Add header to extend server for arduinojson

src/ESPasyncJson.h

@@ -0,0 +1,76 @@
+// ESPasyncJson.h
+/*
+  Async Response to use with arduinoJson and asyncwebserver
+  Written by Andrew Melvin (SticilFace) with help from me-no-dev and BBlanchon.
+
+  example of callback in use
+
+   server.on("/json", HTTP_ANY, [](AsyncWebServerRequest * request) {
+
+    AsyncJsonResponse * response = new AsyncJsonResponse();
+    JsonObject& root = response->getRoot(); 
+    root["key1"] = "key number one";
+    JsonObject& nested = root.createNestedObject("nested"); 
+    nested["key1"] = "key number one";
+
+    response->setLength();
+    request->send(response); 
+  });
+
+*/
+
+#pragma once
+#include <ArduinoJson.h> 
+
+/*
+ * Json Response
+ * */
+
+class ChunkPrint : public Print{
+  private:
+    uint8_t* _destination;
+    size_t _to_skip;
+    size_t _to_write;
+    size_t _pos;
+  public:
+    ChunkPrint(uint8_t* destination, size_t from, size_t len)
+      : _destination(destination), _to_skip(from), _to_write(len), _pos{0} {}
+    size_t write(uint8_t c){
+      if (_to_skip > 0) {
+        _to_skip--;
+        return 0; 
+      } else if (_to_write > 0) {
+        _to_write--;
+        _destination[_pos++] = c;
+        return 1; 
+      }
+      return 0;
+    }
+};
+    
+class AsyncJsonResponse: public AsyncAbstractResponse {
+  private:
+    DynamicJsonBuffer _jsonBuffer;
+    JsonVariant _root;
+    bool _isValid; 
+  public:
+    AsyncJsonResponse(): _isValid{false} {
+      _code = 200;
+      _contentType = "text/json";
+      _root = _jsonBuffer.createObject();
+    }
+    ~AsyncJsonResponse() {}
+    JsonVariant & getRoot() { return _root; }
+    bool _sourceValid() { return _isValid; }
+    bool setLength() { 
+
+      _contentLength = _root.measureLength();
+      if (_contentLength) { _isValid = true; }
+    }
+        
+    size_t _fillBuffer(uint8_t *data, size_t len){
+      ChunkPrint dest(data, _sentLength, len); 
+      _root.printTo( dest ) ;
+      return len; 
+    }
+};