Module smoltcp::wire

source ·
Expand description

Low-level packet access and construction.

The wire module deals with the packet representation. It provides two levels of functionality.

  • First, it provides functions to extract fields from sequences of octets, and to insert fields into sequences of octets. This happens Packet family of structures, e.g. EthernetFrame or Ipv4Packet.
  • Second, in cases where the space of valid field values is much smaller than the space of possible field values, it provides a compact, high-level representation of packet data that can be parsed from and emitted into a sequence of octets. This happens through the Repr family of structs and enums, e.g. ArpRepr or Ipv4Repr.

The functions in the wire module are designed for use together with -Cpanic=abort.

The Packet family of data structures guarantees that, if the Packet::check_len() method returned Ok(()), then no accessor or setter method will panic; however, the guarantee provided by Packet::check_len() may no longer hold after changing certain fields, which are listed in the documentation for the specific packet.

The Packet::new_checked method is a shorthand for a combination of Packet::new_unchecked and Packet::check_len. When parsing untrusted input, it is necessary to use Packet::new_checked(); so long as the buffer is not modified, no accessor will fail. When emitting output, though, it is incorrect to use Packet::new_checked(); the length check is likely to succeed on a zeroed buffer, but fail on a buffer filled with data from a previous packet, such as when reusing buffers, resulting in nondeterministic panics with some network devices but not others. The buffer length for emission is not calculated by the Packet layer.

In the Repr family of data structures, the Repr::parse() method never panics as long as Packet::new_checked() (or Packet::check_len()) has succeeded, and the Repr::emit() method never panics as long as the underlying buffer is exactly Repr::buffer_len() octets long.


To emit an IP packet header into an octet buffer, and then parse it back:

use smoltcp::phy::ChecksumCapabilities;
use smoltcp::wire::*;
let repr = Ipv4Repr {
    src_addr:    Ipv4Address::new(10, 0, 0, 1),
    dst_addr:    Ipv4Address::new(10, 0, 0, 2),
    next_header: IpProtocol::Tcp,
    payload_len: 10,
    hop_limit:   64,
let mut buffer = vec![0; repr.buffer_len() + repr.payload_len];
{ // emission
    let mut packet = Ipv4Packet::new_unchecked(&mut buffer);
    repr.emit(&mut packet, &ChecksumCapabilities::default());
{ // parsing
    let packet = Ipv4Packet::new_checked(&buffer)
                            .expect("truncated packet");
    let parsed = Ipv4Repr::parse(&packet, &ChecksumCapabilities::default())
                          .expect("malformed packet");
    assert_eq!(repr, parsed);


  • pub use self::pretty_print::PrettyPrinter;
  • pub use self::ieee802154::Address as Ieee802154Address;
  • pub use self::ieee802154::AddressingMode as Ieee802154AddressingMode;
  • pub use self::ieee802154::Frame as Ieee802154Frame;
  • pub use self::ieee802154::FrameType as Ieee802154FrameType;
  • pub use self::ieee802154::FrameVersion as Ieee802154FrameVersion;
  • pub use self::ieee802154::Pan as Ieee802154Pan;
  • pub use self::ieee802154::Repr as Ieee802154Repr;





Type Aliases