Optimize ERC20 transferFrom
This commit is contained in:
Remco Bloemen
committed by
Amir Bandeali
Amir Bandeali
parent
744e6e60c5
commit
3ce90b8257
@@ -19,13 +19,137 @@
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pragma solidity ^0.4.24;
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pragma experimental ABIEncoderV2;
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import "./mixins/MAuthorizable.sol";
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import "../../utils/LibBytes/LibBytes.sol";
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import "../../tokens/ERC20Token/IERC20Token.sol";
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contract MixinERC20Transfer {
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contract MixinERC20Transfer is
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MAuthorizable
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{
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using LibBytes for bytes;
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/// @dev Internal version of `transferFrom`.
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/// @param assetData Encoded byte array.
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/// @param from Address to transfer asset from.
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/// @param to Address to transfer asset to.
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/// @param amount Amount of asset to transfer.
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function transferFrom(
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bytes assetData,
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address from,
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address to,
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uint256 amount
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)
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external
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onlyAuthorized()
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{
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// `transferFrom`.
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// The function is marked `external`, so no abi decodeding is done for
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// us. Instead, we expect the `calldata` memory to contain the
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// following:
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//
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// | Area | Offset | Length | Contents |
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// |----------|--------|---------|-------------------------------------|
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// | Header | 0 | 4 | function selector |
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// | Params | | 4 * 32 | function parameters: |
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// | | 4 | | 1. offset to assetData (*) |
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// | | 36 | | 2. from |
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// | | 68 | | 3. to |
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// | | 100 | | 4. amount |
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// | Data | | | assetData: |
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// | | 132 | 32 | assetData Length |
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// | | 164 | ** | assetData Contents |
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//
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// (*): offset is computed from start of function parameters, so offset
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// by an additional 4 bytes in the calldata.
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//
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// WARNING: The ABIv2 specification allows additional padding between
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// the Params and Data section. This will result in a larger
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// offset to assetData.
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// Asset data itself is encoded as follows:
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//
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// | Area | Offset | Length | Contents |
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// |----------|--------|---------|-------------------------------------|
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// | Header | 0 | 4 | function selector |
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// | Params | | 1 * 32 | function parameters: |
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// | | 4 | 12 + 20 | 1. token address |
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// Transfer tokens.
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// We do a raw call so we can check the success separate
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// from the return data.
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// We construct calldata for the `token.transferFrom` ABI.
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// The layout of this calldata is in the table below.
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//
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// | Area | Offset | Length | Contents |
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// |----------|--------|---------|-------------------------------------|
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// | Header | 0 | 4 | function selector |
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// | Params | | 3 * 32 | function parameters: |
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// | | 4 | | 1. from |
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// | | 36 | | 2. to |
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// | | 68 | | 3. amount |
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bytes4 transferFromSelector = IERC20Token(0).transferFrom.selector;
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bool success;
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assembly {
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/////// Token contract address ///////
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// The token address is found as follows:
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// * It is stored at offset 4 in `assetData` contents.
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// * This is stored at offset 32 from `assetData`.
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// * The offset to `assetData` from Params is stored at offset
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// 4 in calldata.
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// * The offset of Params in calldata is 4.
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// So we read location 4 and add 32 + 4 + 4 to it.
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let token := calldataload(add(calldataload(4), 40))
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/////// Setup State ///////
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// `cdStart` is the start of the calldata for `token.transferFrom` (equal to free memory ptr).
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let cdStart := mload(64)
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/////// Setup Header Area ///////
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// This area holds the 4-byte `transferFromSelector`.
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// Any trailing data in transferFromSelector will be
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// overwritten in the next `mstore` call.
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mstore(cdStart, transferFromSelector)
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/////// Setup Params Area ///////
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// We copy the fields `from`, `to` and `amount` in bulk
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// from our own calldata to the new calldata.
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calldatacopy(add(cdStart, 4), 36, 96)
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/////// Call `token.transferFrom` using the calldata ///////
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success := call(
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gas, // forward all gas
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token, // call address of token contract
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0, // don't send any ETH
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cdStart, // pointer to start of input
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100, // length of input
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cdStart, // write output over input
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32 // output size should be 32 bytes
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)
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/////// Check return data. ///////
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// If there is no return data, we assume the token incorrectly
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// does not return a bool. In this case we expect it to revert
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// on failure, which was handled above.
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// If the token does return data, we require that it is a single
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// nonzero 32 bytes value.
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// So the transfer succeeded if the call succeeded and either
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// returned nothing, or returned a non-zero 32 byte value.
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success := and(success, or(
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iszero(returndatasize),
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and(
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eq(returndatasize, 32),
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gt(mload(cdStart), 0)
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)
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))
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}
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require(
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success,
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"TRANSFER_FAILED"
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);
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}
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/// @dev Internal version of `transferFrom`.
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/// @param assetData Encoded byte array.
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/// @param from Address to transfer asset from.
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