FIX Session Manager

• Sequence Number Management: Tracking incoming and outgoing messages, detecting gaps, and requesting resends.
• Heartbeat & Connection Monitoring: Maintaining connectivity and quickly detecting issues.
• Error Handling & Recovery: Efficiently managing out-of-sequence or missing messages to ensure the session remains synchronized.
• Low Latency: Being highly performant to meet the real-time demands of trading operations.

Sequence Number Management

The sequence.rs module handles tracking incoming and outgoing message sequence numbers, detecting gaps, and requesting resends when necessary.

It uses atomic operations for thread safety and includes a buffer for out-of-sequence messages.

Heartbeat & Connection Monitoring

The heartbeat.rs module implements connection monitoring through heartbeats and test requests, quickly detecting connectivity issues through configurable timeouts.

Error Handling & Recovery

The recovery.rs module provides sophisticated error recovery, handling out-of-sequence messages and various error conditions to maintain session synchronization.

Low Latency Design

The implementation is built with performance in mind, using:

• Tokio for asynchronous processing
• Atomic operations where appropriate
• Efficient message buffering
• Minimal locking patterns
• Optimized byte handling with the bytes crate

The session manager is structured to handle the FIX protocol lifecycle efficiently, including:

• Session establishment with logon/logout sequences
• Message sequencing and gap detection
• Heartbeat monitoring and test requests
• Message buffering and recovery for out-of-sequence messages
• Clean error handling using the thiserror crate

The main SessionManager class provides a high-level API with methods to start/stop sessions and send/receive messages, while internally managing all the complex protocol details.

To use this session manager in a real application, you would:

1. Create a SessionConfig with your session parameters
2. Instantiate a SessionManager with this config
3. Implement the SessionCallback trait to receive messages and state changes
4. Connect the msg_receiver to your network transport layer
5. Start the session with session_manager.start()