WiFiUDP:parsePacket() Crashfix

[mrengineer7777]

---

Description of Change

Resolves crash in WiFiUDP:parsePacket() where allocation of new char[1460]; throws an exception under low memory conditions.

Tests scenarios

Tested on FeatherESP32 using UDP socket listener. Using arduino-esp32 core v2.0.5.
Additional testing welcome!

Related links

Closes#4104 (stale/closed), #7558, #7845

[mrengineer7777]

Notes: I'm not sure how to use nothrow with new keyword. malloc does not throw an exception.

Might need nothrow on new cbuf(len);, as well as checking that the allocation succeeded. Feedback welcome.

[mrengineer7777]

Note to maintainers: Not sure that we need to run checks on draft PRs.

[mrengineer7777]

new cbuf(len); calls constructor for cbuf class. The constructor contains a new char[] call. Can this throw an exception?

cbuf::cbuf(size_t size) : next(NULL), _size(size+1), _buf(new char[size+1]), _bufend(_buf + size + 1), _begin(_buf), _end(_begin){} 

[mrengineer7777]

Found the solution for nothrow in esp8266/Arduino@6925982

[me-no-dev]

Hi @mrengineer7777 :) In reality we should transition from using cbuf to something more FreeRTOS related, like Queue (for single bytes) and Ringbuf (for multiple bytes). cbuf should really get phased out and removed in Arduino 3.0.0

[mrengineer7777]

@me-no-dev That is a fantastic idea. For now let's fix the current bug. I will create a new issue (feature request) to remind us to refactor WiFiUDP().

[VojtechBartoska]

@mrengineer7777 Thanks for the fix and also follow-up with the issue.

[me-no-dev]

@mrengineer7777 instead of removing cbuf altogether, I decided to rework it to use FreeRTOS Ringbuffer and Semaphore. You can see the progress here. That should improve it for anything that uses cbuf. Your fixes still apply :)

[me-no-dev]

BTW, what is the status? Does this fix your issue? Can we merge it and have it as part of 2.0.7?

[mrengineer7777]

@me-no-dev I'm excited about the change on cbuf. Looks promising. Will review later.

@me-no-dev This PR fixes the UDP issue for me.