Don't send 103 early hints response when only invalid headers are used (

#3163)

lib/puma/request.rb

@@ -77,7 +77,9 @@ def handle_request(client, requests)
       if @early_hints
         env[EARLY_HINTS] = lambda { |headers|
           begin
-            fast_write_str socket, str_early_hints(headers)
+            unless (str = str_early_hints headers).empty?
+              fast_write_str socket, "HTTP/1.1 103 Early Hints\r\n#{str}\r\n"
+            end
           rescue ConnectionError => e
             @log_writer.debug_error e
             # noop, if we lost the socket we just won't send the early hints
@@ -529,7 +531,7 @@ def req_env_post_parse(env)
     # @version 5.0.3
     #
     def str_early_hints(headers)
-      eh_str = +"HTTP/1.1 103 Early Hints\r\n"
+      eh_str = +""
       headers.each_pair do |k, vs|
         next if illegal_header_key?(k)
 
@@ -538,11 +540,11 @@ def str_early_hints(headers)
             next if illegal_header_value?(v)
             eh_str << "#{k}: #{v}\r\n"
           end
-        else
+        elsif !(vs.to_s.empty? || !illegal_header_value?(vs))
           eh_str << "#{k}: #{vs}\r\n"
         end
       end
-      "#{eh_str}\r\n".freeze
+      eh_str.freeze
     end
     private :str_early_hints
 

test/test_response_header.rb

@@ -83,7 +83,11 @@ def assert_ignore_header(name, value, opts={})
     server_run(app: app, early_hints: opts[:early_hints])
     data = send_http_and_read "GET / HTTP/1.0\r\n\r\n"
 
-    refute_match("#{name}: #{value}", data)
+    if opts[:early_hints]
+      refute_includes data, "HTTP/1.1 103 Early Hints"
+    end
+
+    refute_includes data, "#{name}: #{value}"
   end
 
   # The header must not contain a Status key.