rust-dnsbox/lib/dnsbox-base/src/common_types/name/label_offsets.rs

use smallvec::SmallVec;

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub enum LabelOffset {
	LabelStart(u8),
	PacketStart(u16),
}

// the heap meta data is usually at least 2*usize big; assuming 64-bit
// platforms it should be ok to use 16 bytes in the smallvec.
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub enum LabelOffsets {
	Uncompressed(SmallVec<[u8; 16]>),
	Compressed(usize, SmallVec<[LabelOffset; 4]>),
}

impl LabelOffsets {
	pub fn len(&self) -> u8 {
		let l = match *self {
			LabelOffsets::Uncompressed(ref offs) => offs.len(),
			LabelOffsets::Compressed(_, ref offs) => offs.len(),
		};
		debug_assert!(l < 128);
		l as u8
	}

	pub fn label_pos(&self, ndx: u8) -> usize {
		debug_assert!(ndx < 127);
		match *self {
			LabelOffsets::Uncompressed(ref offs) => offs[ndx as usize] as usize,
			LabelOffsets::Compressed(start, ref offs) => match offs[ndx as usize] {
				LabelOffset::LabelStart(o) => start + (o as usize),
				LabelOffset::PacketStart(o) => o as usize,
			},
		}
	}

	pub fn is_compressed(&self) -> bool {
		match *self {
			LabelOffsets::Uncompressed(_) => false,
			LabelOffsets::Compressed(_, _) => true,
		}
	}
}