Ethereumex

Elixir JSON-RPC client for the Ethereum blockchain

Installation

Add Ethereumex to your mix.exs dependencies:

1. Add ethereumex to your list of dependencies in mix.exs:

def deps do
  [{:ethereumex, "~> 0.3.3"}]
end

2. Ensure ethereumex is started before your application:

def application do
  [applications: [:ethereumex]]
end

Configuration

In config/config.exs, add Ethereum protocol host params to your config file

config :ethereumex,
  url: "http://localhost:8545"

Usage

Available methods:

• web3_clientVersion
• web3_sha3
• net_version
• net_peerCount
• net_listening
• eth_protocolVersion
• eth_syncing
• eth_coinbase
• eth_mining
• eth_hashrate
• eth_gasPrice
• eth_accounts
• eth_blockNumber
• eth_getBalance
• eth_getStorageAt
• eth_getTransactionCount
• eth_getBlockTransactionCountByHash
• eth_getBlockTransactionCountByNumber
• eth_getUncleCountByBlockHash
• eth_getUncleCountByBlockNumber
• eth_getCode
• eth_sign
• eth_sendTransaction
• eth_sendRawTransaction
• eth_call
• eth_estimateGas
• eth_getBlockByHash
• eth_getBlockByNumber
• eth_getTransactionByHash
• eth_getTransactionByBlockHashAndIndex
• eth_getTransactionByBlockNumberAndIndex
• eth_getTransactionReceipt
• eth_getUncleByBlockHashAndIndex
• eth_getUncleByBlockNumberAndIndex
• eth_getCompilers
• eth_compileLLL
• eth_compileSolidity
• eth_compileSerpent
• eth_newFilter
• eth_newBlockFilter
• eth_newPendingTransactionFilter
• eth_uninstallFilter
• eth_getFilterChanges
• eth_getFilterLogs
• eth_getLogs
• eth_getWork
• eth_submitWork
• eth_submitHashrate
• db_putString
• db_getString
• db_putHex
• db_getHex
• shh_post
• shh_version
• shh_newIdentity
• shh_hasIdentity
• shh_newGroup
• shh_addToGroup
• shh_newFilter
• shh_uninstallFilter
• shh_getFilterChanges
• shh_getMessages

Examples

iex> Ethereumex.HttpClient.web3_client_version
{:ok, "Parity//v1.7.2-beta-9f47909-20170918/x86_64-macos/rustc1.19.0"}

# Using the url option will overwrite the configuration
iex> Ethereumex.HttpClient.web3_client_version(url: "http://localhost:8545")
{:ok, "Parity//v1.7.2-beta-9f47909-20170918/x86_64-macos/rustc1.19.0"}

iex> Ethereumex.HttpClient.web3_sha3("wrong_param")
{:error, %{"code" => -32602, "message" => "Invalid params: invalid format."}}

iex> Ethereumex.HttpClient.eth_get_balance("0x407d73d8a49eeb85d32cf465507dd71d507100c1")
{:ok, "0x0"}

Note that all method names are snakecases, so, for example, shh_getMessages method has corresponding Ethereumex.HttpClient.shh_get_messages/1 method. Signatures can be found in Ethereumex.Client.Behaviour. There are more examples in tests.

eth_call example - Read only smart contract calls

In order to call a smart contract using the JSON-RPC interface you need to properly hash the data attribute (this will need to include the contract method signature along with arguments if any). You can do this manually or use a hex package like (ABI)[https://github.com/exthereum/abi] to parse your smart contract interface or encode individual calls.

defp deps do
  [
    ...
    {:ethereumex, "~> 0.3.2"},
    {:abi, "~> 0.1.8"}
    ...
  ]
end

Now load the abi and pass the method signature. Note that the address needs to be converted to bytes

address           = "0x123" |> String.slice(2..-1) |> Base.decode16(case: :mixed)
contract_address  = "0x432"
abi_encoded_data  = ABI.encode("balanceOf(address)", [address]) |> Base.encode16(case: :lower)

Now you can use eth_call to execute this smart contract command:

balance_bytes = Ethereumex.HttpClient.eth_call(%{
  data: "0x" <> abi_encoded_data,
  to: contract_address
})

To convert the balance into an integer:

balance_bytes
|> String.slice(2..-1)
|> Base.decode16!(case: :lower)
|> TypeDecoder.decode_raw([{:uint, 256}])
|> List.first

eth_send_raw_transaction example - Payable smart contract call

Calling a smart contract method that requires computation will cost you gas or ether (if that method requires payment also). This means you will have to sign your transactions using the private key that owns some ethereum. In order to send signed transactions you will need both ABI and Blockchain hex packages.

abi_encoded_data = ABI.encode("transferFrom(address,address,uint)", [from_address, to_address, token_id])
contract_address = "0x123" |> String.slice(2..-1) |> Base.decode16(case: :mixed)

transaction_data = %Blockchain.Transaction{
    data: abi_encoded_data,
    gas_limit: 100_000,
    gas_price: 16_000_000_000,
    init: <<>>,
    nonce: 5,
    to: contract_address,
    value: 0
}
|> Blockchain.Transaction.Signature.sign_transaction(private_key)
|> Blockchain.Transaction.serialize()
|> ExRLP.encode()
|> Base.encode16(case: :lower)

Ethereumex.HttpClient.eth_send_raw_transaction("0x" <> transaction_data)

Custom requests

Many Ethereum protocol implementations support additional JSON-RPC API methods. To use them, you should call Ethereumex.HttpClient.request/3 method.

For example, let's call parity's personal_listAccounts method.

iex> Ethereumex.HttpClient.request("personal_listAccounts", [], [])
{:ok,
 ["0x71cf0b576a95c347078ec2339303d13024a26910",
  "0x7c12323a4fff6df1a25d38319d5692982f48ec2e"]}

Batch requests

To send batch requests use Ethereumex.HttpClient.batch_request/1 method.

requests = [
   {:web3_client_version, []},
   {:net_version, []},
   {:web3_sha3, ["0x68656c6c6f20776f726c64"]}
 ]
 Ethereumex.HttpClient.batch_request(requests)
 {
   :ok,
   [
     "Parity//v1.7.2-beta-9f47909-20170918/x86_64-macos/rustc1.19.0",
     "42",
     "0x47173285a8d7341e5e972fc677286384f802f8ef42a5ec5f03bbfa254cb01fad"
   ]
 }

Contributing

1. Fork it!
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Author

Ayrat Badykov (@ayrat555)

License

Ethereumex is released under the MIT License.