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Merge pull request #2020 from jalextowle/feature/contracts/3.0/rewrit…
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…e-dispatch-transfer-from

Rewrite _dispatchTransferFrom with a Solidity implementation
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@jalextowle
jalextowle authored Aug 2, 2019
2 parents bd42c33 + bf8fae2 commit 92a4556
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Showing 3 changed files with 22 additions and 91 deletions.
4 changes: 4 additions & 0 deletions contracts/exchange/CHANGELOG.json
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Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,10 @@
{
"note": "Updated RichErrors to the library pattern",
"pr": 1913
},
{
"note": "Rewrote _dispatchTransferFrom in Solidity",
"pr": 2020
}
]
},
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107 changes: 17 additions & 90 deletions contracts/exchange/contracts/src/MixinAssetProxyDispatcher.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
pragma solidity ^0.5.9;

import "@0x/contracts-utils/contracts/src/Ownable.sol";
import "@0x/contracts-utils/contracts/src/LibBytes.sol";
import "@0x/contracts-utils/contracts/src/LibRichErrors.sol";
import "./interfaces/IAssetProxy.sol";
import "./interfaces/IAssetProxyDispatcher.sol";
Expand All @@ -30,6 +31,8 @@ contract MixinAssetProxyDispatcher is
Ownable,
IAssetProxyDispatcher
{
using LibBytes for bytes;

// Mapping from Asset Proxy Id's to their respective Asset Proxy
mapping (bytes4 => address) public assetProxies;

Expand Down Expand Up @@ -92,14 +95,8 @@ contract MixinAssetProxyDispatcher is
));
}

// Lookup assetProxy. We do not use `LibBytes.readBytes4` for gas efficiency reasons.
bytes4 assetProxyId;
assembly {
assetProxyId := and(mload(
add(assetData, 32)),
0xFFFFFFFF00000000000000000000000000000000000000000000000000000000
)
}
// Lookup assetProxy.
bytes4 assetProxyId = assetData.readBytes4(0);
address assetProxy = assetProxies[assetProxyId];

// Ensure that assetProxy exists
Expand All @@ -111,89 +108,19 @@ contract MixinAssetProxyDispatcher is
));
}

// Whether the AssetProxy transfer succeeded.
bool didSucceed;
// On failure, the revert data thrown by the asset proxy.
bytes memory revertData;

// We construct calldata for the `assetProxy.transferFrom` 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. offset to assetData (*) |
// | | 36 | | 2. from |
// | | 68 | | 3. to |
// | | 100 | | 4. amount |
// | Data | | | assetData: |
// | | 132 | 32 | assetData Length |
// | | 164 | ** | assetData Contents |

assembly {
/////// Setup State ///////
// `cdStart` is the start of the calldata for `assetProxy.transferFrom` (equal to free memory ptr).
let cdStart := mload(64)
// `dataAreaLength` is the total number of words needed to store `assetData`
// As-per the ABI spec, this value is padded up to the nearest multiple of 32,
// and includes 32-bytes for length.
let dataAreaLength := and(add(mload(assetData), 63), 0xFFFFFFFFFFFE0)
// `cdEnd` is the end of the calldata for `assetProxy.transferFrom`.
let cdEnd := add(cdStart, add(132, dataAreaLength))

/////// Setup Header Area ///////
// This area holds the 4-byte `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.
// Notes:
// 1. The offset to `assetData` is the length of the Params Area (128 bytes).
// 2. A 20-byte mask is applied to addresses to zero-out the unused bytes.
mstore(add(cdStart, 4), 128)
mstore(add(cdStart, 36), and(from, 0xffffffffffffffffffffffffffffffffffffffff))
mstore(add(cdStart, 68), and(to, 0xffffffffffffffffffffffffffffffffffffffff))
mstore(add(cdStart, 100), amount)

/////// Setup Data Area ///////
// This area holds `assetData`.
let dataArea := add(cdStart, 132)
let assetDataArea := assetData
// solhint-disable-next-line no-empty-blocks
for {} lt(dataArea, cdEnd) {} {
mstore(dataArea, mload(assetDataArea))
dataArea := add(dataArea, 32)
assetDataArea := add(assetDataArea, 32)
}

/////// Call `assetProxy.transferFrom` using the constructed calldata ///////
didSucceed := call(
gas, // forward all gas
assetProxy, // call address of asset proxy
0, // don't send any ETH
cdStart, // pointer to start of input
sub(cdEnd, cdStart), // length of input
0, // don't store the returndata
0 // don't store the returndata
)

if iszero(didSucceed) { // Call reverted.
let revertDataSize := returndatasize()
// Construct a `bytes memory` type to hold the revert data
// at `cdStart`.
// The first 32 bytes are the length of the data.
mstore(cdStart, revertDataSize)
// Copy the revert data immediately after the length.
returndatacopy(add(cdStart, 32), 0, revertDataSize)
// We need to move the free memory pointer because we
// still have solidity logic that executes after this assembly.
mstore(64, add(cdStart, add(revertDataSize, 32)))
revertData := cdStart
}
}
// Construct the calldata for the transferFrom call.
bytes memory proxyCalldata = abi.encodeWithSelector(
IAssetProxy(address(0)).transferFrom.selector,
assetData,
from,
to,
amount
);

// Call the asset proxy's transferFrom function with the constructed calldata.
(bool didSucceed, bytes memory revertData) = assetProxy.call(proxyCalldata);

// If the transaction did not succeed, revert with the returned data.
if (!didSucceed) {
LibRichErrors._rrevert(LibExchangeRichErrors.AssetProxyTransferError(
orderHash,
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2 changes: 1 addition & 1 deletion contracts/exchange/contracts/src/interfaces/IAssetProxy.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ contract IAssetProxy {
uint256 amount
)
external;

/// @dev Gets the proxy id associated with the proxy address.
/// @return Proxy id.
function getProxyId()
Expand Down

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