go-honeybee/EXTEND.md

Extending the Pool

The pool owns peer registration, event plumbing, and lifecycle management. The worker owns everything that happens on the wire between registration and the terminal event. Everything between pool.Connect and the final disconnect event is the worker's responsibility, and it is fully replaceable.

The Worker Interface

The pool accepts any type that satisfies:

type Worker interface {
    Start(pool PoolPlugin)
    Stop()
    Send(data []byte) error
    Stats() WorkerStats
}

The behavioral contract for each method:

Start(pool PoolPlugin) Called by the pool in a goroutine it owns. Must block until the worker is finished. The pool monitors this goroutine via a sync.WaitGroup; Start returning is the signal that the worker is done. All I/O, goroutine management, and event emission happen inside Start.

Stop() Must cause Start to return in bounded time. Typically cancels a context. May be called from any goroutine, including concurrently with Start.

Send(data []byte) error Writes data to the remote peer and returns an error if it cannot. Must be safe for concurrent callers. The pool calls Send from whatever goroutine the consumer calls pool.Send from.

Stats() WorkerStats Returns a snapshot of the worker's internal counters and channel depths. Must be safe for concurrent callers and must not block. The pool calls this from pool.Stats() and pool.PeerStats() while holding a read lock.

The PoolPlugin

The pool constructs a PoolPlugin and passes it to Start. It gives the worker access to pool-level channels and the logging handler.

type PoolPlugin struct {
    ID               string
    Inbox            chan<- honeybee.InboxMessage
    Events           chan<- honeybee.PoolEvent
    InboxCounter     *atomic.Uint64
    Dialer           honeybee.Dialer
    ConnectionConfig *transport.ConnectionConfig
    Handler          slog.Handler
}

Inbox The shared channel that delivers received messages to the pool's consumer. All peers in the pool deliver to the same inbox channel. Workers must include their peer ID in each InboxMessage.

Events The shared channel for lifecycle events. Workers emit honeybee.EventConnected and honeybee.EventDisconnected directly. All events include a timestamp in the At field.

InboxCounter An atomic counter owned by the pool. Workers must increment this once for each message forwarded to Inbox. The pool reads it in Stats().

Handler The slog.Handler passed to the pool constructor. The pool constructs and injects scoped loggers before calling the factory, so most workers will use the logger they receive from the factory rather than constructing one from Handler directly. Handler is available for workers that manage sub-components that need their own loggers.

Extending the Pool

Factory Signature

type honeybee.WorkerFactory func(
    ctx    context.Context,
    id     string,
    logger *slog.Logger,
) (honeybee.Worker, error)

The pool calls the factory under its write lock when Connect is called. The factory must return without blocking. The worker is responsible for dialing and managing its own connections. The pool constructs logger from the worker logging config before calling the factory.

The factory is set via honeybee.WithWorkerFactory on the pool config.

Building Blocks

RunDialer(id, ctx, pool, dial, newConn, logger) Listens on dial for connection requests. On each signal, calls connect to dial a new *transport.Connection. While a dial is in progress, drains additional dial signals so that at most one dial runs at a time. On failure, logs the error and waits for the next dial signal. On success, sends the connection on newConn. Exits when ctx is cancelled.

RunKeepalive(ctx, heartbeat, keepalive, timeout, logger) Monitors heartbeat. Resets a timer on each signal. When the timer fires, sends a signal on keepalive to notify the session that the connection should be replaced. When timeout is zero, keepalive is disabled: it drains heartbeat without acting and exits when ctx is cancelled.

RunReader(id, ctx, onStop, conn, inbox, heartbeat, logger) Reads from conn.Incoming() until the channel closes or ctx is cancelled. Builds an InboxMessage inline with the peer ID and writes it directly to inbox. Sends a signal on heartbeat for each message. On exit, calls conn.Close() and then onStop.

RunHeartbeatForwarder(ctx, conn, heartbeat, logger) Reads from conn.Heartbeat() and forwards each signal to heartbeat. Propagates pong replies into the worker's heartbeat channel so pongs reset the keepalive timer alongside data messages and sends.

RunStopMonitor(ctx, onStop, conn, keepalive, logger) Waits for either ctx.Done or a signal on keepalive. On either, calls conn.Close() and then onStop. This is how a keepalive expiry propagates into a session tear-down.

Session The coordination struct that ties the above blocks together for one connection lifecycle. Session.Start runs a loop: request a dial, wait for a connection, run RunReader, RunHeartbeatForwarder, and RunStopMonitor concurrently, wait for them to finish, emit EventDisconnected, sleep for ReconnectDelay, then repeat. Session is exported so it can be embedded or used directly in a custom worker.

Replacement Patterns

Swap one block. The most common case is replacing RunReader to intercept or annotate inbound messages, or replacing RunKeepalive with a different activity metric. Reuse Session for the connection lifecycle and substitute the one goroutine you need to change.

Replace the session loop. Construct your own loop using RunDialer, RunKeepalive, and the session-level blocks. This gives you control over reconnection logic, back-off behavior, or multi-connection strategies while keeping the lower-level I/O blocks intact.

Implement from scratch. Satisfy the Worker interface directly. You are responsible for dialing, managing connection state, forwarding messages to pool.Inbox, emitting honeybee.EventConnected and honeybee.EventDisconnected to pool.Events, and incrementing pool.InboxCounter.

Factory Constraints

The factory is called while the pool holds its write lock. Two constraints follow from this directly.

Factories must not block. Any operation that could wait — dialing a connection, acquiring another lock, reading from a channel — will deadlock or stall the pool. All blocking work belongs inside Start, not inside the factory.

Factories must not call pool methods. pool.Connect, pool.Send, pool.Remove, and similar methods all acquire the same lock the factory is called under. Calling them from the factory will deadlock.

The factory's only job is to construct and return a worker. If construction itself can fail — for example, because a config value is invalid — return the error and the pool will propagate it to the caller of Connect.