The goal is to make a crowdsale smart contract where investors can buy tokens (no cap, no initial supply, all tokens are minted) and sell them to a contract for some price (rate in my case). And I want to burn automatically these tokens after the sale.
I used openzeppelin library, here is a token:
pragma solidity ^0.4.24;
import "./DetailedERC20.sol";
import "./MintableToken.sol";
import "./BurnableToken.sol";
contract myToken is DetailedERC20, MintableToken, BurnableToken {
constructor(
string _name,
string _symbol,
uint8 _decimals
)
DetailedERC20(_name, _symbol, _decimals)
public
{
}
}
The crowdsale contract:
pragma solidity ^0.4.24;
import './Crowdsale.sol';
import './MintedCrowdsale.sol';
import './Ownable.sol';
contract myCrowdsale is Crowdsale, MintedCrowdsale, Ownable {
constructor(uint256 _rate, address _wallet, ERC20 _token) Crowdsale(_rate, _wallet, _token) public {
}
function setRate(uint256 newRate) onlyOwner public {
rate = newRate;
}
}
Crowdsale.sol where I'm trying to implement sellTokens function (we need to transfer ether back to an investor and burn tokens):
pragma solidity ^0.4.24;
import "./ERC20.sol";
import "./SafeMath.sol";
import "./SafeERC20.sol";
import "./BurnableToken.sol";
/**
* @title Crowdsale
* @dev Crowdsale is a base contract for managing a token crowdsale,
* allowing investors to purchase tokens with ether. This contract implements
* such functionality in its most fundamental form and can be extended to provide additional
* functionality and/or custom behavior.
* The external interface represents the basic interface for purchasing tokens, and conform
* the base architecture for crowdsales. They are *not* intended to be modified / overridden.
* The internal interface conforms the extensible and modifiable surface of crowdsales. Override
* the methods to add functionality. Consider using 'super' where appropriate to concatenate
* behavior.
*/
contract Crowdsale is BurnableToken {
using SafeMath for uint256;
using SafeERC20 for ERC20;
// The token being sold
ERC20 public token;
// Address where funds are collected
address public wallet;
// How many token units a buyer gets per wei.
// The rate is the conversion between wei and the smallest and indivisible token unit.
// So, if you are using a rate of 1 with a DetailedERC20 token with 3 decimals called TOK
// 1 wei will give you 1 unit, or 0.001 TOK.
uint256 public rate;
// Amount of wei raised
uint256 public weiRaised;
/**
* Event for token purchase logging
* @param purchaser who paid for the tokens
* @param beneficiary who got the tokens
* @param value weis paid for purchase
* @param amount amount of tokens purchased
*/
event TokenPurchase(
address indexed purchaser,
address indexed beneficiary,
uint256 value,
uint256 amount
);
/**
* @param _rate Number of token units a buyer gets per wei
* @param _wallet Address where collected funds will be forwarded to
* @param _token Address of the token being sold
*/
constructor(uint256 _rate, address _wallet, ERC20 _token) public {
require(_rate > 0);
require(_wallet != address(0));
require(_token != address(0));
rate = _rate;
wallet = _wallet;
token = _token;
}
// -----------------------------------------
// Crowdsale external interface
// -----------------------------------------
/**
* @dev fallback function ***DO NOT OVERRIDE***
*/
function () external payable {
buyTokens(msg.sender);
}
/**
* @dev low level token purchase ***DO NOT OVERRIDE***
* @param _beneficiary Address performing the token purchase
*/
function buyTokens(address _beneficiary) public payable {
uint256 weiAmount = msg.value;
_preValidatePurchase(_beneficiary, weiAmount);
// calculate token amount to be created
uint256 tokens = _getTokenAmount(weiAmount);
// update state
weiRaised = weiRaised.add(weiAmount);
_processPurchase(_beneficiary, tokens);
emit TokenPurchase(
msg.sender,
_beneficiary,
weiAmount,
tokens
);
_updatePurchasingState(_beneficiary, weiAmount);
_forwardFunds();
_postValidatePurchase(_beneficiary, weiAmount);
}
function sellTokens(uint256 amount) public {
uint256 weiAmount = amount.mul(rate);
address myAddress = address(this);
require(myAddress.balance >= weiAmount);
weiRaised = weiRaised.sub(weiAmount);
burn(amount);
}
// -----------------------------------------
// Internal interface (extensible)
// -----------------------------------------
/**
* @dev Validation of an incoming purchase. Use require statements to revert state when conditions are not met. Use `super` in contracts that inherit from Crowdsale to extend their validations.
* Example from CappedCrowdsale.sol's _preValidatePurchase method:
* super._preValidatePurchase(_beneficiary, _weiAmount);
* require(weiRaised.add(_weiAmount) <= cap);
* @param _beneficiary Address performing the token purchase
* @param _weiAmount Value in wei involved in the purchase
*/
function _preValidatePurchase(
address _beneficiary,
uint256 _weiAmount
)
internal
{
require(_beneficiary != address(0));
require(_weiAmount != 0);
}
/**
* @dev Validation of an executed purchase. Observe state and use revert statements to undo rollback when valid conditions are not met.
* @param _beneficiary Address performing the token purchase
* @param _weiAmount Value in wei involved in the purchase
*/
function _postValidatePurchase(
address _beneficiary,
uint256 _weiAmount
)
internal
{
// optional override
}
/**
* @dev Source of tokens. Override this method to modify the way in which the crowdsale ultimately gets and sends its tokens.
* @param _beneficiary Address performing the token purchase
* @param _tokenAmount Number of tokens to be emitted
*/
function _deliverTokens(
address _beneficiary,
uint256 _tokenAmount
)
internal
{
token.safeTransfer(_beneficiary, _tokenAmount);
}
/**
* @dev Executed when a purchase has been validated and is ready to be executed. Not necessarily emits/sends tokens.
* @param _beneficiary Address receiving the tokens
* @param _tokenAmount Number of tokens to be purchased
*/
function _processPurchase(
address _beneficiary,
uint256 _tokenAmount
)
internal
{
_deliverTokens(_beneficiary, _tokenAmount);
}
/**
* @dev Override for extensions that require an internal state to check for validity (current user contributions, etc.)
* @param _beneficiary Address receiving the tokens
* @param _weiAmount Value in wei involved in the purchase
*/
function _updatePurchasingState(
address _beneficiary,
uint256 _weiAmount
)
internal
{
// optional override
}
/**
* @dev Override to extend the way in which ether is converted to tokens.
* @param _weiAmount Value in wei to be converted into tokens
* @return Number of tokens that can be purchased with the specified _weiAmount
*/
function _getTokenAmount(uint256 _weiAmount)
internal view returns (uint256)
{
return _weiAmount.mul(rate);
}
/**
* @dev Determines how ETH is stored/forwarded on purchases.
*/
function _forwardFunds() internal {
wallet.transfer(msg.value);
}
}
So, something goes wrong in this case. What the simplest way to make this work?
