[CLIENT] Meta header: support unknown faraday adapters

Author: derSascha

elasticsearch-transport/lib/elasticsearch/transport/client.rb

@@ -267,6 +267,8 @@ def meta_header_adapter
               {hc: HTTPClient::VERSION}
             when :net_http_persistent
               {np: Net::HTTP::Persistent::VERSION}
+            else
+              {}
             end
           )
         elsif defined?(Transport::HTTP::Curb) && @transport_class == Transport::HTTP::Curb

elasticsearch-transport/spec/elasticsearch/transport/meta_header_spec.rb

@@ -150,6 +150,17 @@ def meta_version
           end
         end
       end
+
+      context 'using other' do
+        let(:adapter) { :some_other_adapter }
+
+        it 'sets adapter in the meta header' do
+          require 'net/http/persistent'
+          Faraday::Adapter.register_middleware some_other_adapter: Faraday::Adapter::NetHttpPersistent
+          expect(headers['x-elastic-client-meta']).to match(regexp)
+          expect(headers).to include('x-elastic-client-meta' => meta_header)
+        end
+      end
     end
 
     if defined?(JRUBY_VERSION)