As per Aave documentation for liquidationCall
one must pass uint(-1) for debtToCover parameter in order to liquidate the maximum amount possible for an account with a healthFactor < 1. How is it possible to encode -1 as a uint256 using web3, ethers, etc?
Attempting this using web3, for example yields an error.
> web3.eth.abi.encodeParameter("uint", "-1")
Uncaught:
Error: value out-of-bounds (argument=null, value="-1", code=INVALID_ARGUMENT, version=abi/5.0.7)
at Logger.makeError (-/node_modules/@ethersproject/logger/lib/index.js:199:21)
at Logger.throwError (-/node_modules/@ethersproject/logger/lib/index.js:208:20)
at Logger.throwArgumentError (-/node_modules/@ethersproject/logger/lib/index.js:211:21)
at NumberCoder.Coder._throwError (-/node_modules/web3-eth-abi/node_modules/@ethersproject/abi/lib/coders/abstract-coder.js:40:16)
at NumberCoder.encode (-/node_modules/web3-eth-abi/node_modules/@ethersproject/abi/lib/coders/number.js:40:18)
at -/node_modules/web3-eth-abi/node_modules/@ethersproject/abi/lib/coders/array.js:71:19
at Array.forEach (<anonymous>)
at Object.pack (-/node_modules/web3-eth-abi/node_modules/@ethersproject/abi/lib/coders/array.js:57:12)
at TupleCoder.encode (-/node_modules/web3-eth-abi/node_modules/@ethersproject/abi/lib/coders/tuple.js:36:24)
at AbiCoder.encode (-/node_modules/web3-eth-abi/node_modules/@ethersproject/abi/lib/abi-coder.js:86:15)
at ABICoder.encodeParameters (-/node_modules/web3-eth-abi/lib/index.js:120:27)
at ABICoder.encodeParameter (-/node_modules/web3-eth-abi/lib/index.js:78:17) {
reason: 'value out-of-bounds',
code: 'INVALID_ARGUMENT',
argument: null,
value: '-1'
uint
stands for "unsigned integer", so it doesn't accept -1
as a valid value.
Solidity converts uint(-1)
to the maximal value of uint
up to the version 0.7.6, because the value underflows.
pragma solidity ^0.7;
contract MyContract {
// returns 115792089237316195423570985008687907853269984665640564039457584007913129639935
function foo() external pure returns (uint256) {
return uint(-1);
}
}
Version 0.8.0 introduced automatic revert on integer underflow/overflow, and it doesn't even allow casting the -1
literal to uint
, but you can test the revert this way:
pragma solidity ^0.8;
contract MyContract {
// reverts on underflow
function foo() external pure returns (uint256) {
uint256 number = 0;
number--;
return number;
}
}
Many JS libraries also don't allow passing -1
to the "unsigned integer" simply because it's an invalid value for the datatype. But since the -1
effectively represents the maximal value in older versions of Solidity, you can pass the uint maximal value.
For uint8
, that's (2^8)-1
(or 255)
const BN = web3.utils.BN;
const number = (new BN(2)).pow(new BN(8)).sub(new BN(1));
console.log(number.toString());
For uint256
, that's (2^256)-1
(or the large number starting 115...)
const BN = web3.utils.BN;
const number = (new BN(2)).pow(new BN(256)).sub(new BN(1));
console.log(number.toString());