asio: Don't send response body if it is not expected by status code or method

src/asio_server_response_impl.cc

@@ -25,6 +25,7 @@
 #include "asio_server_response_impl.h"
 
 #include "asio_server_stream.h"
+#include "asio_server_request_impl.h"
 #include "asio_server_http2_handler.h"
 #include "asio_common.h"
 
@@ -78,9 +79,25 @@ void response_impl::end(generator_cb cb) {
   state_ = response_state::BODY_STARTED;
 }
 
+namespace {
+bool expect_response_body(const std::string &method, int status_code) {
+  return method != "HEAD" && status_code / 100 != 1 && status_code != 304 &&
+         status_code != 204;
+}
+} // namespace
+
 void response_impl::start_response() {
   auto handler = strm_->handler();
 
+  auto &req = strm_->request().impl();
+
+  // if response body is not expected, nullify it so that HEADERS has
+  // END_STREAM flag set.
+  if (!expect_response_body(req.method(), status_code_)) {
+    state_ = response_state::BODY_STARTED;
+    generator_cb_ = generator_cb();
+  }
+
   if (handler->start_response(*strm_) != 0) {
     handler->stream_error(strm_->get_stream_id(), NGHTTP2_INTERNAL_ERROR);
     return;