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diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/MixinTransactions.sol b/packages/contracts/src/2.0.0/protocol/Exchange/MixinTransactions.sol
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+/*
+
+ 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;
+
+import "./libs/LibExchangeErrors.sol";
+import "./mixins/MSignatureValidator.sol";
+import "./mixins/MTransactions.sol";
+import "./libs/LibEIP712.sol";
+
+contract MixinTransactions is
+ LibEIP712,
+ MSignatureValidator,
+ MTransactions
+{
+
+ // Mapping of transaction hash => executed
+ // This prevents transactions from being executed more than once.
+ mapping (bytes32 => bool) public transactions;
+
+ // Address of current transaction signer
+ address public currentContextAddress;
+
+ // Hash for the EIP712 ZeroEx Transaction Schema
+ bytes32 constant EIP712_ZEROEX_TRANSACTION_SCHEMA_HASH = keccak256(abi.encodePacked(
+ "ZeroExTransaction(",
+ "uint256 salt,",
+ "address signerAddress,",
+ "bytes data",
+ ")"
+ ));
+
+ /// @dev Calculates EIP712 hash of the Transaction.
+ /// @param salt Arbitrary number to ensure uniqueness of transaction hash.
+ /// @param signerAddress Address of transaction signer.
+ /// @param data AbiV2 encoded calldata.
+ /// @return EIP712 hash of the Transaction.
+ function hashZeroExTransaction(
+ uint256 salt,
+ address signerAddress,
+ bytes memory data
+ )
+ internal
+ pure
+ returns (bytes32 result)
+ {
+ bytes32 schemaHash = EIP712_ZEROEX_TRANSACTION_SCHEMA_HASH;
+ bytes32 dataHash = keccak256(data);
+ // Assembly for more efficiently computing:
+ // keccak256(abi.encode(
+ // EIP712_ZEROEX_TRANSACTION_SCHEMA_HASH,
+ // salt,
+ // signerAddress,
+ // keccak256(data)
+ // ));
+ assembly {
+ let memPtr := mload(64)
+ mstore(memPtr, schemaHash)
+ mstore(add(memPtr, 32), salt)
+ mstore(add(memPtr, 64), and(signerAddress, 0xffffffffffffffffffffffffffffffffffffffff))
+ mstore(add(memPtr, 96), dataHash)
+ result := keccak256(memPtr, 128)
+ }
+
+ return result;
+ }
+
+ /// @dev Executes an exchange method call in the context of signer.
+ /// @param salt Arbitrary number to ensure uniqueness of transaction hash.
+ /// @param signerAddress Address of transaction signer.
+ /// @param data AbiV2 encoded calldata.
+ /// @param signature Proof of signer transaction by signer.
+ function executeTransaction(
+ uint256 salt,
+ address signerAddress,
+ bytes data,
+ bytes signature
+ )
+ external
+ {
+ // Prevent reentrancy
+ require(
+ currentContextAddress == address(0),
+ "REENTRANCY_ILLEGAL"
+ );
+
+ bytes32 transactionHash = hashEIP712Message(hashZeroExTransaction(
+ salt,
+ signerAddress,
+ data
+ ));
+
+ // Validate transaction has not been executed
+ require(
+ !transactions[transactionHash],
+ "INVALID_TX_HASH"
+ );
+
+ // Transaction always valid if signer is sender of transaction
+ if (signerAddress != msg.sender) {
+ // Validate signature
+ require(
+ isValidSignature(
+ transactionHash,
+ signerAddress,
+ signature
+ ),
+ "INVALID_TX_SIGNATURE"
+ );
+
+ // Set the current transaction signer
+ currentContextAddress = signerAddress;
+ }
+
+ // Execute transaction
+ transactions[transactionHash] = true;
+ require(
+ address(this).delegatecall(data),
+ "FAILED_EXECUTION"
+ );
+
+ // Reset current transaction signer
+ // TODO: Check if gas is paid when currentContextAddress is already 0.
+ currentContextAddress = address(0);
+ }
+
+ /// @dev The current function will be called in the context of this address (either 0x transaction signer or `msg.sender`).
+ /// If calling a fill function, this address will represent the taker.
+ /// If calling a cancel function, this address will represent the maker.
+ /// @return Signer of 0x transaction if entry point is `executeTransaction`.
+ /// `msg.sender` if entry point is any other function.
+ function getCurrentContextAddress()
+ internal
+ view
+ returns (address)
+ {
+ address contextAddress = currentContextAddress == address(0) ? msg.sender : currentContextAddress;
+ return contextAddress;
+ }
+}