lwip lib bundled with esp32 Arduino supports only one ntp server. Any additional servers set are just silently ignored.
This default is different from esp8266 Arduino core and very confusing. Most of the examples provided uses 3 different ntp servers for redundancy while only the first one is used actually.
Addressing issue #4964
This enables customizing HTTP headers which adds some extra flexibility.
This does not break anything of course because this change introduces a new constructor with a new additional HTTPClient argument for HTTPUpdate class.
I spent quite a while today figuring out how to get an OTA update over HTTPS on a custom port working. A part of my problem was not putting a slash before the .bin filename, since it wasn't there in the example. This produced invalid HTTP requests. Adding the slash would make it clear that it needs to be there.
Given that the URL in line 53 contains the same words "server" and "file.bin", one might assume that in line 55, the slash after the port number would get added automatically, however I have found out that without a slash you get an invalid request. Adding the slash removes any doubt.
* Fix error in PR #2048: if ::available() is called before ::connect() _rxBuffer is not initialised
* Fixed flash size check and added SPIFFS size check
* Rewriting ESP.getFreeSketchSpace(), moving code from HTTPUpdate.cpp
* Added HTTPUpdate class for downloading sketches from a server
* Added HTTPUpdate class for downloading sketches from a server
* Added HTTPUpdate to CMakeLists.txt
* Change ESP8266 class references to ESP32 for httpUpdate.ino example
* Change ESP8266 class references to ESP32 for httpUpdate.ino example. setLedPin() commented out because not all boards support LED_BUITLIN
* Added check to handle mixup of old and present api properly
* Correct HTTPClient::setTimeout() to convert milliseconds to seconds. Correct WiFiClient::setTimeout() to call Stream::setTimeout() with seconds converted back to milliseconds. Remove inproper checks for _insecure.
* Added small comment because it looked like the Travis build did not finish
