Merge pull request #99 from PolymathNetwork/burnable-token

burn securities

Author: pabloruiz55

CHANGELOG.md

@@ -23,7 +23,10 @@ All notable changes to this project will be documented in this file.
 * `takeFee()` new function introduced to extract the POLY token from the factory. It only be called by the owner of the factory.      
 * Added ability for issuer to provide a signed piece of data to allow investors to whitelist themselves.
 * `_securityTokenAddress` get indexed in the `LogNewSecurityToken` event.     
-* Now each investor have its `expiryTime` for the KYC. After the expiryTime limit reached, investor will not abe to use transfer related functions.           
+* Now each investor have its `expiryTime` for the KYC. After the expiryTime limit reached, investor will not abe to use transfer related functions.
+* Transfers of tokens gets paused at the level of all TM as well as on the ST level. To facilitate this 3 functions get added namely
+`pause()`, `unpause()`,`freezeTransfers()`. All 3 functions are called by the issuer of the securityToken only.
+* Security token has got a new feature of burning the tokens, To use this feature user need to call the `burn()` function but before that issuer need to deploy the `TokenBurner` contract and set its address into the SecurityToken contract using the function `setTokenBurner()`.            
 
 ## Remove     
 

contracts/helpers/TokenBurner.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.4.23;
+
+import "../interfaces/ISecurityToken.sol";
+import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
+
+contract TokenBurner {
+
+    address public securityToken;
+
+    constructor (address _securityToken) {
+        securityToken = _securityToken;
+    }
+
+    function burn(address _burner, uint256 _value) public returns(bool) {
+        require(msg.sender == securityToken);
+        // Add the schematics for the burner( token holder) that backing the burning of the securities
+        return true; 
+    }
+
+
+}

contracts/interfaces/IST20.sol

@@ -11,6 +11,9 @@ contract IST20 is StandardToken, DetailedERC20 {
     //transfer, transferFrom must respect use respect the result of verifyTransfer
     function verifyTransfer(address _from, address _to, uint256 _amount) public view returns (bool success);
 
-    //used to create tokens
+    // used to create tokens
     function mint(address _investor, uint256 _amount) public returns (bool success);
+
+    // used to burn the tokens
+    function burn(uint256 _value) public;
 }

contracts/tokens/SecurityToken.sol

@@ -9,7 +9,7 @@ import "../interfaces/IST20.sol";
 import "../modules/TransferManager/ITransferManager.sol";
 import "../modules/PermissionManager/IPermissionManager.sol";
 import "../interfaces/ISecurityTokenRegistry.sol";
-
+import "../helpers/TokenBurner.sol";
 
 /**
 * @title SecurityToken
@@ -23,6 +23,10 @@ contract SecurityToken is ISecurityToken {
     using SafeMath for uint256;
 
     bytes32 public securityTokenVersion = "0.0.1";
+
+    // Reference to token burner contract
+    TokenBurner public tokenBurner;
+
     // Use to halt all the transactions
     bool public freeze = false;
     // Reference to the POLY token.
@@ -51,10 +55,12 @@ contract SecurityToken is ISecurityToken {
         uint256 _timestamp
     );
 
+    event LogUpdateTokenDetails(bytes32 _oldDetails, bytes32 _newDetails);
     event LogGranularityChanged(uint256 _oldGranularity, uint256 _newGranularity);
     event LogModuleRemoved(uint8 indexed _type, address _module, uint256 _timestamp);
     event LogModuleBudgetChanged(uint8 indexed _moduleType, address _module, uint256 _budget);
-    event Mint(address indexed to, uint256 amount);
+    event Minted(address indexed to, uint256 amount);
+    event Burnt(address indexed _burner, uint256 _value);
     event LogFreezeTransfers(bool _freeze, uint256 _timestamp);
 
     //if _fallback is true, then we only allow the module if it is set, if it is not set we only allow the owner
@@ -214,6 +220,15 @@ contract SecurityToken is ISecurityToken {
         emit LogModuleBudgetChanged(_moduleType, modules[_moduleType][_moduleIndex].moduleAddress, _budget);
     }
 
+    /**
+     * @dev change the tokenDetails
+     */
+    function updateTokenDetails(bytes32 _newTokenDetails) public onlyOwner {
+        bytes32 _oldTokenDetails = tokenDetails;
+        tokenDetails = _newTokenDetails;
+        emit LogUpdateTokenDetails(_oldTokenDetails, tokenDetails);
+    }
+
     /**
     * @dev allows owner to change token granularity
     */
@@ -310,7 +325,7 @@ contract SecurityToken is ISecurityToken {
         require(verifyTransfer(address(0), _investor, _amount), "Transfer is not valid");
         totalSupply_ = totalSupply_.add(_amount);
         balances[_investor] = balances[_investor].add(_amount);
-        emit Mint(_investor, _amount);
+        emit Minted(_investor, _amount);
         emit Transfer(address(0), _investor, _amount);
         return true;
     }
@@ -329,4 +344,21 @@ contract SecurityToken is ISecurityToken {
             }
         }
     }
+
+    function setTokenBurner(address _tokenBurner) public onlyOwner {
+        tokenBurner = TokenBurner(_tokenBurner);
+    }
+
+    function burn(uint256 _value) checkGranularity(_value) public {
+        require(tokenBurner != address(0), "Token Burner contract address is not set yet");
+        require(_value <= balances[msg.sender], "Value should no be greater than the balance of msg.sender");
+        // no need to require value <= totalSupply, since that would imply the
+        // sender's balance is greater than the totalSupply, which *should* be an assertion failure
+
+        balances[msg.sender] = balances[msg.sender].sub(_value);
+        require(tokenBurner.burn(msg.sender, _value), "Token burner process is not validated");
+        totalSupply_ = totalSupply_.sub(_value);
+        emit Burnt(msg.sender, _value);
+        emit Transfer(msg.sender, address(0), _value);
+    }
 }

test/security_token.js

@@ -15,6 +15,7 @@ const GeneralTransferManager = artifacts.require('./GeneralTransferManager');
 const GeneralPermissionManager = artifacts.require('./GeneralPermissionManager');
 const PolyToken = artifacts.require('./PolyToken.sol');
 const PolyTokenFaucet = artifacts.require('./helpers/contracts/PolyTokenFaucet.sol');
+const TokenBurner = artifacts.require('./TokenBurner.sol');
 
 const Web3 = require('web3');
 const BigNumber = require('bignumber.js');
@@ -56,6 +57,7 @@ contract('SecurityToken', accounts => {
     let I_SecurityToken;
     let I_CappedSTO;
     let I_PolyToken;
+    let I_TokenBurner;
 
     // SecurityToken Details (Launched ST on the behalf of the issuer)
     const swarmHash = "dagwrgwgvwergwrvwrg";
@@ -684,6 +686,32 @@ contract('SecurityToken', accounts => {
                 console.log(await I_SecurityToken.balanceOf(account_investor1));
                 await I_SecurityToken.transfer(account_investor1, web3.utils.toWei('1', 'ether'), {from: account_temp});
            });
+
+           it("Should fail to call the burn the tokens because token burner contract is not set", async() => {
+                // Deploy the token burner contract
+                I_TokenBurner = await TokenBurner.new(I_SecurityToken.address, { from: token_owner });
+
+                let errorThrown = false;
+                try {
+                    await I_SecurityToken.burn(web3.utils.toWei('1', 'ether'),{ from: account_temp });
+                } catch(error) {
+                   console.log('failed in calling burn function because token burner contract is not set');
+                   errorThrown = true;
+                   ensureException(error);
+               }
+               assert.ok(errorThrown, message);
+           });
+
+           it("Should burn the tokens", async ()=> {
+                // Deploy the token burner contract
+                I_TokenBurner = await TokenBurner.new(I_SecurityToken.address, { from: token_owner });
+
+                await I_SecurityToken.setTokenBurner(I_TokenBurner.address, { from: token_owner });
+                assert.equal(await I_SecurityToken.tokenBurner.call(), I_TokenBurner.address);
+        
+                let tx = await I_SecurityToken.burn(web3.utils.toWei('1', 'ether'),{ from: account_temp });
+                assert.equal(tx.logs[0].args._value, web3.utils.toWei('1', 'ether'));
+           });
     });
 
   });