@0x/contracts-asset-proxy: Rename IERC20Bridge.transfer() -> IERC20Bridge.withdrawTo().

`@0x/contracts-asset-proxy`: Make `bridgeData` last parameter in `IERC20Bridge.withdrawTo()`.
`@0x/contracts-asset-proxy`: Reuse `PROXY_ID` as `BRIDGE_SUCCESS`.

contracts/asset-proxy/contracts/src/ERC20BridgeProxy.sol

@@ -34,9 +34,7 @@ contract ERC20BridgeProxy is
     using LibBytes for bytes;
     using LibSafeMath for uint256;
 
-    // @dev Result of a successful bridge call.
-    bytes4 constant public BRIDGE_SUCCESS = 0xb5d40d78;
-    // @dev Id of this proxy.
+    // @dev Id of this proxy. Also the result of a successful bridge call.
     //      bytes4(keccak256("ERC20BridgeProxy(address,address,bytes)"))
     bytes4 constant private PROXY_ID = 0x37708e9b;
 
@@ -75,15 +73,15 @@ contract ERC20BridgeProxy is
         uint256 balanceBefore = balanceOf(tokenAddress, to);
         // Call the bridge, who should transfer `amount` of `tokenAddress` to
         // `to`.
-        bytes4 success = IERC20Bridge(bridgeAddress).transfer(
-            bridgeData,
+        bytes4 success = IERC20Bridge(bridgeAddress).withdrawTo(
             tokenAddress,
             from,
             to,
-            amount
+            amount,
+            bridgeData
         );
-        // Bridge must return the magic bytes to indicate success.
-        require(success == BRIDGE_SUCCESS, "BRIDGE_FAILED");
+        // Bridge must return the proxy ID to indicate success.
+        require(success == PROXY_ID, "BRIDGE_FAILED");
         // Ensure that the balance of `to` has increased by at least `amount`.
         require(
             balanceBefore.safeAdd(amount) <= balanceOf(tokenAddress, to),
@@ -109,9 +107,9 @@ contract ERC20BridgeProxy is
         view
         returns (uint256 balance)
     {
-        (address tokenAddress, ,) = abi.decode(
+        (address tokenAddress) = abi.decode(
             assetData.sliceDestructive(4, assetData.length),
-            (address, address, bytes)
+            (address)
         );
         return balanceOf(tokenAddress, owner);
     }

contracts/asset-proxy/contracts/src/bridges/ERC20Bridge.sol

@@ -0,0 +1,30 @@
+/*
+
+  Copyright 2019 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 ^0.5.9;
+pragma experimental ABIEncoderV2;
+
+import "../interfaces/IERC20Bridge.sol";
+
+
+contract ERC20Bridge is
+    IERC20Bridge
+{
+    // @dev Result of a successful bridge call.
+    bytes4 constant internal BRIDGE_SUCCESS = 0x37708e9b;
+}

contracts/asset-proxy/contracts/src/interfaces/IERC20Bridge.sol

@@ -19,21 +19,21 @@
 pragma solidity ^0.5.9;
 
 
-contract IERC20Bridge {
+interface IERC20Bridge {
 
     /// @dev Transfers `amount` of the ERC20 `tokenAddress` from `from` to `to`.
-    /// @param bridgeData Arbitrary asset data needed by the bridge contract.
     /// @param tokenAddress The address of the ERC20 token to transfer.
     /// @param from Address to transfer asset from.
     /// @param to Address to transfer asset to.
     /// @param amount Amount of asset to transfer.
-    /// @return success The magic bytes `0xb5d40d78` if successful.
-    function transfer(
-        bytes calldata bridgeData,
+    /// @param bridgeData Arbitrary asset data needed by the bridge contract.
+    /// @return success The magic bytes `0x37708e9b` if successful.
+    function withdrawTo(
         address tokenAddress,
         address from,
         address to,
-        uint256 amount
+        uint256 amount,
+        bytes calldata bridgeData
     )
         external
         returns (bytes4 success);

contracts/asset-proxy/contracts/test/TestERC20Bridge.sol

@@ -19,7 +19,7 @@
 pragma solidity ^0.5.9;
 pragma experimental ABIEncoderV2;
 
-import "../src/interfaces/IERC20Bridge.sol";
+import "../src/bridges/ERC20Bridge.sol";
 
 
 /// @dev Test bridge token
@@ -50,16 +50,16 @@ contract TestERC20BridgeToken {
 
 /// @dev Test bridge contract.
 contract TestERC20Bridge is
-    IERC20Bridge
+    ERC20Bridge
 {
     TestERC20BridgeToken public testToken;
 
-    event BridgeTransfer(
-        bytes bridgeData,
+    event BridgeWithdrawTo(
         address tokenAddress,
         address from,
         address to,
-        uint256 amount
+        uint256 amount,
+        bytes bridgeData
     );
 
     constructor() public {
@@ -72,22 +72,22 @@ contract TestERC20Bridge is
         testToken.setBalance(owner, balance);
     }
 
-    function transfer(
-        bytes calldata bridgeData,
+    function withdrawTo(
         address tokenAddress,
         address from,
         address to,
-        uint256 amount
+        uint256 amount,
+        bytes calldata bridgeData
     )
         external
         returns (bytes4)
     {
-        emit BridgeTransfer(
-            bridgeData,
+        emit BridgeWithdrawTo(
             tokenAddress,
             from,
             to,
-            amount
+            amount,
+            bridgeData
         );
         // Unpack the bridgeData.
         (

contracts/asset-proxy/test/erc20bridge_proxy.ts

@@ -16,12 +16,13 @@ import * as _ from 'lodash';
 import {
     artifacts,
     ERC20BridgeProxyContract,
-    TestERC20BridgeBridgeTransferEventArgs,
+    TestERC20BridgeBridgeWithdrawToEventArgs,
     TestERC20BridgeContract,
 } from '../src';
 
 blockchainTests.resets('ERC20BridgeProxy unit tests', env => {
-    const BRIDGE_SUCCESS_RETURN_DATA = hexRightPad('0xb5d40d78');
+    const PROXY_ID = '0xb5d40d78';
+    const BRIDGE_SUCCESS_RETURN_DATA = hexRightPad(PROXY_ID);
     let owner: string;
     let badCaller: string;
     let assetProxy: ERC20BridgeProxyContract;
@@ -162,12 +163,12 @@ blockchainTests.resets('ERC20BridgeProxy unit tests', env => {
             const opts = createTransferFromOpts();
             const logs = await transferFromAsync(opts);
             expect(logs.length).to.eq(1);
-            const args = logs[0].args as TestERC20BridgeBridgeTransferEventArgs;
-            expect(args.bridgeData).to.eq(encodeBridgeData(opts.assetData.bridgeData));
+            const args = logs[0].args as TestERC20BridgeBridgeWithdrawToEventArgs;
             expect(args.tokenAddress).to.eq(opts.assetData.tokenAddress);
             expect(args.from).to.eq(opts.from);
             expect(args.to).to.eq(opts.to);
             expect(args.amount).to.bignumber.eq(opts.amount);
+            expect(args.bridgeData).to.eq(encodeBridgeData(opts.assetData.bridgeData));
         });
 
         it('fails if not called by an authorized address', async () => {
@@ -287,4 +288,11 @@ blockchainTests.resets('ERC20BridgeProxy unit tests', env => {
             expect(actualBalance).to.bignumber.eq(balance);
         });
     });
+
+    describe('getProxyId()', () => {
+        it('returns the correct proxy ID', async () => {
+            const proxyId = await assetProxy.getProxyId.callAsync();
+            expect(proxyId).to.eq(PROXY_ID);
+        });
+    });
 });