Allow the latest block worker to re-enqueue an actual block number

lib/explorer/workers/import_block.ex

@@ -1,16 +1,23 @@
 defmodule Explorer.Workers.ImportBlock do
+  @moduledoc "Imports blocks by web3 conventions."
+
+  import Ethereumex.HttpClient, only: [eth_block_number: 0]
+
   alias Explorer.BlockImporter
 
-  @moduledoc "Imports blocks by web3 conventions."
+  @dialyzer {:nowarn_function, perform: 1}
+  def perform("latest") do
+    case eth_block_number() do
+      {:ok, number} -> perform_later(number)
+      _ -> nil
+    end
+  end
 
   @dialyzer {:nowarn_function, perform: 1}
   def perform(number), do: BlockImporter.import("#{number}")
 
-  @dialyzer {:nowarn_function, perform: 0}
-  def perform, do: perform("latest")
-
-  def perform_later("latest") do
-    Exq.enqueue(Exq.Enqueuer, "blocks", __MODULE__, ["latest"], max_retries: 0)
+  def perform_later("0x" <> number) when is_binary(number) do
+    number |> String.to_integer(16) |> perform_later()
   end
 
   def perform_later(number) do

test/explorer/workers/import_block_test.exs

@@ -32,6 +32,16 @@ defmodule Explorer.Workers.ImportBlockTest do
       end
     end
 
+    test "imports the latest block" do
+      use_cassette "import_block_perform_1_latest" do
+        with_mock Exq, [enqueue: fn (_, _, _, [number]) -> insert(:block, number: number) end] do
+          ImportBlock.perform("latest")
+          last_block = Block |> order_by(asc: :number) |> Repo.one
+          assert last_block.number > 0
+        end
+      end
+    end
+
     test "when there is already a block with the requested hash" do
       use_cassette "import_block_perform_1_duplicate" do
         insert(:block, hash: "0x52c867bc0a91e573dc39300143c3bead7408d09d45bdb686749f02684ece72f3")
@@ -45,7 +55,7 @@ defmodule Explorer.Workers.ImportBlockTest do
   describe "perform_later/1" do
     test "does not retry fetching the latest block" do
       use_cassette "import_block_perform_later_1_latest" do
-        with_mock Exq, [enqueue: fn (_, _, _, _, max_retries: 0) -> insert(:block, number: 1) end] do
+        with_mock Exq, [enqueue: fn (_, _, _, _) -> insert(:block, number: 1) end] do
           ImportBlock.perform_later("latest")
           last_block = Block |> order_by(asc: :number) |> limit(1) |> Repo.one
           assert last_block.number == 1

test/support/fixture/vcr_cassettes/import_block_perform_1_latest.json

@@ -0,0 +1,30 @@
+[
+  {
+    "request": {
+      "body": "{\"params\":[],\"method\":\"eth_blockNumber\",\"jsonrpc\":\"2.0\",\"id\":4}",
+      "headers": {
+        "Content-Type": "application/json"
+      },
+      "method": "post",
+      "options": [],
+      "request_body": "",
+      "url": "https://sokol.poa.network"
+    },
+    "response": {
+      "binary": false,
+      "body": "{\"jsonrpc\":\"2.0\",\"result\":\"0xead0d\",\"id\":4}\n",
+      "headers": {
+        "Date": "Fri, 16 Feb 2018 06:27:57 GMT",
+        "Content-Type": "application/json",
+        "Transfer-Encoding": "chunked",
+        "Connection": "keep-alive",
+        "Set-Cookie": "__cfduid=de29d41d050c846681bac8973c50f5aa51518762476; expires=Sat, 16-Feb-19 06:27:56 GMT; path=/; domain=.poa.network; HttpOnly; Secure",
+        "Expect-CT": "max-age=604800, report-uri=\"https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct\"",
+        "Server": "cloudflare",
+        "CF-RAY": "3ede71a76b58962b-SJC"
+      },
+      "status_code": 200,
+      "type": "ok"
+    }
+  }
+]