Document noThrow wrapper and correct fixed array offset
This commit is contained in:
Remco Bloemen
committed by
Amir Bandeali
Amir Bandeali
parent
6d7097eed5
commit
58c5e800d0
@@ -61,53 +61,95 @@ contract MixinWrapperFunctions is
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public
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returns (bool success, uint256 takerTokenFilledAmount)
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{
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bytes4 FILL_ORDER_FUNCTION_SIGNATURE = bytes4(keccak256("fillOrder(address[5],uint256[6],uint256,uint8,bytes32,bytes32)"));
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// We need to call MExchangeCore.fillOrder using a delegatecall in
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// assembly so that we can intercept a call that throws. For this, we
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// need the input encoded in memory in the Ethereum ABI format [1].
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//
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// | Offset | Length | Contents |
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// |--------|--------|------------------------------|
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// | 0 | 4 | function selector |
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// | 4 | 160 | address[5] orderAddresses |
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// | 164 | 192 | uint256[6] orderValues |
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// | 356 | 32 | uint256 takerTokenFillAmount |
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// | 388 | 32 | len(signature) |
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// | 420 | (1) | signature |
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// | (2) | (3) | padding (zero) |
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// | (4) | | end of input |
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//
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// (1): len(signature)
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// (2): 420 + len(signature)
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// (3): (32 - len(signature)) mod 32
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// (4): 420 + len(signature) + (32 - len(signature)) mod 32
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//
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// [1]: https://solidity.readthedocs.io/en/develop/abi-spec.html
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// Input size is padded to a 4 + n * 32 byte boundary
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// TODO: Construct the input array using readable Solidity instead
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// of assembly.
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uint256 mask = 0x1F;
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uint256 inputSize = 388 + (signature.length + mask) & ~mask;
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// Allocate memory for input
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uint256 signatureLength = signature.length;
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uint256 paddingLength = (32 - signatureLength) % 32
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uint256 inputSize = 420 + signatureLength + paddingLength;
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bytes memory input = new bytes(inputSize);
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// The in memory layout of `bytes memory input` starts with
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// `uint256 length`, the content of the byte array starts at
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// offset 32 from the pointer. We need assembly to access the
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// raw pointer value of `input`.
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// TODO: I can not find an official source for this.
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uint256 start;
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assembly {
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let x := mload(0x40) // free memory pointer
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mstore(x, FILL_ORDER_FUNCTION_SIGNATURE)
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// first 32 bytes of a dynamic in-memory array contains length
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mstore(add(x, 4), add(orderAddresses, 32)) // maker
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mstore(add(x, 36), add(orderAddresses, 64)) // taker
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mstore(add(x, 68), add(orderAddresses, 96)) // makerToken
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mstore(add(x, 100), add(orderAddresses, 128)) // takerToken
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mstore(add(x, 132), add(orderAddresses, 160)) // feeRecipient
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mstore(add(x, 164), add(orderValues, 32)) // makerTokenAmount
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mstore(add(x, 196), add(orderValues, 64)) // takerTokenAmount
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mstore(add(x, 228), add(orderValues, 96)) // makerFee
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mstore(add(x, 260), add(orderValues, 128)) // takerFee
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mstore(add(x, 292), add(orderValues, 160)) // expirationTimestampInSec
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mstore(add(x, 324), add(orderValues, 192)) // salt
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mstore(add(x, 356), takerTokenFillAmount)
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for {
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let src := signature
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let dst := add(x, 388)
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let end := add(add(src, mload(signature)), 32)
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} lt(src, end) {
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src := add(src, 32)
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dst := add(dst, 32)
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} {
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mstore(dst, mload(src))
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// TODO: zero the padding
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start := add(input, 32)
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}
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// Write function signature
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// We use assembly to write four bytes at a time (actually 32,
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// but we are only overwriting uninitialized data). A `bytes4`
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// is stored by value as 256-bit and right-padded with zeros.
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bytes4 FILL_ORDER_FUNCTION_SIGNATURE = bytes4(keccak256("fillOrder(address[5],uint256[6],uint256,uint8,bytes32,bytes32)"));
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assembly {
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mstore(start, FILL_ORDER_FUNCTION_SIGNATURE);
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}
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// Write orderAddresses, orderValues, takerTokenFillAmount
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// and len(signature)
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// It is done in assembly so we can write 32 bytes at a time. In
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// solidity we would have to copy one byte at a time.
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// Fixed size arrays do not have the `uint256 length` prefix that
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// dynamic arrays have [citation needed].
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assembly {
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mstore(add(start, 4), orderAddresses) // maker
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mstore(add(start, 36), add(orderAddresses, 32)) // taker
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mstore(add(start, 68), add(orderAddresses, 64)) // makerToken
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mstore(add(start, 100), add(orderAddresses, 96)) // takerToken
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mstore(add(start, 132), add(orderAddresses, 128)) // feeRecipient
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mstore(add(start, 164), orderValues) // makerTokenAmount
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mstore(add(start, 196), add(orderValues, 32)) // takerTokenAmount
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mstore(add(start, 228), add(orderValues, 64)) // makerFee
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mstore(add(start, 260), add(orderValues, 96)) // takerFee
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mstore(add(start, 292), add(orderValues, 128)) // expiration
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mstore(add(start, 356), takerTokenFillAmount)
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mstore(add(start, 388), signatureLength)
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}
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// Write signature contents and padding one byte at a time
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for (uint256 i = 0; i < signatureLength; i++) {
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input[420 + i] = signature[i];
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}
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for (uint256 i = 0; i < paddingLength; i++) {
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input[420 + signatureLength + i] = 0x00;
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}
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// Call the function
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assembly {
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success := delegatecall(
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gas, // TODO: don't send all gas, save some for returning in case of throw
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gas, // If fillOrder `revert()`s, we recover unused gas
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address, // call this contract
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x, // inputs start at x
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inputSize, // input are size
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x, // store output over input
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start, // pointer to start of input
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inputSize, // length of input
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start, // store output over input
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32 // output is 32 bytes
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)
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takerTokenFilledAmount := mload(x)
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// Read output value (uint256 takerTokenFilledAmount)
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takerTokenFilledAmount := mload(start)
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}
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return (success, takerTokenFilledAmount);
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}
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