Added a getter method for the destination IP address.

[dIoTte]

This is useful when the beginPacket method is called with the hostname parameter.

The method should also be added to Arduino/hardware/arduino/avr/cores/arduino/Udp.h and to Arduino/libraries/WiFi/src/WiFiUdp.h.

[sandeepmistry]

Hey @dIoTte,

Thanks for submitting this PR!

Would you mind sharing an example sketch of how you are using this new capability?

Since the UDP base class of WiFiUDP already has a remoteIP() method, I'm wondering if it's better to make that smarter and return the _sndIP after beginPacket is called. What do you think?

[dIoTte]

Hello @sandeepmistry , I've created https://github.com/dIoTte/ArduinoNTPClient containing an example. Please have a look at the methods NetworkTimeProtocolClient::getCurrentNTPTime() and NetworkTimeProtocolClient::readResponseNTPPacket(IPAddress& destinationIP) that illustrate what I'm explaining below.

The new destinationIP() method would allow to check if a UDP request and response match in the case that several UDP requests are made to different servers in a short period of time. Currently, the only way to achieve this verification is to call the method WiFi.hostByName(const char* aHostname, IPAddress& aResult) to obtain the Destination IP before calling the method beginPacket(IPAddress ip, uint16_t port). The problem is that WiFi101.h and WiFi.h don't have a common class hierarchy and makes it impossible to have polymorphic code. However, Udp.h in the Arduino core is virtual and makes it the perfect place to implement the new capability. Regardless of which Udp.h implementation that would be used, it would work.

To answer your question, could solely relaying on _sndIP would introduce a race condition in certain cases?

Thanks for taking the time to look at this. It is very appreciated.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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