Function encoding_c::encoding_utf8_valid_up_to

#[no_mangle]
pub unsafe extern fn encoding_utf8_valid_up_to(buffer: *const u8,
                                               buffer_len: usize)
                                               -> usize

Validates UTF-8.

Returns the index of the first byte that makes the input malformed as UTF-8 or buffer_len if buffer is entirely valid.

Undefined behavior

UB ensues if buffer and buffer_len don't designate a valid memory block.