<div align="center">
<h1>mdns-proto</h1>
</div>
<div align="center">
Sans-I/O mDNS / DNS-SD protocol state machines — `no_std`-capable,
`no_alloc`-capable, panic-free.
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</div>
## Introduction
`mdns-proto` implements Multicast DNS ([RFC 6762]) and DNS-SD ([RFC 6763]) —
probing, conflict resolution, periodic announcement, known-answer suppression,
cache coherency, and response generation — as deterministic state machines that
perform **no I/O of their own**.
You feed inbound datagrams and timer ticks in via `Endpoint::handle` /
`Endpoint::handle_timeout` and drain outbound datagrams via
`Endpoint::poll_transmit` — the same Sans-I/O shape as [`quinn-proto`]. This
keeps the protocol logic portable and exhaustively testable: the same core runs
under any async runtime, on bare metal, or inside a fuzzer.
The async driver crates in the [hick] family ([`hick-reactor`],
[`hick-compio`], plus the bare-metal [`hick-smoltcp`] / [`hick-embassy`]) are
thin layers over this crate. Most applications want one of those, or the
[`hick`] facade, rather than this core directly.
## Feature tiers
`std` and `alloc` are **independent** features, so the crate scales from a full
`std` host down to bare metal with no allocator:
| Features | Environment |
|----------|-------------|
| `std` *(default)* | `std` hosts (e.g. tokio, smol) |
| `alloc` | `no_std` with a global allocator (Embassy, RTIC, ESP-IDF, wasm32) |
| `no-atomic` | `no_std` + allocator on cores **without** native atomic CAS (Cortex-M0+ / thumbv6m / RP2040): same Endpoint as `alloc`, but the refcounted Name / rdata use `portable-atomic`'s `Arc` (clone via a `critical-section` impl the binary provides) instead of `smol_str` + `bytes`. Mutually exclusive with `alloc` / `std`; no `stats`. |
| `heapless` | `no_std`, fixed-capacity collections, no allocator |
| *(none)* | bare-metal `no_std`, no heap at all |
Other features:
| Feature | Description |
|---------|-------------|
| `slab` *(default)* | Slab-backed state pools for the protocol machines. |
| `tracing` | Emit structured `tracing` events/spans internally (queries, cache, probing, conflicts). |
| `stats` | Enable `no_std`-safe atomic counters; expose a snapshot via `endpoint.stats()`. Requires `alloc`. |
| `metrics` | Bridge counters to the [`metrics`] facade (Prometheus/StatsD). Implies `stats`. Requires `alloc`. |
## Installation
```toml
[dependencies]
mdns-proto = "0.2" # std + slab
# no_std + alloc:
mdns-proto = { version = "0.2", default-features = false, features = ["alloc"] }
# no_std + alloc on a core WITHOUT native atomics (Cortex-M0+ / RP2040):
mdns-proto = { version = "0.2", default-features = false, features = ["no-atomic"] }
# bare no_std (no allocator):
mdns-proto = { version = "0.2", default-features = false }
```
## Observability
### `tracing`
Enable `mdns-proto = { …, features = ["tracing"] }`. The state machine emits
structured `tracing` events (at `DEBUG` / `INFO` / `WARN`) during probing,
conflict resolution, cache inserts/evictions, query state transitions, and
service registration. Wire a subscriber in your application:
```rust,ignore
tracing_subscriber::fmt().init();
```
### `stats` — atomic counters
Enable `features = ["stats"]` (requires `alloc`). `Endpoint::stats()` returns
a `hick_trace::stats::StatsSnapshot`:
```rust,ignore
let snap = endpoint.stats();
println!("packets_rx={} cache_size={}", snap.packets_rx, snap.cache_size);
```
`StatsSnapshot` is a plain `Copy` struct of `u64` fields. Counters include
`packets_rx/tx`, `bytes_rx/tx`, `packets_dropped`, `parse_errors`,
`questions_rx`, `answers_rx/collected`, `cache_inserts/refreshes/evictions/
expirations`, `queries_started/done/timeout`, `services_registered/
established`, `conflicts`, `renames`, `responses_tx`, `probes_tx`,
`announcements_tx`, `goodbyes_tx`, and gauges `cache_size`, `queries_active`,
`services_active`.
### `metrics`
Enable `features = ["metrics"]` (implies `stats`; requires `alloc`). Every
counter/gauge update is forwarded to the [`metrics`] facade so Prometheus,
StatsD, or any other exporter receives the data automatically.
## The hick family
[`hick`] (facade) · **`mdns-proto`** (this crate) · [`hick-udp`] (UDP) ·
[`hick-reactor`] (tokio / smol driver) · [`hick-compio`] (compio driver) ·
[`hick-smoltcp`] (smoltcp engine) · [`hick-embassy`] (embassy driver).
## License
`mdns-proto` is under the terms of both the MIT license and the Apache License
(Version 2.0).
See [LICENSE-APACHE](LICENSE-APACHE), [LICENSE-MIT](LICENSE-MIT) for details.
Copyright (c) 2025 Al Liu.
[`hick`]: https://crates.io/crates/hick
[`hick-udp`]: https://crates.io/crates/hick-udp
[`hick-reactor`]: https://crates.io/crates/hick-reactor
[`hick-compio`]: https://crates.io/crates/hick-compio
[`hick-smoltcp`]: https://crates.io/crates/hick-smoltcp
[`hick-embassy`]: https://crates.io/crates/hick-embassy
[`quinn-proto`]: https://crates.io/crates/quinn-proto
[`metrics`]: https://crates.io/crates/metrics
[hick]: https://github.com/al8n/hick
[RFC 6762]: https://www.rfc-editor.org/rfc/rfc6762
[RFC 6763]: https://www.rfc-editor.org/rfc/rfc6763
[Github-url]: https://github.com/al8n/hick/
[CI-url]: https://github.com/al8n/hick/actions/workflows/ci.yml
[codecov-url]: https://app.codecov.io/gh/al8n/hick/
[doc-url]: https://docs.rs/mdns-proto
[crates-url]: https://crates.io/crates/mdns-proto