Enum PacketInformation 

pub enum PacketInformation {
    None,
    MacOsUtun,
    LinuxTunPi,
}

The platform’s per-packet prefix.

The off-by-four

macOS utun always prepends four bytes to every packet in both directions: the address family as a big-endian u32 (AF_INET = 2, AF_INET6 = 30). Linux /dev/net/tun prepends nothing when the device was opened with IFF_NO_PI, and a different four bytes when it was not: two bytes of flags followed by the big-endian EtherType (0x0800 / 0x86DD).

Getting this wrong does not fail loudly. The IP version nibble lands in the middle of the prefix, so the packet decodes as garbage rather than erroring, and the symptom is “every field is wrong” rather than “the header is misaligned”.

Variants

None

No prefix — Linux with IFF_NO_PI, and what the tun crate hands us after it has normalised the platform difference itself.

MacOsUtun

macOS utun: four bytes of big-endian address family.

LinuxTunPi

Linux without IFF_NO_PI: two bytes of flags, two bytes of big-endian EtherType.

Implementations

impl PacketInformation

pub fn parse(s: &str) -> Result<Self, String>

Parse the packet_information startup parameter.

auto maps to PacketInformation::None: the tun crate strips and re-adds the platform prefix itself (posix::Tun::new sets a read/write offset of PACKET_INFORMATION_LEN whenever packet information is enabled), so by the time a frame reaches NetGet it is already a bare packet. The other values exist for a raw fd handed in from outside that machinery, and for the tests that pin the layout.

pub fn header_len(&self) -> usize

Bytes this mode prepends.

pub fn strip<'a>(&self, frame: &'a [u8]) -> Result<&'a [u8], DecodeError>

Remove the prefix, returning the packet itself.

The prefix is validated, not skipped: a header that does not name IPv4 or IPv6 means the configured mode does not match the device, and silently advancing four bytes there is exactly the failure this type exists to prevent.

pub fn prefix_for(&self, ipv6: bool) -> Option<[u8; 4]>

The prefix that must precede an outgoing packet, if any.

pub fn prepend(&self, packet: &mut Vec<u8>) -> Result<(), BuildError>

Prepend the platform prefix to a freshly built packet, in place.

Trait Implementations

impl Clone for PacketInformation

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for PacketInformation

impl Debug for PacketInformation

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for PacketInformation

impl PartialEq for PacketInformation

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for PacketInformation