domain/base/serial.rs
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//! Serial numbers.
//!
//! DNS uses 32 bit serial numbers in various places that are conceptionally
//! viewed as the 32 bit modulus of a larger number space. Because of that,
//! special rules apply when processing these values. This module provides
//! the type [`Serial`] that implements these rules.
use super::cmp::CanonicalOrd;
use super::scan::{Scan, Scanner};
use super::wire::{Compose, Composer, Parse, ParseError};
#[cfg(feature = "chrono")]
use chrono::{DateTime, TimeZone};
use core::cmp::Ordering;
use core::{cmp, fmt, str};
#[cfg(all(feature = "std", test))]
use mock_instant::thread_local::{SystemTime, UNIX_EPOCH};
use octseq::parse::Parser;
#[cfg(all(feature = "std", not(test)))]
use std::time::{SystemTime, UNIX_EPOCH};
//------------ Serial --------------------------------------------------------
/// A serial number.
///
/// Serial numbers are used in DNS to track changes to resources. For
/// instance, the [`Soa`][crate::rdata::rfc1035::Soa] record type provides
/// a serial number that expresses the version of the zone. Since these
/// numbers are only 32 bits long, they
/// can wrap. [RFC 1982] defined the semantics for doing arithmetics in the
/// face of these wrap-arounds. This type implements these semantics atop a
/// native `u32`.
///
/// The RFC defines two operations: addition and comparison.
///
/// For addition, the amount added can only be a positive number of up to
/// `2^31 - 1`. Because of this, we decided to not implement the
/// [`Add`] trait but rather have a dedicated method `add` so as to not cause
/// surprise panics.
///
/// Serial numbers only implement a partial ordering. That is, there are
/// pairs of values that are not equal but there still isn’t one value larger
/// than the other. Since this is neatly implemented by the [`PartialOrd`]
/// trait, the type implements that.
///
/// [`Add`]: std::ops::Add
/// [RFC 1982]: https://tools.ietf.org/html/rfc1982
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct Serial(pub u32);
impl Serial {
/// Returns a serial number for the current Unix time.
#[cfg(feature = "std")]
#[must_use]
pub fn now() -> Self {
let now = SystemTime::now();
let value = match now.duration_since(UNIX_EPOCH) {
Ok(value) => value,
Err(_) => UNIX_EPOCH.duration_since(now).unwrap(),
};
Self(value.as_secs() as u32)
}
/// Creates a new serial number from its octets in big endian notation.
#[must_use]
pub fn from_be_bytes(bytes: [u8; 4]) -> Self {
Self(u32::from_be_bytes(bytes))
}
/// Returns the serial number as a raw integer.
#[must_use]
pub fn into_int(self) -> u32 {
self.0
}
/// Add `other` to `self`.
///
/// Serial numbers only allow values of up to `2^31 - 1` to be added to
/// them. Therefore, this method requires `other` to be a `u32` instead
/// of a `Serial` to indicate that you cannot simply add two serials
/// together. This is also why we don’t implement the `Add` trait.
///
/// # Panics
///
/// This method panics if `other` is greater than `2^31 - 1`.
#[allow(clippy::should_implement_trait)]
#[must_use]
pub fn add(self, other: u32) -> Self {
assert!(other <= 0x7FFF_FFFF);
Serial(self.0.wrapping_add(other))
}
pub fn scan<S: Scanner>(scanner: &mut S) -> Result<Self, S::Error> {
u32::scan(scanner).map(Into::into)
}
}
/// # Parsing and Composing
///
impl Serial {
pub const COMPOSE_LEN: u16 = u32::COMPOSE_LEN;
pub fn parse<Octs: AsRef<[u8]> + ?Sized>(
parser: &mut Parser<Octs>,
) -> Result<Self, ParseError> {
u32::parse(parser).map(Into::into)
}
pub fn compose<Target: Composer + ?Sized>(
&self,
target: &mut Target,
) -> Result<(), Target::AppendError> {
self.0.compose(target)
}
}
//--- From and FromStr
impl From<u32> for Serial {
fn from(value: u32) -> Serial {
Serial(value)
}
}
impl From<Serial> for u32 {
fn from(serial: Serial) -> u32 {
serial.0
}
}
#[cfg(feature = "chrono")]
#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
impl<T: TimeZone> From<DateTime<T>> for Serial {
fn from(value: DateTime<T>) -> Self {
Self(value.timestamp() as u32)
}
}
impl str::FromStr for Serial {
type Err = <u32 as str::FromStr>::Err;
fn from_str(s: &str) -> Result<Self, Self::Err> {
<u32 as str::FromStr>::from_str(s).map(Into::into)
}
}
//--- Display
impl fmt::Display for Serial {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{}", self.0)
}
}
//--- PartialOrd
impl cmp::PartialOrd for Serial {
fn partial_cmp(&self, other: &Serial) -> Option<cmp::Ordering> {
match self.0.cmp(&other.0) {
Ordering::Equal => Some(Ordering::Equal),
Ordering::Less => {
let sub = other.0 - self.0;
match sub.cmp(&0x8000_0000) {
Ordering::Less => Some(Ordering::Less),
Ordering::Greater => Some(Ordering::Greater),
Ordering::Equal => None,
}
}
Ordering::Greater => {
let sub = self.0 - other.0;
match sub.cmp(&0x8000_0000) {
Ordering::Less => Some(Ordering::Greater),
Ordering::Greater => Some(Ordering::Less),
Ordering::Equal => None,
}
}
}
}
}
impl CanonicalOrd for Serial {
fn canonical_cmp(&self, other: &Self) -> cmp::Ordering {
self.0.cmp(&other.0)
}
}
//============ Errors ========================================================
#[derive(Clone, Copy, Debug)]
pub struct IllegalSignatureTime(());
impl fmt::Display for IllegalSignatureTime {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.write_str("illegal signature time")
}
}
#[cfg(feature = "std")]
impl std::error::Error for IllegalSignatureTime {}
//============ Testing =======================================================
#[cfg(test)]
mod test {
use super::*;
#[test]
fn good_addition() {
assert_eq!(Serial(0).add(4), Serial(4));
assert_eq!(
Serial(0xFF00_0000).add(0x0F00_0000),
Serial(
((0xFF00_0000u64 + 0x0F00_0000u64) % 0x1_0000_0000) as u32
)
);
}
#[test]
#[should_panic]
fn bad_addition() {
let _ = Serial(0).add(0x8000_0000);
}
#[test]
fn comparison() {
use core::cmp::Ordering::*;
assert_eq!(Serial(12), Serial(12));
assert_ne!(Serial(12), Serial(112));
assert_eq!(Serial(12).partial_cmp(&Serial(12)), Some(Equal));
// s1 is said to be less than s2 if [...]
// (i1 < i2 and i2 - i1 < 2^(SERIAL_BITS - 1))
assert_eq!(Serial(12).partial_cmp(&Serial(13)), Some(Less));
assert_ne!(
Serial(12).partial_cmp(&Serial(3_000_000_012)),
Some(Less)
);
// or (i1 > i2 and i1 - i2 > 2^(SERIAL_BITS - 1))
assert_eq!(
Serial(3_000_000_012).partial_cmp(&Serial(12)),
Some(Less)
);
assert_ne!(Serial(13).partial_cmp(&Serial(12)), Some(Less));
// s1 is said to be greater than s2 if [...]
// (i1 < i2 and i2 - i1 > 2^(SERIAL_BITS - 1))
assert_eq!(
Serial(12).partial_cmp(&Serial(3_000_000_012)),
Some(Greater)
);
assert_ne!(Serial(12).partial_cmp(&Serial(13)), Some(Greater));
// (i1 > i2 and i1 - i2 < 2^(SERIAL_BITS - 1))
assert_eq!(Serial(13).partial_cmp(&Serial(12)), Some(Greater));
assert_ne!(
Serial(3_000_000_012).partial_cmp(&Serial(12)),
Some(Greater)
);
// Er, I think that’s what’s left.
assert_eq!(Serial(1).partial_cmp(&Serial(0x8000_0001)), None);
assert_eq!(Serial(0x8000_0001).partial_cmp(&Serial(1)), None);
}
}