Ending a Crowdsale Contract Before End time

I have generated a crowdsale contract with start and end date time. I want to add a CROWDSALEend function. This function will end the crowdsale before end time if the goal is reached and the function will only be called by the owner. Below is my code for Crowdsale.

``````pragma solidity ^0.4.18;

contract ERC20Basic {
uint256 public totalSupply;
function balanceOf(address who) public view returns (uint256);
function transfer(address to, uint256 value) public returns (bool);
}

library SafeMath {
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
if (a == 0) {
return 0;
}
uint256 c = a * b;
assert(c / a == b);
return c;
}

function div(uint256 a, uint256 b) internal pure returns (uint256) {
// assert(b > 0); // Solidity automatically throws when dividing by 0
uint256 c = a / b;
// assert(a == b * c + a % b); // There is no case in which this doesn't hold
return c;
}

function sub(uint256 a, uint256 b) internal pure returns (uint256) {
assert(b <= a);
return a - b;
}

function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
assert(c >= a);
return c;
}
}

contract BasicToken is ERC20Basic {
using SafeMath for uint256;

/**
* @dev transfer token for a specified address
* @param _to The address to transfer to.
* @param _value The amount to be transferred.
*/
function transfer(address _to, uint256 _value) public returns (bool) {
require(_value <= balances[msg.sender]);

// SafeMath.sub will throw if there is not enough balance.
balances[msg.sender] = balances[msg.sender].sub(_value);
Transfer(msg.sender, _to, _value);
return true;
}

/**
* @dev Gets the balance of the specified address.
* @param _owner The address to query the the balance of.
* @return An uint256 representing the amount owned by the passed address.
*/
function balanceOf(address _owner) public view returns (uint256 balance) {
return balances[_owner];
}

}

contract ERC20 is ERC20Basic {
function approve(address spender, uint256 value) public returns (bool);
}

contract StandardToken is ERC20, BasicToken {

/**
* @dev Transfer tokens from one address to another
* @param _from address The address which you want to send tokens from
* @param _to address The address which you want to transfer to
* @param _value uint256 the amount of tokens to be transferred
*/
require(_value <= balances[_from]);
require(_value <= allowed[_from][msg.sender]);

balances[_from] = balances[_from].sub(_value);
allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
Transfer(_from, _to, _value);
return true;
}

/**
* @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
*
* Beware that changing an allowance with this method brings the risk that someone may use both the old
* and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
* race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
* @param _spender The address which will spend the funds.
* @param _value The amount of tokens to be spent.
*/
function approve(address _spender, uint256 _value) public returns (bool) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}

/**
* @dev Function to check the amount of tokens that an owner allowed to a spender.
* @return A uint256 specifying the amount of tokens still available for the spender.
*/
return allowed[_owner][_spender];
}

/**
* approve should be called when allowed[_spender] == 0. To increment
* allowed value is better to use this function to avoid 2 calls (and wait until
* the first transaction is mined)
* From MonolithDAO Token.sol
*/
Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
return true;
}

function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
uint oldValue = allowed[msg.sender][_spender];
if (_subtractedValue > oldValue) {
allowed[msg.sender][_spender] = 0;
} else {
allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
}
Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
return true;
}

}

contract TOKKA is StandardToken {
string public name = "EGaming Token";
string public symbol = "GT";
uint256 public decimals = 18;

uint256 constant INITIAL_SUPPLY = 6000000 * 10**18;
function TOKKA () public {
balances[msg.sender] = INITIAL_SUPPLY;
}
}

contract Crowdsale {
using SafeMath for uint256;

// The token being sold
TOKKA public token;

// start and end timestamps where investments are allowed (both inclusive)
uint256 public startTime;
uint256 public endTime;

// address where funds are collected

// how many token units a buyer gets per wei
uint256 public rate;

// amount of raised money in wei
uint256 public weiRaised;

uint256 public CAP = 3000000000000000000;

function Crowdsale(uint256 _startTime, uint256 _endTime, uint256 _rate, address _wallet) public {
require(_startTime >= now);
require(_endTime >= _startTime);
require(_rate > 0);

startTime = _startTime;
endTime = _endTime;
rate = _rate;
wallet = _wallet;
token = createTokenContract();
}

// creates the token to be sold.
// override this method to have crowdsale of a specific mintable token.
function createTokenContract() internal returns (TOKKA) {
return new TOKKA();
}

// fallback function can be used to buy tokens
function () external payable {
}

// low level token purchase function
require(validPurchase());

uint256 weiAmount = msg.value;

// calculate token amount to be created
uint256 tokens = weiAmount.mul(rate);

// update state

// transfer tokens purchased
//ERC20(token).transfer(this, tokens);
//StandardToken(token).transfer(this, tokens);
StandardToken(token).transfer(beneficiary, tokens);

TokenPurchase(msg.sender, beneficiary, weiAmount, tokens);

forwardFunds();
}

function forwardFunds() internal {
wallet.transfer(msg.value);
}

function validPurchase() internal view returns (bool) {
bool withinPeriod = now >= startTime && now <= endTime;
bool nonZeroPurchase = msg.value != 0;
return withinPeriod && nonZeroPurchase;
}

function hasEnded() public view returns (bool) {
return now > endTime;
}

function GoalReached() public view returns (bool) {
return (weiRaised >= CAP);
}

}
``````

Can anyone help me with this. Any help will be appreciated. Thanks

Right now the only function that you have that cares about whether or not the crowdsale has ended is the `buyTokens()` function.
You could add a new state variable `bool hasPrematurelyEnded` and add a function that can only be called by the owner that sets this bool to true.
Then, on `buyTokens()` and other functions that should check this, you could add `require(!hasPrematurelyEnded);`.