Contract Source Code:

// Copyright (C) 2018  Argent Labs Ltd. <https://argent.xyz>

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity ^0.5.4;

/**
 * @title Proxy
 * @dev Basic proxy that delegates all calls to a fixed implementing contract.
 * The implementing contract cannot be upgraded.
 * @author Julien Niset - <[email protected]>
 */
contract Proxy {

    address implementation;

    event Received(uint indexed value, address indexed sender, bytes data);

    constructor(address _implementation) public {
        implementation = _implementation;
    }

    function() external payable {

        if (msg.data.length == 0 && msg.value > 0) {
            emit Received(msg.value, msg.sender, msg.data);
        } else {
            // solium-disable-next-line security/no-inline-assembly
            assembly {
                let target := sload(0)
                calldatacopy(0, 0, calldatasize())
                let result := delegatecall(gas, target, 0, calldatasize(), 0, 0)
                returndatacopy(0, 0, returndatasize())
                switch result
                case 0 {revert(0, returndatasize())}
                default {return (0, returndatasize())}
            }
        }
    }
}

Contract Source Code:

// Copyright (C) 2018  Argent Labs Ltd. <https://argent.xyz>

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity ^0.5.4;

/**
 * @title Proxy
 * @dev Basic proxy that delegates all calls to a fixed implementing contract.
 * The implementing contract cannot be upgraded.
 * @author Julien Niset - <[email protected]>
 */
contract Proxy {

    address implementation;

    event Received(uint indexed value, address indexed sender, bytes data);

    constructor(address _implementation) public {
        implementation = _implementation;
    }

    function() external payable {

        if (msg.data.length == 0 && msg.value > 0) {
            emit Received(msg.value, msg.sender, msg.data);
        } else {
            // solium-disable-next-line security/no-inline-assembly
            assembly {
                let target := sload(0)
                calldatacopy(0, 0, calldatasize())
                let result := delegatecall(gas, target, 0, calldatasize(), 0, 0)
                returndatacopy(0, 0, returndatasize())
                switch result
                case 0 {revert(0, returndatasize())}
                default {return (0, returndatasize())}
            }
        }
    }
}