Replace use of strcpy by memcpy on String::concat(const char*,uint32_t) ?

[bilaliscarioth]

Hello Arduino Core Teams,

Can we replace the use of strcpy(2) from String::concat(const char*, uint32_t) by strlcpy(2) or even memcpy ?

Without referencing strcpy(2) on your documentation, if we cast a struct into char*, we could had
a null terminator between the start and the end, and strcpy(2) will never copy at the last char.

unsigned char String::concat(const char *cstr, unsigned int length)
{
	unsigned int newlen = len + length;
	if (!cstr) return 0;
	if (length == 0) return 1;
	if (!reserve(newlen)) return 0;
	strcpy(buffer + len, cstr);
	len = newlen;
	return 1;
}

Is it by choice, by using strcpy ?

Edit: The length is not taked care by strcpy, many edge case could resolve into BO

[bilaliscarioth]

Duplicated of #530