Get the total number of bytes in a buffer sequence.

template<
    typename BufferSequence>
std::size_t buffer_size(
    const BufferSequence & b,
    typename enable_if< is_const_buffer_sequence< BufferSequence >::value >::type *  = 0);

The BufferSequence template parameter may meet either of the ConstBufferSequence or MutableBufferSequence type requirements.