Xogmios

Docs

Xogmios is an Elixir client for the Cardano blockchain. You can use it to perform queries, stream blocks as they become available and submit transactions to the network.

It connects to a Cardano node through Ogmios.

Ogmios is a lightweight bridge interface for a Cardano node. It offers a WebSockets API that enables local clients to speak Ouroboros' mini-protocols via JSON/RPC. - https://ogmios.dev/

Mini-Protocols supported by this library:

• Chain Synchronization
• State Query
• Tx Submission
• Mempool Monitoring (reads transactions only)

See Examples section below for information on how to use this library.

Installation

Add the dependency to mix.exs:

defp deps do
  [
    {:xogmios, ">= 0.0.0"}
  ]
end

Then run mix deps.get

Setup

The mix task xogmios.gen.client is available to help generate the necessary client code for each of the supported mini-protocols. Information on usage can be found by running the following mix task:

mix help xogmios.gen.client

For example, the following mix task generates a client module for the ChainSync mini-protocol:

mix xogmios.gen.client -p chain_sync ChainSyncClient

A new file should be created at ./lib/my_app/chain_sync_client.ex

defmodule MyApp.ChainSyncClient do
  @moduledoc """
  This module syncs with the chain and reads new blocks
  as they become available.
  """

  use Xogmios, :chain_sync

  def start_link(opts) do
    initial_state = []
    opts = Keyword.merge(opts, initial_state)
    Xogmios.start_chain_sync_link(__MODULE__, opts)
  end

  @impl true
  def handle_block(block, state) do
    IO.puts("handle_block #{block["height"]}")
    {:ok, :next_block, state}
  end
end

Add this new module to your application's supervision tree as such:

# file: application.ex
def start(_type, _args) do
  ogmios_url = System.fetch_env!("OGMIOS_URL")

  children = [
    {MyApp.ChainSyncClient, url: ogmios_url}
  ]
  #...
end

Be sure the env OGMIOS_URL is populated and then start your mix application.

The value for the url option should be set to the address of your Ogmios instance.

If you don't have access to an Ogmios endpoint, you can use https://demeter.run/ and start one for free.

Note: Xogmios only accepts ws or wss schemes. In order to connect to the Demeter Ogmios endpoint, you might need to replace the https scheme with wss on the URI that is displayed on the Demeter console.

See section below for examples of client modules.

Examples

Chain Sync

The following is an example of a module that implement the Chain Sync behaviour. In this example, the client syncs with the tip of the chain, reads the next 3 blocks and then closes the connection with the server.

defmodule ChainSyncClient do
  use Xogmios, :chain_sync

  def start_link(opts) do
    initial_state = [counter: 3]
    opts = Keyword.merge(opts, initial_state)
    Xogmios.start_chain_sync_link(__MODULE__, opts)
  end

  @impl true
  def handle_block(block, %{counter: counter} = state) when counter > 1 do
    IO.puts("handle_block #{block["height"]}")
    {:ok, :next_block, %{state | counter: counter - 1}}
  end

  @impl true
  def handle_block(block, state) do
    IO.puts("final handle_block #{block["height"]}")
    {:close, state}
  end

  @impl true
  def handle_rollback(point, state) do
    IO.puts("handle_rollback")

    # Use this information to update your custom state accordingly
    IO.puts("Block id: #{point["id"]}")
    IO.puts("Slot: #{point["slot"]}")

    {:ok, :next_block, state}
  end
end

State Query

The following illustrates working with the State Query protocol. It runs queries against the tip of the chain.

defmodule StateQueryClient do
  use Xogmios, :state_query
  alias Xogmios.StateQuery

  def start_link(opts) do
    Xogmios.start_state_link(__MODULE__, opts)
  end

  def get_current_epoch(pid \\ __MODULE__) do
    # Defaults to Ledger-state queries.
    # The following call is the same as calling
    # `StateQuery.send_query(pid, "queryLedgerState/epoch")`
    StateQuery.send_query(pid, "epoch")
  end

  def get_network_height(pid \\ __MODULE__) do
    # For network queries, scope must be explicitly used.
    StateQuery.send_query(pid, "queryNetwork/blockHeight")`
  end

  def send_query_no_params(pid \\ __MODULE__, query_name) do
    StateQuery.send_query(pid, query_name)
  end

  def send_query(pid \\ __MODULE__, query_name, query_params) do
    # Optional query params are sent as the third argument
    # to StateQuery.send_query/3
    StateQuery.send_query(pid, query_name, query_params)
  end
end

Tx Submission

The following illustrates working with the Transaction Submission protocol. It submits a signed transaction, represented as a CBOR, to the Ogmios server.

defmodule TxSubmissionClient do
  use Xogmios, :tx_submission
  alias Xogmios.TxSubmission

  def start_link(opts) do
    Xogmios.start_tx_submission_link(__MODULE__, opts)
  end

  def submit_tx(pid \\ __MODULE__, cbor) do
    # The CBOR must be a valid transaction,
    # properly built and signed
    TxSubmission.submit_tx(pid, cbor)
  end
end

Mempool Monitoring

The following illustrates working with the Mempool Monitoring protocol. It provides a way to list transactions in the mempool.

defmodule MempoolTxsClient do
  @moduledoc """
  This module prints transactions as they become available
  in the mempool
  """
  use Xogmios, :mempool_txs

  def start_link(opts) do
    Xogmios.start_mempool_txs_link(__MODULE__, opts)
  end

  # Callbacks
  @impl true
  def handle_acquired(%{"slot" => slot} = _snapshot, state) do
    IO.puts("Snapshot acquired at slot #{slot}")

    {:ok, :next_transaction, state}
  end

  @impl true
  def handle_transaction(transaction, state) do
    IO.puts("Transaction: #{transaction["id"]}")

    {:ok, :next_transaction, state}
  end
end

For examples of applications using this library, see Blocks and xogmios_watcher.

Test

Run mix test. Tests do NOT rely on a running Ogmios instance.

Help

Join the #elixir channel in the TxPipe Discord