# M4b task 14: the serve loop posts approvals and marks them

**Branch:** `m4b` (run `git switch m4b`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `gatewayd: serve, posting approvals, marking them, and the listener`

## Goal

The serve loop does what `gateway.sock` connections ask (M4b spec, sections 6 and 8):

- **Show**: place the approval (its session's turn in flight: that thread; otherwise the first
  approver's direct messages, as a new thread), post its parts in order, record the posts in the
  state file, register it for answers (task 11), and reply with the post ids, or why it could not
  be posted.
- **Ended**: forget it, and add how it ended to its last post, naming who answered.
- At the **first connection after a start**, the approval posts the last run left behind are
  marked: their last post is replaced by its title and the restart line.
- `run` opens `gateway.sock` before connecting; a failure stops `gatewayd` at start
  (`Stop::Start`, pointer `gatewayd-start-failed`).

## Files

- Copy: the skeleton `crates/gatewayd/src/serve/approvals.rs`,
  `crates/gatewayd/tests/serve_approvals.rs`, `crates/gatewayd/tests/support/brokerd_client.rs`,
  and a **new version** of the given `crates/gatewayd/tests/support/fake_mm.rs` (it gains post
  edits, user names, and refusing posts)
- Modify: `crates/gatewayd/src/serve/mod.rs`, `docs/implementer-log.md`

## The skeleton

Written: `Open`, **`gateway_requests`** (drain the channel, never blocking) and **`show`** (read
both first). To fill, each with its steps in its comment: `place`, `ended`, `mark_left_behind`,
`mark`.

## `serve/mod.rs`, exactly

1. `mod approvals;` before `mod handle;`. Imports: `use std::collections::HashMap;`,
   `use crate::approvals::Registry;`, `use crate::gateway::{self, ToLoop};`.
2. Three fields at the end of `struct Gateway`:

```rust
    /// The approvals posted here, shared with the turns (for the notice) and judged by commands.
    registry: Arc<Registry>,
    /// What `gateway.sock` connections ask of the loop.
    gateway_rx: Receiver<ToLoop>,
    /// The last post of each approval posted here and not yet ended.
    open: HashMap<u64, approvals::Open>,
```

3. `Gateway::new` gains a last parameter `gateway_rx: Receiver<ToLoop>`, and sets
   `registry: Arc::new(Registry::new()), gateway_rx, open: HashMap::new(),`.
4. In `run`, right before `let client = Arc::new(Client::new(…));`:

```rust
    let listener = match gateway::listen(&config.gateway_socket()) {
        Ok(listener) => listener,
        Err(why) => return Stop::Start(why),
    };
    let (gateway_tx, gateway_rx) = mpsc::channel();
    if let Err(e) = gateway::serve(
        listener,
        gateway_tx,
        gateway::Timing::default(),
        Arc::clone(&log),
    ) {
        return Stop::Start(format!("cannot start the gateway.sock thread: {e}"));
    }
```

   and `Gateway::new(config, client, state, log)` becomes
   `Gateway::new(config, client, state, log, gateway_rx)`.
5. In `connected`, inside `if !self.restarted { … }`, after the `take_in_flight` loop:
   `self.mark_left_behind()?;`
6. In `event_loop`, after `self.finished()?;`: `self.gateway_requests()?;`

## Steps

- [ ] **1. Copy.** `git switch m4b`, then
  `cp docs/plans/M4b/files/crates/gatewayd/src/serve/approvals.rs crates/gatewayd/src/serve/ && cp docs/plans/M4b/files/crates/gatewayd/tests/serve_approvals.rs crates/gatewayd/tests/ && cp docs/plans/M4b/files/crates/gatewayd/tests/support/brokerd_client.rs docs/plans/M4b/files/crates/gatewayd/tests/support/fake_mm.rs crates/gatewayd/tests/support/`
- [ ] **2. Make the six `serve/mod.rs` changes.** `cargo build -p gatewayd` must succeed.
- [ ] **3. See it fail.** `cargo test -p gatewayd --test serve_approvals`. Expected: 4 fail, 1
  passes (the socket is there while `gatewayd` runs).
- [ ] **4. Fill `mark`, `place`, `ended`, `mark_left_behind`**, `cargo check -p gatewayd` after
  each.
- [ ] **5. See it pass.** `cargo test -p gatewayd --test serve_approvals`, three times: 5 passed.
  Then `cargo test -p gatewayd`: every suite passes.
- [ ] **6. Run the gate.** `cargo fmt --all`, then `make gate`. Expected last line: `gate: ok`.
- [ ] **7. Log and commit.** `git add crates/gatewayd docs/implementer-log.md Cargo.lock && git commit`

## Done when

- `cargo test -p gatewayd` passes; `make gate` prints `gate: ok`.

## Stop and report if

- A comment above a `todo!()` does not fit its function, or contradicts a test: quote it.
- `show` or `gateway_requests` seems to need a change: they are given.