I'm trying to implement an upgradable function through delegation. Essentially, the fallback function of contract A is implemented in such a way that when calling function F on contract A, the execution is delegated to function F (same function signature( on contract B.
Callback function looks like this
function() external payable {
address delegate = delegates[msg.sig];
require(delegate != address(0), "Function does not exist.");
assembly {
let ptr := mload(0x40)
calldatacopy(ptr, 0, calldatasize)
let result := delegatecall(gas, delegate, ptr, calldatasize, 0, 0)
let size := returndatasize
returndatacopy(ptr, 0, size)
switch result
case 0 {revert(ptr, size)}
default {return (ptr, size)}
}
}
I ran into problem when trying to use web3.py to call function F in said contract A. I trie a few different things:
// Case 1
Contract.functions.F().buildTransaction()
^ this caused the web3.py to complain that function F is not in contract A's ABI. So then I thought the fallback function uses msg.sig as function signature, so I tried to pass the signature as "data".
// Case 2
Contract.fallback.buildTransaction({'data': "0x61455567"})
// 0x61455567 == bytes4(keccak256("updateContract(address,string,string)"))
which also didn't work because web3.py says "data" cannot be called when building transaction. Finally, I thought I could pass the data field after building the transaction, so I did:
// Case 3
txn_hash = Contract.fallback.buildTransaction({'gas': 1000000})
txn_hash['data'] = "0x837b4bd1"
This time, web3.py didn't complain but the transaction failed on the blockchain (on Rinkeby testnet).
Any help on how to use web3.py to call a custom fallback function?
You can simply use sendTransaction and then it will go into the fallback function.
web3.eth.sendTransaction({'to': contractAddress, 'from': yourAddress, 'data': "0x61455567"})
EDIT:
You can also sign a transaction locally, reference
Related
I am writing a pull payment function and, as with any external call it is good practice validate the result and check successful execution. I am using the following interface:
interface IAaveLendingPool {
function deposit(
address asset,
uint256 amount,
address onBehalfOf,
uint16 referralCode
) external;
function withdraw(
address asset,
uint256 amount,
address to
) external;
function getReservesList() external view returns (address[] memory);
}
aAveLendingPool= IAaveLendingPool(0x0543958349aAve_pooladdress)
The interface provided by Aave doesn't specify a return either. The withdraw function of the LendingPool.sol contract returns external override whenNotPaused returns (uint256).
The question: Can I use the returned uint to validate successful execution or aAveLendingPool.withdraw() returns a boolean? Will the following work as expected?
///#notice assigns dai to caller
require( aaveLendingPool.withdraw(
address(dai),
amount,
msg.sender), "Error, contract does not have enough DAI")
Please provide a solidity docs link to external function call return value, if any.
According to the Consensys Diligence Aave V2 audit:
ERC20 implementations are not always consistent. Some implementations of transfer and transferFrom could return ‘false’ on failure instead of reverting. It is safer to wrap such calls into require() statements to these failures.
Therefore, wrapping the transfer call in a require check is safe and sufficient.
require( aaveLendingPool.withdraw(
address(dai),
amount,
msg.sender), "Error, contract does not have enough DAI")
I can use the router02 function to swap tokens on uniswap:
route02.swapExactTokensForTokens(amtIn, amtOut,
[t1.address, t2.address], addr, deadline(), {gasLimit: 4000000});
But how to call the low level swap function for uniswap directly? Here is my code but it didn't work. I have already send tokens to uni_v2_address before this function call.
const ethers = require('ethers');
const uni = new ethers.Contract(UNI_V2_ADDRESS, IUniswapV2Pair.abi, wallet);
let amt0out = BigInt(1) * BigInt(10**16);
let amt1out = BigInt(0);
//do swap
let tx = await uni.swap(amt0out, amt1out,
addr, 0x0, {gasLimit: 4000000});
Remove the fourth parameter "data" like this:
let tx = await uni.swap(amt0out, amt1out, addr, {gasLimit: 4000000});
Passing anything in the fourth "data" parameter initiates a Flash Swap, optimistically transferring tokens to addr and attempting to call a function named "uniswapV2Call" on the addr as described here:
Uniswap Flash Swaps Documentation
This really needs to be done from a contract, hence the router. This is not safe to do without a contract, as you either have to handle the callback (like above using flashswap) or you have to send the tokens to the contract and then call the swap function. If not done in same transaction you will lose the tokens
I have a problem about handle function value.
likes the title ..
I already know contract's function call other contract's function depend on：
addr.call(abi.encodeWithSignature("function(parameter_type)", parameter ));
but what if I want to handle the function's value(ex：bool) temporarily (memory) for condition .
I had seen abi.encodePacked() , but I don't even know what parameter feedback to me (compile error , different parameter type), that I can't even storage it .
Some articles write it only for bytes, uint , but I only want to do condition(bool).
You don't need to do that .call unless you want to preserve the msg.sender.
If the msg.sender does not matter for you, I recommend you to look at interfaces. Now, what you have to do, is to create an interface with the functionB definition of that you want to call, and then call it.
Example:
(some deployed contract)
contract MySecondContract {
function functionB() public returns(bool) {
return true;
}
}
(get the deployed contract address and use it in your code like)
interface IMySecondContract {
function functionB() external returns(bool);
}
contract MyFirstContract {
function functionA() public returns(bool) {
bool result = IMySecondContract(MySecondContract-address-here).functionB();
return result;
}
}
If you do want to keep using .call, here you can see that the .call method returns two values.
Something like
(bool success, bytes myReturn) = addr.call(...);
and then this, might work.
Something else that might help is this new way of debugging.
I am trying to learn solidity through coding the smart contract below (see snippet below) .
I have been able to successfully compile (i.e. without bugs) the smart contract, the object of which is to payout an inheritance from one ethereum wallet address to another (e.g. a family member).
I have also been able to deploy it but I get the following error message (also see attached pic) when i try to transfer an inheritance to a payee.
Any help is greatly appreciated !
error message:
"transact to Will.setInheritance errored: VM error: revert.
revert The transaction has been reverted to the initial state.
Note: The constructor should be payable if you send value. Debug the transaction to get more information"
pragma solidity ^0.5.1;
//Use a double forward slash to write a like this one
// Line1 : First we nominate which version of the SOLIDITY code we are using.
//This is always the first step in our code.
// Here we tell REMIX that the the source code we are using is version 0.5.1 or above (by using the ^ - carrot symbol)
// We will start building our SC which will eventually split the inheritance of a persons will (e.g. Grandfather) amongst the Family members
contract Will {
//Line 9 : Each new contract must be named as “contract”, then the name with the first letter always CAPITALIZED, followed by open/close curly brackets to contain the logic.
address owner;
uint fortune;
bool isDeceased;
// Line 13: here we declare the variables of the smart contract - each variable must be listed along with its variable type in SOLIDITY
// Line 13: owner is of the address type of variable in SOLIDITY (unique variable in SOLIDITY - refers to an ethereum network address)
// Line 14: fortune is of the type uint (unsigned integer = a positive only integer)
// Line 15: isDeceased is a boolean variable (i.e. TRUE or FALSE type)
constructor() public payable {
owner = msg.sender;
fortune = msg.value;
isDeceased = false;
}
// Line 22: here we use a constructor function to set these values in he contract
// The “public” keyword is what’s known as a “visibility modifier” which tells the contract who is allowed to call the function.
// Public means that the function can be called within the contract and outside of it by someone else or another contract.
// The “payable” keyword allows the function to send and receive ether.
// When we deploy the contract we can initialize it with an ether balance.
// When the contract receives ether, it will store it in its own address.
// Then we will use the SC to transfer the ether to another adress (or inheritor)
// Line 23: we set the owner to “msg.sender”, which is a built-in global variable representative of the address that is calling the function.
//In this case, it will be the owner of the funds.
// Line 24: The fortune is set to “msg.value”, which is another built-in variable that tells us how much ether has been sent.
// Line 25: We set the isDeceased to false
modifier onlyOwner {
require (msg.sender ==owner);
_;
}
modifier mustBeDeceased {
require (isDeceased == true);
_;
}
// Modifiers are add-ons to functions that contain conditional logic.
// Line 41 declares “onlyOwner” modifier.
// If added to a function, it can only be called if the caller (msg.sender) is equivalent to the owner variable as stated above (remember how we set the owner in the constructor). We will need this to allow the distribution of funds, which will be implemented later.
// The “require” keyword states that we want isDeceased to be true otherwise solidity will throw an error and the execution will stop.
// The “_;” at the end tells the execution to shift to the actual function after it’s done reading the modifier.
// Now we must declare how the inheritance is divided amongst the family members.
// We will need their public wallet keys (addresses) and their desired allotments.
// First we create a list to store the wallet addresses (of the family members)
// And we create a and a function that sets the inheritance for each address.
address payable[] wallets;
//ABOVE WE HAVE TO ENTER payable to tell SOLIDITY that the address for the payout of the money is the wallet address
// function will not work without adding "address" here
mapping (address => uint) inheritance;
function setInheritance(address payable _wallet, uint _inheritance) public onlyOwner {
wallets.push(_wallet);
inheritance [_wallet] = _inheritance;
}
// Line 67: declares an empty array called “wallets” for storing the family members’ wallet addresses.
// This is a list-like data structure . The square brackets after “address” indicate it’s an array of items rather than a single variable.
// Line 69: Creates a mapping from an address type to a uint type named “inheritance”
// We will use this for distributing the inheritance to a family members wallet (It’s the equivalent of a “dictionary” in other languages such as Python and Javascript, Key/Value Pair).
// Line 71 declares the function that adds an address to the (empty) inheritance array we just created and then sets the inheritance to be provided to this address.
// We added the the “onlyOwner” modifier we added to this function, which means that only the owner of the money can distribute the funds
// Finally we create the payout function, i.e. the actual transfer of the funds
function payout() private mustBeDeceased {
for (uint i=0; i<wallets.length; i++) {
wallets[i].transfer(inheritance[wallets[i]]);
}
}
function deceased() public payable onlyOwner {
isDeceased = true;
payout();
}
}
Solidity error message i receive when i try to transfer the payment to the payee
I executed your code and examine in depth. Note that currently remix and solidity does not show good and meaningful error messages.
The problem here is your constructor function is payable:
constructor() public payable {
owner = msg.sender;
fortune = msg.value;
isDeceased = false;
}
And if you execute constructor without any value it will execute also the setInheritance will execute without error and when you try to run the deceased function which is another payable function, then the things will blast. The remix will say the constructor is payable but did not sent any value.
Please try to send some value if you want to run any payable function. Here you can write value for payable functions.
Hope it helps.
In the http://truffleframework.com/tutorials/pet-shop example, there is the following contract, and the function adopt(uint petId) has only one parameter.
contract Adoption {
address[16] public adopters;
function adopt(uint petId) public returns (uint) {
require(petId >= 0 && petId <= 15);
adopters[petId] = msg.sender;
return petId;
}
function getAdopters() public returns (address[16]) {
return adopters;
}
}
However, in the javascript code app.js, the handleAdopt function call the contract function using the following code.
App.contracts.Adoption.deployed().then(function(instance) {
adoptionInstance = instance;
return adoptionInstance.adopt(petId, {from: account});
})
The function is called with the extra object {from: account}. Why? And is this parameter discarded in the solidity code?
BTW, there is an undefined global variable web3? Is the value be assigned by the MetaMask extension?
That is the transactionObject which describes general information about all transaction calls (gas limit, price, amount of ether to send, etc.). The JS code you posted is using the web3 library. That's not the direct call to the contract API. The web3 library converts it to an RPC. The transactionObject comes after all of the contract parameters. There is another parameter that comes after which is the callback with the results of the contract call (see here).
These are all of the options for the transactionobject described from the docs:
from: String - The address for the sending account. Uses the web3.eth.defaultAccount property, if not specified.
to: String - (optional) The destination address of the message, left undefined for a contract-creation transaction.
value: Number|String|BigNumber - (optional) The value transferred for the transaction in Wei, also the endowment if it's a contract-creation transaction.
gas: Number|String|BigNumber - (optional, default: To-Be-Determined) The amount of gas to use for the transaction (unused gas is refunded).
gasPrice: Number|String|BigNumber - (optional, default: To-Be-Determined) The price of gas for this transaction in wei, defaults to the mean network gas price.
data: String - (optional) Either a byte string containing the associated data of the message, or in the case of a contract-creation transaction, the initialisation code.
nonce: Number - (optional) Integer of a nonce. This allows to overwrite your own pending transactions that use the same nonce.