 'Content-Type': 'text/html' },
+            body: request_fixture('oembed_youtube.html'),
+          )
+          stub_request(:get, 'https://www.youtube.com/oembed?format=json&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DIPSbNdBmWKE').to_return(
+            status: 200,
+            headers: { 'Content-Type': 'text/html' },
+            body: request_fixture('oembed_json_empty.html')
+          )
+        end
+
+        it 'returns new OEmbed::Provider for JSON provider' do
+          subject.call('https://www.youtube.com/watch?v=IPSbNdBmWKE')
+          expect(subject.endpoint_url).to eq 'https://www.youtube.com/oembed?format=json&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DIPSbNdBmWKE'
+          expect(subject.format).to eq :json
+        end
+
+        it 'stores URL template' do
+          subject.call('https://www.youtube.com/watch?v=IPSbNdBmWKE')
+          expect(Rails.cache.read('oembed_endpoint:www.youtube.com')[:endpoint]).to eq 'https://www.youtube.com/oembed?format=json&url={url}'
+        end
+      end
+
       context 'Both of JSON and XML provider are discoverable' do
         before do
           stub_request(:get, 'https://host.test/oembed.html').to_return(
@@ -33,6 +59,11 @@ describe FetchOEmbedService, type: :service do
           expect(subject.endpoint_url).to eq 'https://host.test/provider.xml'
           expect(subject.format).to eq :xml
         end
+
+        it 'does not cache OEmbed endpoint' do
+          subject.call('https://host.test/oembed.html', format: :xml)
+          expect(Rails.cache.exist?('oembed_endpoint:host.test')).to eq false
+        end
       end
 
       context 'JSON provider is discoverable while XML provider is not' do
@@ -49,6 +80,11 @@ describe FetchOEmbedService, type: :service do
           expect(subject.endpoint_url).to eq 'https://host.test/provider.json'
           expect(subject.format).to eq :json
         end
+
+        it 'does not cache OEmbed endpoint' do
+          subject.call('https://host.test/oembed.html')
+          expect(Rails.cache.exist?('oembed_endpoint:host.test')).to eq false
+        end
       end
 
       context 'XML provider is discoverable while JSON provider is not' do
@@ -65,6 +101,11 @@ describe FetchOEmbedService, type: :service do
           expect(subject.endpoint_url).to eq 'https://host.test/provider.xml'
           expect(subject.format).to eq :xml
         end
+
+        it 'does not cache OEmbed endpoint' do
+          subject.call('https://host.test/oembed.html')
+          expect(Rails.cache.exist?('oembed_endpoint:host.test')).to eq false
+        end
       end
 
       context 'Invalid XML provider is discoverable while JSON provider is not' do