nghttpx: Add mruby env.server_port to return frontend server side port

doc/nghttpx.h2r

@@ -267,6 +267,11 @@ respectively.
 
         Return IP address of a remote client.
 
+    .. rb:attr_reader:: server_port
+
+        Return port number of the server frontend which accepted the
+        connection from client.
+
 .. rb:class:: Request
 
     Object to represent request from client.  The modification to

src/shrpx_client_handler.cc

@@ -1281,4 +1281,6 @@ StringRef ClientHandler::get_forwarded_for() const {
   return StringRef{forwarded_for_};
 }
 
+const UpstreamAddr *ClientHandler::get_upstream_addr() const { return faddr_; }
+
 } // namespace shrpx

src/shrpx_client_handler.h

@@ -144,6 +144,8 @@ public:
 
   Http2Session *select_http2_session(DownstreamAddrGroup &group);
 
+  const UpstreamAddr *get_upstream_addr() const;
+
 private:
   Connection conn_;
   ev_timer reneg_shutdown_timer_;

src/shrpx_mruby_module_env.cc

@@ -92,6 +92,18 @@ mrb_value env_get_remote_addr(mrb_state *mrb, mrb_value self) {
 }
 } // namespace
 
+namespace {
+mrb_value env_get_server_port(mrb_state *mrb, mrb_value self) {
+  auto data = static_cast<MRubyAssocData *>(mrb->ud);
+  auto downstream = data->downstream;
+  auto upstream = downstream->get_upstream();
+  auto handler = upstream->get_client_handler();
+  auto faddr = handler->get_upstream_addr();
+
+  return mrb_fixnum_value(faddr->port);
+}
+} // namespace
+
 void init_env_class(mrb_state *mrb, RClass *module) {
   auto env_class =
       mrb_define_class_under(mrb, module, "Env", mrb->object_class);
@@ -103,6 +115,8 @@ void init_env_class(mrb_state *mrb, RClass *module) {
   mrb_define_method(mrb, env_class, "phase", env_get_phase, MRB_ARGS_NONE());
   mrb_define_method(mrb, env_class, "remote_addr", env_get_remote_addr,
                     MRB_ARGS_NONE());
+  mrb_define_method(mrb, env_class, "server_port", env_get_server_port,
+                    MRB_ARGS_NONE());
 }
 
 } // namespace mruby