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use super::{Error, Result};
use core::fmt;
use byteorder::{ByteOrder, NetworkEndian};
/// A read/write wrapper around an IPv6 Fragment Header.
#[derive(Debug, PartialEq, Eq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct Header<T: AsRef<[u8]>> {
buffer: T,
}
// Format of the Fragment Header
//
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Next Header | Reserved | Fragment Offset |Res|M|
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Identification |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
// See https://tools.ietf.org/html/rfc8200#section-4.5 for details.
//
// **NOTE**: The fields start counting after the header length field.
mod field {
use crate::wire::field::*;
// 16-bit field containing the fragment offset, reserved and more fragments values.
pub const FR_OF_M: Field = 0..2;
// 32-bit field identifying the fragmented packet
pub const IDENT: Field = 2..6;
/// 1 bit flag indicating if there are more fragments coming.
pub const M: usize = 1;
}
impl<T: AsRef<[u8]>> Header<T> {
/// Create a raw octet buffer with an IPv6 Fragment Header structure.
pub const fn new_unchecked(buffer: T) -> Header<T> {
Header { buffer }
}
/// Shorthand for a combination of [new_unchecked] and [check_len].
///
/// [new_unchecked]: #method.new_unchecked
/// [check_len]: #method.check_len
pub fn new_checked(buffer: T) -> Result<Header<T>> {
let header = Self::new_unchecked(buffer);
header.check_len()?;
Ok(header)
}
/// Ensure that no accessor method will panic if called.
/// Returns `Err(Error)` if the buffer is too short.
pub fn check_len(&self) -> Result<()> {
let data = self.buffer.as_ref();
let len = data.len();
if len < field::IDENT.end {
Err(Error)
} else {
Ok(())
}
}
/// Consume the header, returning the underlying buffer.
pub fn into_inner(self) -> T {
self.buffer
}
/// Return the fragment offset field.
#[inline]
pub fn frag_offset(&self) -> u16 {
let data = self.buffer.as_ref();
NetworkEndian::read_u16(&data[field::FR_OF_M]) >> 3
}
/// Return more fragment flag field.
#[inline]
pub fn more_frags(&self) -> bool {
let data = self.buffer.as_ref();
(data[field::M] & 0x1) == 1
}
/// Return the fragment identification value field.
#[inline]
pub fn ident(&self) -> u32 {
let data = self.buffer.as_ref();
NetworkEndian::read_u32(&data[field::IDENT])
}
}
impl<T: AsRef<[u8]> + AsMut<[u8]>> Header<T> {
/// Set reserved fields.
///
/// Set 8-bit reserved field after the next header field.
/// Set 2-bit reserved field between fragment offset and more fragments.
#[inline]
pub fn clear_reserved(&mut self) {
let data = self.buffer.as_mut();
// Retain the higher order 5 bits and lower order 1 bit
data[field::M] &= 0xf9;
}
/// Set the fragment offset field.
#[inline]
pub fn set_frag_offset(&mut self, value: u16) {
let data = self.buffer.as_mut();
// Retain the lower order 3 bits
let raw = ((value & 0x1fff) << 3) | ((data[field::M] & 0x7) as u16);
NetworkEndian::write_u16(&mut data[field::FR_OF_M], raw);
}
/// Set the more fragments flag field.
#[inline]
pub fn set_more_frags(&mut self, value: bool) {
let data = self.buffer.as_mut();
// Retain the high order 7 bits
let raw = (data[field::M] & 0xfe) | (value as u8 & 0x1);
data[field::M] = raw;
}
/// Set the fragmentation identification field.
#[inline]
pub fn set_ident(&mut self, value: u32) {
let data = self.buffer.as_mut();
NetworkEndian::write_u32(&mut data[field::IDENT], value);
}
}
impl<T: AsRef<[u8]> + ?Sized> fmt::Display for Header<&T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match Repr::parse(self) {
Ok(repr) => write!(f, "{repr}"),
Err(err) => {
write!(f, "IPv6 Fragment ({err})")?;
Ok(())
}
}
}
}
/// A high-level representation of an IPv6 Fragment header.
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct Repr {
/// The offset of the data following this header, relative to the start of the Fragmentable
/// Part of the original packet.
pub frag_offset: u16,
/// When there are more fragments following this header
pub more_frags: bool,
/// The identification for every packet that is fragmented.
pub ident: u32,
}
impl Repr {
/// Parse an IPv6 Fragment Header and return a high-level representation.
pub fn parse<T>(header: &Header<&T>) -> Result<Repr>
where
T: AsRef<[u8]> + ?Sized,
{
header.check_len()?;
Ok(Repr {
frag_offset: header.frag_offset(),
more_frags: header.more_frags(),
ident: header.ident(),
})
}
/// Return the length, in bytes, of a header that will be emitted from this high-level
/// representation.
pub const fn buffer_len(&self) -> usize {
field::IDENT.end
}
/// Emit a high-level representation into an IPv6 Fragment Header.
pub fn emit<T: AsRef<[u8]> + AsMut<[u8]> + ?Sized>(&self, header: &mut Header<&mut T>) {
header.clear_reserved();
header.set_frag_offset(self.frag_offset);
header.set_more_frags(self.more_frags);
header.set_ident(self.ident);
}
}
impl fmt::Display for Repr {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
"IPv6 Fragment offset={} more={} ident={}",
self.frag_offset, self.more_frags, self.ident
)
}
}
#[cfg(test)]
mod test {
use super::*;
// A Fragment Header with more fragments remaining
static BYTES_HEADER_MORE_FRAG: [u8; 6] = [0x0, 0x1, 0x0, 0x0, 0x30, 0x39];
// A Fragment Header with no more fragments remaining
static BYTES_HEADER_LAST_FRAG: [u8; 6] = [0xa, 0x0, 0x0, 0x1, 0x9, 0x32];
#[test]
fn test_check_len() {
// less than 6 bytes
assert_eq!(
Err(Error),
Header::new_unchecked(&BYTES_HEADER_MORE_FRAG[..5]).check_len()
);
// valid
assert_eq!(
Ok(()),
Header::new_unchecked(&BYTES_HEADER_MORE_FRAG).check_len()
);
}
#[test]
fn test_header_deconstruct() {
let header = Header::new_unchecked(&BYTES_HEADER_MORE_FRAG);
assert_eq!(header.frag_offset(), 0);
assert!(header.more_frags());
assert_eq!(header.ident(), 12345);
let header = Header::new_unchecked(&BYTES_HEADER_LAST_FRAG);
assert_eq!(header.frag_offset(), 320);
assert!(!header.more_frags());
assert_eq!(header.ident(), 67890);
}
#[test]
fn test_repr_parse_valid() {
let header = Header::new_unchecked(&BYTES_HEADER_MORE_FRAG);
let repr = Repr::parse(&header).unwrap();
assert_eq!(
repr,
Repr {
frag_offset: 0,
more_frags: true,
ident: 12345
}
);
let header = Header::new_unchecked(&BYTES_HEADER_LAST_FRAG);
let repr = Repr::parse(&header).unwrap();
assert_eq!(
repr,
Repr {
frag_offset: 320,
more_frags: false,
ident: 67890
}
);
}
#[test]
fn test_repr_emit() {
let repr = Repr {
frag_offset: 0,
more_frags: true,
ident: 12345,
};
let mut bytes = [0u8; 6];
let mut header = Header::new_unchecked(&mut bytes);
repr.emit(&mut header);
assert_eq!(header.into_inner(), &BYTES_HEADER_MORE_FRAG[0..6]);
let repr = Repr {
frag_offset: 320,
more_frags: false,
ident: 67890,
};
let mut bytes = [0u8; 6];
let mut header = Header::new_unchecked(&mut bytes);
repr.emit(&mut header);
assert_eq!(header.into_inner(), &BYTES_HEADER_LAST_FRAG[0..6]);
}
#[test]
fn test_buffer_len() {
let header = Header::new_unchecked(&BYTES_HEADER_MORE_FRAG);
let repr = Repr::parse(&header).unwrap();
assert_eq!(repr.buffer_len(), BYTES_HEADER_MORE_FRAG.len());
}
}