frameassembly 1.5.1

A DSL for creating custom .pcap/.pcapng captures and decompiling captures to .fasm for testing firewalls, IDS rules, SNMP traps, and pentesting.
Documentation 
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//! Generic Network Virtualization Encapsulation (GENEVE, RFC 8926) Layer 3 PCAP-to-`.fasm` decompiler.
//!
//! This module implements the fuzz-safe PCAP and PCAPNG decompiler for RFC 8926 `GENEVE` overlay
//! tunnel packets carried over UDP port `6081`. It validates the GENEVE version and variable
//! option-length fields, extracts the 24-bit Virtual Network Identifier (`vni`), inner EtherType
//! (`protocol_type`), and optional TLV header (`opt_class`, `opt_type`), and elides the default
//! 42-byte FrameAssembly overlay inner frame when unchanged.

use alloc::string::String;
use core::fmt::Write as _;

use crate::ast::Protocol;
use crate::reverse::{ProtocolDissection, be_u16, be_u32, push_hex, push_if, sd};

use super::is_default_overlay_inner;

/// Decompiles an RFC 8926 `GENEVE` UDP payload (port `6081`) into a [`ProtocolDissection`].
pub(crate) fn dissect_geneve(b: &[u8]) -> Option<ProtocolDissection> {
    let obl = ((b.first()? & 0x3F) as usize) * 4;
    if b.len() < 8 + obl || (b[0] >> 6) != 0 {
        return None;
    }
    let (vni, mut t) = (be_u32(b, 4) >> 8, String::from("geneve"));
    push_if(&mut t, "vni", vni, 4096);
    push_hex(&mut t, "protocol_type", u64::from(be_u16(b, 2)), 0x6558, 4);
    if obl >= 4 {
        let _ = write!(t, " opt_class 0x{:04x}", be_u16(b, 8));
        push_if(&mut t, "opt_type", b[10], 0);
    }
    let inner = &b[8 + obl..];
    let rem = if is_default_overlay_inner(inner) {
        &[][..]
    } else {
        inner
    };
    Some(sd(Protocol::Geneve, t, rem.to_vec()))
}