v1.6.0 to save heap when sending large data

#### Releases v1.6.0

1. Support using `CString` to save heap to send `very large data`. Check [request->send(200, textPlainStr, jsonChartDataCharStr); - Without using String Class - to save heap #8](khoih-prog/Portenta_H7_AsyncWebServer#8)
2. Add multiple examples to demo the new feature

Author: khoih-prog

changelog.md

@@ -11,6 +11,7 @@
 ## Table of contents
 
 * [Changelog](#changelog)
+  * [Releases v1.6.0](#releases-v160)
   * [Releases v1.5.0](#releases-v150)
   * [Releases v1.4.1](#releases-v141)
   * [Releases v1.4.0](#releases-v140)
@@ -25,6 +26,11 @@
 
 ## Changelog
 
+#### Releases v1.6.0
+
+1. Support using `CString` to save heap to send `very large data`. Check [request->send(200, textPlainStr, jsonChartDataCharStr); - Without using String Class - to save heap #8](https://github.com/khoih-prog/Portenta_H7_AsyncWebServer/pull/8)
+2. Add multiple examples to demo the new feature
+
 #### Releases v1.5.0
 
 1. Fix AsyncWebSocket bug

examples/Async_AdvancedWebServer_MemoryIssues_SendArduinoString/Async_AdvancedWebServer_MemoryIssues_SendArduinoString.ino

@@ -0,0 +1,273 @@
+/****************************************************************************************************************************
+  Async_AdvancedWebServer_MemoryIssues_SendArduinoString.ino -  Dead simple AsyncWebServer for WT32_ETH01
+  
+  For LAN8720 Ethernet in WT32_ETH01 (ESP32 + LAN8720)
+
+  AsyncWebServer_WT32_ETH01 is a library for the Ethernet LAN8720 in WT32_ETH01 to run AsyncWebServer
+
+  Based on and modified from ESPAsyncWebServer (https://github.com/me-no-dev/ESPAsyncWebServer)
+  Built by Khoi Hoang https://github.com/khoih-prog/AsyncWebServer_WT32_ETH01
+  Licensed under GPLv3 license 
+
+  Copyright (c) 2015, Majenko Technologies
+  All rights reserved.
+
+  Redistribution and use in source and binary forms, with or without modification,
+  are permitted provided that the following conditions are met:
+
+  Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+  Redistributions in binary form must reproduce the above copyright notice, this
+  list of conditions and the following disclaimer in the documentation and/or
+  other materials provided with the distribution.
+
+  Neither the name of Majenko Technologies nor the names of its
+  contributors may be used to endorse or promote products derived from
+  this software without specific prior written permission.
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+  ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+  (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+  LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+  ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *****************************************************************************************************************************/
+
+#if !( defined(ESP32) )
+  #error This code is designed for WT32_ETH01 to run on ESP32 platform! Please check your Tools->Board setting.
+#endif
+
+#include <Arduino.h>
+
+#define _ASYNC_WEBSERVER_LOGLEVEL_       2
+
+// Select the IP address according to your local network
+IPAddress myIP(192, 168, 2, 232);
+IPAddress myGW(192, 168, 2, 1);
+IPAddress mySN(255, 255, 255, 0);
+
+// Google DNS Server IP
+IPAddress myDNS(8, 8, 8, 8);
+
+#include <AsyncTCP.h>
+
+#include <AsyncWebServer_WT32_ETH01.h>
+
+// In bytes
+#define STRING_SIZE                    40000
+
+AsyncWebServer    server(80);
+
+int reqCount = 0;                // number of requests received
+
+#define BUFFER_SIZE         512
+char temp[BUFFER_SIZE];
+
+void handleRoot(AsyncWebServerRequest *request)
+{
+  int sec = millis() / 1000;
+  int min = sec / 60;
+  int hr = min / 60;
+  int day = hr / 24;
+
+  snprintf(temp, BUFFER_SIZE - 1,
+           "<html>\
+<head>\
+<meta http-equiv='refresh' content='60'/>\
+<title>AsyncWebServer-%s</title>\
+<style>\
+body { background-color: #cccccc; font-family: Arial, Helvetica, Sans-Serif; Color: #000088; }\
+</style>\
+</head>\
+<body>\
+<h2>AsyncWebServer_WT32_ETH01!</h2>\
+<h3>running on %s</h3>\
+<p>Uptime: %d d %02d:%02d:%02d</p>\
+<img src=\"/test.svg\" />\
+</body>\
+</html>", BOARD_NAME, BOARD_NAME, day, hr % 24, min % 60, sec % 60);
+
+  request->send(200, "text/html", temp);
+}
+
+void handleNotFound(AsyncWebServerRequest *request)
+{
+  String message = "File Not Found\n\n";
+
+  message += "URI: ";
+  message += request->url();
+  message += "\nMethod: ";
+  message += (request->method() == HTTP_GET) ? "GET" : "POST";
+  message += "\nArguments: ";
+  message += request->args();
+  message += "\n";
+
+  for (uint8_t i = 0; i < request->args(); i++)
+  {
+    message += " " + request->argName(i) + ": " + request->arg(i) + "\n";
+  }
+
+  request->send(404, "text/plain", message);
+}
+
+void PrintHeapData(String hIn)
+{
+  static uint32_t maxFreeHeap = 0xFFFFFFFF;
+  static uint32_t totalHeap = ESP.getHeapSize();
+
+  uint32_t freeHeap  = ESP.getFreeHeap();
+  
+  // Print and update only when larger heap
+  if (maxFreeHeap > freeHeap)
+  {
+    maxFreeHeap = freeHeap;
+  
+    Serial.print("\nHEAP DATA - ");
+    Serial.print(hIn);
+    
+    Serial.print("  Max heap: ");
+    Serial.print(totalHeap);
+    Serial.print("  Free heap: ");
+    Serial.print(ESP.getFreeHeap());
+    Serial.print("  Used heap: ");
+    Serial.println(totalHeap - freeHeap);
+  }
+}
+
+void PrintStringSize(String & out)
+{ 
+  static uint32_t count = 0;
+
+  // Print only when cStr length too large and corrupting memory or every (20 * 5) s
+  if ( (out.length() >= STRING_SIZE) || (++count > 20) )
+  {
+    Serial.print("\nOut String Length=");
+    Serial.println(out.length());
+
+    count = 0;
+  }
+}
+
+void drawGraph(AsyncWebServerRequest *request)
+{
+  String out;
+
+  out.reserve(STRING_SIZE);
+  char temp[70];
+
+  out += "<svg xmlns=\"http://www.w3.org/2000/svg\" version=\"1.1\" width=\"1810\" height=\"150\">\n";
+  out += "<rect width=\"1810\" height=\"150\" fill=\"rgb(250, 230, 210)\" stroke-width=\"2\" stroke=\"rgb(0, 0, 0)\" />\n";
+  out += "<g stroke=\"blue\">\n";
+  int y = rand() % 130;
+
+  for (int x = 10; x < 5000; x += 10)
+  {
+    int y2 = rand() % 130;
+    sprintf(temp, "<line x1=\"%d\" y1=\"%d\" x2=\"%d\" y2=\"%d\" stroke-width=\"2\" />\n", x, 140 - y, x + 10, 140 - y2);
+    out += temp;
+    y = y2;
+  }
+  
+  out += "</g>\n</svg>\n";
+
+  PrintHeapData("Pre Send");
+
+  PrintStringSize(out);
+
+  request->send(200, "image/svg+xml", out);
+
+  PrintHeapData("Post Send");
+}
+
+void setup()
+{
+  Serial.begin(115200);
+  while (!Serial && millis() < 5000);
+
+  delay(200);
+
+  Serial.print("\nStart Async_AdvancedWebServer_MemoryIssues_SendArduinoString on "); Serial.print(BOARD_NAME);
+  Serial.print(" with "); Serial.println(SHIELD_TYPE);
+  Serial.println(ASYNC_WEBSERVER_WT32_ETH01_VERSION);
+
+  // To be called before ETH.begin()
+  WT32_ETH01_onEvent();
+
+  //bool begin(uint8_t phy_addr=ETH_PHY_ADDR, int power=ETH_PHY_POWER, int mdc=ETH_PHY_MDC, int mdio=ETH_PHY_MDIO, 
+  //           eth_phy_type_t type=ETH_PHY_TYPE, eth_clock_mode_t clk_mode=ETH_CLK_MODE);
+  //ETH.begin(ETH_PHY_ADDR, ETH_PHY_POWER, ETH_PHY_MDC, ETH_PHY_MDIO, ETH_PHY_TYPE, ETH_CLK_MODE);
+  ETH.begin(ETH_PHY_ADDR, ETH_PHY_POWER);
+
+  // Static IP, leave without this line to get IP via DHCP
+  //bool config(IPAddress local_ip, IPAddress gateway, IPAddress subnet, IPAddress dns1 = 0, IPAddress dns2 = 0);
+  ETH.config(myIP, myGW, mySN, myDNS);
+
+  WT32_ETH01_waitForConnect();
+
+  ///////////////////////////////////
+ 
+  server.on("/", HTTP_GET, [](AsyncWebServerRequest * request)
+  {
+    handleRoot(request);
+  });
+
+  server.on("/test.svg", HTTP_GET, [](AsyncWebServerRequest * request)
+  {
+    drawGraph(request);
+  });
+
+  server.on("/inline", [](AsyncWebServerRequest * request)
+  {
+    request->send(200, "text/plain", "This works as well");
+  });
+
+  server.onNotFound(handleNotFound);
+
+  server.begin();
+
+  Serial.print(F("HTTP EthernetWebServer is @ IP : "));
+  Serial.println(ETH.localIP());
+
+  PrintHeapData("Pre Create Arduino String");
+}
+
+void heartBeatPrint()
+{
+  static int num = 1;
+
+  Serial.print(F("."));
+
+  if (num == 80)
+  {
+    Serial.println();
+    num = 1;
+  }
+  else if (num++ % 10 == 0)
+  {
+    Serial.print(F(" "));
+  }
+}
+
+void check_status()
+{
+  static unsigned long checkstatus_timeout = 0;
+
+#define STATUS_CHECK_INTERVAL     10000L
+
+  // Send status report every STATUS_REPORT_INTERVAL (60) seconds: we don't need to send updates frequently if there is no status change.
+  if ((millis() > checkstatus_timeout) || (checkstatus_timeout == 0))
+  {
+    heartBeatPrint();
+    checkstatus_timeout = millis() + STATUS_CHECK_INTERVAL;
+  }
+}
+
+void loop()
+{
+  check_status();
+}