Fix FetchAtomService content type handling (mastodon#9132)

* Add profile to json+ld in Accept

It's required by the ActivityPub spec

* Use headers['Content-type'] instead of mime_type

mime_type strips the profile from the content type, but it's still available raw in the headers hash

* Add test for ld+json with profile

app/services/fetch_atom_service.rb

@@ -29,17 +29,19 @@ def process(url, terminal = false)
 
   def perform_request(&block)
     accept = 'text/html'
-    accept = 'application/activity+json, application/ld+json, application/atom+xml, ' + accept unless @unsupported_activity
+    accept = 'application/activity+json, application/ld+json; profile="https://www.w3.org/ns/activitystreams", application/atom+xml, ' + accept unless @unsupported_activity
 
     Request.new(:get, @url).add_headers('Accept' => accept).perform(&block)
   end
 
   def process_response(response, terminal = false)
     return nil if response.code != 200
 
-    if response.mime_type == 'application/atom+xml'
+    response_type = response.headers['Content-type']
+
+    if response_type == 'application/atom+xml'
       [@url, { prefetched_body: response.body_with_limit }, :ostatus]
-    elsif ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(response.mime_type)
+    elsif ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(response_type)
       body = response.body_with_limit
       json = body_to_json(body)
       if supported_context?(json) && equals_or_includes_any?(json['type'], ActivityPub::FetchRemoteAccountService::SUPPORTED_TYPES) && json['inbox'].present?
@@ -55,7 +57,7 @@ def process_response(response, terminal = false)
 
       if link_header&.find_link(%w(rel alternate))
         process_link_headers(link_header)
-      elsif response.mime_type == 'text/html'
+      elsif response_type == 'text/html'
         process_html(response)
       end
     end

spec/services/fetch_atom_service_spec.rb

@@ -60,13 +60,20 @@
         it { is_expected.to eq [url, { :prefetched_body => "" }, :ostatus] }
       end
 
-      context 'content_type is json' do
+      context 'content_type is activity+json' do
         let(:content_type) { 'application/activity+json' }
         let(:body) { json }
 
         it { is_expected.to eq [1, { prefetched_body: body, id: true }, :activitypub] }
       end
 
+      context 'content_type is ld+json with profile' do
+        let(:content_type) { 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"' }
+        let(:body) { json }
+
+        it { is_expected.to eq [1, { prefetched_body: body, id: true }, :activitypub] }
+      end
+
       before do
         WebMock.stub_request(:get, url).to_return(status: 200, body: body, headers: headers)
         WebMock.stub_request(:get, 'http://example.com/foo').to_return(status: 200, body: json, headers: { 'Content-Type' => 'application/activity+json' })