bitsandbytes 0.3.2

An owned, bit-aware binary codec: fast bit/byte field types and the unified #[bin] macro.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

//! `restore_position` + `SeekSource` (ROADMAP Phase 3): `#[br(restore_position)]`
//! reads a field (a peek), then rewinds so a later field re-reads the same bytes.
//! It needs a seekable source (the slice `BitReader`); on a forward stream it errors
//! (`ErrorKind::NotSeekable`), and `#[bin(forward_only)]` makes it a compile error.

mod macro_ {

    use bnb::{bin, u4};

    #[bin]
    #[derive(Debug, PartialEq, Eq, Clone)]
    struct Frame {
        flags: u4,
        #[br(restore_position)]
        peek: u8, // peek the byte at the value's offset...
        value: u16, // ...then read the full value from the same offset
    }

    #[test]
    fn restore_position_peeks_then_rereads() {
        let f = Frame {
            flags: u4::new(0x5),
            peek: 0xAB, // the high byte of `value`
            value: 0xABCD,
        };
        let bytes = f.to_bytes().unwrap();
        // flags(0101) | value(0xABCD, 16 bits) — `peek` overlaps `value`, not written.
        assert_eq!(bytes, [0x5A, 0xBC, 0xD0]);

        let decoded = Frame::decode_exact(&bytes).unwrap();
        assert_eq!(decoded.value, 0xABCD);
        assert_eq!(decoded.peek, 0xAB, "peeked the high byte at value's offset");
        assert_eq!(decoded, f);
    }
}