pub fn main(world: World) -> Void raises {
    let path: String = "conformance/fixtures/std-fs-read.txt"
    var out_buf: [16]u8 = [0_u8; 16]
    var chunk: [4]u8 = [0_u8; 4]
    var offset: usize = 0
    var total: usize = 0
    var saw_truncation: Bool = true
    var ok: Bool = true
    var done: Bool = false
    while ok && !done {
        let read: Maybe<usize> = std.fs.readBytesAt(path, offset, chunk)
        if !read.has {
            ok = false
        } else {
            total = read.value
            if total <= 4 {
                saw_truncation = false
            }
            var valid: usize = 0
            if offset < total {
                valid = total - offset
                if valid > 4 {
                    valid = 4
                }
            }
            let copied: usize = std.mem.copy(out_buf[offset..], chunk[..valid])
            if copied != valid {
                ok = false
            }
            offset = offset + valid
            if offset >= total {
                done = true
            }
        }
    }
    let whole: Maybe<usize> = std.fs.readBytes(path, out_buf)
    if ok && saw_truncation && total == 10 && whole.has && whole.value == 10 && std.mem.eqlBytes(out_buf[..total], std.mem.span("zero file\n")) {
        check world.out.write("fs read chunks ok\n")
    } else {
        check world.out.write("fs read chunks failed\n")
    }
}