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PR_DESCRIPTION_RPC_FALLBACK.md

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Summary

Adds a Redis-backed last-known-good fallback cache for Stellar RPC calls so callers can receive stale-but-functional data while the RPC circuit breaker is OPEN.

Changes

  • Cache successful Stellar RPC responses with configurable RPC_FALLBACK_CACHE_TTL_SECONDS.
  • Serve cached responses on OPEN circuit hits before throwing CircuitOpenError.
  • Add X-RPC-Cache: stale for HTTP responses that used stale RPC fallback data.
  • Track rpc_circuit_open_fallback_hits_total and rpc_circuit_open_fallback_misses_total.
  • Document circuit breaker states, fallback behavior, TTL, metrics, and security assumptions.
  • Add focused tests for CLOSED, OPEN hit/miss, HALF_OPEN probe, TTL expiry, parameter isolation, and stale response headers.

Validation

  • npm exec vitest -- run tests/services/stellarRpc.fallback.test.ts
  • npm exec vitest -- run tests/stellar-rpc.test.ts
  • npm exec tsc -- --noEmit --target ES2020 --module commonjs --moduleResolution node --esModuleInterop --skipLibCheck src/services/stellar-rpc.ts src/middleware/rpcDegradation.ts src/redis/rpcFallbackCache.ts src/metrics/rpcMetrics.ts tests/services/stellarRpc.fallback.test.ts

Security Notes

  • Raw account identifiers are hashed before use in Redis cache keys.
  • Cache keys use fixed operation names and safe hashed parts only.
  • Cached values are JSON serialized and never evaluated.
  • Redis failures degrade to cache misses or no-op writes.