# M5a task 03: the `memoryd` crate, its configuration and sockets

**Branch:** `m5a` (run `git switch m5a`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `memoryd: the crate, memoryd.toml, and listening on a socket`

## Goal

A new role crate, `memoryd` (M5a spec, sections 2, 7 and 11), with its configuration and the
socket helper its three sockets will use. It depends on `proto` and on one new crate, `rusqlite`
(the index, from task 08), which is added to the workspace now so the dependency checks pass
once. `memoryd serve --config <path>` reads its configuration and says "not implemented" until
task 10.

## Files

- Copy (whole, nothing to fill): `crates/memoryd/Cargo.toml`, `crates/memoryd/src/lib.rs`,
  `crates/memoryd/src/main.rs`
- Copy (skeletons): `crates/memoryd/src/config.rs`, `crates/memoryd/src/socket.rs`
- Copy (tests): `crates/memoryd/tests/config.rs`, `crates/memoryd/tests/socket.rs`,
  `crates/memoryd/tests/support/tmp.rs`
- Append: `docs/plans/M5a/files/runbook-memoryd-start-failed.md` to the end of `docs/runbook.md`
  (a blank line before it)
- Modify: `Cargo.toml`, `deny.toml`, `docs/dependencies.md`, `docs/implementer-log.md`

## The edits, exactly

**`Cargo.toml` (the workspace):** add `"crates/memoryd",` to `members` after
`"crates/gatewayd",`, and at the end of `[workspace.dependencies]` add

```toml
rusqlite = { version = "0.40.2", features = ["bundled"] }
```

**`deny.toml`:** the line `allow = ["MIT", "Apache-2.0", "Unicode-3.0", "ISC", "BSD-3-Clause"]`
becomes `allow = ["MIT", "Apache-2.0", "Unicode-3.0", "ISC", "BSD-3-Clause", "Zlib"]`
(`foldhash`, a dependency of `rusqlite`, is Zlib-licensed).

**`docs/dependencies.md`:** add this row at the end of the table:

```markdown
| `rusqlite` | 0.40.2 | `memoryd` from M5a | The full-text index (`index/memory.sqlite3`, FTS5), disposable and rebuilt from files. Feature `bundled`: `libsqlite3-sys` compiles SQLite from source with FTS5 on, so no system SQLite is needed. With its dependencies: `libsqlite3-sys` (MIT; build: `cc`, `pkg-config`, `vcpkg`), `hashlink`, `hashbrown`, `foldhash` (Zlib, added to `deny.toml` for it), `fallible-iterator`, `fallible-streaming-iterator`, `smallvec`, `bitflags`. MIT. |
```

## The skeletons

`config.rs`: the types, `Config::parse` and the path methods are written; fill `Config::load` and
`Config::socket`. `socket.rs`: fill `listen`, the same five steps as `listen` in
`crates/brokerd/src/serve.rs` (read it; no crate may depend on another role's crate, so this is a
copy with `String` errors).

## Steps

- [ ] **1. Copy** every file above from `docs/plans/M5a/files/` to the same path; make the three
  edits; append the runbook entry.
- [ ] **2. Build.** `cargo build -p memoryd`. The first build downloads `rusqlite` and compiles
  SQLite; it takes a few minutes. Then `cargo deny check`: expected `advisories ok, bans ok,
  licenses ok, sources ok` (it needs the network).
- [ ] **3. See it fail.** `cargo test -p memoryd --test config --test socket`: expected
  `config` 3 failed, 1 passed; `socket` 2 failed.
- [ ] **4. Fill** `Config::load`, `Config::socket` and `listen`. `cargo fmt --all`.
- [ ] **5. See it pass.** The same command: 4 and 2 passed.
- [ ] **6. Run the gate.** `make gate`: `gate: ok`, with 6 more tests than before (about 868).
- [ ] **7. Log and commit.** `git add -A Cargo.toml Cargo.lock deny.toml crates/memoryd docs/runbook.md docs/dependencies.md docs/implementer-log.md && git commit`

## Done when

- `make gate` prints `gate: ok`, and `cargo deny check` passes.

## Stop and report if

- `cargo deny check` reports anything but the four "ok"s: a licence other than Zlib, or two
  versions of one crate. Do not edit `deny.toml` beyond the one line above.
- The build cannot download `rusqlite`.