Start realtime index immediately from latest block on boot.

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc.ex

@@ -56,6 +56,17 @@ defmodule EthereumJSONRPC do
   """
   @type quantity :: String.t()
 
+  @typedoc """
+  A logic block tag that can be used in place of a block number.
+
+  | Tag          | Description                    |
+  |--------------|--------------------------------|
+  | `"earliest"` | The first block in the chain   |
+  | `"latest"`   | The latest collated block.     |
+  | `"pending"`  | The next block to be collated. |
+  """
+  @type tag :: String.t()
+
   @typedoc """
   Unix timestamp encoded as a hexadecimal number in a `String.t`
   """
@@ -107,7 +118,7 @@ defmodule EthereumJSONRPC do
     block_hashes
     |> get_block_by_hash_requests()
     |> json_rpc(config(:url))
-    |> handle_get_block()
+    |> handle_get_blocks()
     |> case do
       {:ok, _next, results} -> {:ok, results}
       {:error, reason} -> {:error, reason}
@@ -121,7 +132,30 @@ defmodule EthereumJSONRPC do
     block_start
     |> get_block_by_number_requests(block_end)
     |> json_rpc(config(:url))
-    |> handle_get_block()
+    |> handle_get_blocks()
+  end
+
+  @doc """
+  Fetches block number by `t:tag/0`.
+
+  The `"earliest"` tag is the earlist block number, which is `0`.
+
+      iex> EthereumJSONRPC.fetch_block_number_by_tag("earliest")
+      {:ok, 0}
+
+  ## Returns
+
+   * `{:ok, number}` - the block number for the given `tag`.
+   * `{:error, :invalid_tag}` - When `tag` is not a valid `t:tag/0`.
+   * `{:error, reason}` - other JSONRPC error.
+
+  """
+  @spec fetch_block_number_by_tag(tag()) :: {:ok, non_neg_integer()} | {:error, reason :: :invalid_tag | term()}
+  def fetch_block_number_by_tag(tag) when tag in ~w(earliest latest pending) do
+    tag
+    |> get_block_by_tag_request()
+    |> json_rpc(config(:url))
+    |> handle_get_block_by_tag()
   end
 
   @doc """
@@ -215,6 +249,11 @@ defmodule EthereumJSONRPC do
     request(%{id: id, method: "eth_getBlockByNumber", params: get_block_by_number_params(options)})
   end
 
+  defp get_block_by_tag_request(tag) do
+    # eth_getBlockByNumber accepts either a number OR a tag
+    get_block_by_number_request(%{id: tag, tag: tag, transactions: :hashes})
+  end
+
   defp request(%{id: id, method: method, params: params}) do
     %{
       "id" => id,
@@ -271,7 +310,7 @@ defmodule EthereumJSONRPC do
       raise("bad jason")
   end
 
-  defp handle_get_block({:ok, results}) do
+  defp handle_get_blocks({:ok, results}) do
     {blocks, next} =
       Enum.reduce(results, {[], :more}, fn
         %{"result" => nil}, {blocks, _} -> {blocks, :end_of_chain}
@@ -290,10 +329,15 @@ defmodule EthereumJSONRPC do
      }}
   end
 
-  defp handle_get_block({:error, reason}) do
-    {:error, reason}
+  defp handle_get_blocks({:error, _} = error), do: error
+
+  defp handle_get_block_by_tag({:ok, %{"number" => quantity}}) do
+    {:ok, quantity_to_integer(quantity)}
   end
 
+  defp handle_get_block_by_tag({:error, %{"code" => -32602}}), do: {:error, :invalid_tag}
+  defp handle_get_block_by_tag({:error, _} = error), do: error
+
   defp handle_response(resp, 200) do
     case resp do
       [%{} | _] = batch_resp -> {:ok, batch_resp}

apps/ethereum_jsonrpc/test/etheream_jsonrpc_test.exs

@@ -0,0 +1,5 @@
+defmodule EthereumJSONRPCTest do
+  use ExUnit.Case, async: true
+
+  doctest EthereumJSONRPC
+end

apps/explorer/lib/explorer/indexer/block_fetcher.ex

@@ -74,7 +74,12 @@ defmodule Explorer.Indexer.BlockFetcher do
       receipts_concurrency: Keyword.get(opts, :receipts_concurrency, @receipts_concurrency)
     }
 
-    {:ok, schedule_next_catchup_index(state)}
+    scheduled_state =
+      state
+      |> schedule_next_catchup_index()
+      |> schedule_next_realtime_fetch()
+
+    {:ok, scheduled_state}
   end
 
   @impl GenServer
@@ -100,8 +105,8 @@ defmodule Explorer.Indexer.BlockFetcher do
   end
 
   def handle_info({:DOWN, _ref, :process, pid, :normal}, %{genesis_task: pid} = state) do
-    Logger.info(fn -> "Finished index from genesis. Transitioning to realtime index." end)
-    {:noreply, schedule_next_realtime_fetch(%{state | genesis_task: nil})}
+    Logger.info(fn -> "Finished index from genesis. Transitioning to only realtime index." end)
+    {:noreply, %{state | genesis_task: nil}}
   end
 
   def handle_info({:DOWN, _ref, :process, pid, _reason}, %{genesis_task: pid} = state) do
@@ -222,7 +227,8 @@ defmodule Explorer.Indexer.BlockFetcher do
   end
 
   defp realtime_task(%{} = state) do
-    {:ok, seq} = Sequence.start_link([], Indexer.next_block_number(), 2)
+    {:ok, latest_block_number} = EthereumJSONRPC.fetch_block_number_by_tag("latest")
+    {:ok, seq} = Sequence.start_link([], latest_block_number, 2)
     stream_import(state, seq, max_concurrency: 1)
   end