How to build and use ERC-1155 tokens
An intro to the new standard for having many tokens in one
ERC-1155 allows you to send multiple different token classes in one transactions. You can imagine it as transferring Chinese Yuan and US Dollars in a single transfer. ERC-1155 is most commonly known for being used in games, but there are many more use cases for it.
First of all though, what are those multi tokens?
What is ERC-1155?
The key feature introduced by ERC-1155 is multi token support. Let's say we are in a world where each airline has its own token. In a way that's not too far from reality where each airline sits in a different country with its own national currency. Now let's say I wanted to book a flight across the world with three connecting flights from three different airlines. To pay for my flight ticket, I would need to make three separate transactions and pay for each individually.
Many things could go wrong this way. What if I pay for flight 1, but then flight 2 is already booked out? Now I have to find a new connections. In the real world with centralized currencies this job is done by the online travel agency (OTA) or a more old-school traditional agency. In our example though, one would have to create a new smart contract that does all three trades in a row, deploy it and then call the trade function. A bit complicated to only pay for one flight trip, isn't it?
What if instead we created a single multi-token contract which holds the individual tokens for every airline? That's exactly what ERC-1155 allows you to do. Instead of just one token class, we can add as many as we want. Let's look at the functionality in more depth.
ERC-1155 Functions and Features:
- Batch Transfer: Transfer multiple assets in a single call.
- Batch Balance: Get the balances of multiple assets in a single call.
- Batch Approval: Approve all tokens to an address.
- EIP-165 Support: Declare supported interfaces.
- Hooks: Receive tokens hook.
- NFT support: If supply is only 1, treat it as NFT.
- Safe Transfer Rules: Set of rules for secure transfer.
1. Batch Transfer
The batch transfer works very similar to regular ERC-20 transfers. Let's look at the regular ERC-20 transferFrom function:
// ERC-20
function transferFrom(address from, address to, uint256 value) external returns (bool);The only difference in ERC-1155 is that we pass the values as an array and we also pass an array of id's. For example given _ids=[3, 6, 13] and _values=[100, 200, 5], the resulting transfers will be
- Transfer 100 tokens with id 3 from
_fromto_to. - Transfer 200 tokens with id 6 from
_fromto_to. Transfer 5 tokens with id 13 from
_fromto_to.
In ERC-1155 we only have transferFrom, no transfer. To use it like a regular transfer, just set the from address to the address that's calling the function.
- Why is it called 'safe'-BatchTransferFrom? - See section 7 below about safe transfer rules.
- Why is it not returning boolean? - The transaction reverts on failure, same as the SafeERC-20 implementation we discussed previously.
- What is the bytes data field? - Just as in ERC-777, you can pass arbitrary data along with the call which will also be passed to the receive hook.
// ERC-1155
function safeBatchTransferFrom(
address _from,
address _to,
uint256[] calldata _ids,
uint256[] calldata _values,
bytes calldata _data
) external;2. Batch Balance
The respective ERC-20 balanceOf call likewise has its partner function with batch support. As a reminder, this is the ERC-20 version:
// ERC-20
function balanceOf(address owner) external view returns (uint256);Even simpler for the balance call, we can retrieve multiple balances in a single call. We pass the array of owners, followed by the array of token ids.
For example given _ids=[3, 6, 13] and _owners=[0xbeef..., 0x1337..., 0x1111...], the return value will be
[
balanceOf(0xbeef...),balanceOf(0x1337...),balanceOf(0x1111...)
]
// ERC-1155
function balanceOfBatch(
address[] calldata _owners,
uint256[] calldata _ids
) external view returns (uint256[] memory);3. Batch Approval
The approvals are slightly different from ERC-20. Instead of approving specific amounts, you simply set an operator to approved or not approved via setApprovalForAll.
Reading the current status can be done via isApprovedForAll. As you can see, it's an all or nothing. You cannot define how many tokens to approve or even which token class.
This is intentionally designed with simplicity in mind. You can only approve everything for one address. If you need more fine granular control over specific approvals, check out EIP-1761.
// ERC-1155
function setApprovalForAll(
address _operator,
bool _approved
) external;// ERC-1155
function isApprovedForAll(
address _owner,
address _operator
) external view returns (bool);4. EIP-165 Support
If you don't know what EIP-165 is yet, see my tutorial here. In short it's way for smart contracts to define what interfaces they support. So for example, does the smart contract support receiving ERC-1155 tokens? If it does, the respective supportsInterface function must exist and return true for that contract.
Which brings us directly to the next point: hooks.
5. Receive Hook
Given the EIP-165 support, ERC-1155 supports receive hooks for smart contracts only. The hook function must return a magic predefined bytes4 value which is given as:
bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))When the receiving contract returns this value, it is assumed the contract accepts the transfer and knows how to handle the ERC-1155 tokens. Great, no more stuck tokens in a contract!
function onERC1155BatchReceived(
address _operator,
address _from,
uint256[] calldata _ids,
uint256[] calldata _values,
bytes calldata _data
) external returns(bytes4);6. NFT Support
When a supply is given as just one, the token is essentially a non-fungible token (NFT). And as is standard for ERC-721, you can define a metadata URL. The URL can be read and modified by clients, see here.
7. Safe Transfer Rules
We've touched on a few safe transfer rules already in the previous explanations. But let's look at the most important of the rules:
The caller must be approved to spend the tokens for the
_fromaddress or the caller must equal_from.- The transfer call must revert if
_toaddress is 0.- length of
_idsis not the same as length of_values. - any of the balance(s) of the holder(s) for token(s) in
_idsis lower than the respective amount(s) in_valuessent to the recipient. - any other error occurs.
Note: All batch functions including the hook also exist as version without batch. This is done for gas efficiency, considering transferring just one asset will likely still be the most commonly used way. We've left them out for simplicity in the explanations, incl. safe transfer rules. The names are identical, just remove the 'Batch'.
Implementing our Airline-Tokens with ERC-1155
We can implement the ERC-1155 very easily with the well-documented and audited Openzeppelin contracts. Install them via npm or import the Github URL directly in Remix. The documentation for the Openzeppelin ERC-1155 can be seen here.
Our previous Airline example could implemented like this:
import "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";
contract AirlineTokens is ERC1155 {
address public governance;
uint256 public airlineCount;
modifier onlyGovernance() {
require(msg.sender == governance, "only governance can call this");
_;
}
constructor(address governance_) public ERC1155("") {
governance = governance_;
airlineCount = 0;
}
function addNewAirline(uint256 initialSupply) external onlyGovernance {
airlineCount++;
uint256 airlineTokenClassId = airlineCount;
_mint(msg.sender, airlineTokenClassId, initialSupply, "");
}
}This is all we need. Now someone can call
AirlineTokens.safeBatchTransferFrom(myBuyerAddress, sellerAddress, [airlineId1, airlineId2, airlineId3], [firstFlightPrice, secondFlightPrice, thirdFlightPrice], '").
And pay in each airline currency in a single transaction. Great!
Simpler Alternative: ERC-1178
Solidity Developer
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How to get a Solidity developer job?
There are many ways to get a Solidity job and it might be easier than you think!
You have mastered the basics of Solidity, created your first few useful projects and now want to get your hands on some real-world projects. Getting a Solidity developer job might be easier than you think. There are generally plenty of options to choose from and often times not a lot of...
Design Pattern Solidity: Mock contracts for testing
Why you should make fun of your contracts
Mock objects are a common design pattern in object-oriented programming. Coming from the old French word 'mocquer' with the meaning of 'making fun of', it evolved to 'imitating something real' which is actually what we are doing in programming. Please only make fun of your smart contracts if you...
Kickstart your Dapp frontend development with create-eth-app
An overview on how to use the app and its features
Last time we looked at the big picture of Solidity and already mentioned the create-eth-app. Now you will find out how to use it, what features are integrated and additional ideas on how to expand on it. Started by Paul Razvan Berg, the founder of sablier, this app will kickstart your frontend...
The big picture of Solidity and Blockchain development in 2020
Overview of the most important technologies, services and tools that you need to know
Now, I do not know about you, but I remember when I first started with Solidity development being very confused by all the tools and services and how they work in connection with one another. If you are like me, this overview will help you understand the big picture of Solidity development. As I...
Design Pattern Solidity: Free up unused storage
Why you should clean up after yourself
You may or may not be used to a garbage collectors in your previous programming language. There is no such thing in Solidity and even if there was a similar concept, you would still be better off managing state data yourself. Only you as a programmer can know exactly which data will not be used...
How to setup Solidity Developer Environment on Windows
What you need to know about developing on Windows
Using Windows for development, especially for Solidity development, can be a pain sometimes, but it does not have to be. Once you have configured your environment properly, it can actually be extremely efficient and Windows is a very, very stable OS, so your overall experience can be amazing. The...
Avoiding out of gas for Truffle tests
How you do not have to worry about gas in tests anymore
You have probably seen this error message a lot of times: Error: VM Exception while processing transaction: out of gas Disclaimer : Unfortunately, this does not always actually mean what it is saying when using Truffle , especially for older versions. It can occur for various reasons and might be...
Design Pattern Solidity: Stages
How you can design stages in your contract
Closely related to the concept of finite-state machines, this pattern will help you restrict functions in your contract. You will find a lot of situations where it might be useful. Any time a contract should allow function calls only in certain stages. Let's look at an example: contract Pool {...
Web3 1.2.5: Revert reason strings
How to use the new feature
A new Web3 version was just released and it comes with a new feature that should make your life easier. With the latest version 1.2.5, you can now see the the revert reason if you use the new handleRevert option. You can activate it easily by using web3.eth.handleRevert = true . Now when you use...
Gaining back control of the internet
How Ocelot is decentralizing cloud computing
I recently came across an ambitious company that will completely redefine the way we are using the internet. Or rather, the way we are using its underlying infrastructure which ultimately is the internet. While looking at their offering, I also learned how to get anonymous cloud machines, you...
Devcon 5 - Review
Impressions from the conference
I had a lot to catch up on after Devcon. Also things didn't go quite as planned, so please excuse my delayed review! This year's Devcon was certainly stormy with a big typhoon warning already on day 1. Luckily (for us, not the people in Tokyo), it went right past Osaka. Nevertheless, a lot of...
Devcon 5 - Information, Events, Links, Telegram
What you need to know
Devcon 5 is coming up soon and there are already lots of events available, information about Osaka and more. Here is a short overview: Events Events Calendar Events Google Docs Events Kickback Most events are in all three, but if you really want to see all, you will have to look at all three...
Design Pattern Solidity: Off-chain beats on-chain
Why you should do as much as possible off-chain
As you might have realized, Ethereum transactions are anything but cheap. In particular, if you are computing complex things or storing a lot of data. That means sometimes we cannot put all logic inside Solidity. Instead, we can utilize off-chain computations to help us. A very simple example...
Design Pattern Solidity: Initialize Contract after Deployment
How to use the Initializable pattern
There are a few reasons why you might want to initialize a contract after deployment and not directly by passing constructor arguments. But first let's look at an example: contract MyCrowdsale { uint256 rate; function initialize(uint256 _rate) public { rate = _rate; } } What's the advantage over...
Consensys Blockchain Jobs Report
What the current blockchain job market looks like
Consensys published their blockchain jobs report which you can checkout in their Blockchain Developer Job Kit. The most interesting aspects are Blockchain developer jobs have been growing at a rate of 33x of the previous year according to LinkedIns jobs report Typical salary is about...
Provable — Randomness Oracle
How the Oraclize random number generator works
One particularly interesting approach by Provable is the usage of a hardware security device, namely the Ledger Nano S. It uses a trusted execution environment to generate random numbers and provides a Provable Connector Contract as interface. How to use the Provable Randomness Oracle? Use the...
Solidity Design Patterns: Multiply before Dividing
Why the correct order matters!
There has been a lot of progress since the beginning of Ethereum about best practices in Solidity. Unfortunately, I have the feeling that most of the knowledge is within the circle of experienced people and there aren’t that many online resources about it. That is why I would like to start this...
Devcon 5 Applications closing in one week
Devcon 5 Applications closing
Watch out for the Devcon 5 applications. You only have one week left to apply either as Buidler Student Scholarship Press Devcon is by far the biggest and most impressive Ethereum conference in the world. And it's full of developers! I am especially excited about the cool location this year in...
Randomness and the Blockchain
How to achieve secure randomness for Solidity smart contracts?
When we talk about randomness and blockchain, these are really two problems: 1. How to generate randomness in smart contracts? 2. How to produce randomness for proof-of-stake (POS) systems? Or more generally, how to produce trusted randomness in public distributed systems? There is some overlap...