Merge branch 'v2-prototype' into feature/combinatorial-testing

* v2-prototype:
  Improve 'web3-provider-engine' typings
  Fix build
  Update artifacts
  Add more revert reasons to tests
  Make dispatchTransferFrom revert with reason from AssetProxy on failure
  Remove redundant files, hard code function selector in dispatchTransferFrom, and modify revert reason
  Updated offset of receiverData length to reflect new assetData encoding.
  ERC20 Custom storage layout
  Golf the authorization check
  ERC20 manual memory layout
  ERC20 inline return
  ERC721 inline return
  Golf ERC721 transferFrom
  Inline ERC20 tranferFrom selector constant
  Optimize ERC20 transferFrom
  Polish asset picker layout
  Update relayer grid fallback icon
  Change metamask install link based on browser
  Use ethereumjs-tx@1.3.5 instead of our fork

# Conflicts:
#	packages/contracts/test/asset_proxy/proxies.ts
#	packages/contracts/test/exchange/core.ts
#	packages/migrations/artifacts/2.0.0/DummyERC721Token.json

12 files changed, 312 insertions, 517 deletions

diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol
index b74d2c231..b4780b52b 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol
@@ -20,17 +20,140 @@ pragma solidity ^0.4.24;
 pragma experimental ABIEncoderV2;
 
 import "../../utils/LibBytes/LibBytes.sol";
-import "./MixinAssetProxy.sol";
+import "./interfaces/IAssetProxy.sol";
 import "./MixinAuthorizable.sol";
-import "./MixinERC20Transfer.sol";
 
 contract ERC20Proxy is
-    MixinAssetProxy,
-    MixinAuthorizable,
-    MixinERC20Transfer
+    IAssetProxy,
+    MixinAuthorizable
 {
     // Id of this proxy.
     bytes4 constant PROXY_ID = bytes4(keccak256("ERC20Token(address)"));
+    
+    /// @dev Internal version of `transferFrom`.
+    /// @param assetData Encoded byte array.
+    /// @param from Address to transfer asset from.
+    /// @param to Address to transfer asset to.
+    /// @param amount Amount of asset to transfer.
+    function transferFrom(
+        bytes assetData,
+        address from,
+        address to,
+        uint256 amount
+    )
+        external
+    {
+        require(
+            authorized[msg.sender],
+            "SENDER_NOT_AUTHORIZED"
+        );
+
+        // `transferFrom`.
+        // The function is marked `external`, so no abi decodeding is done for
+        // us. Instead, we expect the `calldata` memory to contain the
+        // following:
+        //
+        // | Area     | Offset | Length  | Contents                            |
+        // |----------|--------|---------|-------------------------------------|
+        // | Header   | 0      | 4       | function selector                   |
+        // | Params   |        | 4 * 32  | function parameters:                |
+        // |          | 4      |         |   1. offset to assetData (*)        |
+        // |          | 36     |         |   2. from                           |
+        // |          | 68     |         |   3. to                             |
+        // |          | 100    |         |   4. amount                         |
+        // | Data     |        |         | assetData:                          |
+        // |          | 132    | 32      | assetData Length                    |
+        // |          | 164    | **      | assetData Contents                  |
+        //
+        // (*): offset is computed from start of function parameters, so offset
+        //      by an additional 4 bytes in the calldata.
+        //
+        // WARNING: The ABIv2 specification allows additional padding between
+        //          the Params and Data section. This will result in a larger
+        //          offset to assetData.
+        
+        // Asset data itself is encoded as follows:
+        //
+        // | Area     | Offset | Length  | Contents                            |
+        // |----------|--------|---------|-------------------------------------|
+        // | Header   | 0      | 4       | function selector                   |
+        // | Params   |        | 1 * 32  | function parameters:                |
+        // |          | 4      | 12 + 20 |   1. token address                  |
+        
+        // Transfer tokens.
+        // We do a raw call so we can check the success separate
+        // from the return data.
+        // We construct calldata for the `token.transferFrom` ABI.
+        // The layout of this calldata is in the table below.
+        // 
+        // | Area     | Offset | Length  | Contents                            |
+        // |----------|--------|---------|-------------------------------------|
+        // | Header   | 0      | 4       | function selector                   |
+        // | Params   |        | 3 * 32  | function parameters:                |
+        // |          | 4      |         |   1. from                           |
+        // |          | 36     |         |   2. to                             |
+        // |          | 68     |         |   3. amount                         |
+        
+        assembly {
+            /////// Token contract address ///////
+            // The token address is found as follows:
+            // * It is stored at offset 4 in `assetData` contents.
+            // * This is stored at offset 32 from `assetData`.
+            // * The offset to `assetData` from Params is stored at offset
+            //   4 in calldata.
+            // * The offset of Params in calldata is 4.
+            // So we read location 4 and add 32 + 4 + 4 to it.
+            let token := calldataload(add(calldataload(4), 40))
+            
+            /////// Setup Header Area ///////
+            // This area holds the 4-byte `transferFrom` selector.
+            // Any trailing data in transferFromSelector will be
+            // overwritten in the next `mstore` call.
+            mstore(0, 0x23b872dd00000000000000000000000000000000000000000000000000000000)
+            
+            /////// Setup Params Area ///////
+            // We copy the fields `from`, `to` and `amount` in bulk
+            // from our own calldata to the new calldata.
+            calldatacopy(4, 36, 96)
+
+            /////// Call `token.transferFrom` using the calldata ///////
+            let success := call(
+                gas,            // forward all gas
+                token,          // call address of token contract
+                0,              // don't send any ETH
+                0,              // pointer to start of input
+                100,            // length of input
+                0,              // write output over input
+                32              // output size should be 32 bytes
+            )
+
+            /////// Check return data. ///////
+            // If there is no return data, we assume the token incorrectly
+            // does not return a bool. In this case we expect it to revert
+            // on failure, which was handled above.
+            // If the token does return data, we require that it is a single
+            // nonzero 32 bytes value.
+            // So the transfer succeeded if the call succeeded and either
+            // returned nothing, or returned a non-zero 32 byte value. 
+            success := and(success, or(
+                iszero(returndatasize),
+                and(
+                    eq(returndatasize, 32),
+                    gt(mload(0), 0)
+                )
+            ))
+            if success {
+                return(0, 0)
+            }
+            
+            // Revert with `Error("TRANSFER_FAILED")`
+            mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
+            mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
+            mstore(64, 0x0000000f5452414e534645525f4641494c454400000000000000000000000000)
+            mstore(96, 0)
+            revert(0, 100)
+        }
+    }
 
     /// @dev Gets the proxy id associated with the proxy address.
     /// @return Proxy id.
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol
index f6293f97d..8d7cea717 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol
@@ -20,18 +20,181 @@ pragma solidity ^0.4.24;
 pragma experimental ABIEncoderV2;
 
 import "../../utils/LibBytes/LibBytes.sol";
-import "./MixinAssetProxy.sol";
+import "./interfaces/IAssetProxy.sol";
 import "./MixinAuthorizable.sol";
-import "./MixinERC721Transfer.sol";
 
 contract ERC721Proxy is
-    MixinAssetProxy,
-    MixinAuthorizable,
-    MixinERC721Transfer
+    IAssetProxy,
+    MixinAuthorizable
 {
     // Id of this proxy.
     bytes4 constant PROXY_ID = bytes4(keccak256("ERC721Token(address,uint256,bytes)"));
 
+    /// @dev Internal version of `transferFrom`.
+    /// @param assetData Encoded byte array.
+    /// @param from Address to transfer asset from.
+    /// @param to Address to transfer asset to.
+    /// @param amount Amount of asset to transfer.
+    function transferFrom(
+        bytes assetData,
+        address from,
+        address to,
+        uint256 amount
+    )
+        external
+    {
+        require(
+            authorized[msg.sender],
+            "SENDER_NOT_AUTHORIZED"
+        );
+    
+        // `transferFrom`.
+        // The function is marked `external`, so no abi decodeding is done for
+        // us. Instead, we expect the `calldata` memory to contain the
+        // following:
+        //
+        // | Area     | Offset | Length  | Contents                            |
+        // |----------|--------|---------|-------------------------------------|
+        // | Header   | 0      | 4       | function selector                   |
+        // | Params   |        | 4 * 32  | function parameters:                |
+        // |          | 4      |         |   1. offset to assetData (*)        |
+        // |          | 36     |         |   2. from                           |
+        // |          | 68     |         |   3. to                             |
+        // |          | 100    |         |   4. amount                         |
+        // | Data     |        |         | assetData:                          |
+        // |          | 132    | 32      | assetData Length                    |
+        // |          | 164    | **      | assetData Contents                  |
+        //
+        // (*): offset is computed from start of function parameters, so offset
+        //      by an additional 4 bytes in the calldata.
+        //
+        // WARNING: The ABIv2 specification allows additional padding between
+        //          the Params and Data section. This will result in a larger
+        //          offset to assetData.
+        
+        // Asset data itself is encoded as follows:
+        //
+        // | Area     | Offset | Length  | Contents                            |
+        // |----------|--------|---------|-------------------------------------|
+        // | Header   | 0      | 4       | function selector                   |
+        // | Params   |        | 3 * 32  | function parameters:                |
+        // |          | 4      | 12 + 20 |   1. token address                  |
+        // |          | 36     |         |   2. tokenId                        |
+        // |          | 68     |         |   3. offset to receiverData (*)     |
+        // | Data     |        |         | receiverData:                       |
+        // |          | 100    | 32      | receiverData Length                 |
+        // |          | 132    | **      | receiverData Contents               |
+        
+        // We construct calldata for the `token.safeTransferFrom` ABI.
+        // The layout of this calldata is in the table below.
+        // 
+        // | Area     | Offset | Length  | Contents                            |
+        // |----------|--------|---------|-------------------------------------|
+        // | Header   | 0      | 4       | function selector                   |
+        // | Params   |        | 4 * 32  | function parameters:                |
+        // |          | 4      |         |   1. from                           |
+        // |          | 36     |         |   2. to                             |
+        // |          | 68     |         |   3. tokenId                        |
+        // |          | 100    |         |   4. offset to receiverData (*)     |
+        // | Data     |        |         | receiverData:                       |
+        // |          | 132    | 32      | receiverData Length                 |
+        // |          | 164    | **      | receiverData Contents               |
+
+        assembly {
+            // There exists only 1 of each token.
+            // require(amount == 1, "INVALID_AMOUNT")
+            if sub(calldataload(100), 1) {
+                // Revert with `Error("INVALID_AMOUNT")`
+                mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
+                mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
+                mstore(64, 0x0000000e494e56414c49445f414d4f554e540000000000000000000000000000)
+                mstore(96, 0)
+                revert(0, 100)
+            }
+            
+            // Require assetData to be at least 132 bytes
+            let offset := calldataload(4)
+            if lt(calldataload(add(offset, 4)), 132) {
+                // Revert with `Error("LENGTH_GREATER_THAN_131_REQUIRED")`
+                mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
+                mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
+                mstore(64, 0x000000204c454e4754485f475245415445525f5448414e5f3133315f52455155)
+                mstore(96, 0x4952454400000000000000000000000000000000000000000000000000000000)
+                revert(0, 100)
+            }
+            
+            /////// Setup State ///////
+            // `cdStart` is the start of the calldata for
+            // `token.safeTransferFrom` (equal to free memory ptr).
+            let cdStart := mload(64)
+            // `dataAreaLength` is the total number of words
+            // needed to store `receiverData`
+            // As-per the ABI spec, this value is padded up to
+            // the nearest multiple of 32,
+            // and includes 32-bytes for length.
+            // It's calculated as folows:
+            //      - Unpadded length in bytes = `mload(receiverData) + 32`
+            //      - Add 31 to convert rounding down to rounding up.
+            //        Combined with the previous and this is `63`.
+            //      - Round down to nearest multiple of 32 by clearing
+            //        bits 0x1F. This is done with `and` and a mask.
+
+            /////// Setup Header Area ///////
+            // This area holds the 4-byte `transferFromSelector`.
+            // Any trailing data in transferFromSelector will be
+            // overwritten in the next `mstore` call.
+            mstore(cdStart, 0xb88d4fde00000000000000000000000000000000000000000000000000000000)
+            
+            /////// Setup Params Area ///////
+            // Each parameter is padded to 32-bytes.
+            // The entire Params Area is 128 bytes.
+            // Notes:
+            //   1. A 20-byte mask is applied to addresses
+            //      to zero-out the unused bytes.
+            //   2. The offset to `receiverData` is the length
+            //      of the Params Area (128 bytes).
+            
+            let length := calldataload(add(offset, 136))
+            let token := calldataload(add(offset, 40))
+            
+            // Round length up to multiple of 32
+            length := and(add(length, 31), 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFE0)
+            
+            // Copy `from` and `to`
+            calldatacopy(add(cdStart, 4), 36, 64)
+            
+            // TokenId
+            mstore(add(cdStart, 68), calldataload(add(offset, 72)))
+            
+            // Offset to receiverData
+            mstore(add(cdStart, 100), 128)
+            
+            // receiverData (including length)
+            calldatacopy(add(cdStart, 132), add(offset, 136), add(length, 32))
+            
+            /////// Call `token.safeTransferFrom` using the calldata ///////
+            let success := call(
+                gas,                    // forward all gas
+                token,                  // call address of token contract
+                0,                      // don't send any ETH
+                cdStart,                // pointer to start of input
+                add(length, 164),       // length of input
+                0,                      // write output to null
+                0                       // output size is 0 bytes
+            )
+            if success {
+                return(0, 0)
+            }
+            
+            // Revert with `Error("TRANSFER_FAILED")`
+            mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
+            mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
+            mstore(64, 0x0000000f5452414e534645525f4641494c454400000000000000000000000000)
+            mstore(96, 0)
+            revert(0, 100)
+        }
+    }
+
     /// @dev Gets the proxy id associated with the proxy address.
     /// @return Proxy id.
     function getProxyId()
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
deleted file mode 100644
index 9032658e7..000000000
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
+++ /dev/null
@@ -1,75 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-
-pragma solidity ^0.4.24;
-pragma experimental ABIEncoderV2;
-
-import "./mixins/MAuthorizable.sol";
-import "./mixins/MAssetProxy.sol";
-
-contract MixinAssetProxy is
-    MAuthorizable,
-    MAssetProxy
-{
-
-    /// @dev Transfers assets. Either succeeds or throws.
-    /// @param assetData Encoded byte array.
-    /// @param from Address to transfer asset from.
-    /// @param to Address to transfer asset to.
-    /// @param amount Amount of asset to transfer.
-    function transferFrom(
-        bytes assetData,
-        address from,
-        address to,
-        uint256 amount
-    )
-        external
-        onlyAuthorized
-    {
-        transferFromInternal(
-            assetData,
-            from,
-            to,
-            amount
-        );
-    }
-
-    /// @dev Makes multiple transfers of assets. Either succeeds or throws.
-    /// @param assetData Array of byte arrays encoded for the respective asset proxy.
-    /// @param from Array of addresses to transfer assets from.
-    /// @param to Array of addresses to transfer assets to.
-    /// @param amounts Array of amounts of assets to transfer.
-    function batchTransferFrom(
-        bytes[] memory assetData,
-        address[] memory from,
-        address[] memory to,
-        uint256[] memory amounts
-    )
-        public
-        onlyAuthorized
-    {
-        for (uint256 i = 0; i < assetData.length; i++) {
-            transferFromInternal(
-                assetData[i],
-                from[i],
-                to[i],
-                amounts[i]
-            );
-        }
-    }
-}
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol
deleted file mode 100644
index a09db43bd..000000000
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol
+++ /dev/null
@@ -1,113 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-
-pragma solidity ^0.4.24;
-pragma experimental ABIEncoderV2;
-
-import "../../utils/LibBytes/LibBytes.sol";
-import "../../tokens/ERC20Token/IERC20Token.sol";
-
-contract MixinERC20Transfer {
-
-    using LibBytes for bytes;
-
-    /// @dev Internal version of `transferFrom`.
-    /// @param assetData Encoded byte array.
-    /// @param from Address to transfer asset from.
-    /// @param to Address to transfer asset to.
-    /// @param amount Amount of asset to transfer.
-    function transferFromInternal(
-        bytes memory assetData,
-        address from,
-        address to,
-        uint256 amount
-    )
-        internal
-    {
-        // Decode asset data.
-        address token = assetData.readAddress(16);
-        
-        // Transfer tokens.
-        // We do a raw call so we can check the success separate
-        // from the return data.
-        // We construct calldata for the `token.transferFrom` ABI.
-        // The layout of this calldata is in the table below.
-        // 
-        // | Area     | Offset | Length  | Contents                            |
-        // |----------|--------|---------|-------------------------------------|
-        // | Header   | 0      | 4       | function selector                   |
-        // | Params   |        | 3 * 32  | function parameters:                |
-        // |          | 4      |         |   1. from                           |
-        // |          | 36     |         |   2. to                             |
-        // |          | 68     |         |   3. amount                         |
-        
-        bytes4 transferFromSelector = IERC20Token(token).transferFrom.selector;
-        bool success;
-        assembly {
-            /////// Setup State ///////
-            // `cdStart` is the start of the calldata for `token.transferFrom` (equal to free memory ptr).
-            let cdStart := mload(64)
-
-            /////// Setup Header Area ///////
-            // This area holds the 4-byte `transferFromSelector`.
-            // Any trailing data in transferFromSelector will be
-            // overwritten in the next `mstore` call.
-            mstore(cdStart, transferFromSelector)
-
-            /////// Setup Params Area ///////
-            // Each parameter is padded to 32-bytes.
-            // The entire Params Area is 96 bytes.
-            // A 20-byte mask is applied to addresses to
-            // zero-out the unused bytes.
-            mstore(add(cdStart, 4), and(from, 0xffffffffffffffffffffffffffffffffffffffff))
-            mstore(add(cdStart, 36), and(to, 0xffffffffffffffffffffffffffffffffffffffff))
-            mstore(add(cdStart, 68), amount)
-
-            /////// Call `token.transferFrom` using the calldata ///////
-            success := call(
-                gas,            // forward all gas
-                token,          // call address of token contract
-                0,              // don't send any ETH
-                cdStart,        // pointer to start of input
-                100,            // length of input
-                cdStart,        // write output over input
-                32              // output size should be 32 bytes
-            )
-
-            /////// Check return data. ///////
-            // If there is no return data, we assume the token incorrectly
-            // does not return a bool. In this case we expect it to revert
-            // on failure, which was handled above.
-            // If the token does return data, we require that it is a single
-            // nonzero 32 bytes value.
-            // So the transfer succeeded if the call succeeded and either
-            // returned nothing, or returned a non-zero 32 byte value. 
-            success := and(success, or(
-                iszero(returndatasize),
-                and(
-                    eq(returndatasize, 32),
-                    gt(mload(cdStart), 0)
-                )
-            ))
-        }
-        require(
-            success,
-            "TRANSFER_FAILED"
-        );
-    }
-}
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol
deleted file mode 100644
index c170917ea..000000000
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol
+++ /dev/null
@@ -1,168 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-
-pragma solidity ^0.4.24;
-pragma experimental ABIEncoderV2;
-
-import "../../utils/LibBytes/LibBytes.sol";
-import "../../tokens/ERC721Token/ERC721Token.sol";
-import "./libs/LibTransferErrors.sol";
-
-contract MixinERC721Transfer is
-    LibTransferErrors
-{
-    using LibBytes for bytes;
-    
-    bytes4 constant SAFE_TRANSFER_FROM_SELECTOR = bytes4(keccak256("safeTransferFrom(address,address,uint256,bytes)"));
-    
-    /// @dev Internal version of `transferFrom`.
-    /// @param assetData Encoded byte array.
-    /// @param from Address to transfer asset from.
-    /// @param to Address to transfer asset to.
-    /// @param amount Amount of asset to transfer.
-    function transferFromInternal(
-        bytes memory assetData,
-        address from,
-        address to,
-        uint256 amount
-    )
-        internal
-    {
-        // There exists only 1 of each token.
-        require(
-            amount == 1,
-            INVALID_AMOUNT
-        );
-    
-        // Decode asset data.
-        (
-            address token,
-            uint256 tokenId,
-            bytes memory receiverData
-        ) = decodeERC721AssetData(assetData);
-
-        // We construct calldata for the `token.safeTransferFrom` ABI.
-        // The layout of this calldata is in the table below.
-        // 
-        // | Area     | Offset | Length  | Contents                            |
-        // |----------|--------|---------|-------------------------------------|
-        // | Header   | 0      | 4       | function selector                   |
-        // | Params   |        | 4 * 32  | function parameters:                |
-        // |          | 4      |         |   1. from                           |
-        // |          | 36     |         |   2. to                             |
-        // |          | 68     |         |   3. tokenId                        |
-        // |          | 100    |         |   4. offset to receiverData (*)     |
-        // | Data     |        |         | receiverData:                       |
-        // |          | 132    | 32      | receiverData Length                 |
-        // |          | 164    | **      | receiverData Contents               |
-
-        bytes4 safeTransferFromSelector = SAFE_TRANSFER_FROM_SELECTOR;
-        bool success;
-        assembly {
-            /////// Setup State ///////
-            // `cdStart` is the start of the calldata for
-            // `token.safeTransferFrom` (equal to free memory ptr).
-            let cdStart := mload(64)
-            // `dataAreaLength` is the total number of words
-            // needed to store `receiverData`
-            // As-per the ABI spec, this value is padded up to
-            // the nearest multiple of 32,
-            // and includes 32-bytes for length.
-            // It's calculated as folows:
-            //      - Unpadded length in bytes = `mload(receiverData) + 32`
-            //      - Add 31 to convert rounding down to rounding up.
-            //        Combined with the previous and this is `63`.
-            //      - Round down to nearest multiple of 32 by clearing
-            //        bits 0x1F. This is done with `and` and a mask.
-            let dataAreaLength := and(add(mload(receiverData), 63), 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFE0)
-            // `cdEnd` is the end of the calldata for `token.safeTransferFrom`.
-            let cdEnd := add(cdStart, add(132, dataAreaLength))
-
-            /////// Setup Header Area ///////
-            // This area holds the 4-byte `transferFromSelector`.
-            // Any trailing data in transferFromSelector will be
-            // overwritten in the next `mstore` call.
-            mstore(cdStart, safeTransferFromSelector)
-            
-            /////// Setup Params Area ///////
-            // Each parameter is padded to 32-bytes.
-            // The entire Params Area is 128 bytes.
-            // Notes:
-            //   1. A 20-byte mask is applied to addresses
-            //      to zero-out the unused bytes.
-            //   2. The offset to `receiverData` is the length
-            //      of the Params Area (128 bytes).
-            mstore(add(cdStart, 4), and(from, 0xffffffffffffffffffffffffffffffffffffffff))
-            mstore(add(cdStart, 36), and(to, 0xffffffffffffffffffffffffffffffffffffffff))
-            mstore(add(cdStart, 68), tokenId)
-            mstore(add(cdStart, 100), 128)
-
-            /////// Setup Data Area ///////
-            // This area holds `receiverData`.
-            let dataArea := add(cdStart, 132)
-            for {} lt(dataArea, cdEnd) {} {
-                mstore(dataArea, mload(receiverData))
-                dataArea := add(dataArea, 32)
-                receiverData := add(receiverData, 32)
-            }
-            
-            /////// Call `token.safeTransferFrom` using the calldata ///////
-            success := call(
-                gas,                    // forward all gas
-                token,                  // call address of token contract
-                0,                      // don't send any ETH
-                cdStart,                // pointer to start of input
-                sub(cdEnd, cdStart),    // length of input
-                cdStart,                // write output over input
-                0                       // output size is 0 bytes
-            )
-        }
-        require(
-            success,
-            TRANSFER_FAILED
-        );
-    }
-
-    /// @dev Decodes ERC721 Asset data.
-    /// @param assetData Encoded byte array.
-    /// @return proxyId Intended ERC721 proxy id.
-    /// @return token ERC721 token address.
-    /// @return tokenId ERC721 token id.
-    /// @return receiverData Additional data with no specific format, which
-    ///                      is passed to the receiving contract's onERC721Received.
-    function decodeERC721AssetData(bytes memory assetData)
-        internal
-        pure
-        returns (
-            address token,
-            uint256 tokenId,
-            bytes memory receiverData
-        )
-    {
-        // Decode asset data.
-        token = assetData.readAddress(16);
-        tokenId = assetData.readUint256(36);
-        receiverData = assetData.readBytesWithLength(100);
-
-        return (
-            token,
-            tokenId,
-            receiverData
-        );
-    }
-}
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol
index d12d23610..ae8e195da 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol
@@ -38,19 +38,6 @@ contract IAssetProxy is
     )
         external;
     
-    /// @dev Makes multiple transfers of assets. Either succeeds or throws.
-    /// @param assetData Array of byte arrays encoded for the respective asset proxy.
-    /// @param from Array of addresses to transfer assets from.
-    /// @param to Array of addresses to transfer assets to.
-    /// @param amounts Array of amounts of assets to transfer.
-    function batchTransferFrom(
-        bytes[] memory assetData,
-        address[] memory from,
-        address[] memory to,
-        uint256[] memory amounts
-    )
-        public;
-
     /// @dev Gets the proxy id associated with the proxy address.
     /// @return Proxy id.
     function getProxyId()
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibAssetProxyErrors.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibAssetProxyErrors.sol
index b0b20c044..338cb12e2 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibAssetProxyErrors.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibAssetProxyErrors.sol
@@ -23,9 +23,14 @@ pragma solidity ^0.4.24;
 contract LibAssetProxyErrors {
 
     /// Authorizable errors ///
-    string constant SENDER_NOT_AUTHORIZED = "SENDER_NOT_AUTHORIZED";              // Sender not authorized to call this method.
-    string constant TARGET_NOT_AUTHORIZED = "TARGET_NOT_AUTHORIZED";              // Target address not authorized to call this method.
-    string constant TARGET_ALREADY_AUTHORIZED = "TARGET_ALREADY_AUTHORIZED";      // Target address must not already be authorized.
-    string constant INDEX_OUT_OF_BOUNDS = "INDEX_OUT_OF_BOUNDS";                  // Specified array index is out of bounds.
-    string constant AUTHORIZED_ADDRESS_MISMATCH = "AUTHORIZED_ADDRESS_MISMATCH";  // Address at index does not match given target address.
+    string constant SENDER_NOT_AUTHORIZED = "SENDER_NOT_AUTHORIZED";                        // Sender not authorized to call this method.
+    string constant TARGET_NOT_AUTHORIZED = "TARGET_NOT_AUTHORIZED";                        // Target address not authorized to call this method.
+    string constant TARGET_ALREADY_AUTHORIZED = "TARGET_ALREADY_AUTHORIZED";                // Target address must not already be authorized.
+    string constant INDEX_OUT_OF_BOUNDS = "INDEX_OUT_OF_BOUNDS";                            // Specified array index is out of bounds.
+    string constant AUTHORIZED_ADDRESS_MISMATCH = "AUTHORIZED_ADDRESS_MISMATCH";            // Address at index does not match given target address.
+
+    /// Transfer errors ///
+    string constant INVALID_AMOUNT = "INVALID_AMOUNT";                                      // Transfer amount must equal 1.
+    string constant TRANSFER_FAILED = "TRANSFER_FAILED";                                    // Transfer failed.
+    string constant LENGTH_GREATER_THAN_131_REQUIRED = "LENGTH_GREATER_THAN_131_REQUIRED";  // Byte array must have a length greater than 0.
 }
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibTransferErrors.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibTransferErrors.sol
deleted file mode 100644
index 88187f196..000000000
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/libs/LibTransferErrors.sol
+++ /dev/null
@@ -1,28 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-
-pragma solidity ^0.4.24;
-
-/// @dev This contract documents the revert reasons used in the `transferFrom` methods of different AssetProxy contracts.
-/// This contract is intended to serve as a reference, but is not actually used for efficiency reasons.
-contract LibTransferErrors {
-
-    /// Transfer errors ///
-    string constant INVALID_AMOUNT = "INVALID_AMOUNT";                            // Transfer amount must equal 1.
-    string constant TRANSFER_FAILED = "TRANSFER_FAILED";                          // Transfer failed.
-}
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
deleted file mode 100644
index a52cb56f9..000000000
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
+++ /dev/null
@@ -1,40 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-
-pragma solidity ^0.4.24;
-pragma experimental ABIEncoderV2;
-
-import "../interfaces/IAssetProxy.sol";
-
-contract MAssetProxy is
-    IAssetProxy
-{
-
-    /// @dev Internal version of `transferFrom`.
-    /// @param assetData Encoded byte array.
-    /// @param from Address to transfer asset from.
-    /// @param to Address to transfer asset to.
-    /// @param amount Amount of asset to transfer.
-    function transferFromInternal(
-        bytes memory assetData,
-        address from,
-        address to,
-        uint256 amount
-    )
-        internal;
-}
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
index 3203322aa..f7086f543 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
@@ -135,7 +135,6 @@ contract MixinAssetProxyDispatcher is
             // |          | 132    | 32      | assetData Length                            |
             // |          | 164    | **      | assetData Contents                          |
 
-            bytes4 transferFromSelector = IAssetProxy(assetProxy).transferFrom.selector;
             bool success;
             assembly {
                 /////// Setup State ///////
@@ -151,7 +150,8 @@ contract MixinAssetProxyDispatcher is
                 
                 /////// Setup Header Area ///////
                 // This area holds the 4-byte `transferFromSelector`.
-                mstore(cdStart, transferFromSelector)
+                // bytes4(keccak256("transferFrom(bytes,address,address,uint256)")) = 0xa85e59e4
+                mstore(cdStart, 0xa85e59e400000000000000000000000000000000000000000000000000000000)
                 
                 /////// Setup Params Area ///////
                 // Each parameter is padded to 32-bytes. The entire Params Area is 128 bytes.
@@ -180,13 +180,12 @@ contract MixinAssetProxyDispatcher is
                     cdStart,                // pointer to start of input
                     sub(cdEnd, cdStart),    // length of input  
                     cdStart,                // write output over input
-                    0                       // output size is 0 bytes
+                    512                     // reserve 512 bytes for output
                 )
+                if eq(success, 0) {
+                    revert(cdStart, returndatasize())
+                }
             }
-            require(
-                success,
-                "TRANSFER_FAILED"
-            );
         }
     }
 }
diff --git a/packages/contracts/src/contracts/current/test/TestAssetDataDecoders/TestAssetDataDecoders.sol b/packages/contracts/src/contracts/current/test/TestAssetDataDecoders/TestAssetDataDecoders.sol
deleted file mode 100644
index 5987291d2..000000000
--- a/packages/contracts/src/contracts/current/test/TestAssetDataDecoders/TestAssetDataDecoders.sol
+++ /dev/null
@@ -1,56 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-
-pragma solidity ^0.4.24;
-pragma experimental ABIEncoderV2;
-
-import "../../protocol/AssetProxy/ERC20Proxy.sol";
-import "../../protocol/AssetProxy/ERC721Proxy.sol";
-
-contract TestAssetDataDecoders is
-    ERC721Proxy
-{
-    /// @dev Decodes ERC721 Asset data.
-    /// @param assetData Encoded byte array.
-    /// @return proxyId Intended ERC721 proxy id.
-    /// @return token ERC721 token address.
-    /// @return tokenId ERC721 token id.
-    /// @return receiverData Additional data with no specific format, which
-    ///                      is passed to the receiving contract's onERC721Received.
-    function publicDecodeERC721Data(bytes memory assetData)
-        public
-        pure
-        returns (
-            address token,
-            uint256 tokenId,
-            bytes memory receiverData
-        )
-    {
-        (
-            token,
-            tokenId,
-            receiverData
-        ) = decodeERC721AssetData(assetData);
-
-        return (
-            token,
-            tokenId,
-            receiverData
-        );
-    }
-}
diff --git a/packages/contracts/src/utils/artifacts.ts b/packages/contracts/src/utils/artifacts.ts
index a46bab9ae..d58e7973c 100644
--- a/packages/contracts/src/utils/artifacts.ts
+++ b/packages/contracts/src/utils/artifacts.ts
@@ -11,7 +11,6 @@ import * as ExchangeWrapper from '../artifacts/ExchangeWrapper.json';
 import * as MixinAuthorizable from '../artifacts/MixinAuthorizable.json';
 import * as MultiSigWallet from '../artifacts/MultiSigWallet.json';
 import * as MultiSigWalletWithTimeLock from '../artifacts/MultiSigWalletWithTimeLock.json';
-import * as TestAssetDataDecoders from '../artifacts/TestAssetDataDecoders.json';
 import * as TestAssetProxyDispatcher from '../artifacts/TestAssetProxyDispatcher.json';
 import * as TestAssetProxyOwner from '../artifacts/TestAssetProxyOwner.json';
 import * as TestLibBytes from '../artifacts/TestLibBytes.json';
@@ -39,7 +38,6 @@ export const artifacts = {
     MultiSigWalletWithTimeLock: (MultiSigWalletWithTimeLock as any) as ContractArtifact,
     TestAssetProxyOwner: (TestAssetProxyOwner as any) as ContractArtifact,
     TestAssetProxyDispatcher: (TestAssetProxyDispatcher as any) as ContractArtifact,
-    TestAssetDataDecoders: (TestAssetDataDecoders as any) as ContractArtifact,
     TestLibBytes: (TestLibBytes as any) as ContractArtifact,
     TestLibs: (TestLibs as any) as ContractArtifact,
     TestSignatureValidator: (TestSignatureValidator as any) as ContractArtifact,