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Summary

This PR implements 4 critical tasks to enhance the security and reliability of the TeachLink contract system.

Tasks Completed

Task 1: Rewards Overflow Protection (Critical)

Files Modified: contracts/teachlink/src/rewards.rs, contracts/teachlink/src/errors.rs

Changes:

  • Added checked arithmetic operations to prevent overflow
  • Implemented input validation with MAX_REWARD_AMOUNT constant (i128::MAX / 2)
  • Added ArithmeticOverflow and AmountExceedsMaxLimit error types
  • All reward calculations now handle overflow gracefully
  • Added comprehensive test cases for overflow detection

Impact: Prevents incorrect reward distribution due to integer overflow with large values.

Task 2: Event Queue Memory Leak Fix

Files Modified: contracts/teachlink/src/notification.rs, contracts/teachlink/src/storage.rs

Changes:

  • Added TTL (Time-To-Live) mechanism with 7-day default for notification events
  • Implemented queue size limits (10,000 events maximum)
  • Added automatic cleanup of expired events with configurable intervals (1 hour)
  • Events now stored with timestamps
  • Added cleanup_expired_events(), get_queue_stats(), and update_ttl_config() functions
  • Automatic cleanup triggered when queue reaches capacity

Impact: Prevents unbounded memory growth from processed events accumulating indefinitely.

Task 3: Contract Upgrade Mechanism

Files Created: contracts/teachlink/src/upgrade.rs Files Modified: contracts/teachlink/src/lib.rs

Changes:

  • Created comprehensive upgrade system with state preservation
  • Version tracking with complete upgrade history
  • Automated state backup before upgrades
  • Rollback support within 30-day window
  • Admin-controlled upgrade process with validation
  • Added 7 new public functions for upgrade management

Impact: Enables safe contract upgrades without losing state, with rollback capability.

Task 4: Network Failure Recovery

Files Created: contracts/teachlink/src/network_recovery.rs Files Modified: contracts/teachlink/src/lib.rs

Changes:

  • Implemented retry logic with exponential backoff (1min to 1hr max)
  • State preservation for failed operations
  • User notification system for retry attempts
  • Fallback mechanisms when max retries (5) exceeded
  • Configurable retry parameters
  • Circuit breaker pattern support
  • Added 6 new public functions for recovery management

Impact: Transforms hard errors into graceful recovery with automatic retries and user notifications.

Testing

All modules include comprehensive unit tests:

  • Overflow protection tests
  • Retry logic and backoff tests
  • Upgrade lifecycle tests
  • Rollback window tests

Acceptance Criteria Met

Task 1:

  • Add checked arithmetic operations
  • Validate input ranges
  • Handle overflow gracefully
  • Add overflow test cases

Task 2:

  • Remove processed events from queue
  • Implement queue size limits
  • Add TTL for events

Task 3:

  • Preserve state during upgrades
  • Track versions
  • Automate migration
  • Support rollback

Task 4:

  • Add retry logic
  • Preserve state
  • Notify users
  • Implement fallback mechanisms

Breaking Changes

None - All changes are additive and backward compatible.

Migration Notes

  • Existing notification logs will be migrated to new format with timestamps on next write
  • Upgrade system initializes at version 1
  • Recovery system uses default configuration (can be customized by admin)