Update Interfaces for IValidator and IWallet

contracts/exchange/contracts/examples/Validator.sol

@@ -21,7 +21,7 @@ pragma solidity ^0.5.5;
 import "../src/interfaces/IValidator.sol";
 
 
-contract Validator is 
+contract Validator is
     IValidator
 {
 
@@ -48,9 +48,11 @@ contract Validator is
     )
         external
         view
-        returns (bool isValid)
+        returns (bytes4)
     {
-        return (signerAddress == VALID_SIGNER);
+        require(signerAddress == VALID_SIGNER, "INVALID_SIGNER");
+        bytes4 magic_salt = bytes4(keccak256("isValidValidatorSignature(address,bytes32,address,bytes)"));
+        return magic_salt;
     }
     // solhint-enable no-unused-vars
 }

contracts/exchange/contracts/examples/Wallet.sol

@@ -22,7 +22,7 @@ import "../src/interfaces/IWallet.sol";
 import "@0x/contracts-utils/contracts/src/LibBytes.sol";
 
 
-contract Wallet is 
+contract Wallet is
     IWallet
 {
     using LibBytes for bytes;
@@ -48,7 +48,7 @@ contract Wallet is
     )
         external
         view
-        returns (bool isValid)
+        returns (bytes4)
     {
         require(
             eip712Signature.length == 65,
@@ -59,7 +59,8 @@ contract Wallet is
         bytes32 r = eip712Signature.readBytes32(1);
         bytes32 s = eip712Signature.readBytes32(33);
         address recoveredAddress = ecrecover(hash, v, r, s);
-        isValid = WALLET_OWNER == recoveredAddress;
-        return isValid;
+        require(WALLET_OWNER == recoveredAddress, "INVALID_SIGNATURE");
+        bytes4 magic_salt = bytes4(keccak256("isValidWalletSignature(bytes32,address,bytes)"));
+        return magic_salt;
     }
 }

contracts/exchange/contracts/src/interfaces/IValidator.sol

@@ -25,7 +25,8 @@ contract IValidator {
     /// @param hash Message hash that is signed.
     /// @param signerAddress Address that should have signed the given hash.
     /// @param signature Proof of signing.
-    /// @return Validity of order signature.
+    /// @return Magic bytes4 value if the signature is valid.
+    ///         Magic value is bytes4(keccak256("isValidValidatorSignature(address,bytes32,address,bytes)"))
     function isValidSignature(
         bytes32 hash,
         address signerAddress,
@@ -33,5 +34,5 @@ contract IValidator {
     )
         external
         view
-        returns (bool isValid);
+        returns (bytes4 isValid);
 }

contracts/exchange/contracts/src/interfaces/IWallet.sol

@@ -24,12 +24,13 @@ contract IWallet {
     /// @dev Verifies that a signature is valid.
     /// @param hash Message hash that is signed.
     /// @param signature Proof of signing.
-    /// @return Validity of order signature.
+    /// @return Magic bytes4 value if the signature is valid.
+    ///         Magic value is bytes4(keccak256("isValidWalletSignature(bytes32,address,bytes)"))
     function isValidSignature(
         bytes32 hash,
         bytes calldata signature
     )
         external
         view
-        returns (bool isValid);
+        returns (bytes4 isValid);
 }