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OPL SDK

The OPL SDK is available in our Solidity library. The SDK wraps the Celer Inter-Chain Message (IM) and makes it easy and straight forward to integrate Sapphire and its privacy features into your existing or future Web3 applications.

Overview​

Transaction Flow

  1. The user submits a transaction on the Home network to a contract which uses postMessage to emit an event about a the cross-chain message.
  2. The Celer State Guardian Network (SGN) monitors for transactions which trigger a cross-chain message event and create attestation.
  3. The Executor waits, when the SGN approves the message the Executor submits a transaction to the target contract on Sapphire.

Fees​

The Home Contract pays the SGN to watch and approve the message, but the Executor needs to be run by somebody willing to pay for the gas to submit transactions to the destination chain.

More details to the Celer Executor you can find here.

Quickstart​

A pair of contracts are linked bidirectionally 1-1 to each other across chains, with one end on Sapphire and the other on a supported EVM-compatible chain (the Home Network). They can post and receive messages to & from each other using the message-passing bridge, but must register endpoints to define which messages they handle from each other.

Setup​

Start by adding the @oasisprotocol/sapphire-contracts NPM package to your Hardhat project so you can import OPL.sol:

npm install @oasisprotocol/sapphire-contracts

Now define the two contracts:

  • A contract on Sapphire which runs inside the confidential enclave
  • A contract on the home chain as a host which triggers the example

Sapphire Contract​

On Sapphire use the constructor to provide the Sapphire contract with the location (address and chain) of the contract on the Home chain and register an endpoint called secretExample.

import {Enclave, Result, autoswitch} from "@oasisprotocol/sapphire-contracts/contracts/OPL.sol";

contract SapphireContract is Enclave {
    constructor(address otherEnd, string chain) Enclave(otherEnd, autoswitch(chain)) {
        registerEndpoint("secretExample", on_example);
    }
    function on_example(bytes calldata _args) internal returns (Result) {
        (uint256 a, bool b) = abi.decode(args, (uint256, bool));
        // TODO: do confidential things here
        return Result.Success;
    }
}

Home Contract​

On the other chain, define your contract which can be called via triggerExample to send a message to the contract on Sapphire using the postMessage interface.

import {Host, Result} from "@oasisprotocol/sapphire-contracts/contracts/OPL.sol";

contract HomeContract is Host {
    constructor(address otherEnd) Host(otherEnd) {
    }
    function triggerExample (uint256 a, bool b) external payable {
        postMessage("secretExample", abi.encode(a, b));
    }
}

After a few minutes the bridge will detect and then the executor will invoke the SapphireContract.on_example method.

info

As noted in the fees section, an exectuor needs to relay your messages. Please refer to the Celer Executor section on how to get on the shared Message Executor or how to set up your own executor.