Returns byte array instead of memory range for encoding fillOrder calldata

2 files changed, 26 insertions, 24 deletions

diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/MixinWrapperFunctions.sol b/packages/contracts/src/2.0.0/protocol/Exchange/MixinWrapperFunctions.sol
index a5038f5cf..567f26c52 100644
--- a/packages/contracts/src/2.0.0/protocol/Exchange/MixinWrapperFunctions.sol
+++ b/packages/contracts/src/2.0.0/protocol/Exchange/MixinWrapperFunctions.sol
@@ -71,14 +71,10 @@ contract MixinWrapperFunctions is
         returns (FillResults memory fillResults)
     {
         // ABI encode calldata for `fillOrder`
-        (
-            uint256 calldataBegin,
-            uint256 calldataLength
-        ) = abiEncodeFillOrder(
+        bytes memory fillOrderCalldata = abiEncodeFillOrder(
             order,
             takerAssetFillAmount,
-            signature,
-            this.fillOrder.selector
+            signature
         );
 
         // Delegate to `fillOrder` and handle any exceptions gracefully
@@ -86,9 +82,9 @@ contract MixinWrapperFunctions is
             let success := delegatecall(
                 gas,                                // forward all gas, TODO: look into gas consumption of assert/throw
                 address,                            // call address of this contract
-                calldataBegin,                      // pointer to start of input
-                calldataLength,                     // length of input
-                calldataBegin,                      // write output over input
+                add(fillOrderCalldata, 32),         // pointer to start of input (skip array length in first 32 bytes)
+                mload(fillOrderCalldata),           // length of input
+                fillOrderCalldata,                  // write output over input
                 128                                 // output size is 128 bytes
             )
             switch success
@@ -99,10 +95,10 @@ contract MixinWrapperFunctions is
                 mstore(add(fillResults, 96), 0)
             }
             case 1 {
-                mstore(fillResults, mload(calldataBegin))
-                mstore(add(fillResults, 32), mload(add(calldataBegin, 32)))
-                mstore(add(fillResults, 64), mload(add(calldataBegin, 64)))
-                mstore(add(fillResults, 96), mload(add(calldataBegin, 96)))
+                mstore(fillResults, mload(fillOrderCalldata))
+                mstore(add(fillResults, 32), mload(add(fillOrderCalldata, 32)))
+                mstore(add(fillResults, 64), mload(add(fillOrderCalldata, 64)))
+                mstore(add(fillResults, 96), mload(add(fillOrderCalldata, 96)))
             }
         }
         return fillResults;
diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibAbiEncoder.sol b/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibAbiEncoder.sol
index 5bea607d6..507e69712 100644
--- a/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibAbiEncoder.sol
+++ b/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibAbiEncoder.sol
@@ -23,6 +23,10 @@ import "./LibOrder.sol";
 
 
 contract LibAbiEncoder {
+
+    // solhint-disable max-line-length
+    bytes4 constant internal FILL_ORDER_SELECTOR = bytes4(keccak256("fillOrder((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),uint256,bytes)"));
+    // solhint-enable max-line-length
    
     /// @dev ABI encodes calldata for `fillOrder` in memory and returns the address range.
     ///      This range can be passed into `call` or `delegatecall` to invoke an external
@@ -35,14 +39,10 @@ contract LibAbiEncoder {
     function abiEncodeFillOrder(
         LibOrder.Order memory order,
         uint256 takerAssetFillAmount,
-        bytes memory signature,
-        bytes4 fillOrderSelector
+        bytes memory signature
     )
         public
-        returns (
-            uint256 calldataBegin,
-            uint256 calldataLength
-        )
+        returns (bytes memory fillOrderCalldata)
     {
         // We need to call MExchangeCore.fillOrder using a delegatecall in
         // assembly so that we can intercept a call that throws. For this, we
@@ -83,6 +83,8 @@ contract LibAbiEncoder {
 
         // [1]: https://solidity.readthedocs.io/en/develop/abi-spec.html
 
+        bytes4 fillOrderSelector = FILL_ORDER_SELECTOR;
+
         assembly {
 
             // Areas below may use the following variables:
@@ -96,9 +98,10 @@ contract LibAbiEncoder {
 
             /////// Setup Header Area ///////
             // Load free memory pointer
-            calldataBegin := mload(0x40)
-            mstore(calldataBegin, fillOrderSelector)
-            let headerAreaEnd := add(calldataBegin, 0x4)
+            fillOrderCalldata := mload(0x40)
+            // Leave 0x20 bytes to store the length
+            mstore(add(fillOrderCalldata, 0x20), fillOrderSelector)
+            let headerAreaEnd := add(fillOrderCalldata, 0x24)
 
             /////// Setup Params Area ///////
             // This area is preallocated and written to later.
@@ -207,9 +210,12 @@ contract LibAbiEncoder {
             }
 
             // Set length of calldata
-            calldataLength := sub(dataAreaEnd, calldataBegin)
+            mstore(
+                fillOrderCalldata,
+                sub(dataAreaEnd, add(fillOrderCalldata, 0x20))
+            )
         }
 
-        return (calldataBegin, calldataLength);
+        return fillOrderCalldata;
     }
 }