From df9ec7cafdbe60f227c0caddd82b9f6a5e1f50bb Mon Sep 17 00:00:00 2001
From: Greg Hysen <greg.hysen@gmail.com>
Date: Thu, 14 Mar 2019 13:38:16 -0700
Subject: [PATCH] Do not revert if value or amount are zero. Only if amount is
 non-zero and there is an overflow.

---
 .../contracts/src/ERC1155Proxy.sol            | 23 ++++---------
 contracts/asset-proxy/test/erc1155_proxy.ts   | 33 -------------------
 packages/types/src/index.ts                   |  2 --
 3 files changed, 7 insertions(+), 51 deletions(-)

diff --git a/contracts/asset-proxy/contracts/src/ERC1155Proxy.sol b/contracts/asset-proxy/contracts/src/ERC1155Proxy.sol
index 57862138e0..c847d07779 100644
--- a/contracts/asset-proxy/contracts/src/ERC1155Proxy.sol
+++ b/contracts/asset-proxy/contracts/src/ERC1155Proxy.sol
@@ -176,7 +176,7 @@ contract ERC1155Proxy is
                 )
 
                 ////////// STEP 2/4 //////////
-                let scaleAmount := calldataload(100)
+                let amount := calldataload(100)
                 let valuesOffset := add(mload(100), 4) // add 4 for calldata offset
                 let valuesLengthInBytes := mul(
                     mload(valuesOffset),
@@ -190,22 +190,13 @@ contract ERC1155Proxy is
                 {
                     // Load token value and generate scaled value
                     let tokenValue := mload(tokenValueOffset)
-                    let scaledTokenValue := mul(tokenValue, scaleAmount)
-                    
-                    // Check if scaled value is zero
-                    if iszero(scaledTokenValue) {
-                        // Revert with `Error("TRANSFER_GREATER_THAN_ZERO_REQUIRED")`
-                        mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
-                        mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
-                        mstore(64, 0x000000235452414e534645525f475245415445525f5448414e5f5a45524f5f52)
-                        mstore(96, 0x4551554952454400000000000000000000000000000000000000000000000000)
-                        mstore(128, 0)
-                        revert(0, 132)
-                    }
+                    let scaledTokenValue := mul(tokenValue, amount)
 
-                    // Check for multiplication overflow
-                    let expectedTokenValue := div(scaledTokenValue, scaleAmount)
-                    if iszero(eq(expectedTokenValue, tokenValue)) {
+                    // Revert if `amount` != 0 and multiplication resulted in an overflow
+                    if iszero(or(
+                        iszero(amount),
+                        eq(div(scaledTokenValue, amount), tokenValue)
+                    )) {
                         // Revert with `Error("UINT256_OVERFLOW")`
                         mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                         mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
diff --git a/contracts/asset-proxy/test/erc1155_proxy.ts b/contracts/asset-proxy/test/erc1155_proxy.ts
index 01368f7833..e69bfb6900 100644
--- a/contracts/asset-proxy/test/erc1155_proxy.ts
+++ b/contracts/asset-proxy/test/erc1155_proxy.ts
@@ -540,39 +540,6 @@ describe('ERC1155Proxy', () => {
                 RevertReason.NFTNotOwnedByFromAddress,
             );
         });
-        it('should revert if tansferring 0 amount of any token', async () => {
-            // setup test parameters
-            const tokenHolders = [spender, receiver];
-            const tokensToTransfer = nonFungibleTokensOwnedBySpender.slice(0, 3);
-            const valuesToTransfer = [nonFungibleValueToTransfer, new BigNumber(0), nonFungibleValueToTransfer];
-            const perUnitValue = perUnitValueNft;
-            // check balances before transfer
-            const expectedInitialBalances = [
-                // spender
-                nftOwnerBalance,
-                nftOwnerBalance,
-                nftOwnerBalance,
-                // receiver
-                nftNotOwnerBalance,
-                nftNotOwnerBalance,
-                nftNotOwnerBalance,
-            ];
-            await erc1155Wrapper.assertBalancesAsync(tokenHolders, tokensToTransfer, expectedInitialBalances);
-            // execute transfer
-            await expectTransactionFailedAsync(
-                erc1155ProxyWrapper.transferFromAsync(
-                    spender,
-                    receiver,
-                    erc1155Contract.address,
-                    tokensToTransfer,
-                    valuesToTransfer,
-                    perUnitValue,
-                    receiverCallbackData,
-                    authorized,
-                ),
-                RevertReason.TransferGreaterThanZeroRequired,
-            );
-        });
         it('should revert if there is a multiplication overflow', async () => {
             // setup test parameters
             const tokenHolders = [spender, receiver];
diff --git a/packages/types/src/index.ts b/packages/types/src/index.ts
index 49bf741e48..23cc118b2e 100644
--- a/packages/types/src/index.ts
+++ b/packages/types/src/index.ts
@@ -309,8 +309,6 @@ export enum RevertReason {
     TriedToMintNonFungibleForFungibleToken = 'TRIED_TO_MINT_NON_FUNGIBLE_FOR_FUNGIBLE_TOKEN',
     TransferRejected = 'TRANSFER_REJECTED',
     Uint256Underflow = 'UINT256_UNDERFLOW',
-    // ERC1155 Proxy
-    TransferGreaterThanZeroRequired = 'TRANSFER_GREATER_THAN_ZERO_REQUIRED',
 }
 
 export enum StatusCodes {