Individual Handler Files & Advanced Error Handling

[takker99]

Problem Statement:
Complete the modularization by splitting function code handlers into individual files and implementing advanced error handling patterns for production use.

Goals:

• Individual handler files for each function code
• Rust-style Result type error handling throughout
• Request queue/scheduler for RTU protocol
• Advanced error recovery and retry mechanisms

Tasks:

Individual Handler Files

• Create src/handlers/ directory structure
• Implement individual files:
  • src/handlers/read-coils.ts (FC 01)
  • src/handlers/read-discrete-inputs.ts (FC 02)
  • src/handlers/read-holding-registers.ts (FC 03)
  • src/handlers/read-input-registers.ts (FC 04)
  • src/handlers/write-single-coil.ts (FC 05)
  • src/handlers/write-single-register.ts (FC 06)
  • src/handlers/write-multiple-coils.ts (FC 15)
  • src/handlers/write-multiple-registers.ts (FC 16)
• Update frame builder/parser to use handler files
• Implement handler registry for dynamic loading

Advanced Error Handling

• Implement Result<T, E> type system throughout codebase
• Replace Promise rejections with Result returns
• Add error recovery strategies (retry, timeout, fallback)
• Implement detailed error context (device info, timing, etc.)

Request Scheduler

• Create src/scheduler/request-scheduler.ts
• Implement RTU request serialization
• Add request prioritization and queuing
• Implement timeout and retry logic
• Add request cancellation support

Testing & Performance

• Add comprehensive handler tests
• Add scheduler tests with timing verification
• Add error handling scenario tests
• Performance benchmarks for new architecture
• Memory usage optimization

Acceptance Criteria:

• All function codes have individual handler files
• Result type system implemented without breaking changes
• Request scheduler handles concurrent requests properly
• Error recovery mechanisms work reliably
• Performance is maintained or improved
• Full test coverage for new components

Dependencies:

• Requires Phase 2 (Transport Abstraction & Classless API #51 ) transport abstraction to be completed first