I'm not having so much experience with ERC721 token standard, currently I'm working on a real-estate DAPP. I have a question. if I want to add external information related to a specific property like Location, Price, property number etc. every time if a new property register, what will be the best way to do that..?? but I don't want this with solidity Struct, is it possible to extend the ERC721 Metadata Interface Contract?? or any other solution??
I have tried almost everything but I think I'm missing something.
If you want to store the data on-chain, a mapping (uint256 => Property), where the uint256 is the token ID and Property is "struct(location, price, ...)", containing the data is probably the cheapest option gas-wise.
But since your question states you don't want to use struct, you can chose to store the data on-chain with a series of mappings:
mapping (uint256 => string) tokenIdToLocation;
mapping (uint256 => uint64) tokenIdToUsdPrice;
// etc.
You can also decide to store the data off-chain, and link to this storage from your contract. In that case, you'd implement the tokenURI() function of the ERC721Metadata interface (both defined in the ERC-721 standard). The tokenUri() would return a (string) URL of an off-chain resource where you can display the (off-chain) data.
Please see this post where I finally found a solution. It includes a sample implementation for both ERC20 and ERC721, forked from an implementation of Kaleido's Firefly and amended to cater for the mentioned Real Estate dApp. Hope it helps someone.
https://ethereum.stackexchange.com/questions/139698/example-adding-custom-data-to-erc20-token-transfer/
Related
When I decoded and checked a transaction's log about the polygon contract (0x0000000000000000000000000000000000001010), I found the signature like "LogFeeTransfer(address,address,address,uint256,uint256,uint256,uint256,uint256)".
However I can't find that polygon contract emits this event.
What's this event for and where is used in the contract?
Thank you.
I searched the contract source code on polygonscan for "emit LogFeeContract".
This address on Polygon most likely holds a precompiled contract - which is usually not written in Solidity but in language of the client software (Golang, JS, ...).
My guess is that it's just a Solidity representation of the original Golang (or any other) code, so that it doesn't confuse users that there is no contract on this address on PolygonScan even though this address is publicly known as the native token address.
The Golang implementation can also emit events, as it's literally part of the node client software.
I wasn't able to find any specific implementation in other language apart from Solidity, but my answer is based on the fact that the ...1010 address is within the range of reserved addresses for precompiled contracts on Ethereum - https://eips.ethereum.org/EIPS/eip-1352. Even though Polygon might technically ignore this EIP.
More info on precompiles: https://ethereum.stackexchange.com/search?q=precompiled
I can't figure out if i need to Deploy a smart contract for each transfer? or can 1 smart contract serve several transactions? Thanks ahead
You don't need to deploy another smart contract to transfer NFTs.
Info about each token ownership is stored in its collection contract. So you just need to execute the safeTransferFrom() function on the collection contract from the current owner address, passing it following params:
current owner (_from)
receiver (_to)
token ID (_tokenId)
There are several ways to execute the function from a regular (non-contract) address, for example using the UI of EtherScan/BSCScan under the Contract -> Write Contract section on the detail page of the collection contract address.
Note: All assuming the collection contract follows the ERC-721 standard.
When looking at other team's smart contracts, I often see code like this:
address constant public token = address(0xabc123...);
Where the hexadecimal number is the address of an earlier-deployed smart contract. Coming from JS and C++ background, I'm not a fan of this because it effectively hardcodes what should be in a configuration file directly into the smart contract code. Several questions come to mind when I see code like this:
What if I want to deploy this to another EVM-compatible network?
What if I want to deploy this to testnet?
I'm still relatively new to Solidity, so it's possible I'm missing some feature of truffle that allows me to insert these strings at the time of deployment, but I didn't see this mentioned in any of the tutorials I went through. I would much rather have something like a JSON configuration file for testnet/mainnet/L2-chain/etc instead of having N versions of the same file with minor differences. How should I handle these cases?
You can have a variable (instead of a constant) containing the token address. And this variable can be set from a constructor.
So you can effectively pass the value from an environment variable to the contract constructor, to the contract storage.
Example:
.env
TOKEN_ADDRESS=0x123
deploy.js using Truffle (docs) for example
MyContract.new(process.env.TOKEN_ADDRESS)
You can also use Hardhat (docs) or any other library allowing you to deploy to any network depending on the config.
MyContract.sol
pragma solidity ^0.8;
contract MyContract {
address token;
constructor(address _token) {
token = _token;
}
}
Given an address of a smart contract deployed to RSK, how can I tell if it is an NFT or not? Is there a "standard" way to do this?
Yes there is a definitive way to do this,
if the smart contracts implement well-known token standards for NFTs,
which in turn implement the well-known EIP165 Standard Interface Definition.
(1) The easiest way to do this is to simply look up the address on the RSK block explorer.
If the smart contract address is 0x814eb350813c993df32044f862b800f91e0aaaf0, then go to
https://explorer.rsk.co/address/0x814eb350813c993df32044f862b800f91e0aaaf0
On this page, you will see a row for "Contract Interfaces",
and in the case of this smart contract,
displays ERC165 ERC721 ERC721Enumerable ERC721Metadata.
Since this contains ERC721, we know that it implements that token standard for non-fungible tokens.
(2) The more programmatic/ DIY way to do this is to use the function defined in the EIP165 standard, whose interface is copied below:
interface ERC165 {
/// #notice Query if a contract implements an interface
/// #param interfaceID The interface identifier, as specified in ERC-165
/// #dev Interface identification is specified in ERC-165. This function
/// uses less than 30,000 gas.
/// #return `true` if the contract implements `interfaceID` and
/// `interfaceID` is not 0xffffffff, `false` otherwise
function supportsInterface(bytes4 interfaceID) external view returns (bool);
}
Without going too much into the math of how this is calculated,
(read the EIP-165 standard for the full description/ explanation)
if invoking supportsInterface returns true, then you know
that that this smart contracts (claims to) implement that particular interface.
If you wish to test if a particular smart contract implements the
"Non-Fungible Token Standard":
call supportsInterface(0x80ac58cd)
If you wish to test if a particular smart contract implements the
"Multi Token Standard",
which is presently the 2nd most popular NFT standard:
call supportsInterface(0xd9b67a26)
(Note that while both of the above values are stated in their respective standards,
you may also wish to calculate them yourself, and the EIP-165 standard includes section on how to do this.)
I have a Solidity smart contract which relies on Chainlink oracles for external data that has a lot of functionality code that does not need to be replicated on a per contract basis but does change the state of the contract instance, which is why I decided the proxy pattern using delegate calls makes the most sense. In the proxy pattern I only have to deploy the byte-code for my contracts functions once, and then all other instances of my contract will just delegate call to the implementation contract, and the only new information added to the block chain will be instance fields of that specific contract.
I am able to get an implementation contract deployed and point my deployed proxy to its functions, but then when I call the lock function on the proxy I fail the check require(owner == msg.sender,"Owner only") which doesnt make sense since delegate calls are supposed to pass msg.sender and I set the owner field to msg.sender in the proxy's constructor. If I remove the require, I can call the function without a revert but the locked and debugAddr fields are unchanged, even though the lock function should change them(I thought delegate call was executed in the context of the caller?). Does anyone know what is wrong with my proxy and implementation contracts? I can guess it is to do with memory layouts or the assembly im using to do delegate calls, but I am not yet on the level where I can use my googling skills to find out what is wrong, so if someone can spot where my proxy contract is incorrect/badly formatted please let me know.
Thanks,
Ben
Lock function code snippet
//Locks in the contract, buyer should have already provided data scientist an upload only API key and their model ID
function lock() public returns (bool success)
{
debugAddr = msg.sender;
uint tempStamp = now;
//THIS IS THE REQUIRE THAT FAILS WHEN IT SHOULDNT WHEN I UNCOMMENT THIS AND DEPLOY/RUN
require(msg.sender == owner, "Only owner can lock contract.");
//require(!locked, "Cannot lock contract that is already locked.");
//require(buyer != address(0),"No buyer to lock.");
//require(bytes(buyerModelName).length != 0,"No buyerModelName to lock.");
//require((tempStamp - startTimestamp) < 158400,"Cannot lock contract that was entered by buyer over 44 hours ago.");
//require((getWeekday(tempStamp) == 0) || (getWeekday(tempStamp) == 1 && getHour(tempStamp) < 14),"Contract can only be locked in between Sunday 00:00 UTC and Monday 14:00 UTC");
LinkTokenInterface link = LinkTokenInterface(chainlinkTokenAddress());
//require(link.balanceOf(address(this)) >= totalFee, "Contract requires 0.5 LINK total to operate once locked, current LINK balance is under 0.5.");
locked = true;
return true;
}
Proxy contract with require commented(also see the contract's txs, you can see me call lock):
https://kovan.etherscan.io/address/0x1f805d559f6eb7d7b19bf0340db288503f448ae8
Implementation contract the proxy points to:
https://kovan.etherscan.io/address/0xfb41ea6452da396279cbd9d9d8c136121e38fab6
Proxy contract with require uncommented(also see the contract's txs, you can see me call lock, and the revert):
https://kovan.etherscan.io/address/0x2d59aa0c1dd9a77d592167c43f2e65adcb275bfe
Implementation contract the proxy points to:
0x20a1f27d69f7a257741eddaec433642194af0215
Proxy Code and Implementation Code
Referenced Code: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/proxy/Proxy.sol
Proxy: https://github.com/benschreyer/Steak/blob/main/SteakQuarterly/ProxyPattern/SteakQuarterlyProxy.sol
Important Note In my proxy I do not want to declare the contract as a ChainlinkClient since then ChainlinkClient's functions will be included in the proxy which is unnecessary as the implementation should have those methods already. Instead I only declare the fields and of ChainlinkClient on my own. I feel like this is a prime place for my implementation to be wrong, but I am not sure what needs to change/if this is even feasible
Implementation: https://github.com/benschreyer/Steak/blob/main/SteakQuarterly/ProxyPattern/SteakQuarterlyDelegate.sol
EDIT: MINIMAL CODE EXAMPLE THAT STILL FAILS
This contract should have the minimal requirements to be a proxy for a ChainlinkClient and only has the lock function and a constructor, I get the same revert on require(owner == msg.sender). If I remove the require, the call to lock on the proxy contract says confirmed, but the proxy's state variables remain unchanged (debugAddr is 0, locked stays false)
Here is the minimal example code(I deployed on remix IDE compiled 0.6.12, the proxy's lock function was called by using at address retrieval with the delegate code compiled so that the abi of the delegate is used): https://github.com/benschreyer/Steak/tree/main/MinimalCodeExample
EDIT 2:
If I remove the ChainlinkClient portion/fields of my proxy and implementation minimum examples as linked above, I get a proxy contract that works and can accept external function calls defined in the implementation contract as it should.
So my question now is how do I write proxy and implementation contract that supports Chainlink GET request functionality? What fields/constants/events/interfaces does my proxy need defined or imported and where should I define/import them to allow for Chainlink to work? For example if I wanted to have my contract retrieve the temperature in Paris from an API via Chainlink, but also be a proxy so that I do not have to redploy all its functions and save on gas price.
Anything I have tried so far(see minimal breaking example) does not work once I add Chainlink into the mix, as I am not sure about how to structure the Proxy contract class so that the storage of the proxy and the access/write of the delegate call to the implementation line up. Here is the minimal code that works after I remove Chainlink functionality:
https://github.com/benschreyer/Steak/tree/main/MinimalCodeExample/WorkingButNoChainlink
A version of my working example proxy/implementation pattern contracts but with Chainlink functionality, or pointers on what fields/events/cosntant the proxy contract needs in order for it to make calls to oracles would be much appreciated.
Instead of defining the fields of ChainlinkClient in your proxy class, write a class ChainlinkClientStorage that holds the fields of ChainlinkClient, then declare your Proxy as inheriting from ChainlinkClientStorage
https://github.com/benschreyer/Steak/blob/main/SteakQuarterly/ProxyPattern/ChainlinkClientStorage.sol
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/proxy/Proxy.sol
contract MyProxy is ChainlinkClientStorage, MyContractStorage{}