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Elixir Ethers

Ethers is a comprehensive Web3 library for interacting with smart contracts on the Ethereum (Or any EVM based blockchain) using Elixir.

Inspired by ethers.js and web3.js, Ethers leverages Elixir's amazing meta-programming capabilities to generate Elixir modules for give smart contracts from their ABI. It also generates beautiful documentation for those modules which can further help developers.

Installation

You can install the package by adding ethers (and optionally ex_secp256k1) to the list of dependencies in your mix.exs file:

def deps do
  [
    {:ethers, "~> 0.5.5"},
    # Uncomment next line if you want to use local signers
    # {:ex_secp256k1, "~> 0.7.2"}
  ]
end

The complete documentation is available on hexdocs.

Configuration

To use Elixir Ethers, ensure you have a configured JSON-RPC endpoint. Configure the endpoint using the following configuration parameter.

# config.exs
config :ethers,
  rpc_client: Ethereumex.HttpClient, # Defaults to: Ethereumex.HttpClient
  keccak_module: ExKeccak, # Defaults to: ExKeccak
  json_module: Jason, # Defaults to: Jason
  secp256k1_module: ExSecp256k1, # Defaults to: ExSecp256k1
  default_signer: nil, # Defaults to: nil, see Ethers.Signer for more info
  default_signer_opts: [] # Defaults to: []

# If using Ethereumex, you can specify a default JSON-RPC server url here for all requests.
config :ethereumex, url: "[URL_HERE]"

You can use one of the RPC URLs for your chain/wallet of choice or try out one of them from chainlist.org.

For more configuration options, refer to ethereumex.

To send transactions, you need a wallet client capable of signing transactions and exposing a JSON-RPC endpoint.

Usage

To use Elixir Ethers, you must have your contract's ABI in json format, which can be obtained from etherscan.io. This library also contains standard contract interfaces such as ERC20, ERC721 and some more by default (refer to built-in contracts in hexdocs).

Create a module for your contract as follows:

defmodule MyERC20Token do
  use Ethers.Contract,
    abi_file: "path/to/abi.json",
    default_address: "[Contract address here (optional)]"

  # You can also add more code here in this module if you wish
end

Calling contract functions

After defining the module, all the functions can be called like any other Elixir module.

To fetch the results (return value(s)) of a function you can pass your function result to the Ethers.call/2 function.

# Calling functions on the blockchain
iex> MyERC20Token.balance_of("0x[Address]") |> Ethers.call()
{:ok, 654294510138460920346}

Refer to Ethers.call/2 for more information.

Sending transaction

To send transaction (eth_sendTransaction) to the blockchain, you can use the Ethers.send/2 function.

Ensure that you specify a from option to inform your client which account to use as the signer:

iex> MyERC20Token.transfer("0x[Recipient]", 1000) |> Ethers.send(from: "0x[Sender]")
{:ok, "0xf313ff7ff54c6db80ad44c3ad58f72ff0fea7ce88e5e9304991ebd35a6e76000"}

Refer to Ethers.send/2 for more information.

Getting Logs (Events)

Ethers provides functionality for creating event filters and fetching related events from the blockchain. Each contract generated by Ethers also will have EventFilters module (e.g. MyERC20Token.EventFilters) that can be used to create filters for events.

To create an event filter and then use Ethers.get_logs/2 function like the below example.

# Create The Event Filter
# (`nil` can be used for a parameter in EventFilters functions to indicate no filtering)
iex> filter = MyERC20Token.EventFilters.transfer("0x[From Address Here]", nil)

# Then you can simply list the logs using `Ethers.get_logs/2`

iex> Ethers.get_logs(filter)
{:ok,
 [
   %Ethers.Event{
     address: "0x5883c66ca442461d406f330775d42954bfcf7d92",
     block_hash: "0x83de67fd285067b838790406ea68f21a3afbc0ade534047725b5ccfb904c9ed3",
     block_number: 17077047,
     topics: ["Transfer(address,address,uint256)",
      "0x6b75d8af000000e20b7a7ddf000ba900b4009a80",
      "0x230507f6a391ae5ac0ec124f1c5b8ce454fe3f3d"],
     topics_raw: ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
      "0x0000000000000000000000006b75d8af000000e20b7a7ddf000ba900b4009a80",
      "0x000000000000000000000000230507f6a391ae5ac0ec124f1c5b8ce454fe3f3d"],
     transaction_hash: "0xaa6fb2e1bbb27f667e76b03e8cde23db694207e06b9aa810d4c20c1f109a58e5",
     transaction_index: 0,
     data: [761112156078097834180608],
     log_index: 0,
     removed: false
   },
   %Ethers.Event{...},
    ...
 ]}

Resolving Ethereum names (ENS domains) using Ethers

To resolve ENS or any other name service provider (which are ENS compatible) in the blockchain you can simply use Ethers.NameService module.

iex> Ethers.NameService.resolve("vitalik.eth")
{:ok, "0xd8da6bf26964af9d7eed9e03e53415d37aa96045"}

Built-in contract interfaces in Ethers

Ethers already includes some of the well-known contract interface standards for you to use. Here is a list of them.

ERC20 - The well know fungible token standard
ERC165 - Standard Interface detection
ERC721 - Non-Fungible tokens (NFTs) standard
ERC777 - Improved fungible token standard
ERC1155 - Multi-Token standard (Fungible, Non-Fungible or Semi-Fungible)
Multicall - Multicall3

To use them you just need to specify the target contract address (:to option) of your token and call the functions. Example:

iex> tx_data = Ethers.Contracts.ERC20.balance_of("0x[Holder Address]")
#Ethers.TxData<
  function balanceOf(
    address _owner "0x[Holder Address]"
  ) view returns (
    uint256 balance
  )
>

iex> Ethers.call(tx_data, to: "0x[Token Address]")
{:ok, 123456}

Documentation

For a detailed documentation visit Ethers hexdocs page.

Generated documentation for functions and event filters

Ethers generates documentation for all the functions and event filters based on the ABI data. To get the documentation you can either use the h/1 IEx helper function or generate HTML/epub docs using ExDoc.

Get the documentation of a contract function

iex(3)> h MyERC20Token.balance_of

                             def balance_of(owner)

  @spec balance_of(Ethers.Types.t_address()) :: Ethers.TxData.t()

Prepares balanceOf(address _owner) call parameters on the contract.

This function should only be called for result and never in a transaction on
its own. (Use Ethers.call/2)

State mutability: view

## Function Parameter Types

  • _owner: `:address`

## Return Types (when called with `Ethers.call/2`)

  • balance: {:uint, 256}

Inspecting TxData and EventFilter structs

One cool and potentially useful feature of Ethers is how you can inspect the call

Get the documentation of a event filter

iex(4)> h MyERC20Token.EventFilters.transfer

                             def transfer(from, to)

  @spec transfer(Ethers.Types.t_address(), Ethers.Types.t_address()) ::
          Ethers.EventFilter.t()

Create event filter for Transfer(address from, address to, uint256 value)

For each indexed parameter you can either pass in the value you want to filter
or nil if you don't want to filter.

## Parameter Types (Event indexed topics)

  • from: :address
  • to: :address

## Event `data` Types (when called with `Ethers.get_logs/2`)

These are non-indexed topics (often referred to as data) of the event log.

  • value: {:uint, 256}

Signing Transactions

By default, Ethers will rely on the default blockchain endpoint to handle the signing (using eth_sendTransaction RPC function). Obviously public endpoints cannot help you with signing the transactions since they do not hold your private keys.

To sign transactions on Ethers, You can specify a signer module when sending/signing transactions. A signer module is a module which implements the Ethers.Signer behaviour.

Ethers has these built-in signers to use:

Ethers.Signer.Local: A local signer which loads a private key from signer_opts and signs the transactions.
Ethers.Signer.JsonRPC: Uses eth_signTransaction Json RPC function to sign transactions. (Using services like Consensys/web3signer or geth)

For more information on signers, visit hexdocs.

Example

MyERC20Token.transfer("0x[Recipient]", 1000)
|> Ethers.send(
  from: "0x[Sender]",
  signer: Ethers.Signer.Local,
  signer_opts: [private_key: "0x..."]
)

Switching the ex_keccak library

ex_keccak is a Rustler NIF that brings keccak256 hashing to elixir. It is the default used library in ex_abi and ethers. If for some reason you need to use a different library (e.g. target does not support rustler) you can use the Application config value and on top of that set the environment variable SKIP_EX_KECCAK=true so ex_keccak is marked as optional in hex dependencies.

# config.exs
config :ethers, keccak_module: MyKeccakModule

# Also make sure to set SKIP_EX_KECCAK=true when fetching dependencies and building them

Contributing

All contributions are very welcome (as simple as fixing typos). Please feel free to open issues and push Pull Requests. Just remember to be respectful to everyone!

To run the tests locally, follow below steps:

Install ethereum and solc. For example, on MacOS

brew install ethereum
npm install -g solc

Run anvil (from foundry). After installing anvil, just run the following in a new window

> anvil

Then you should be able to run tests through mix test.

Acknowledgements

Ethers was possible to make thanks to the great contributors of the following libraries.

And also all the people who contributed to this project in any ways.

License

Apache License 2.0

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