Module cache 

Response caching layer for RPC transports.

CacheTransport wraps any Arc<dyn RpcTransport> and caches successful responses for configurable methods. Cache keys are computed as a hash of (method, params) so identical requests share a single cache entry.

Tiered Caching

When a CacheTierResolver is configured, the cache classifies each method+params pair into one of four CacheTiers, each with its own TTL:

• Immutable — results that never change (1 hour TTL).
• SemiStable — results that change infrequently (5 minutes TTL).
• Volatile — results that change frequently (2 seconds TTL).
• NeverCache — write methods and subscriptions (never cached).

Without a tier resolver, the cache falls back to the flat default_ttl behavior for all methods listed in cacheable_methods.

Finality Awareness

The CacheTransport::invalidate_for_reorg method removes cached entries that reference blocks at or above a given block number, enabling safe cache invalidation during chain reorganizations.

Design

• Only explicitly cacheable methods are cached (opt-in via CacheConfig).
• Expired entries are evicted lazily on access.
• When the cache exceeds max_entries, the oldest entry is evicted (LRU-ish).
• Thread-safe: the cache is behind a Mutex and the struct is Send + Sync.

Structs

CacheConfig

Configuration for the response cache.

CacheStats

Aggregate cache statistics.

CacheTierResolver

Determines the CacheTier for a given RPC request.

CacheTransport

A caching wrapper around an RPC transport.

Enums

CacheTier

Classification of an RPC method’s caching behavior.