Implement Horizon streaming for real-time payment monitoring

[prodbycorne]

Overview

Classic Stellar payment operations to airdrop recipient addresses need to be tracked via Horizon's event streaming API. This enables confirming recipient payouts and detecting trust-line establishment in real time.

What to Stream

• Payment operations to tracked recipient addresses
• Trust line changes — detect when recipients establish the required trust line before claiming
• Account created — detect when a new account is funded by an airdrop operation

Architecture

Horizon SSE (/accounts/:id/operations)
     │
     ▼
StreamManager (reconnects on disconnect, tracks cursor)
     │
     ▼
PaymentProcessor (validates, deduplicates, stores)
     │
     ▼
DB (payment_operations table) + Webhook dispatcher

Implementation

// src/indexer/horizonStream.js
const { Horizon } = require('@stellar/stellar-sdk');

class HorizonStreamManager {
  constructor(server, accounts) { ... }
  start() { /* opens SSE stream per tracked account */ }
  stop() { /* closes all streams */ }
  onPayment(handler) { ... }
}

• Use stellar-sdk's server.operations().forAccount(id).stream()
• Persist last paging token per account to DB
• Resume from stored cursor on service restart
• Reconnect with exponential backoff (1s → 5s → 30s)

Acceptance Criteria

• HorizonStreamManager implemented
• Streams payment operations for dynamically tracked addresses
• Cursor persisted and resumed on restart
• Auto-reconnects after stream disconnect
• Payment events forwarded to webhook dispatcher
• Stream health exposed in /api/v1/indexer/status
• Unit tests with mocked Horizon SDK

[Oluwasuyi-Timilehin]

Hello maintainers I'm a full stack developer experience in building scalable systems I can handle this perfectly if assigned

[grantfox-oss]

🦊 GrantFox — @Oluwasuyi-Timilehin has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #19)
2. Your PR will be reviewed by the SmartDropLabs maintainers

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