Implement auto-reconnection for SUB sockets#230
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This commit adds automatic reconnection support to zmq.rs SUB sockets when connected peers disconnect and reconnect. When a connection is lost, a background task attempts to reconnect with exponential backoff (100ms to 30s), and on successful reconnection, subscriptions are automatically re-sent to restore the subscription state. The implementation includes: - New src/reconnect.rs module with ReconnectConfig and spawn_reconnect_task - FairQueue enhancements: on_disconnect callback to detect peer disconnections - Backend shutdown fix: clear fair_queue streams to ensure TCP connections close - SubSocketBackend with disconnect notifier support for reconnection tasks - SubSocket override of connect() to spawn background reconnection monitors - Updated reconnection_compliant test that now passes (previously ignored) All CI checks pass: formatting, clippy (--deny warnings), and tests across all three runtime backends (tokio, async-std, async-dispatcher).
Address three issues identified in code review: 1. Arc cycle fix: Use Arc::downgrade() in fair_queue on_disconnect callback to capture a Weak reference instead of a strong Arc. This prevents the cycle: backend -> fair_queue_inner -> callback -> backend. 2. Shutdown check in retry loop: Add shutdown signal check during backoff sleep using futures::select!. The shutdown_rx is now fused so it can be polled multiple times. This ensures ReconnectHandle::shutdown() works even when the endpoint is down and retries are in progress. 3. Emit Connected event on reconnect: try_reconnect now returns the resolved endpoint, and the reconnect task emits SocketEvent::Connected after successful reconnection. This ensures monitor consumers see matching Connected/Disconnected events.
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Summary
This PR implements automatic reconnection support for zmq.rs SUB sockets. When a connected peer disconnects, a background task automatically reconnects with exponential backoff, and subscriptions are automatically re-sent on reconnection. This restores standard ZeroMQ behavior where SUB sockets maintain connectivity.
Implementation Details
src/reconnect.rsmodule providingReconnectConfigandspawn_reconnect_task