I am trying to write upgradable smart contract in ethereum. Can anyone give an example of upgradable smart contract in ethereum and accessing data.
To write an upgradable smart contract I suggest you do the following (works for me):
Create a storage contract on which you will store all your map and variables. Add a modifier to the functions changing state. This modifier should require that an address must be present in a specific map (let’s call it authorized) to change the state of map or variable. Place the owner’s address in that map.
Write a function to authorize external address on the storage contract
Deploy another contract containing the logic of your app.
Autorise the logic contract on the storage contract.
Upon upgrade of the logic, deny access to the storage contract from the logic contract, deploy your upgraded logic and link the new contract to the storage.
Tadaa you now have an upgradable set of smart contracts.
Smart Contract cannot be replaced, but you can create a smart contract proxy to be able to replace the calling of all new Smart Contract functions (previous smart contracts cannot be removed on the main network ethereum).
Complete explanation and examples can be seen Here
You can implement follow Proxy Pattern
Blog
https://medium.com/nomic-labs-blog/malicious-backdoors-in-ethereum-proxies-62629adf3357
Smart contract upgradability is a state of the art area. Currently, there are a few solutions, but each of them has its own pros and cons. Here are the solutions with examples:
https://consensys.github.io/smart-contract-best-practices/software_engineering/
Related
I am planning to issue erc20 token on ethereum and I want to use it as a payment for dapps on polygon.
How may I estublish the interaction between the contracts? A potential answer to that question might be bridging. But I tried to look for every platform to understand, how can I use my coin tokens after bridging, but failed to find any definite answer.
so my question is, if two contracts are on the same chain-
IERC20 token = IERC20(some_address);
We use the above line to call our coin token from our dapp. Since, our coin token is on different ethereum chain, after bridging, how do we call it feom a contract that will be deployed on polygon?
Will the above line of code work? Will I get a new address on polygon for my token contract?
(Recently I have seen a technique, but couldn't understand the underlying mechanism. So, there is a website called Coinvise, they let you deploy your coin airdrop contract on polygon and let you set the nft address (to know if user holds that particular nft) as eligibility condition that is deployed on ethereum. They do it on chain using something called 'sub-graph'. I do not know what this is but I'd like to know if it helps in my case.)
I am new to blockchain, please help
I'm building a DeFi application on Ethereum, and I would like to implement the Deposit function. Everything works fine between ETH and a ERC20 token that I built, but I would like to add some tokens like aToken for AAVE or cTokens for Compound that the user will receive after a Deposit call.
So the question is: is it possible to add a function in my smart contract to create multiple tokens without creating a smart contract for each of them? If not, I have to create a different contract for each token I want to add in my app or there is a best method to do it?
Yes this is possible. You can transfer the tokens to the user's address after the Compound Protocol mint operation. This can be made generic using the ERC-20 transfer interface. Be sure to account the amounts users are due and beware of the reentrancy vulnerability.
We have a smart contract factory which deploys smart contract instances. These smart contract instances use SafeMath.
We want verify code for these instance on Etherscan. But, Etherscan requires SafeMath library address to verify contract code.
How can I get the SafeMath library address for each instance?
SafeMath functions are all internal. There is no external library to link to. Hence no need to specify a library for Etherscan verification.
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol
https://solidity.readthedocs.io/en/latest/contracts.html#libraries
... code of internal library functions and all functions called from therein will at compile time be pulled into the calling contract, and a regular JUMP call will be used instead of a DELEGATECALL.
You can also ask questions about using OpenZeppelin on the Community Forum: https://forum.openzeppelin.com
Disclosure: I am the Community Manager at OpenZeppelin
When I publish a new smart contract to the Ethereum blockchain, I want to notify another contract about it.
Is there any option to do that? For example, to send transaction automatically when contract reaches the blockchain.
No, but Yes.
It wouldn't be possible to notify a contract about any contract created, and I don't see an obvious way to notify about all contracts created by a specific user.
But, there's a way to notify a contract about all instances of a certain species of contract. I suspect this is a reasonable assumption, because the interested contract is probably only interested in a certain type(s) of contract.
You would implement a factory pattern and get it to deploy the instances. The function that does the deployment would be responsible for required notifications.
Hope it helps.
So lets call E your existing contract. Ensure it has a method that we can call notify for instance. When you create your new contract, from the constructor (called when it gets deployed) then call the notify method of E.
Currently I'm trying to learn ethereum and smart contract. I read this tutorial: Dapps for beginners
I'm just wondering now, if I have to call everytime a function from a contract (as in the tutorial above) or is it possible that a specific function is executed when I just transfer some ethereum to that contract address?
Example:
I execute the code below, and the receiver address is also a address with a contract. One specific function should now be executed at the receiver function.
eth.sendTransaction({from:sender, to:receiver, value: amount})
You should create a nameless payable function in your smart contract.
This will then be the default function to execute if someone sends a raw transaction at your contract's address.
function() payable public {
}
Also, the other answer here states that you need to know the contract ABI to communicate with contracts but this is not true.
You need to know the contract address, the function name and the input and output parameter types. (You could use Web3's method.call or method.sendTransaction to send the encoded data in the transaction object and interact with the contract.)
The ABI may have this information, but the ABI is not required itself.
You can only communicate with contracts if you know the ABI which is the application binary interface.
In general, an ABI is the interface between two program modules, one of which is often at the level of machine code. The interface is the de facto method for encoding/decoding data into/out of the machine code. In ethereum, it's basicly how you can encode solidity contracts for the EVM and backwards how to read the data out of transactions.
If you have the JSON ABI of a contract, you still have to decide if you want to make calls or transactions. The difference between a call and a transaction is the following:
Transactions are created by your client, signed and broadcasted to the network. They will eventually alter the state of the blockchain, e.g., by manipulating balances or values in smart contracts.
Calls are only executed locally on your computer and not broadcasted to the network, e.g., a dry run.
Calls are usefull for debugging smart contracts as they do not cost transaction fees or gas.
So if you only send a transaction to a contract without using any interface, you wont be able to execute any code on the contract.