ERC827Test.sol

pragma solidity ^0.4.24;

import "./openzeppelin-solidity/ownership/Ownable.sol";
import "./openzeppelin-solidity/token/ERC20/StandardToken";

contract Token is StandardToken, Ownable {
    uint256 public constant decimals = 0;
    string public constant name = "ERC827 Token";
    string public constant symbol = "TOK";
    
    mapping (address => bool) erc827Whitelist;
    
    constructor(uint256 initialSupply) public {
        owner = msg.sender;
        totalSupply_ = initialSupply;
        balances[msg.sender] = initialSupply;
        emit Transfer(address(0), msg.sender, initialSupply);
    }
    
    function addToERC827Whitelist(address _spender) public onlyOwner {
        erc827Whitelist[_spender] = true;
    }
    
    function approveAndCallWithSender(
        address _spender,
        uint256 _value,
        bytes4 selector,
        bytes call_params
    )
        public
        payable
        returns (bool)
    {
        require(_spender != address(this) && erc827Whitelist[_spender]);
        
        super.approve(_spender, _value);
        
        bytes memory call_data = abi.encodePacked(selector, uint256(msg.sender), call_params);
        require(_spender.call.value(msg.value)(call_data));
        
        return true;
    }
    
    // TODO: similarly wrapped versions of increaseApprovalAndCall, etc.
}

contract Marketplace {
    event Listing(address _seller, uint256 _deposit, bytes32 ipfshHash);
    
    Token token;
    
    constructor(Token _token) public {
        token = _token;
    }
    function proxiedCreateListing(address _seller, uint256 _deposit, bytes32 _ipfsHash) public payable {
        // msg.sender would be token address here
        require(msg.sender == address(token), "proxied function must be called by token");
        require(_seller != address(token), "token can't be the seller");
        require(address(this) != address(token), "marketplace can't be the seller");
        
        require(token.transferFrom(_seller, address(this), _deposit));
        emit Listing(_seller, _deposit, _ipfsHash);
    }
}