Core / ZeroCopy: Added Doxygen API documentation and 2 new c++ samples demonstrating usage of low level zero copy API

[rex-schilasky]

Pull request type

Please check the type of change your PR introduces:

• Feature
• Documentation content changes

What is the current behavior?
We missed samples to demonstrate low level zero copy API and the CPayloadWriter class was not documented (Doxygen).

Issue Number: #1145

What is the new behavior?
Two new binary send / rec zero copy samples added, CPayloadWriter class documented.

Does this introduce a breaking change?

• Yes
• No

Cherry-Pick to

• 5.12

[FlorianReimold]

If I see correctly, this PR basically contains 2 changes:

1. It adds the samples
2. More importantly: It adds doxygen documentation to the payload writer (public API)

The latter change requires this commit to be cherry-picked to 5.12.

@rex-schilasky can you confirm this?

[rex-schilasky]

If I see correctly, this PR basically contains 2 changes:

1. It adds the samples
2. More importantly: It adds doxygen documentation to the payload writer (public API)

The latter change requires this commit to be cherry-picked to 5.12.

@rex-schilasky can you confirm this?

This is all correct. The doxygen documented CPayloadWriter class and both samples demonstrating the usage of this class should go to 5.12.

[FlorianReimold]

After reviewing the Doxygen I don't really get what "data to be written" means here. I assume that this term refers to the size of the underlying memory file?

[FlorianReimold]

Is this really the "data to be written"? If so, why isn't this just a temporary locally scoped variable? Or is this capacity of the memory file, as the GetSize() function says?

Either way, I guess either the documentation of the variable or the GetSize() function is wrong

[rex-schilasky]

The CBufferPayloadWriter is a kind of primitive wrapper of the classic CBufferPayloadWriter(const void* const buffer_, size_t size_) Send API. Basically it stores the arguments buffer_ and size_ into the internals of CBufferPayloadWriter and does the memcpy action in the Write call.
GetSize reports the needed size correctly, Write is just doing the copy.