Refactor ws_service_stats.rs to reduce cognitive_complexity and add test coverage

[mukeshblackhat]

ws_service_stats.rs has two suppressions: run_service_collector (line 254) and handle_stats_socket (line 436), both #[allow(clippy::cognitive_complexity)].

What they do

• run_service_collector (~90 lines) — resolves the inner container for a service, then polls docker stats --no-stream every 2 seconds in a loop, parses JSON, pushes to history ring, broadcasts to subscribers
• handle_stats_socket (~55 lines) — replays history buffer to a newly connected WebSocket client, then runs a tokio::select! loop relaying broadcast receiver output to the socket (same pattern as ws_stats.rs and ws_host_service_stats.rs)

What to do

1. Extract single-poll execution in run_service_collector

Lines 290–323 build exec options, run create_exec + start_exec, accumulate stdout, and parse JSON. Extract:

async fn poll_service_stats(
    docker: &bollard::Docker,
    coast_container_id: &str,
    stats_cmd: &str,
) -> Option<serde_json::Value>

2. Extract history push + broadcast

Lines 325–335 push the new value into the history ring and send to the broadcast channel. Extract (could be shared with ws_host_service_stats.rs and ws_stats.rs):

async fn push_stats_to_history_and_broadcast(
    history: &Mutex<HashMap<String, VecDeque<serde_json::Value>>>,
    key: &str,
    val: serde_json::Value,
    tx: &broadcast::Sender<serde_json::Value>,
)

3. Extract history replay for handle_stats_socket

Lines 440+ replay the history ring to the socket. Extract (shared with ws_stats.rs and ws_host_service_stats.rs):

async fn replay_stats_history(
    socket: &mut WebSocket,
    history: &Mutex<HashMap<String, VecDeque<serde_json::Value>>>,
    key: &str,
) -> ControlFlow<()>

4. Extract broadcast forwarding loop

The tokio::select! loop in handle_stats_socket that forwards broadcast messages to the socket. Shared across all three stats handlers. Extract into a common module if possible:

async fn relay_broadcast_to_socket(
    socket: &mut WebSocket,
    rx: &mut broadcast::Receiver<serde_json::Value>,
    key: &str,
)

5. Add unit tests

poll_service_stats and broadcast/history helpers are hard to unit test without mocks. Focus on:

• Any pure helpers that come out of extraction (JSON parsing, key construction, etc.)

Important

The workspace Cargo.toml sets cognitive_complexity, too_many_lines, too_many_arguments, and several other clippy lints to warn globally. Run make lint after every change and make sure the output is clean. Don't fix a suppression here only to create new warnings elsewhere.

Acceptance criteria

• poll_service_stats extracted (from run_service_collector)
• push_stats_to_history_and_broadcast extracted (shared if possible)
• replay_stats_history extracted (shared with other stats handlers)
• relay_broadcast_to_socket extracted (shared)
• Both functions use the new helpers
• All tests pass (make test)
• make lint passes with zero new warnings
• Remove both #[allow(clippy::cognitive_complexity)] suppressions if make lint passes without them, keep any still needed (note why)

Related

Tracking issue pattern from previous PRs: #122, #133, #157, #158, #171, #172, #173, #174, #175