From 7762b7b665e798cf6b9461523e2877e8670e0e35 Mon Sep 17 00:00:00 2001
From: Lawrence Forman <lawrence@0xproject.com>
Date: Sat, 28 Sep 2019 01:54:09 -0400
Subject: [PATCH] `@0x/contracts-asset-proxy`: Add signature validation.

---
 contracts/asset-proxy/CHANGELOG.json          |  2 +-
 .../contracts/src/bridges/Eth2DaiBridge.sol   | 28 +++++++++++++++++--
 contracts/asset-proxy/test/eth2dai_bridge.ts  | 11 +++++++-
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/contracts/asset-proxy/CHANGELOG.json b/contracts/asset-proxy/CHANGELOG.json
index 344060b59c..65526c41c3 100644
--- a/contracts/asset-proxy/CHANGELOG.json
+++ b/contracts/asset-proxy/CHANGELOG.json
@@ -24,7 +24,7 @@
             },
             {
                 "note": "Add `Eth2DaiBridge`",
-                "pr": "TODO"
+                "pr": 2221
             }
         ]
     },
diff --git a/contracts/asset-proxy/contracts/src/bridges/Eth2DaiBridge.sol b/contracts/asset-proxy/contracts/src/bridges/Eth2DaiBridge.sol
index 46cffb9c3c..ab56e1bf66 100644
--- a/contracts/asset-proxy/contracts/src/bridges/Eth2DaiBridge.sol
+++ b/contracts/asset-proxy/contracts/src/bridges/Eth2DaiBridge.sol
@@ -20,13 +20,17 @@ pragma solidity ^0.5.9;
 pragma experimental ABIEncoderV2;
 
 import "@0x/contracts-erc20/contracts/src/interfaces/IERC20Token.sol";
+import "@0x/contracts-exchange/contracts/src/interfaces/IWallet.sol";
 import "./ERC20Bridge.sol";
 import "../interfaces/IEth2Dai.sol";
 
 
+// solhint-disable space-after-comma
 contract Eth2DaiBridge is
-    ERC20Bridge
+    ERC20Bridge,
+    IWallet
 {
+    bytes4 private constant LEGACY_WALLET_MAGIC_VALUE = 0xb0671381;
     /* Mainnet addresses */
     address constant public ETH2DAI_ADDRESS = 0x39755357759cE0d7f32dC8dC45414CCa409AE24e;
     address constant public WETH_ADDRESS = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;
@@ -38,7 +42,14 @@ contract Eth2DaiBridge is
         _getDaiContract().approve(address(_getEth2DaiContract()), uint256(-1));
     }
 
-    // solhint-disable space-after-comma
+    /// @dev Callback for `IERC20Bridge`. Tries to buy `amount` of
+    ///      `toTokenAddress` tokens by selling the entirety of the opposing asset
+    ///      (DAI or WETH) to the Eth2Dai contract, then transfers the bought
+    ///      tokens to `to`.
+    /// @param toTokenAddress The token to give to `to` (either DAI or WETH).
+    /// @param to The recipient of the bought tokens.
+    /// @param amount Minimum amount of `toTokenAddress` tokens to buy.
+    /// @return success The magic bytes `0xb5d40d78` if successful.
     function transfer(
         bytes calldata /* bridgeData */,
         address toTokenAddress,
@@ -73,6 +84,19 @@ contract Eth2DaiBridge is
         return BRIDGE_SUCCESS;
     }
 
+    /// @dev `SignatureType.Wallet` callback, so that this bridge can be the maker
+    ///      and sign for itself in orders. Always succeeds.
+    function isValidSignature(
+        bytes32,
+        bytes calldata
+    )
+        external
+        view
+        returns (bytes4 magicValue)
+    {
+        return LEGACY_WALLET_MAGIC_VALUE;
+    }
+
     /// @dev Overridable way to get the weth contract.
     function _getWethContract()
         internal
diff --git a/contracts/asset-proxy/test/eth2dai_bridge.ts b/contracts/asset-proxy/test/eth2dai_bridge.ts
index b63fb7c216..9d1cd32585 100644
--- a/contracts/asset-proxy/test/eth2dai_bridge.ts
+++ b/contracts/asset-proxy/test/eth2dai_bridge.ts
@@ -4,6 +4,7 @@ import {
     expect,
     filterLogsToArguments,
     getRandomInteger,
+    hexRandom,
     Numberish,
     randomAddress,
     TransactionHelper,
@@ -20,7 +21,7 @@ import {
     TestEth2DaiBridgeTokenTransferEventArgs,
 } from '../src';
 
-blockchainTests.resets('Eth2DaiBridge unit tests', env => {
+blockchainTests.resets.only('Eth2DaiBridge unit tests', env => {
     const txHelper = new TransactionHelper(env.web3Wrapper, artifacts);
     let testContract: TestEth2DaiBridgeContract;
     let daiTokenAddress: string;
@@ -47,6 +48,14 @@ blockchainTests.resets('Eth2DaiBridge unit tests', env => {
         });
     });
 
+    describe('isValidSignature()', () => {
+        it('returns success bytes', async () => {
+            const LEGACY_WALLET_MAGIC_VALUE = '0xb0671381';
+            const result = await testContract.isValidSignature.callAsync(hexRandom(), hexRandom(_.random(0, 32)));
+            expect(result).to.eq(LEGACY_WALLET_MAGIC_VALUE);
+        });
+    });
+
     describe('transfer()', () => {
         interface TransferOpts {
             toTokenAddress: string;