Transports — gRPC & REST¶

Pour can communicate with chain nodes via two transports: gRPC (default) and REST (LCD). Both support the same five wire operations and behave identically from the faucet's perspective.

Wire operations¶

Every drip request resolves to exactly five remote calls:

Operation	gRPC	REST
Query account	`cosmos.auth.v1beta1.Query/Account`	`GET /cosmos/auth/v1beta1/accounts/{address}`
Simulate	`cosmos.tx.v1beta1.Service/Simulate`	`POST /cosmos/tx/v1beta1/simulate`
Broadcast tx	`cosmos.tx.v1beta1.Service/BroadcastTx`	`POST /cosmos/tx/v1beta1/txs`
Get tx	`cosmos.tx.v1beta1.Service/GetTx`	`GET /cosmos/tx/v1beta1/txs/{hash}`
Query balance	`cosmos.bank.v1beta1.Query/Balance`	`GET /cosmos/bank/v1beta1/balances/{addr}/by_denom`

Configuring endpoints¶

endpoints:
  grpc:
    - grpc.osmosis.zone:443         # no scheme; plain or TLS auto-detected
    - grpc-fallback.osmosis.zone:443
  rest:
    - https://lcd.osmosis.zone      # scheme required
    - https://lcd-fallback.osmosis.zone

Multiple endpoints of the same type form a pool. Pour rotates through them round-robin, marking endpoints unhealthy when they fail and skipping them until they recover.

Transport selection and failover¶

Pour selects the initial transport at startup:

If endpoints.grpc is non-empty → start with gRPC
Else if endpoints.rest is non-empty → start with REST
Both empty → error at startup

At runtime, when an endpoint returns an unavailable error (connection refused, gRPC UNAVAILABLE, 5xx from REST, or timeout):

gRPC endpoint A fails
  → try gRPC endpoint B
  → gRPC pool exhausted
  → switch to REST endpoint A
  → try REST endpoint B
  → REST pool exhausted
  → ErrNoEndpointAvailable

The switch to REST is transparent — signing, fee estimation, and sequence management are unchanged.

Note

Simulation (Simulate) returns (0, nil) on REST when the node returns a non-2xx response. Pour treats this as "simulation unavailable" and falls back to the configured gas price without simulation, the same behaviour as when simulation is not supported on a gRPC endpoint.

Endpoint health probing¶

Pour runs a background probe loop for each endpoint pool. Unhealthy endpoints are re-probed periodically; once they respond successfully they re-enter the rotation.

REST-only chains¶

Chains that expose only a REST/LCD endpoint (no gRPC) work end-to-end:

endpoints:
  rest:
    - http://localhost:1317

Fee estimation, sequence management, broadcast, and confirmation polling all operate over REST.

gRPC TLS¶

Pour auto-detects TLS for gRPC endpoints on port 443. For non-standard TLS ports, no additional configuration is needed — the endpoint URL is used as-is and TLS is negotiated based on the port and server capabilities.

Checking the active transport¶

The chain status endpoint shows which transport is currently in use:

curl -s http://localhost:8080/admin/chains/mychain-1/status \
  -H "Authorization: Bearer $(cat .pour-admin-token)"