fix: headers before flushing (#1622)

* add tests

* fix test

* attempt to send headers when flushing

* Update testdata/only-headers.php

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

---------

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

frankenphp.c

@@ -588,6 +588,7 @@ static int frankenphp_send_headers(sapi_headers_struct *sapi_headers) {
 }
 
 static void frankenphp_sapi_flush(void *server_context) {
+  sapi_send_headers();
   if (go_sapi_flush(thread_index)) {
     php_handle_aborted_connection();
   }

frankenphp.go

@@ -492,6 +492,10 @@ func addHeader(fc *frankenPHPContext, cString *C.char, length C.int) {
 func go_write_headers(threadIndex C.uintptr_t, status C.int, headers *C.zend_llist) C.bool {
 	fc := phpThreads[threadIndex].getRequestContext()
 
+	if fc == nil {
+		return C.bool(false)
+	}
+
 	if fc.isDone {
 		return C.bool(false)
 	}

frankenphp_test.go

@@ -1023,6 +1023,22 @@ func testRejectInvalidHeaders(t *testing.T, opts *testOptions) {
 	}
 }
 
+func TestFlushEmptyResponse_module(t *testing.T) { testFlushEmptyResponse(t, &testOptions{}) }
+func TestFlushEmptyRespnse_worker(t *testing.T) {
+	testFlushEmptyResponse(t, &testOptions{workerScript: "only-headers.php"})
+}
+
+func testFlushEmptyResponse(t *testing.T, opts *testOptions) {
+	runTest(t, func(handler func(http.ResponseWriter, *http.Request), _ *httptest.Server, _ int) {
+		req := httptest.NewRequest("GET", "http://example.com/only-headers.php", nil)
+		w := httptest.NewRecorder()
+		handler(w, req)
+
+		resp := w.Result()
+		assert.Equal(t, 204, resp.StatusCode)
+	}, opts)
+}
+
 // Worker mode will clean up unreferenced streams between requests
 // Make sure referenced streams are not cleaned up
 func TestFileStreamInWorkerMode(t *testing.T) {

testdata/only-headers.php

@@ -0,0 +1,11 @@
+<?php
+
+require_once __DIR__.'/_executor.php';
+
+return function () {
+    header('Content-Type: application/json');
+    header('HTTP/1.1 204 No Content', true, 204);
+
+    echo '{"status": "test"}';
+    flush();
+};