Feature: Customization to define custom allocators

[sigvartmh]

Some constrained systems may require the use of custom allocator like some ports using freeRTOS. So a way of redefining the allocators for _cbor_value_dup_string could be useful.

[sigvartmh]

I'll try to do a proposal and submit a pull request.

[thiagomacieira]

There's no need for new API. If you need a custom allocator, do:

    size_t n;
    err = cbor_value_calculate_string_length(value, &n);
    if (!err) {
        buffer = allocate_somehow(n);
        err = cbor_value_copy_text_string(value, buffer, &n, &value);
    }
    return err;

[sigvartmh]

https://github.com/01org/tinycbor/blob/70f58e8b8adaed0cc7828c2d75f147a63af50eba/src/cborparser_dup_string.c#L102

Since malloc/free already exists in a function of the parser wouldn't it be better just to allow the user to set custom allocators instead of reimplementing the function?

I know it's in the documentation, but I don't think it would increase the code size or complexity that much.

[thiagomacieira]

I will accept a patch that allows you to choose your allocator at compile time. I will not accept a patch that stores anything.