Add per-IP connection limits to SSE endpoint

[ogazboiz]

Join our community: https://t.me/+DOylgFv1jyJlNzM0

Description

The SSE endpoint has no connection limits per IP. A single client could open thousands of connections, exhausting server file descriptors.

What Needs to Happen

• Track active connections per source IP in-memory
• Max 5 concurrent connections per IP — return 429 with Retry-After: 60
• Global max 10,000 connections via MAX_SSE_CONNECTIONS env var — return 503 at capacity
• Clean up IP entry when all connections from that IP close
• Expose per-IP peak in admin metrics

Files

• backend/src/services/sse.service.ts
• backend/src/routes/v1/events.routes.ts

Acceptance Criteria

• 6th connection from same IP returns 429
• Global capacity returns 503
• IP map cleaned up on disconnect

[xeladev4]

@xeladev4 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi maintainer, I’d like to work on this issue.
I have experience building and securing Stellar/Soroban smart contracts. I focus on clean implementations.
I’ll ensure the solution follows the project’s architecture and security best practices.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @xeladev4 to this issue.

[drips-wave]

Congratulations, @xeladev4! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @xeladev4: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @xeladev4 as part of the Stellar Wave Program's 4th Wave 🥳

😎 @xeladev4: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.