No content check (#823)

* No content check

* unit test for no content

* fixing merge conflict break

* oops during manual merge conflict

httplib.h

@@ -5544,7 +5544,7 @@ inline bool ClientImpl::process_request(Stream &strm, const Request &req,
   }
 
   // Body
-  if (req.method != "HEAD" && req.method != "CONNECT") {
+  if ((res.status != 204) && req.method != "HEAD" && req.method != "CONNECT") {
     auto out =
         req.content_receiver_
             ? static_cast<ContentReceiverWithProgress>(

test/test.cc

@@ -953,6 +953,31 @@ TEST(ErrorHandlerTest, ContentLength) {
   ASSERT_FALSE(svr.is_running());
 }
 
+TEST(NoContentTest, ContentLength) {
+  Server svr;
+
+  svr.Get("/hi", [](const Request & /*req*/, Response &res) {
+    res.status = 204;
+  });
+  auto thread = std::thread([&]() { svr.listen(HOST, PORT); });
+
+  // Give GET time to get a few messages.
+  std::this_thread::sleep_for(std::chrono::seconds(1));
+
+  {
+    Client cli(HOST, PORT);
+
+    auto res = cli.Get("/hi");
+    ASSERT_TRUE(res);
+    EXPECT_EQ(204, res->status);
+    EXPECT_EQ("0", res->get_header_value("Content-Length"));
+  }
+
+  svr.stop();
+  thread.join();
+  ASSERT_FALSE(svr.is_running());
+}
+
 TEST(RoutingHandlerTest, PreRoutingHandler) {
   Server svr;