Graph: Round-off error buffer (#111)

* Upgrade packages

* Graph: Round-off errors

* Graph: Integration test for round-off

Author: reubenr0d

contracts/tenderizer/integrations/graph/Graph.sol

@@ -131,8 +131,16 @@ contract Graph is Tenderizer {
         } else {
             // Check that gov withdrawal for that unstake has occured
             require(_unstakeLockID < governanceLastProcessedUnstakeLockID, "GOV_WITHDRAW_PENDING");
+            
             // Transfer amount from unbondingLock to _account
-            steak.transfer(_account, amount);
+            try steak.transfer(_account, amount) {
+            } catch {
+                // Account for roundoff errors in shares calculations
+                uint256 steakBal = steak.balanceOf(address(this));
+                if (amount > steakBal) { 
+                    steak.transfer(_account, steakBal); 
+                }
+            }
         }
 
         emit Withdraw(account, amount, _unstakeLockID);

test/integration/graph.test.ts

@@ -472,6 +472,35 @@ describe('Graph Integration Test', () => {
       it('should emit Withdraw event from Tenderizer', async () => {
         expect(tx).to.emit(Tenderizer, 'Withdraw').withArgs(deployer, withdrawAmount, unbondLockID)
       })
+
+      it('should withdraw tenderizer GRT balance if < requested amount', async () => {
+        await Controller.connect(signers[2]).unlock(secondDeposit)
+        let txData = ethers.utils.arrayify(Tenderizer.interface.encodeFunctionData('unstake',
+          [Controller.address, ethers.utils.parseEther('0')]))
+        await Controller.execute(Tenderizer.address, 0, txData)
+        txData = txData = ethers.utils.arrayify(Tenderizer.interface.encodeFunctionData('withdraw',
+          [Controller.address, 3]))
+        await Controller.execute(Tenderizer.address, 0, txData)
+        const amountToBurn = (await GraphToken.balanceOf(Tenderizer.address)).sub(secondDeposit).add(1)
+        await hre.network.provider.request({
+          method: 'hardhat_impersonateAccount',
+          params: [Tenderizer.address]
+        }
+        )
+        const signer = await ethers.provider.getSigner(Tenderizer.address)
+        await hre.network.provider.send('hardhat_setBalance', [
+          Tenderizer.address,
+          `0x${ethers.utils.parseEther('10')}`
+        ])
+        await GraphToken.connect(signer).transfer(deployer, amountToBurn)
+        await hre.network.provider.request({
+          method: 'hardhat_stopImpersonatingAccount',
+          params: [Tenderizer.address]
+        }
+        )
+        await Controller.connect(signers[2]).withdraw(2)
+        expect(await GraphToken.balanceOf(signers[2].address)).to.eq(secondDeposit.sub(1))
+      })
     })
   })