[C] strjoin / strjoin.c / strjoin in c

Allocates (with malloc(3)) and returns a new string, 
which is the result of the concatenation of ’s1’ and ’s2’.

char	*ft_strjoin(char const *s1, char const *s2)
{
	char	*result;
	size_t	total_length;

	if (!s1 || !s2)
		return (NULL);
	total_length = (ft_strlen(s1) + ft_strlen(s2) + 1);
	result = (char *)malloc(sizeof(char) * total_length);
	if (!result)
		return (NULL);
	ft_strlcpy(result, s1, total_length);
	ft_strlcat(result, s2, total_length);
	return (result);
}