diff options
| -rw-r--r-- | packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol | 48 |
1 files changed, 35 insertions, 13 deletions
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol index 54fe7d726..32d5f394e 100644 --- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol +++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC20Transfer.sol @@ -44,38 +44,60 @@ contract MixinERC20Transfer is // Decode asset data. address token = assetData.readAddress(16); + // Transfer tokens. + // We do a raw call so we can check the success separate + // from the return data. + // We construct calldata for the `token.transferFrom` ABI. + // The layout of this calldata is in the table below. + // + // | Area | Offset | Length | Contents | + // |----------|--------|---------|-------------------------------------| + // | Header | 0 | 4 | function selector | + // | Params | | 3 * 32 | function parameters: | + // | | 4 | | 1. from | + // | | 36 | | 2. to | + // | | 68 | | 3. amount | + bytes4 transferFromSelector = IERC20Token(token).transferFrom.selector; bool success; assembly { /////// Setup State /////// // `cdStart` is the start of the calldata for `token.transferFrom` (equal to free memory ptr). let cdStart := mload(64) - // `cdEnd` is the end of the calldata for `token.transferFrom`. - let cdEnd := add(cdStart, 100) /////// Setup Header Area /////// // This area holds the 4-byte `transferFromSelector`. + // Any trailing data in transferFromSelector will be + // overwritten in the next `mstore` call. mstore(cdStart, transferFromSelector) /////// Setup Params Area /////// - // Each parameter is padded to 32-bytes. The entire Params Area is 96 bytes. - // A 20-byte mask is applied to addresses to zero-out the unused bytes. + // Each parameter is padded to 32-bytes. + // The entire Params Area is 96 bytes. + // A 20-byte mask is applied to addresses to + // zero-out the unused bytes. mstore(add(cdStart, 4), and(from, 0xffffffffffffffffffffffffffffffffffffffff)) mstore(add(cdStart, 36), and(to, 0xffffffffffffffffffffffffffffffffffffffff)) mstore(add(cdStart, 68), amount) - /////// Call `token.transferFrom` using the constructed calldata /////// + /////// Call `token.transferFrom` using the calldata /////// success := call( - gas, - token, - 0, - cdStart, - sub(cdEnd, cdStart), - cdStart, - 32 + gas, // forward all gas + token, // call address of token contract + 0, // don't send any ETH + cdStart, // pointer to start of input + 100, // length of input + cdStart, // write output over input + 32 // output size should be 32 bytes ) - // The transfer succeeded if the call succeeded and either + /////// Check return data. /////// + // If there is no return data, we assume the token incorrectly + // does not return a bool. In this case we expect it to revert + // on failure, which was handled above. + // If the token does return data, we require that it is a single + // nonzero 32 bytes value. + // So the transfer succeeded if the call succeeded and either // returned nothing, or returned a non-zero 32 byte value. success := and(success, or( iszero(returndatasize), |