A dart library that connects to interact with the Ethereum blockchain. It connects to an Ethereum node to send transactions, interact with smart contracts and much more!
- Connect to an Ethereum node with the rpc-api, call common methods
- Send signed Ethereum transactions
- Generate private keys, setup new Ethereum addresses
- Call functions on smart contracts and listen for contract events
- Code generation based on smart contract ABI for easier interaction
- Encode all supported solidity types, although only (u)fixed, which are not commonly used, are not supported at the moment.
Credentials and Wallets
In order to send transactions on the Ethereum network, some credentials are required. The library supports raw private keys and v3 wallet files.
import 'dart:math'; //used for the random number generator import 'package:web3lib/web3lib.dart'; // You can create Credentials from private keys Credentials fromHex = EthPrivateKey.fromHex("c87509a[...]dc0d3"); // Or generate a new key randomly var rng = Random.secure(); Credentials random = EthPrivateKey.createRandom(rng); // In either way, the library can derive the public key and the address // from a private key: var address = await credentials.extractAddress(); print(address.hex);
Another way to obtain
Credentials which the library uses to sign
transactions is the usage of a wallet file. Wallets store a private
key securely and require a password to unlock. The library has experimental
support for version 3 wallets commonly generated by other Ethereum clients:
import 'dart:io'; import 'package:web3lib/web3lib.dart'; String content = File("wallet.json").readAsStringSync(); Wallet wallet = Wallet.fromJson(content, "testpassword"); Credentials unlocked = wallet.privateKey; // You can now use these credentials to sign transactions or messages
You can also create Wallet files with this library. To do so, you first need the private key you want to encrypt and a desired password. Then, create your wallet with
Wallet wallet = Wallet.createNew(credentials, "password", random); print(wallet.toJson());
You can also write
wallet.toJson() into a file which you can later open
(select Keystore / JSON File) or other Ethereum clients like geth.
If you want to integrate
web3lib with other wallet providers, you can implement
Credentials and override the appropriate methods.
Connecting to an RPC server
The library won't send signed transactions to miners itself. Instead, it relies on an RPC client to do that. You can use a public RPC API like infura, setup your own using geth or, if you just want to test things out, use a private testnet with truffle and ganache. All these options will give you an RPC endpoint to which the library can connect.
import 'package:http/http.dart'; //You can also import the browser version import 'package:web3lib/web3lib.dart'; var apiUrl = "http://localhost:7545"; //Replace with your API var httpClient = Client(); var ethClient = Web3Client(apiUrl, httpClient); var credentials = ethClient.credentialsFromPrivateKey("0x..."); // You can now call rpc methods. This one will query the amount of Ether you own EtherAmount balance = ethClient.getBalance(credentials.address); print(balance.getValueInUnit(EtherUnit.ether));
Of course, this library supports creating, signing and sending Ethereum transactions:
import 'package:web3lib/web3lib.dart'; /// [...], you need to specify the url and your client, see example above var ethClient = Web3Client(apiUrl, httpClient); var credentials = ethClient.credentialsFromPrivateKey("0x..."); await client.sendTransaction( credentials, Transaction( to: EthereumAddress.fromHex('0xC91...3706'), gasPrice: EtherAmount.inWei(BigInt.one), maxGas: 100000, value: EtherAmount.fromUnitAndValue(EtherUnit.ether, 1), ), );
Missing data, like the gas price, the sender and a transaction nonce will be
obtained from the connected node when not explicitly specified. If you only need
the signed transaction but don't intend to send it, you can use
The library can parse the abi of a smart contract and send data to it. It can also listen for events emitted by smart contracts. See this file for an example.
Dart Code Generator
By using Dart's build system, web3lib can generate Dart code to easily access smart contracts.
To use this feature, put a contract abi json somewhere into
The filename has to end with
Then, add a
dev_dependency on the
build_runner package and run
pub run build_runner build
You'll now find a
.g.dart file containing code to interact with the contract.
Optional: Ignore naming suggestions for generated files
If importing contract ABIs with function names that don't follow dart's naming conventions, the dart analyzer will (by default) be unhappy about it, and show warnings.
This can be mitigated by excluding all the generated files from being analyzed.
Note that this has the side effect of suppressing serious errors as well, should there exist any. (There shouldn't as these files are automatically generated).
Create a file named
analysis_options.yaml in the root directory of your project:
analyzer: exclude: - '**/*.g.dart'
See Customizing static analysis for advanced options.
Feature requests and bugs
Please file feature requests and bugs at the issue tracker. If you want to contribute to this library, please submit a Pull Request.
- Support for using web3lib with browser clients such as MetaMask. [...]
- Library to interact with ethereum smart contracts. Handles encoding and decoding of the solidity contact ABI and creating transactions for calls on smart contracts.
- Library to create and unlock Ethereum wallets and operate with private keys.
- Exports low-level cryptographic operations needed to sign Ethereum transactions.