dispatch-service

Runs on the indexer alongside an Ethereum node. Validates TAP receipts, proxies JSON-RPC requests, signs responses, and persists receipts to PostgreSQL.

Routes

Method	Path	Description
POST	`/rpc/{chain_id}`	JSON-RPC request (single or batch)
GET	`/ws/{chain_id}`	WebSocket proxy for `eth_subscribe`
GET	`/health`	Liveness check
GET	`/version`	Version info
GET	`/chains`	List of supported chains
GET	`/block/{chain_id}`	Unauthenticated probe — returns current block number (used by gateways for QoS freshness scoring)

Request flow

Gateway POST /rpc/42161
  + TAP-Receipt: { signed EIP-712 receipt }
        │
        ▼
TAP middleware
  - recover signer from EIP-712 signature
  - check sender is in authorized_senders
  - check timestamp not stale (configurable window)
  - persist receipt to tap_receipts table (async)
        │
        ▼
Parse JSON-RPC method + params
        │
        ▼
Forward to backend Ethereum client (chain_id → backend URL mapping)
        │
        ▼
Sign response attestation:
  keccak256(chainId || method || paramsHash || responseHash || blockNumber || blockHash)
        │
        ▼
Return JSON-RPC response
  + X-Dispatch-Attestation: <signature>

TAP receipt validation

The service validates every incoming receipt before forwarding the request:

Signature: EIP-712 ECDSA recovery against GraphTallyCollector as verifying contract
Sender authorisation: recovered signer must be in authorized_senders config list
Staleness: timestamp_ns must be within the configured window
Data service: data_service field must match RPCDataService address

Invalid receipts are rejected with 400 Bad Request.

Archive tier detection

The service inspects block parameters to determine if a request requires archive state:

Hex block numbers below current head - 128 → routed to archive backend
String tags "earliest", "pending" → archive
JSON integers → parsed and compared against head

This allows a single endpoint to serve both standard and archive requests when both backends are configured.