md-codec 0.34.0

Reference implementation of the Mnemonic Descriptor (MD) format for engravable BIP 388 wallet policy backups
Documentation 
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//! Forward-compat tests: unknown TLV tags are skipped/preserved per D6.

use md_codec::bitstream::BitWriter;
use md_codec::decode::decode_payload;
use md_codec::encode::{Descriptor, encode_payload};
use md_codec::origin_path::{OriginPath, PathComponent, PathDecl, PathDeclPaths};
use md_codec::tag::Tag;
use md_codec::tlv::TlvSection;
use md_codec::tree::{Body, Node};
use md_codec::use_site_path::UseSitePath;

fn bip84_descriptor_with_unknown_tlv() -> Descriptor {
    // Synthesize an unknown-tag TLV. Tags 0x00..0x03 are now claimed
    // (UseSitePathOverrides, Fingerprints, Pubkeys, OriginPathOverrides), so
    // 0x04 is the next free tag a future spec might allocate. A v0.13
    // decoder must round-trip this opaque blob unchanged per D6.
    let mut sub = BitWriter::new();
    sub.write_bits(0x42, 8); // arbitrary payload byte
    sub.write_bits(0x99, 8);
    let payload_bit_len = sub.bit_len();
    let payload = sub.into_bytes();

    let mut tlv = TlvSection::new_empty();
    tlv.unknown.push((0x04, payload, payload_bit_len));

    Descriptor {
        n: 1,
        path_decl: PathDecl {
            n: 1,
            paths: PathDeclPaths::Shared(OriginPath {
                components: vec![
                    PathComponent {
                        hardened: true,
                        value: 84,
                    },
                    PathComponent {
                        hardened: true,
                        value: 0,
                    },
                    PathComponent {
                        hardened: true,
                        value: 0,
                    },
                ],
            }),
        },
        use_site_path: UseSitePath::standard_multipath(),
        tree: Node {
            tag: Tag::Wpkh,
            body: Body::KeyArg { index: 0 },
        },
        tlv,
    }
}

#[test]
fn unknown_tlv_round_trip_preserved() {
    let d = bip84_descriptor_with_unknown_tlv();
    let (bytes, total_bits) = encode_payload(&d).unwrap();
    let d2 = decode_payload(&bytes, total_bits).unwrap();
    assert_eq!(d.tlv.unknown, d2.tlv.unknown);
}