moqtap-codec

MoQT wire codec — a parser and writer for every MoQT draft from draft-07 through draft-19.

Pure encoding and decoding: no I/O, no async runtime, no network dependencies. It depends only on bytes and thiserror.

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)
Variable-length integers, in whichever encoding the draft uses: RFC 9000 Section 16 through draft-16, and MoQT's own (Section 1.4.1) from draft-17, where the length is the number of leading 1 bits in the first byte. DraftVersion::varint_encoding maps drafts to encodings
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
Draft-neutral object framing on the same seam (AnySubgroupObjectReader, AnySubgroupObjectWriter, AnyFetchObjectReader, AnyFetchObjectWriter and the values they hand back), so a caller frames a data stream into individually addressable objects without naming a draftNN type. Subgroup and fetch streams on every draft 07-19
Structured parameter values, rather than opaque bytes: the AUTHORIZATION TOKEN structure (auth_token), the subscription filter (subscription_filter), and draft-19's Range Filter parameters (range_filter)

Module layout

Each draft lives in its own module with an independent implementation; no wire-level code is shared across drafts. Shared primitives sit at the crate root.

moqtap_codec::
    varint, kvp, types, version, error   (shared primitives)
    auth_token, subscription_filter,
    range_filter                         (structured parameter values)
    dispatch, data_dispatch              (runtime Any* enums and object framing)
    draft07, draft08, ..., draft19       (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 = "0.4"

# draft-14 only
moqtap-codec = { version = "0.4", default-features = false, features = ["draft14"] }

# draft-07 plus draft-14 for runtime dispatch
moqtap-codec = { version = "0.4", 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 in benches/codec.rs cover varint, KVP, control-message, data-stream header and subgroup decode paths. They need the draft17 feature, which is on by default.

cargo bench -p moqtap-codec

License

MIT

moqtap-codec 0.4.1