(PUP-11900) Notify when X-Puppet-Compiler-Name header found

This change will emit a notice when http traffic from a puppetserver
sends the `X-Puppet-Compiler-Name` header; this should help for
debugging purposes when troubleshooting compilation issues and
several compilers are behind a load balancer.

lib/puppet/http/session.rb

@@ -90,6 +90,9 @@ def process_response(response)
       site = Puppet::HTTP::Site.from_uri(response.url)
       @server_versions[site] = version
     end
+    if compiler = response['X-Puppet-Compiler-Name']
+      Puppet.notice("Catalog compiled by #{compiler}")
+    end
   end
 
   # Determine if a session supports a capability. Depending on the server version

spec/integration/application/agent_spec.rb

@@ -33,6 +33,19 @@ def copy_fixtures(sources, dest)
     end
   end
 
+  context 'server identification' do
+    it 'emits a notice if the server sends the X-Puppet-Compiler-Name header' do
+      server.start_server do |port|
+        Puppet[:serverport] = port
+        expect {
+          agent.command_line.args << '--test'
+          agent.run
+        }.to exit_with(0)
+               .and output(%r{Notice: Catalog compiled by test-compiler-hostname}).to_stdout
+      end
+    end
+  end
+
   context 'server_list' do
     it "uses the first server in the list" do
       Puppet[:server_list] = '127.0.0.1'

spec/lib/puppet_spec/puppetserver.rb

@@ -19,6 +19,7 @@ def do_GET request, response
   class CatalogServlet < WEBrick::HTTPServlet::AbstractServlet
     def do_POST request, response
       response['Content-Type'] = 'application/json'
+      response['X-Puppet-Compiler-Name'] = 'test-compiler-hostname'
       catalog = Puppet::Resource::Catalog.new(Puppet[:certname], 'production')
       response.body = catalog.render(:json)
     end