bitsandbytes 0.1.0

An owned, bit-aware binary codec: fast bit/byte field types and the unified #[bin] macro.
Documentation 
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//! `#[bitflags]` behavior: flag consts, set algebra, per-flag accessors,
//! iteration, dual-use retain, and composition (nesting in a `#[bitfield]`).
//! Codec-only, so it runs with and without the binrw feature.

use bnb::{bitfield, bitflags, u4};

#[bitflags(u8)]
#[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
struct TcpFlags {
    fin: bool,
    syn: bool,
    rst: bool,
    psh: bool,
    ack: bool,
    urg: bool,
    ece: bool,
    cwr: bool,
}

impl TcpFlags {
    // A combination const, built with the generated const helpers.
    const HANDSHAKE: Self = Self::SYN.union(Self::ACK);
}

#[test]
fn flag_consts_and_all_empty() {
    assert_eq!(TcpFlags::FIN.bits(), 0b0000_0001);
    assert_eq!(TcpFlags::SYN.bits(), 0b0000_0010);
    assert_eq!(TcpFlags::ACK.bits(), 0b0001_0000);
    assert_eq!(TcpFlags::CWR.bits(), 0b1000_0000);
    assert_eq!(TcpFlags::all().bits(), 0xFF);
    assert_eq!(TcpFlags::empty().bits(), 0);
    assert!(TcpFlags::empty().is_empty());
}

#[test]
fn set_algebra_via_operators() {
    let f = TcpFlags::SYN | TcpFlags::ACK;
    assert_eq!(f.bits(), 0b0001_0010);
    assert!(f.contains(TcpFlags::SYN));
    assert!(f.contains(TcpFlags::HANDSHAKE));
    assert!(!f.contains(TcpFlags::FIN));
    assert!(f.intersects(TcpFlags::ACK));
    assert_eq!((f & TcpFlags::SYN), TcpFlags::SYN);
    assert_eq!((f - TcpFlags::SYN), TcpFlags::ACK);
    assert_eq!((f ^ TcpFlags::SYN), TcpFlags::ACK);
    assert_eq!(!TcpFlags::empty(), TcpFlags::all());
}

#[test]
fn assign_operators_and_mutators() {
    let mut f = TcpFlags::empty();
    f |= TcpFlags::SYN;
    f.insert(TcpFlags::ACK);
    assert!(f.contains(TcpFlags::HANDSHAKE));
    f -= TcpFlags::SYN;
    assert!(!f.syn() && f.ack());
    f.toggle(TcpFlags::FIN);
    assert!(f.fin());
}

#[test]
fn per_flag_accessors() {
    let mut f = TcpFlags::empty();
    assert!(!f.syn());
    f.set_syn(true);
    assert!(f.syn());
    let g = f.with_ack(true);
    assert!(g.ack() && g.syn());
    f.set_syn(false);
    assert!(!f.syn());
}

#[test]
fn iter_yields_set_single_bit_flags_in_order() {
    let f = TcpFlags::SYN | TcpFlags::ACK | TcpFlags::FIN;
    let set: Vec<_> = f.iter().collect();
    // declaration order: fin (0), syn (1), ack (4).
    assert_eq!(set, vec![TcpFlags::FIN, TcpFlags::SYN, TcpFlags::ACK]);
    assert_eq!(TcpFlags::empty().iter().count(), 0);
}

// A small flag set with undefined high bits, to prove dual-use retain.
#[bitflags(u8)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
struct Few {
    a: bool,
    b: bool,
    #[flag(3)]
    c: bool, // pinned to bit 3, leaving bits 2/4..7 undefined
}

#[test]
fn from_bits_retains_unknown_but_truncate_drops_them() {
    assert_eq!(Few::all().bits(), 0b0000_1011); // a|b|c
    // 0xFF has undefined bits set: retain keeps them, truncate drops them.
    assert_eq!(Few::from_bits(0xFF).bits(), 0xFF);
    assert_eq!(Few::from_bits_truncate(0xFF).bits(), 0b0000_1011);
    assert_eq!(Few::C.bits(), 0b0000_1000);
}

// Flags compose as a field inside a #[bitfield] (they implement Bits).
#[bitfield(u16, bits = msb)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
struct Frame {
    kind: u4,
    flags: TcpFlags, // an 8-bit flag set
    rsvd: u4,
}

#[test]
fn flags_nest_in_a_bitfield() {
    let frame = Frame::new()
        .with_kind(u4::new(0xA))
        .with_flags(TcpFlags::SYN | TcpFlags::ACK);
    // kind in bits 12..=15, flags in 4..=11, rsvd in 0..=3.
    assert_eq!(frame.flags(), TcpFlags::SYN | TcpFlags::ACK);
    assert_eq!(
        frame.raw(),
        (0xA << 12) | ((TcpFlags::SYN | TcpFlags::ACK).bits() as u16) << 4
    );
    assert!(frame.flags().ack());
}