Module packet

UDP Packet Header Construction

Purpose

This module provides a utility to construct the headers for a UDP/IPv4/Ethernet packet. This is essential for applications using AF_XDP that need to manually build entire packets before sending them.

How it works

It uses the etherparse crate’s PacketBuilder to efficiently layer the Ethernet II, IPv4, and UDP headers. The headers are written directly into a fixed-size [u8; 42] array to avoid heap allocations. A custom HdrWrite struct, which implements std::io::Write, acts as a temporary writer to capture the builder’s output.

Main components

• write_udp_header_for(): The primary function that takes source/destination addresses and ports and returns a 42-byte array containing the packet header.
• HdrWrite: A helper struct implementing io::Write to enable writing into a fixed-size buffer without extra allocations.

Structs

HdrWrite

A helper struct that implements std::io::Write for a fixed-size byte array.

Functions

write_udp_header_for

Constructs Ethernet, IPv4, and UDP headers for a packet.