Add OPL SDK

[nhynes]

This SDK makes it very easy to use OPL. All you need to do is split your dapp and drop in the addresses.

Features:

• minimal boilerplate code (partial message decoding, consolidated access control)
• automatic mainnet/testnet/localnet switching
  • contracts all deployed on the same network don't need to use the bridge
• automatic _msgSender for easier billing of gas
• specify the home chain using name instead of id
• mostly gas efficient (except for one place, which has been commented). depends a lot on inlining and constant evaluation for code size reduction
• GSN integration

Here's a hello world example:

pragma solidity ^0.8.0;

import "@oasisprotocol/sapphire-contracts/contracts/opl/Host.sol";

contract ScoreNFT is Host {
    constructor(address _scorer) Host(_scorer) {
        registerEndpoint("score", _oplReceiveScore);
    }
    
    function mintScore() external {
        postMessage("genScore");
    }

    function _oplReceiveScore(bytes calldata scoreBytes) internal returns (Result) {
        _mint(_msgActor(), uint256(bytes32(scoreBytes)));
        return Result.Success;
    }
}

pragma solidity ^0.8.0;

import "@oasisprotocol/sapphire-contracts/contracts/opl/Enclave.sol";

contract Scorer is Enclave {
    constructor(address _nft) Enclave(_nft, autoswitch("ethereum")) {
        registerEndpoint("genScore", _oplGenScore);
    }

    function _oplGenScore(bytes calldata) internal returns (Result) {
        postMessage("score", bytes(bytes32(secretAlgorithm(_msgActor()))));
        return Result.Success;
    }
}

I'd also like to generate a lot of overloads for the receiver methods so you get automatic decoding, but that'll might make the compiler slow.

[kostko]

Nice!

The example above has the following in _oplReceiveScore:

_mint(msg.sender, score);

Shouldn't it instead use whom not msg.sender as the sender would probably be the relayer?

[kostko]

Looks good, would be nice to have some E2E tests for this somewhere.