Contract Source Code:
File 1 of 1 : SmartToken
pragma solidity ^0.4.18;
/*
Utilities & Common Modifiers
*/
contract Utils {
/**
constructor
*/
function Utils() public {
}
// verifies that an amount is greater than zero
modifier greaterThanZero(uint256 _amount) {
require(_amount > 0);
_;
}
// validates an address - currently only checks that it isn't null
modifier validAddress(address _address) {
require(_address != address(0));
_;
}
// verifies that the address is different than this contract address
modifier notThis(address _address) {
require(_address != address(this));
_;
}
// Overflow protected math functions
/**
@dev returns the sum of _x and _y, asserts if the calculation overflows
@param _x value 1
@param _y value 2
@return sum
*/
function safeAdd(uint256 _x, uint256 _y) internal pure returns (uint256) {
uint256 z = _x + _y;
assert(z >= _x);
return z;
}
/**
@dev returns the difference of _x minus _y, asserts if the subtraction results in a negative number
@param _x minuend
@param _y subtrahend
@return difference
*/
function safeSub(uint256 _x, uint256 _y) internal pure returns (uint256) {
assert(_x >= _y);
return _x - _y;
}
/**
@dev returns the product of multiplying _x by _y, asserts if the calculation overflows
@param _x factor 1
@param _y factor 2
@return product
*/
function safeMul(uint256 _x, uint256 _y) internal pure returns (uint256) {
uint256 z = _x * _y;
assert(_x == 0 || z / _x == _y);
return z;
}
}
/*
ERC20 Standard Token interface
*/
contract IERC20Token {
// these functions aren't abstract since the compiler emits automatically generated getter functions as external
function name() public view returns (string) {}
function symbol() public view returns (string) {}
function decimals() public view returns (uint8) {}
function totalSupply() public view returns (uint256) {}
function balanceOf(address _owner) public view returns (uint256) { _owner; }
function allowance(address _owner, address _spender) public view returns (uint256) { _owner; _spender; }
function transfer(address _to, uint256 _value) public returns (bool success);
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
function approve(address _spender, uint256 _value) public returns (bool success);
}
/**
ERC20 Standard Token implementation
*/
contract ERC20Token is IERC20Token, Utils {
string public standard = 'Token 0.1';
string public name = '';
string public symbol = '';
uint8 public decimals = 0;
uint256 public totalSupply = 0;
mapping (address => uint256) public balanceOf;
mapping (address => mapping (address => uint256)) public allowance;
event Transfer(address indexed _from, address indexed _to, uint256 _value);
event Approval(address indexed _owner, address indexed _spender, uint256 _value);
/**
@dev constructor
@param _name token name
@param _symbol token symbol
@param _decimals decimal points, for display purposes
*/
function ERC20Token(string _name, string _symbol, uint8 _decimals) public {
require(bytes(_name).length > 0 && bytes(_symbol).length > 0); // validate input
name = _name;
symbol = _symbol;
decimals = _decimals;
}
/**
@dev send coins
throws on any error rather then return a false flag to minimize user errors
@param _to target address
@param _value transfer amount
@return true if the transfer was successful, false if it wasn't
*/
function transfer(address _to, uint256 _value)
public
validAddress(_to)
returns (bool success)
{
balanceOf[msg.sender] = safeSub(balanceOf[msg.sender], _value);
balanceOf[_to] = safeAdd(balanceOf[_to], _value);
Transfer(msg.sender, _to, _value);
return true;
}
/**
@dev an account/contract attempts to get the coins
throws on any error rather then return a false flag to minimize user errors
@param _from source address
@param _to target address
@param _value transfer amount
@return true if the transfer was successful, false if it wasn't
*/
function transferFrom(address _from, address _to, uint256 _value)
public
validAddress(_from)
validAddress(_to)
returns (bool success)
{
allowance[_from][msg.sender] = safeSub(allowance[_from][msg.sender], _value);
balanceOf[_from] = safeSub(balanceOf[_from], _value);
balanceOf[_to] = safeAdd(balanceOf[_to], _value);
Transfer(_from, _to, _value);
return true;
}
/**
@dev allow another account/contract to spend some tokens on your behalf
throws on any error rather then return a false flag to minimize user errors
also, to minimize the risk of the approve/transferFrom attack vector
(see https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/), approve has to be called twice
in 2 separate transactions - once to change the allowance to 0 and secondly to change it to the new allowance value
@param _spender approved address
@param _value allowance amount
@return true if the approval was successful, false if it wasn't
*/
function approve(address _spender, uint256 _value)
public
validAddress(_spender)
returns (bool success)
{
// if the allowance isn't 0, it can only be updated to 0 to prevent an allowance change immediately after withdrawal
require(_value == 0 || allowance[msg.sender][_spender] == 0);
allowance[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}
}
/*
Owned contract interface
*/
contract IOwned {
// this function isn't abstract since the compiler emits automatically generated getter functions as external
function owner() public view returns (address) {}
function transferOwnership(address _newOwner) public;
function acceptOwnership() public;
}
/*
Provides support and utilities for contract ownership
*/
contract Owned is IOwned {
address public owner;
address public newOwner;
event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);
/**
@dev constructor
*/
function Owned() public {
owner = msg.sender;
}
// allows execution by the owner only
modifier ownerOnly {
assert(msg.sender == owner);
_;
}
/**
@dev allows transferring the contract ownership
the new owner still needs to accept the transfer
can only be called by the contract owner
@param _newOwner new contract owner
*/
function transferOwnership(address _newOwner) public ownerOnly {
require(_newOwner != owner);
newOwner = _newOwner;
}
/**
@dev used by a new owner to accept an ownership transfer
*/
function acceptOwnership() public {
require(msg.sender == newOwner);
OwnerUpdate(owner, newOwner);
owner = newOwner;
newOwner = address(0);
}
}
/*
Token Holder interface
*/
contract ITokenHolder is IOwned {
function withdrawTokens(IERC20Token _token, address _to, uint256 _amount) public;
}
/*
We consider every contract to be a 'token holder' since it's currently not possible
for a contract to deny receiving tokens.
The TokenHolder's contract sole purpose is to provide a safety mechanism that allows
the owner to send tokens that were sent to the contract by mistake back to their sender.
*/
contract TokenHolder is ITokenHolder, Owned, Utils {
/**
@dev constructor
*/
function TokenHolder() public {
}
/**
@dev withdraws tokens held by the contract and sends them to an account
can only be called by the owner
@param _token ERC20 token contract address
@param _to account to receive the new amount
@param _amount amount to withdraw
*/
function withdrawTokens(IERC20Token _token, address _to, uint256 _amount)
public
ownerOnly
validAddress(_token)
validAddress(_to)
notThis(_to)
{
assert(_token.transfer(_to, _amount));
}
}
/*
Smart Token interface
*/
contract ISmartToken is IOwned, IERC20Token {
function disableTransfers(bool _disable) public;
function issue(address _to, uint256 _amount) public;
function destroy(address _from, uint256 _amount) public;
}
/*
Smart Token v0.3
'Owned' is specified here for readability reasons
*/
contract SmartToken is ISmartToken, Owned, ERC20Token, TokenHolder {
string public version = '0.3';
bool public transfersEnabled = true; // true if transfer/transferFrom are enabled, false if not
// triggered when a smart token is deployed - the _token address is defined for forward compatibility, in case we want to trigger the event from a factory
event NewSmartToken(address _token);
// triggered when the total supply is increased
event Issuance(uint256 _amount);
// triggered when the total supply is decreased
event Destruction(uint256 _amount);
/**
@dev constructor
@param _name token name
@param _symbol token short symbol, minimum 1 character
@param _decimals for display purposes only
*/
function SmartToken(string _name, string _symbol, uint8 _decimals)
public
ERC20Token(_name, _symbol, _decimals)
{
NewSmartToken(address(this));
}
// allows execution only when transfers aren't disabled
modifier transfersAllowed {
assert(transfersEnabled);
_;
}
/**
@dev disables/enables transfers
can only be called by the contract owner
@param _disable true to disable transfers, false to enable them
*/
function disableTransfers(bool _disable) public ownerOnly {
transfersEnabled = !_disable;
}
/**
@dev increases the token supply and sends the new tokens to an account
can only be called by the contract owner
@param _to account to receive the new amount
@param _amount amount to increase the supply by
*/
function issue(address _to, uint256 _amount)
public
ownerOnly
validAddress(_to)
notThis(_to)
{
totalSupply = safeAdd(totalSupply, _amount);
balanceOf[_to] = safeAdd(balanceOf[_to], _amount);
Issuance(_amount);
Transfer(this, _to, _amount);
}
/**
@dev removes tokens from an account and decreases the token supply
can be called by the contract owner to destroy tokens from any account or by any holder to destroy tokens from his/her own account
@param _from account to remove the amount from
@param _amount amount to decrease the supply by
*/
function destroy(address _from, uint256 _amount) public {
require(msg.sender == _from || msg.sender == owner); // validate input
balanceOf[_from] = safeSub(balanceOf[_from], _amount);
totalSupply = safeSub(totalSupply, _amount);
Transfer(_from, this, _amount);
Destruction(_amount);
}
// ERC20 standard method overrides with some extra functionality
/**
@dev send coins
throws on any error rather then return a false flag to minimize user errors
in addition to the standard checks, the function throws if transfers are disabled
@param _to target address
@param _value transfer amount
@return true if the transfer was successful, false if it wasn't
*/
function transfer(address _to, uint256 _value) public transfersAllowed returns (bool success) {
assert(super.transfer(_to, _value));
return true;
}
/**
@dev an account/contract attempts to get the coins
throws on any error rather then return a false flag to minimize user errors
in addition to the standard checks, the function throws if transfers are disabled
@param _from source address
@param _to target address
@param _value transfer amount
@return true if the transfer was successful, false if it wasn't
*/
function transferFrom(address _from, address _to, uint256 _value) public transfersAllowed returns (bool success) {
assert(super.transferFrom(_from, _to, _value));
return true;
}
}