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
Packetfamily 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
Reprfamily 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.
Examples
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),
protocol: 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);
}Re-exports
pub use self::pretty_print::PrettyPrinter;