Initial commit: wireframe packet capture/analysis tool

Terminal packet capture and analysis tool built to learn the C++
memory model (byte layout, alignment, endianness, std::span over
unowned buffers) via a real capture pipeline.

- Hand-rolled L2-L4 decoders (Ethernet, IPv4, IPv6 with extension
  header walking, TCP, UDP) over std::span, no struct-casting
- L7 dissector interface with DNS, HTTP, and TLS SNI implementations
- pcapng read/write for Wireshark-compatible capture files
- Bounded capture queue: drop-on-backpressure for live capture,
  blocking push for faithful file replay
- Kernel-level BPF filtering (-f) and a separate display-only search
  (-g / interactive) that doesn't touch what's captured
- Replay mode (-r) reads a saved pcapng file back through the same
  pipeline as live capture, no root or live device needed
- pcap_stats() surfaces kernel/interface drops invisible to the
  capture queue's own counter
- Three frontends sharing one CaptureSession setup path: CLI, TUI
  (FTXUI, primary), GUI (Dear ImGui + SDL3, secondary)
- 89 unit tests (doctest) plus 9 libFuzzer harnesses covering every
  hand-rolled parser; fuzzing found and fixed a real OOM in the
  pcapng reader (unbounded allocation from an untrusted length field)

1 files changed, 35 insertions, 0 deletions

diff --git a/include/wireframe/net/udp.hpp b/include/wireframe/net/udp.hpp
new file mode 100644
index 0000000..07664c2
--- /dev/null
+++ b/include/wireframe/net/udp.hpp
@@ -0,0 +1,35 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <span>
+
+#include "wireframe/byteio.hpp"
+
+namespace wireframe::net {
+
+inline constexpr std::size_t kUdpHeaderLen = 8;
+
+struct UdpHeader {
+    std::uint16_t src_port;
+    std::uint16_t dst_port;
+    std::uint16_t length;
+};
+
+struct UdpDatagram {
+    UdpHeader header;
+    std::span<const unsigned char> payload;
+};
+
+inline std::optional<UdpDatagram> parse_udp(std::span<const unsigned char> bytes) {
+    if (bytes.size() < kUdpHeaderLen) return std::nullopt;
+
+    UdpHeader header{};
+    header.src_port = read_be16(bytes, 0);
+    header.dst_port = read_be16(bytes, 2);
+    header.length = read_be16(bytes, 4);
+
+    return UdpDatagram{header, bytes.subspan(kUdpHeaderLen)};
+}
+
+}  // namespace wireframe::net