f765fc2b27
LEARNING.md indexes ten concept-to-file pointers (the spec floor was five) — the newtype pattern, exhaustive enum match, sans-IO, trait extension seams, thiserror + hot-path match-and-continue, Arc<Mutex> vs Arc<RwLock>, DashMap, str0m's single-mutation invariant, graceful shutdown, include_str!. fuzz/README.md pre-paves the layout (no hostile-bytes surface in slice 1; harnesses land at step 5 per the out-of-scope table). README's new dev-loop section documents the libopus FFI prerequisite and the manual e2e steps.
75 lines
3.7 KiB
Markdown
75 lines
3.7 KiB
Markdown
# LEARNING.md — to learn concept X, read file Y
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This index maps a Rust concept you might be learning to the file where
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slice 1 makes the concept concrete. Each entry is a worked example you
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can read in `cargo doc --open` plus the source file itself.
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## Concepts + pointers
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- **Newtype pattern (type-safety via single-field wrappers)** →
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`crates/rutster-call-model/src/lib.rs` — `ChannelId(Uuid)`. The newtype
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stops us from mixing up a `ChannelId` with some future `SessionId` at
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the type-system level. Compile-enforced where a comment could only ask.
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- **`enum` for closed state sets + exhaustive `match`** →
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`crates/rutster-call-model/src/lib.rs` — `ChannelState` (New →
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Connecting → Connected → Closing → Closed). Exhaustiveness checking
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forces every `match` to consider each state; adding a state later
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surfaces every site that needs handling.
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- **Sans-IO pattern (no I/O inside the library; input via method calls,
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output via return values)** → `crates/rutster-media/src/loop_driver.rs`
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— the str0m poll loop. `Rtc::handle_input` takes a network packet as a
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struct argument, not from a socket the library owns; `poll_output`
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returns `Transmit` packets the caller sends. Fully testable without a
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network — str0m integration tests use this property to drive faster
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than realtime.
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- **Trait design for extension points (a futures-compatible seam)** →
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`crates/rutster-media/src/pcm.rs` — the `AudioSource` / `AudioSink`
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traits. Slice 1 wires an `EchoAudioPipe` between them; step 2 swaps
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that for a real WSS tap client without touching `RtcSession`. The
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traits describe *what* the splice point does, not *how* it's filled.
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- **Error enums with `thiserror` + hot-path match-and-continue** →
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`crates/rutster-media/src/lib.rs` (`MediaError`) and
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`crates/rutster-media/src/opus_codec.rs` (`OpusDecoder::decode` returns
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`Option<PcmFrame>`). Cold path: `thiserror`-derived enum + `?`. Hot
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path: match-and-continue, never `?`, never panic — "drop + observe,
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don't crash" (spec §3.8).
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- **`Arc<Mutex<T>>` vs `Arc<RwLock<T>>` — when each is right** →
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`crates/rutster/src/session_map.rs`. The `RtcSession` lives behind
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`Arc<Mutex<...>>` because every access mutates it (str0m's `&mut self`
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contract) — `RwLock`'s read-mode would be useless. Comment on the
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struct explains the trade-off.
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- **`DashMap` for sharded concurrent maps** →
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`crates/rutster/src/session_map.rs`. `DashMap` shards its inner map so
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two handlers operating on different `ChannelId`s don't contend;
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`HashMap` wrapped in a single `Mutex` would serialize every access.
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- **str0m 0.21's single-mutation invariant** →
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`crates/rutster-media/src/loop_driver.rs`. Mutate (handle_input /
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Writer::write) → drain `poll_output` to `Output::Timeout` → next
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mutate. Violating this leaves str0m in an inconsistent state.
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- **tokio graceful shutdown via signal handlers** →
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`crates/rutster/src/main.rs` (`shutdown_signal`). Ctrl-C / SIGTERM
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drops the AppState; the AppState drops the DashMap; the DashMap drops
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every RtcSession. No in-flight call preservation in slice 1.
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- **`include_str!` for embedding static assets** →
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`crates/rutster/src/routes.rs` (`include_str!("../static/index.html")`).
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The HTML test client is compiled into the binary at build time — no
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separate file to ship, no disk IO to serve it.
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## How to read
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1. `cargo doc --open` — every module has a `//!` doc comment; the doc
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tree is the high-level map.
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2. Pick a concept above; open the named file. The first occurrence of
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each non-obvious pattern has a `//` comment explaining *why*.
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3. Cross-ref back to the spec sections cited inline (`spec §3.8`,
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`ADR-0002`, etc.) for the architecture-level rationale.
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