Support for replacing a response by a new one

README.md

@@ -121,3 +121,18 @@ If you have smaller messages, you can increase `WS_MAX_QUEUED_MESSAGES` to 128.
   -D CONFIG_ASYNC_TCP_STACK_SIZE=4096
   -D WS_MAX_QUEUED_MESSAGES=64
 ```
+
+## Replace response
+
+```c++
+  // It is possible to replace a response.
+  // The previous one will be deleted.
+  // Response sending happens when the handler returns.
+  server.on("/replace", HTTP_GET, [](AsyncWebServerRequest* request) {
+    request->send(200, "text/plain", "Hello, world");
+    // oups! finally we want to send a different response
+    request->send(400, "text/plain", "validation error");
+  });
+```
+
+This will send error 400 instead of 200.

docs/index.md

@@ -121,3 +121,18 @@ If you have smaller messages, you can increase `WS_MAX_QUEUED_MESSAGES` to 128.
   -D CONFIG_ASYNC_TCP_STACK_SIZE=4096
   -D WS_MAX_QUEUED_MESSAGES=64
 ```
+
+## Replace response
+
+```c++
+  // It is possible to replace a response.
+  // The previous one will be deleted.
+  // Response sending happens when the handler returns.
+  server.on("/replace", HTTP_GET, [](AsyncWebServerRequest* request) {
+    request->send(200, "text/plain", "Hello, world");
+    // oups! finally we want to send a different response
+    request->send(400, "text/plain", "validation error");
+  });
+```
+
+This will send error 400 instead of 200.

examples/SimpleServer/SimpleServer.ino

@@ -90,6 +90,19 @@ void setup() {
     // handler forgot to send a response to the client => 501 Not Implemented
   });
 
+  // This is possible to replace a response.
+  // the previous one will be deleted.
+  // response sending happens when the handler returns.
+  // curl -v -X GET http://192.168.4.1/replace
+  server.on("/replace", HTTP_GET, [](AsyncWebServerRequest* request) {
+    request->send(200, "text/plain", "Hello, world");
+    // oups! finally we want to send a different response
+    request->send(400, "text/plain", "validation error");
+#ifndef TARGET_RP2040
+    Serial.printf("Free heap: %" PRIu32 "\n", ESP.getFreeHeap());
+#endif
+  });
+
   ///////////////////////////////////////////////////////////////////////
   // Request header manipulations
   ///////////////////////////////////////////////////////////////////////

src/ESPAsyncWebServer.h

@@ -311,7 +311,7 @@ class AsyncWebServerRequest {
     void redirect(const String& url) { return redirect(url.c_str()); };
 
     void send(AsyncWebServerResponse* response);
-    const AsyncWebServerResponse* sentResponse() const { return _response; }
+    AsyncWebServerResponse* getResponse() const { return _response; }
 
     void send(int code, const char* contentType = asyncsrv::empty, const char* content = asyncsrv::empty, AwsTemplateProcessor callback = nullptr) { send(beginResponse(code, contentType, content, callback)); }
     void send(int code, const String& contentType, const String& content = emptyString, AwsTemplateProcessor callback = nullptr) { send(beginResponse(code, contentType, content, callback)); }

src/WebRequest.cpp

@@ -140,8 +140,13 @@ void AsyncWebServerRequest::_onData(void* buf, size_t len) {
         _parseState = PARSE_REQ_END;
         if (_handler)
           _handler->handleRequest(this);
-        if (!_sent)
+        if (!_sent) {
+          if (!_response)
             send(501, T_text_plain, "Handler did not handle the request");
+          _client->setRxTimeout(0);
+          _response->_respond(this);
+          _sent = true;
+        }
       }
     }
     break;
@@ -574,8 +579,13 @@ void AsyncWebServerRequest::_parseLine() {
         _parseState = PARSE_REQ_END;
         if (_handler)
           _handler->handleRequest(this);
-        if (!_sent)
+        if (!_sent) {
+          if (!_response)
             send(501, T_text_plain, "Handler did not handle the request");
+          _client->setRxTimeout(0);
+          _response->_respond(this);
+          _sent = true;
+        }
       }
     } else
       _parseReqHeader();
@@ -709,6 +719,10 @@ AsyncWebServerResponse* AsyncWebServerRequest::beginResponse(int code, const Str
 #endif
 
 void AsyncWebServerRequest::send(AsyncWebServerResponse* response) {
+  if (_sent)
+    return;
+  if (_response)
+    delete _response;
   _response = response;
   if (_response == NULL) {
     _client->close(true);
@@ -716,15 +730,8 @@ void AsyncWebServerRequest::send(AsyncWebServerResponse* response) {
     _sent = true;
     return;
   }
-  if (!_response->_sourceValid()) {
-    delete response;
-    _response = NULL;
+  if (!_response->_sourceValid())
     send(500);
-  } else {
-    _client->setRxTimeout(0);
-    _response->_respond(this);
-    _sent = true;
-  }
 }
 
 void AsyncWebServerRequest::redirect(const char* url) {