moqtap-codec

Zero-dependency MoQT wire codec — draft-conforming parser and writer for every MoQT draft from draft-07 through draft-18.

This crate handles pure encoding and decoding of MoQT protocol messages with no I/O, no async runtime, and no network dependencies. It is the foundational building block that every other moqtap crate depends on.

What it does

Encodes and decodes every MoQT control message type per each supported draft (setup, subscribe, publish, fetch, namespace, track status, goaway)
Encodes and decodes data stream headers (subgroup, datagram, fetch, object)
QUIC variable-length integer (VarInt) encoding per RFC 9000
Key-value parameter (KVP) pairs
Core protocol types: TrackNamespace, Location, FilterType, GroupOrder, ObjectStatus
Session and request error codes, per-draft
Runtime draft dispatch via the dispatch module (AnyControlMessage, AnySubgroupHeader, AnyFetchHeader, AnyDatagramHeader, AnyObjectHeader) — one enum variant per enabled draft feature, decode selects the draft at runtime from a DraftVersion

Module layout

Each draft lives in its own module with an independent implementation; no wire-level code is shared across drafts. Shared primitives (varint, kvp, types, version, error) sit at the crate root.

moqtap_codec::
    varint, kvp, types, version, error   (shared)
    dispatch                             (runtime Any* enums)
    draft07, draft08, ..., draft18       (per-draft wire format)

Draft selection

Each draft is behind a feature flag. Enable the ones you need. The default is all-drafts.

# every draft (default)
moqtap-codec = "0.2"

# draft-14 only
moqtap-codec = { version = "0.2", default-features = false, features = ["draft14"] }

# draft-07 plus draft-14 for runtime dispatch
moqtap-codec = { version = "0.2", default-features = false, features = ["draft07", "draft14"] }

Usage

Per-draft (compile-time)

use moqtap_codec::draft14::message::{ControlMessage, ClientSetup};
use moqtap_codec::varint::VarInt;

let msg = ControlMessage::ClientSetup(ClientSetup {
    supported_versions: vec![VarInt::from_u64(0xff00000e).unwrap()],
    parameters: vec![],
});
let mut buf = Vec::new();
msg.encode(&mut buf).unwrap();

let mut cursor = &buf[..];
let decoded = ControlMessage::decode(&mut cursor).unwrap();
assert_eq!(msg, decoded);

Runtime dispatch across drafts

use moqtap_codec::dispatch::AnyControlMessage;
use moqtap_codec::version::DraftVersion;

let mut cursor: &[u8] = &wire_bytes;
let msg = AnyControlMessage::decode(DraftVersion::Draft14, &mut cursor)?;
match msg {
    AnyControlMessage::Draft14(inner) => { /* ... */ }
    _ => {}
}

Benchmarks

Criterion benches live in benches/codec.rs and exercise varint, KVP, control-message, data-stream header, and synthetic subgroup decode paths. The conformance test vectors under test-vectors/transport/draft17/ provide realistic message bytes; a synthetic generator covers larger subgroup streams for throughput curves.

# full run (requires draft17 feature — enabled by default)
cargo bench -p moqtap-codec

# quick smoke run
cargo bench -p moqtap-codec --bench codec -- \
    --warm-up-time 1 --measurement-time 2 --sample-size 10

# only one group
cargo bench -p moqtap-codec --bench codec -- varint

# save a baseline, change code, then compare
cargo bench -p moqtap-codec --bench codec -- --save-baseline before
# … make changes …
cargo bench -p moqtap-codec --bench codec -- --baseline before

HTML reports are written to target/criterion/report/index.html.

License

MIT

moqtap-codec 0.2.0