Fix decrease allowance and add non-zero address precondition to approve (#1293)

* rename {increase,decrease}Approval to {increase,decrease}Allowance

* add non-zero spender check to approve and {increase,decrease}Allowance

* Updated tests to reflect the new behavior.

* fix wrong test description

* fix old function names

* Fixed linter error.

* Fixed typo.

contracts/token/ERC20/ERC20.sol

@@ -78,6 +78,8 @@ contract ERC20 is IERC20 {
    * @param _value The amount of tokens to be spent.
    */
   function approve(address _spender, uint256 _value) public returns (bool) {
+    require(_spender != address(0));
+
     allowed_[msg.sender][_spender] = _value;
     emit Approval(msg.sender, _spender, _value);
     return true;
@@ -117,13 +119,15 @@ contract ERC20 is IERC20 {
    * @param _spender The address which will spend the funds.
    * @param _addedValue The amount of tokens to increase the allowance by.
    */
-  function increaseApproval(
+  function increaseAllowance(
     address _spender,
     uint256 _addedValue
   )
     public
     returns (bool)
   {
+    require(_spender != address(0));
+
     allowed_[msg.sender][_spender] = (
       allowed_[msg.sender][_spender].add(_addedValue));
     emit Approval(msg.sender, _spender, allowed_[msg.sender][_spender]);
@@ -139,19 +143,17 @@ contract ERC20 is IERC20 {
    * @param _spender The address which will spend the funds.
    * @param _subtractedValue The amount of tokens to decrease the allowance by.
    */
-  function decreaseApproval(
+  function decreaseAllowance(
     address _spender,
     uint256 _subtractedValue
   )
     public
     returns (bool)
   {
-    uint256 oldValue = allowed_[msg.sender][_spender];
-    if (_subtractedValue >= oldValue) {
-      allowed_[msg.sender][_spender] = 0;
-    } else {
-      allowed_[msg.sender][_spender] = oldValue.sub(_subtractedValue);
-    }
+    require(_spender != address(0));
+
+    allowed_[msg.sender][_spender] = (
+      allowed_[msg.sender][_spender].sub(_subtractedValue));
     emit Approval(msg.sender, _spender, allowed_[msg.sender][_spender]);
     return true;
   }

contracts/token/ERC20/ERC20Pausable.sol

@@ -44,7 +44,7 @@ contract ERC20Pausable is ERC20, Pausable {
     return super.approve(_spender, _value);
   }
 
-  function increaseApproval(
+  function increaseAllowance(
     address _spender,
     uint _addedValue
   )
@@ -52,10 +52,10 @@ contract ERC20Pausable is ERC20, Pausable {
     whenNotPaused
     returns (bool success)
   {
-    return super.increaseApproval(_spender, _addedValue);
+    return super.increaseAllowance(_spender, _addedValue);
   }
 
-  function decreaseApproval(
+  function decreaseAllowance(
     address _spender,
     uint _subtractedValue
   )
@@ -63,6 +63,6 @@ contract ERC20Pausable is ERC20, Pausable {
     whenNotPaused
     returns (bool success)
   {
-    return super.decreaseApproval(_spender, _subtractedValue);
+    return super.decreaseAllowance(_spender, _subtractedValue);
   }
 }

test/token/ERC20/ERC20Pausable.test.js

@@ -196,7 +196,7 @@ contract('ERC20Pausable', function ([_, pauser, otherPauser, recipient, anotherA
       });
 
       it('allows to decrease approval when unpaused', async function () {
-        await this.token.decreaseApproval(anotherAccount, 40, { from: pauser });
+        await this.token.decreaseAllowance(anotherAccount, 40, { from: pauser });
 
         (await this.token.allowance(pauser, anotherAccount)).should.be.bignumber.equal(60);
       });
@@ -205,7 +205,7 @@ contract('ERC20Pausable', function ([_, pauser, otherPauser, recipient, anotherA
         await this.token.pause({ from: pauser });
         await this.token.unpause({ from: pauser });
 
-        await this.token.decreaseApproval(anotherAccount, 40, { from: pauser });
+        await this.token.decreaseAllowance(anotherAccount, 40, { from: pauser });
 
         (await this.token.allowance(pauser, anotherAccount)).should.be.bignumber.equal(60);
       });
@@ -213,7 +213,7 @@ contract('ERC20Pausable', function ([_, pauser, otherPauser, recipient, anotherA
       it('reverts when trying to transfer when paused', async function () {
         await this.token.pause({ from: pauser });
 
-        await assertRevert(this.token.decreaseApproval(anotherAccount, 40, { from: pauser }));
+        await assertRevert(this.token.decreaseAllowance(anotherAccount, 40, { from: pauser }));
       });
     });
 
@@ -223,7 +223,7 @@ contract('ERC20Pausable', function ([_, pauser, otherPauser, recipient, anotherA
       });
 
       it('allows to increase approval when unpaused', async function () {
-        await this.token.increaseApproval(anotherAccount, 40, { from: pauser });
+        await this.token.increaseAllowance(anotherAccount, 40, { from: pauser });
 
         (await this.token.allowance(pauser, anotherAccount)).should.be.bignumber.equal(140);
       });
@@ -232,7 +232,7 @@ contract('ERC20Pausable', function ([_, pauser, otherPauser, recipient, anotherA
         await this.token.pause({ from: pauser });
         await this.token.unpause({ from: pauser });
 
-        await this.token.increaseApproval(anotherAccount, 40, { from: pauser });
+        await this.token.increaseAllowance(anotherAccount, 40, { from: pauser });
 
         (await this.token.allowance(pauser, anotherAccount)).should.be.bignumber.equal(140);
       });
@@ -240,7 +240,7 @@ contract('ERC20Pausable', function ([_, pauser, otherPauser, recipient, anotherA
       it('reverts when trying to increase approval when paused', async function () {
         await this.token.pause({ from: pauser });
 
-        await assertRevert(this.token.increaseApproval(anotherAccount, 40, { from: pauser }));
+        await assertRevert(this.token.increaseAllowance(anotherAccount, 40, { from: pauser }));
       });
     });
   });