bridge_messages_getProof - JSON-RPC Method

Description

bridge_messages_getProof builds a Merkle proof for messages stored in a bridge outbound lane. Relayers use this proof together with the corresponding GRANDPA finality proof to deliver XCM or Snowbridge messages to destination networks.

The response bundles lane state, pending message commitments, and proof nodes so the target chain can independently verify inclusion without trusting the relayer.

Parameters

Parameter	Type	Required	Description
bridge	string	Yes	Bridge instance to query ("westend", "polkadot_bulletin", "snowbridge").
laneId	string	Yes	Hex-encoded 64-bit lane identifier (e.g., "0x0000000000000000" for lane 0).
begin	number	Yes	First outbound message nonce to include (inclusive).
end	number	Yes	Last outbound message nonce to include (inclusive).

Returns

Field	Type	Description
laneState	object	Snapshot of the outbound lane (latest generated, confirmed, and received nonces).
messages	array	SCALE-encoded outbound messages (payload + metadata).
proof	array	Merkle proof nodes required to verify each message on the destination chain.
bridgedHeaderHash	string	The bridged relay-chain header hash the proof is derived from.

Request Example

{
  "jsonrpc": "2.0",
  "method": "bridge_messages_getProof",
  "params": [
    {
      "bridge": "snowbridge",
      "laneId": "0x0000000000000000",
      "begin": 1,
      "end": 5
    }
  ],
  "id": 7
}

Response Example

{
  "jsonrpc": "2.0",
  "id": 7,
  "result": {
    "laneState": {
      "latest_generated_nonce": 12,
      "latest_received_nonce": 9,
      "latest_confirmed_nonce": 9
    },
    "messages": [
      "0x5804...",
      "0x5a04..."
    ],
    "proof": [
      "0x1234...",
      "0xabcd..."
    ],
    "bridgedHeaderHash": "0x8cf2d8b30b86c7a8123ed5a3b92fe74195117cf1999440db0b9c7df24b5e70f1"
  }
}

Code Examples

cURL

curl https://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "bridge_messages_getProof",
    "params": [{
      "bridge": "snowbridge",
      "laneId": "0x0000000000000000",
      "begin": 1,
      "end": 5
    }],
    "id": 7
  }'

JavaScript (polkadot.js)

import { ApiPromise, WsProvider } from '@polkadot/api';

const api = await ApiPromise.create({
  provider: new WsProvider('wss://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY')
});

const proof = await api.rpc.bridgeMessages.getProof({
  bridge: 'snowbridge',
  laneId: '0x0000000000000000',
  begin: 1,
  end: 5
});

console.log('Lane state:', proof.laneState.toHuman());
console.log('Proof nodes:', proof.proof.length);

Python (substrate-interface)

from substrateinterface import SubstrateInterface

substrate = SubstrateInterface(
    url="wss://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY"
)

payload = {
    "bridge": "snowbridge",
    "laneId": "0x0000000000000000",
    "begin": 1,
    "end": 5
}

result = substrate.rpc_request("bridge_messages_getProof", [payload])

lane_state = result['result']['laneState']
print("Latest generated nonce:", lane_state['latest_generated_nonce'])
print("Proof nodes:", len(result['result']['proof']))

Rust (jsonrpsee)

use jsonrpsee::{rpc_params, ws_client::WsClientBuilder};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = WsClientBuilder::default()
        .build("wss://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY")
        .await?;

    let response: serde_json::Value = client
        .request(
            "bridge_messages_getProof",
            rpc_params![{"bridge": "snowbridge", "laneId": "0x0000000000000000", "begin": 1, "end": 5}]
        )
        .await?;

    println!("Message proof: {response:#?}");
    Ok(())
}

Usage Notes

• Pair this proof with the GRANDPA finality proof from bridge_grandpa_getProof so the destination chain can authenticate the outbound lane updates.
• Keep the nonce interval tight. Large ranges increase proof size and transaction weight on the target chain.
• Acknowledge delivered messages by monitoring inbound lane confirmations to avoid resubmitting stale proofs.