RPC Subscription

Overview

Meaning and scope

RPC Subscription is a persistent or long-lived RPC registration through which a client receives notifications when selected blockchain or node conditions change. It pushes updates and reduces polling, but delivery can be interrupted, duplicated, delayed, or provider-specific and therefore should not be the sole source of authoritative state.

Mechanism and operation

Replay of RPC Subscription should preserve original identifiers and timestamps so historical processing cannot masquerade as a new event. A production implementation should record subscription IDs and filters, reconnect with backoff, detect gaps, resynchronize through queries, choose commitment or finality carefully, bound local queues, and unsubscribe cleanly. The RPC Subscription path should preserve ordering and duplicate evidence so delayed delivery cannot silently overwrite a newer state. Useful measures include active subscriptions, disconnect rate, reconnect time, notification lag, detected gaps, duplicate events, and successful query-based resynchronization. Recovery for RPC Subscription should combine replay controls with an authoritative status check rather than trusting delivery history alone.

Practical payment example

A node sends block notifications through a persistent RPC subscription. The client resynchronizes from a known checkpoint after disconnect because notifications may have been missed during the gap.

Operational checks

A receiver should treat transport acknowledgement and successful downstream processing as separate states for RPC Subscription. An RPC Subscription handler should acknowledge only after durable receipt when the provider’s retry contract depends on the response. Business actions triggered by RPC Subscription should be idempotent and should verify the current object state before fulfillment or accounting updates.

Distinctions and limits

Key risks include silent disconnects, missed events, duplicate notifications, unsupported methods, inconsistent provider semantics, memory leaks, and acting on a notification before the required finality level.

Related reading

Related definitions: Ethereum JSON-RPC, Signature Subscription.