Implement Event Processing Rate Limiting

[0xNinx]

Overview

I've successfully implemented configurable RPC rate limiting for event ingestion. Here's a summary of the changes:

Implementation Summary

Created Files:

• listener/src/services/rpc-rate-limiter.ts - Token bucket rate limiter class
• listener/src/services/rpc-rate-limiter.test.ts - Comprehensive unit tests (14 tests passing)

Modified Files:

• listener/src/types/index.ts - Added RpcRateLimitConfig interface and integrated into Config
• listener/src/config.ts - Added loadRpcRateLimitConfig() function and validation
• listener/src/services/event-subscriber.ts - Integrated rate limiter into getContractEvents() method
• listener/.env.example - Added RPC rate limiting configuration documentation

Key Features

Configuration Parameters:

• RPC_RATE_LIMIT_ENABLED - Enable/disable rate limiting (default: true)
• RPC_RATE_LIMIT_MAX_REQUESTS_PER_SECOND - Sustained rate limit (default: 10)
• RPC_RATE_LIMIT_BURST_SIZE - Burst capacity (default: 20)
• RPC_RATE_LIMIT_THROTTLE_DELAY_MS - Throttle delay when exceeded (default: 1000ms)

Algorithm:

• Token bucket algorithm allows short bursts while enforcing sustained rate
• Tokens refill over time based on maxRequestsPerSecond
• Requests exceeding burst are throttled with configurable delay
• Metrics tracking for monitoring (total, allowed, throttled requests)

Acceptance Criteria Met:

• ✅ Processing rate is configurable via environment variables
• ✅ Excessive requests are throttled with delays
• ✅ Normal event processing remains unaffected (rate limiter can be disabled)
• ✅ Unit tests validate the implementation

Related Issue

Closes #828

Closes #866

Changes

Verification

# e.g.
cd dashboard && npm test
cd listener && npm run typecheck && npm test
cd contract/contracts/hello-world && cargo test

How to Test

Checklist

• Branch is up to date with main
• Tests added/updated and all pass locally
• cargo fmt --all run (if Rust changes)
• npm run lint passes (if TypeScript changes)
• Documentation updated if behavior changed

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@0xNinx Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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