Fix serialization of ServerName extension for empty server_name

unasuke · unasuke · commit cbe054e9c03f · 2025-08-31T23:34:23.000+09:00
diff --git a/lib/raiha/tls/handshake/extension/server_name.rb b/lib/raiha/tls/handshake/extension/server_name.rb
@@ -33,10 +33,15 @@ def extension_data=(data)
           end
 
           def serialize
-            server_name = [0].pack("C") + # host_name(0)
-              [@server_name.bytesize].pack("n") + @server_name # HostName
-            server_name_list = [server_name.bytesize].pack("n") + server_name
-            [EXTENSION_TYPE_NUMBER].pack("n") + [server_name_list.bytesize].pack("n") + server_name_list
+            if @server_name.nil? || @server_name.empty?
+              # On EncryptedExtensions, the server_name is empty
+              [EXTENSION_TYPE_NUMBER].pack("n") + [0].pack("n")
+            else
+              server_name = [0].pack("C") + # host_name(0)
+                [@server_name.bytesize].pack("n") + @server_name # HostName
+              server_name_list = [server_name.bytesize].pack("n") + server_name
+              [EXTENSION_TYPE_NUMBER].pack("n") + [server_name_list.bytesize].pack("n") + server_name_list
+            end
           end
         end
       end
diff --git a/test/raiha/tls/handshake/extension/server_name_test.rb b/test/raiha/tls/handshake/extension/server_name_test.rb
@@ -11,6 +11,10 @@ class RaihaTLSHandshakeExtensionServerNameTest < Minitest::Test
     00 00 00 0f 00 0d 00 00 0a 67 6f 6f 67 6c 65 2e
     63 6f 6d
   DATA
+
+  TLS13_SERVER_NAME_EXTENSION_DATA_EMPTY = [<<~DATA.gsub(/[[:space:]]/, '')].pack("H*")
+    00 00 00 00
+  DATA
   def test_serialize
     www_example_com = Raiha::TLS::Handshake::Extension::ServerName.new(on: :client_hello)
     www_example_com.server_name = "www.example.com"
@@ -19,5 +23,8 @@ def test_serialize
     google_com = Raiha::TLS::Handshake::Extension::ServerName.new(on: :client_hello)
     google_com.server_name = "google.com"
     assert_equal TLS13_SERVER_NAME_EXTENSION_DATA_GOOGLE_COM, google_com.serialize
+
+    empty = Raiha::TLS::Handshake::Extension::ServerName.new(on: :encrypted_extensions)
+    assert_equal TLS13_SERVER_NAME_EXTENSION_DATA_EMPTY, empty.serialize
   end
 end
