module xml

import io

fn next_char(mut reader io.Reader, mut buf []u8) !u8 {
    if reader.read(mut buf)! == 0 {
        return error('Unexpected End Of File.')
    }
    return buf[0]
}

struct FullBufferReader {
    contents []u8
mut:
    position int
}

@[direct_array_access]
fn (mut fbr FullBufferReader) read(mut buf []u8) !int {
    if fbr.position >= fbr.contents.len {
        return io.Eof{}
    }
    remaining := fbr.contents.len - fbr.position
    n := if buf.len < remaining { buf.len } else { remaining }
    unsafe {
        vmemcpy(&u8(buf.data), &u8(fbr.contents.data) + fbr.position, n)
    }
    fbr.position += n
    return n
}