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use super::super::*;
use std::slice::from_raw_parts;
/// IPv6 fragment header.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Ipv6FragmentHeader {
/// IP protocol number specifying the next header or transport layer protocol.
///
/// See [IpNumber] or [ip_number] for a definition of the known values.
pub next_header: u8,
/// Offset in 8 octets
///
/// Note: In the header only 13 bits are used, so the allowed range
/// of the value is between 0 and 0x1FFF (inclusive).
pub fragment_offset: u16,
/// True if more fragment packets will follow. False if this is the last packet.
pub more_fragments: bool,
/// Identifcation value generated by the source.
pub identification: u32
}
impl Ipv6FragmentHeader {
/// Create a new fragmentation header with the given parameters.
///
/// Note that the `fragment_offset` can only support values between 0 and 0x1fff (inclusive).
pub const fn new(next_header: u8, fragment_offset: u16, more_fragments: bool, identification: u32) -> Ipv6FragmentHeader {
Ipv6FragmentHeader{
next_header,
fragment_offset,
more_fragments,
identification
}
}
/// Read an Ipv6FragmentHeader from a slice and return the header & unused parts of the slice.
pub fn from_slice(slice: &[u8]) -> Result<(Ipv6FragmentHeader, &[u8]), ReadError> {
let s = Ipv6FragmentHeaderSlice::from_slice(slice)?;
let rest = &slice[8..];
let header = s.to_header();
Ok((
header,
rest
))
}
/// Read an fragment header from the current reader position.
pub fn read<T: io::Read + io::Seek + Sized>(reader: &mut T) -> Result<Ipv6FragmentHeader, ReadError> {
let buffer = {
let mut buffer : [u8;8] = [0;8];
reader.read_exact(&mut buffer)?;
buffer
};
Ok(Ipv6FragmentHeader {
next_header: buffer[0],
fragment_offset: u16::from_be_bytes(
[
(buffer[2] >> 3) & 0b0001_1111u8,
((buffer[2] << 5) & 0b1110_0000u8) |
(buffer[3] & 0b0001_1111u8)
]
),
more_fragments: 0 != buffer[3] & 0b1000_0000u8,
identification: u32::from_be_bytes(
[
buffer[4],
buffer[5],
buffer[6],
buffer[7],
]
),
})
}
/// Writes a given IPv6 fragment header to the current position.
pub fn write<T: io::Write + Sized>(&self, writer: &mut T) -> Result<(), WriteError> {
Ok(writer.write_all(&self.to_bytes()?)?)
}
/// Length of the header in bytes.
#[inline]
pub fn header_len(&self) -> usize {
8
}
/// Checks if the fragment header actually fragments the packet.
///
/// Returns false if the fragment offset is 0 and the more flag
/// is not set. Otherwise returns true.
///
/// [RFC8200](https://datatracker.ietf.org/doc/html/rfc8200) explicitly
/// states that fragment headers that don't fragment the packet payload are
/// allowed. See the following quote from
/// RFC8200 page 32:
///
/// > Revised the text to handle the case of fragments that are whole
/// > datagrams (i.e., both the Fragment Offset field and the M flag
/// > are zero). If received, they should be processed as a
/// > reassembled packet. Any other fragments that match should be
/// > processed independently. The Fragment creation process was
/// > modified to not create whole datagram fragments (Fragment
/// > Offset field and the M flag are zero). See
/// > [RFC6946](https://datatracker.ietf.org/doc/html/6946) and
/// > [RFC8021](https://datatracker.ietf.org/doc/html/rfc8021) for more
/// > information."
///
/// ```
/// use etherparse::{Ipv6FragmentHeader, ip_number::UDP};
///
/// // offset 0 & no more fragments result in an unfragmented payload
/// {
/// let header = Ipv6FragmentHeader::new(UDP, 0, false, 123);
/// assert!(false == header.is_fragmenting_payload());
/// }
///
/// // offset 0 & but more fragments will come -> fragmented
/// {
/// let header = Ipv6FragmentHeader::new(UDP, 0, true, 123);
/// assert!(header.is_fragmenting_payload());
/// }
///
/// // offset non zero & no more fragments will come -> fragmented
/// {
/// let header = Ipv6FragmentHeader::new(UDP, 1, false, 123);
/// assert!(header.is_fragmenting_payload());
/// }
/// ```
#[inline]
pub fn is_fragmenting_payload(&self) -> bool {
self.more_fragments ||
(0 != self.fragment_offset)
}
/// Returns the serialized form of the header as a statically
/// sized byte array.
///
/// The `fragment_offset` is only allowed to have the maximum
/// size of `0x1FFF`.
#[inline]
pub fn to_bytes(&self) -> Result<[u8;8], ValueError> {
use ErrorField::*;
max_check_u16(
self.fragment_offset,
0b0001_1111_1111_1111u16,
Ipv6FragmentOffset
)?;
let fo_be: [u8;2] = self.fragment_offset.to_be_bytes();
let id_be = self.identification.to_be_bytes();
Ok(
[
self.next_header,
0,
(
((fo_be[0] << 3) & 0b1111_1000u8) |
((fo_be[1] >> 5) & 0b0000_0111u8)
),
(
(fo_be[1] & 0b0001_1111u8) |
if self.more_fragments {
0b1000_0000u8
} else {
0
}
),
id_be[0],
id_be[1],
id_be[2],
id_be[3],
]
)
}
}
/// Slice containing an IPv6 fragment header.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Ipv6FragmentHeaderSlice<'a> {
/// Slice containing the packet data.
slice: &'a [u8]
}
impl<'a> Ipv6FragmentHeaderSlice<'a> {
/// Creates a hop by hop header slice from a slice.
pub fn from_slice(slice: &'a[u8]) -> Result<Ipv6FragmentHeaderSlice<'a>, ReadError> {
// the fragmentation header has the exact size of 8 bytes
use crate::ReadError::*;
if slice.len() < 8 {
Err(UnexpectedEndOfSlice(8))
} else {
Ok(Ipv6FragmentHeaderSlice {
// SAFETY:
// Safe as slice length is checked to be at least 8 before this
// code can be reached.
slice: unsafe {
from_raw_parts(
slice.as_ptr(),
8
)
}
})
}
}
/// Creates a hop by hop header slice from a slice (assumes slice size & content was validated before).
///
/// # Safety
///
/// This function assumes that the passed slice has at least the length
/// of 8. If a slice with length less then 8 is passed to this function
/// the behavior will be undefined.
pub unsafe fn from_slice_unchecked(slice: &'a[u8]) -> Ipv6FragmentHeaderSlice<'a> {
// the fragmentation header has the exact size of 8 bytes
Ipv6FragmentHeaderSlice {
slice: from_raw_parts(
slice.as_ptr(),
8
)
}
}
/// Returns the slice containing the ipv6 fragment header.
#[inline]
pub fn slice(&self) -> &'a[u8] {
self.slice
}
/// Returns the IP protocol number of the next header.
///
/// See [IpNumber] or [ip_number] for a definition of the known values.
#[inline]
pub fn next_header(&self) -> u8 {
// SAFETY:
// Slice size checked to be at least 8 bytes in constructor.
unsafe {
*self.slice.get_unchecked(0)
}
}
/// Fragment offset in 8 octets.
///
/// Note: In the header only 13 bits are used, so the allowed range
/// of the value is between 0 and 0x1FFF (inclusive).
#[inline]
pub fn fragment_offset(&self) -> u16 {
u16::from_be_bytes(
// SAFETY:
// Slice size checked to be at least 8 bytes in constructor.
unsafe {
[
(*self.slice.get_unchecked(2) >> 3) & 0b0001_1111u8,
((*self.slice.get_unchecked(2) << 5) & 0b1110_0000u8) |
(*self.slice.get_unchecked(3) & 0b0001_1111u8)
]
}
)
}
/// True if more fragment packets will follow. False if this is the last packet.
#[inline]
pub fn more_fragments(&self) -> bool {
// SAFETY:
// Slice size checked to be at least 8 bytes in constructor.
unsafe {
0 != *self.slice.get_unchecked(3) & 0b1000_0000u8
}
}
/// Checks if the fragment header actually fragments the packet.
///
/// Returns false if the fragment offset is 0 and the more flag
/// is not set. Otherwise returns true.
///
/// [RFC8200](https://datatracker.ietf.org/doc/html/rfc8200) explicitly
/// states that fragment headers that don't fragment the packet payload are
/// allowed. See the following quote from
/// RFC8200 page 32:
///
/// > Revised the text to handle the case of fragments that are whole
/// > datagrams (i.e., both the Fragment Offset field and the M flag
/// > are zero). If received, they should be processed as a
/// > reassembled packet. Any other fragments that match should be
/// > processed independently. The Fragment creation process was
/// > modified to not create whole datagram fragments (Fragment
/// > Offset field and the M flag are zero). See
/// > [RFC6946](https://datatracker.ietf.org/doc/html/6946) and
/// > [RFC8021](https://datatracker.ietf.org/doc/html/rfc8021) for more
/// > information."
///
/// ```
/// use etherparse::Ipv6FragmentHeaderSlice;
///
/// {
/// let slice = Ipv6FragmentHeaderSlice::from_slice(&[
/// 0, 0, 0, 0, // offset 0 & more_fragments not set
/// 1, 2, 3, 4,
/// ]).unwrap();
/// assert!(false == slice.is_fragmenting_payload());
/// }
///
/// {
/// let slice = Ipv6FragmentHeaderSlice::from_slice(&[
/// 0, 0, 0, 0b1000_0000u8, // more_fragments set
/// 1, 2, 3, 4,
/// ]).unwrap();
/// assert!(slice.is_fragmenting_payload());
/// }
///
/// {
/// let slice = Ipv6FragmentHeaderSlice::from_slice(&[
/// 0, 0, 1, 0, // non zero offset
/// 1, 2, 3, 4,
/// ]).unwrap();
/// assert!(slice.is_fragmenting_payload());
/// }
/// ```
#[inline]
pub fn is_fragmenting_payload(&self) -> bool {
// SAFETY:
// Slice size checked to be at least 8 bytes in constructor.
unsafe {
0 != *self.slice.get_unchecked(2) ||
0 != (*self.slice.get_unchecked(3) & 0b1001_1111u8) // exclude the reserved bytes
}
}
/// Identifcation value generated by the source
pub fn identification(&self) -> u32 {
// SAFETY:
// Slice size checked to be at least 8 bytes in constructor.
unsafe {
get_unchecked_be_u32(self.slice.as_ptr().add(4))
}
}
/// Decode some of the fields and copy the results to a
/// Ipv6FragmentHeader struct.
pub fn to_header(&self) -> Ipv6FragmentHeader {
Ipv6FragmentHeader{
next_header: self.next_header(),
fragment_offset: self.fragment_offset(),
more_fragments: self.more_fragments(),
identification: self.identification()
}
}
}