From f0ace70d9b86ad4c8ff0cf131b6fbf03f025d8b9 Mon Sep 17 00:00:00 2001
From: Doc Ritezel <doc@ministryofvelocity.com>
Date: Sun, 4 Feb 2018 17:22:21 -0800
Subject: [PATCH] Switch to a worker model for job scheduling and execution

---
 Procfile                                      |  1 +
 bin/deploy                                    | 10 +++
 circle.yml                                    |  1 +
 config/config.exs                             | 15 ++++
 config/dev.exs                                |  6 +-
 config/prod.exs                               |  8 ++-
 lib/explorer/application.ex                   | 29 ++++----
 lib/explorer/block.ex                         | 13 +++-
 lib/explorer/fetcher.ex                       | 40 ++++++-----
 lib/explorer/latest_block.ex                  | 16 -----
 lib/explorer/skipped_blocks.ex                | 33 ++++-----
 lib/explorer/workers/import_block.ex          | 17 +++++
 lib/explorer/workers/import_skipped_blocks.ex | 16 +++++
 lib/explorer_web/router.ex                    | 34 ++++++++-
 lib/mix/tasks/backfill.ex                     | 12 ----
 lib/mix/tasks/exq.start.ex                    | 18 +++++
 lib/mix/tasks/scrape.ex                       | 13 ----
 mix.exs                                       | 13 ++--
 mix.lock                                      |  4 ++
 test/explorer/block_test.exs                  | 15 ++++
 test/explorer/latest_block_test.exs           | 31 --------
 test/explorer/skipped_blocks_test.exs         | 71 ++++++++++++-------
 test/explorer/workers/import_block_test.exs   | 38 ++++++++++
 .../workers/import_skipped_blocks_test.exs    | 23 ++++++
 test/explorer_web/features/exq_test.exs       | 11 +++
 test/mix/tasks/backfill_test.exs              | 21 ------
 test/mix/tasks/scrape_test.exs                | 19 -----
 .../backfill_skipped_blocks_perform_1.json    |  1 +
 .../import_block_perform_1_duplicate.json     | 30 ++++++++
 .../import_block_perform_1_earliest.json      | 30 ++++++++
 .../import_block_perform_1_integer.json       | 30 ++++++++
 .../import_block_perform_1_string.json        | 30 ++++++++
 .../import_skipped_blocks_perform_1.json      |  1 +
 33 files changed, 452 insertions(+), 198 deletions(-)
 delete mode 100644 lib/explorer/latest_block.ex
 create mode 100644 lib/explorer/workers/import_block.ex
 create mode 100644 lib/explorer/workers/import_skipped_blocks.ex
 delete mode 100644 lib/mix/tasks/backfill.ex
 create mode 100644 lib/mix/tasks/exq.start.ex
 delete mode 100644 lib/mix/tasks/scrape.ex
 delete mode 100644 test/explorer/latest_block_test.exs
 create mode 100644 test/explorer/workers/import_block_test.exs
 create mode 100644 test/explorer/workers/import_skipped_blocks_test.exs
 create mode 100644 test/explorer_web/features/exq_test.exs
 delete mode 100644 test/mix/tasks/backfill_test.exs
 delete mode 100644 test/mix/tasks/scrape_test.exs
 create mode 100644 test/support/fixture/vcr_cassettes/backfill_skipped_blocks_perform_1.json
 create mode 100644 test/support/fixture/vcr_cassettes/import_block_perform_1_duplicate.json
 create mode 100644 test/support/fixture/vcr_cassettes/import_block_perform_1_earliest.json
 create mode 100644 test/support/fixture/vcr_cassettes/import_block_perform_1_integer.json
 create mode 100644 test/support/fixture/vcr_cassettes/import_block_perform_1_string.json
 create mode 100644 test/support/fixture/vcr_cassettes/import_skipped_blocks_perform_1.json

diff --git a/Procfile b/Procfile
index 6506faf1e9..9ebfcf0148 100644
--- a/Procfile
+++ b/Procfile
@@ -1 +1,2 @@
 web: mix phx.server
+worker: mix exq.start
diff --git a/bin/deploy b/bin/deploy
index 25d2fd0749..6aac93df55 100755
--- a/bin/deploy
+++ b/bin/deploy
@@ -12,25 +12,31 @@ then
   git fetch heroku
 fi
 
+WORKER_COUNT=$(heroku ps | grep 'worker\.' | wc -l)
+
 if ! git diff HEAD heroku/master --exit-code -- priv/repo
 then
   if heroku features --app $HEROKU_APPLICATION | grep '\[+\] preboot'
   then
     heroku features:disable preboot --app $HEROKU_APPLICATION
     heroku maintenance:on --app $HEROKU_APPLICATION
+    heroku scale worker=0 --app $HEROKU_APPLICATION
     heroku pg:killall --app $HEROKU_APPLICATION
     git push heroku $CIRCLE_SHA1:refs/heads/master
     heroku pg:backups capture --app $HEROKU_APPLICATION
     heroku run "POOL_SIZE=2 mix ecto.migrate" --app $HEROKU_APPLICATION
+    heroku scale worker=$WORKER_COUNT --app $HEROKU_APPLICATION
     heroku restart --app $HEROKU_APPLICATION
     heroku maintenance:off --app $HEROKU_APPLICATION
     heroku features:enable preboot --app $HEROKU_APPLICATION
   else
     heroku maintenance:on --app $HEROKU_APPLICATION
+    heroku scale worker=0 --app $HEROKU_APPLICATION
     heroku pg:killall --app $HEROKU_APPLICATION
     git push heroku $CIRCLE_SHA1:refs/heads/master
     heroku pg:backups capture --app $HEROKU_APPLICATION
     heroku run "POOL_SIZE=2 mix ecto.migrate" --app $HEROKU_APPLICATION
+    heroku scale worker=$WORKER_COUNT --app $HEROKU_APPLICATION
     heroku restart --app $HEROKU_APPLICATION
     heroku maintenance:off --app $HEROKU_APPLICATION
   fi
@@ -38,3 +44,7 @@ else
   git push heroku $CIRCLE_SHA1:refs/heads/master
   heroku pg:backups capture --app $HEROKU_APPLICATION
 fi
+
+set +x
+
+heroku config:set ADMIN_PASSWORD=$(mix phx.gen.secret) --app $HEROKU_APPLICATION
diff --git a/circle.yml b/circle.yml
index 7e8ec36579..5c920d1d7b 100644
--- a/circle.yml
+++ b/circle.yml
@@ -10,6 +10,7 @@ machine:
     version: 9.4.0
   services:
     - postgresql
+    - redis
   pre:
     - mkdir -p $CIRCLE_TEST_REPORTS/exunit
     - mkdir -p $CIRCLE_TEST_REPORTS/eslint
diff --git a/config/config.exs b/config/config.exs
index 005435476d..206c554239 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -18,6 +18,9 @@ config :explorer, ExplorerWeb.Endpoint,
   render_errors: [view: ExplorerWeb.ErrorView, accepts: ~w(html json)],
   pubsub: [name: Explorer.PubSub, adapter: Phoenix.PubSub.PG2]
 
+config :explorer, Explorer.Integrations.EctoLogger,
+  query_time_ms_threshold: 2_000
+
 # Configures Elixir's Logger
 config :logger, :console,
   format: "$time $metadata[$level] $message\n",
@@ -33,6 +36,18 @@ config :ethereumex,
    locales: ["en"],
    gettext: ExplorerWeb.Gettext
 
+config :exq,
+  host: "localhost",
+  port: 6379,
+  namespace: "exq",
+  start_on_application: false,
+  scheduler_enable: true,
+  shutdown_timeout: 5000,
+  max_retries: 10
+
+config :exq_ui,
+  server: false
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{Mix.env}.exs"
diff --git a/config/dev.exs b/config/dev.exs
index 9f10572d27..7c56438136 100644
--- a/config/dev.exs
+++ b/config/dev.exs
@@ -58,7 +58,11 @@ config :explorer, Explorer.Repo,
 # Configure Quantum
 config :explorer, Explorer.Scheduler,
   jobs: [
-    {"* * * * *", {Mix.Tasks.Scrape, :run, [:ok]}},
+    [schedule: {:extended, "*/5 * * * * *"}, task: {Explorer.Workers.ImportBlock, :perform_later, ["latest"]}],
+    [schedule: {:extended, "*/15 * * * * *"}, task: {Explorer.Workers.ImportSkippedBlocks, :perform_later, [1]}],
   ]
 
+config :exq,
+  concurrency: 4
+
 import_config "dev.secret.exs"
diff --git a/config/prod.exs b/config/prod.exs
index 713fe95cc3..22470cd2bc 100644
--- a/config/prod.exs
+++ b/config/prod.exs
@@ -46,5 +46,11 @@ config :ethereumex,
 # Configure Quantum
 config :explorer, Explorer.Scheduler,
   jobs: [
-    {"@secondly", {Mix.Tasks.Scrape, :run, [[]]}}
+    [schedule: {:extended, "* * * * * *"}, task: {Explorer.Workers.ImportBlock, :perform_later, ["latest"]}],
+    [schedule: {:extended, "*/15 * * * * *"}, task: {Explorer.Workers.ImportSkippedBlocks, :perform_later, [5]}],
   ]
+
+# Configure Exq
+config :exq,
+  url: {:system, "REDIS_URL"},
+  concurrency: 10
diff --git a/lib/explorer/application.ex b/lib/explorer/application.ex
index f6f0e1bba1..1e1a8826e9 100644
--- a/lib/explorer/application.ex
+++ b/lib/explorer/application.ex
@@ -8,22 +8,10 @@ defmodule Explorer.Application do
   # See https://hexdocs.pm/elixir/Application.html
   # for more information on OTP Applications
   def start(_type, _args) do
-    import Supervisor.Spec
-
-    # Define workers and child supervisors to be supervised
-    children = [
-      # Start the Ecto repository
-      supervisor(Explorer.Repo, []),
-      # Start the endpoint when the application starts
-      supervisor(ExplorerWeb.Endpoint, []),
-      # Start your own worker by calling: Explorer.Worker.start_link(a, b, c)
-      worker(Explorer.Scheduler, []),
-    ]
-
     # See https://hexdocs.pm/elixir/Supervisor.html
     # for other strategies and supported options
     opts = [strategy: :one_for_one, name: Explorer.Supervisor]
-    Supervisor.start_link(children, opts)
+    Supervisor.start_link(children(Mix.env), opts)
   end
 
   # Tell Phoenix to update the endpoint configuration
@@ -33,4 +21,19 @@ defmodule Explorer.Application do
     Endpoint.config_change(changed, removed)
     :ok
   end
+
+  defp children(:test), do: children()
+  defp children(_) do
+    import Supervisor.Spec
+    exq_options = [] |> Keyword.put(:mode, :enqueuer)
+    [supervisor(Exq, [exq_options]) | children()]
+  end
+
+  defp children do
+    import Supervisor.Spec
+    [
+      supervisor(Explorer.Repo, []),
+      supervisor(ExplorerWeb.Endpoint, []),
+    ]
+  end
 end
diff --git a/lib/explorer/block.ex b/lib/explorer/block.ex
index 2ef9527c31..3c56533909 100644
--- a/lib/explorer/block.ex
+++ b/lib/explorer/block.ex
@@ -1,10 +1,11 @@
 defmodule Explorer.Block do
-  @moduledoc false
-
   use Ecto.Schema
   import Ecto.Changeset
+  import Ecto.Query
   alias Explorer.Block
 
+  @moduledoc false
+
   @timestamps_opts [type: Timex.Ecto.DateTime,
                     autogenerate: {Timex.Ecto.DateTime, :autogenerate, []}]
 
@@ -38,4 +39,12 @@ defmodule Explorer.Block do
     |> update_change(:hash, &String.downcase/1)
     |> unique_constraint(:hash)
   end
+
+  def null do
+    %Block{number: -1}
+  end
+
+  def latest(query) do
+    query |> order_by(desc: :number)
+  end
 end
diff --git a/lib/explorer/fetcher.ex b/lib/explorer/fetcher.ex
index a3709ab035..51b41c9f6f 100644
--- a/lib/explorer/fetcher.ex
+++ b/lib/explorer/fetcher.ex
@@ -6,17 +6,17 @@ defmodule Explorer.Fetcher  do
   alias Explorer.Repo
   alias Explorer.ToAddress
   alias Explorer.Transaction
+
   import Ethereumex.HttpClient, only: [eth_get_block_by_number: 2]
 
   @dialyzer {:nowarn_function, fetch: 1}
   def fetch(block_number) do
     raw_block = block_number |> download_block
-
     Repo.transaction fn ->
       raw_block
       |> extract_block
       |> prepare_block
-      |> Repo.insert!
+      |> Repo.insert_or_update!
       |> extract_transactions(raw_block["transactions"])
     end
   end
@@ -49,12 +49,13 @@ defmodule Explorer.Fetcher  do
     end)
   end
 
-  def create_transaction(block, transaction) do
-    %Transaction{}
-    |> Transaction.changeset(extract_transaction(block, transaction))
-    |> Repo.insert!
-    |> create_from_address(transaction["from"])
-    |> create_to_address(transaction["to"] || transaction["creates"])
+  def create_transaction(block, changes) do
+    transaction = Repo.get_by(Transaction, hash: changes["hash"]) || %Transaction{}
+    transaction
+    |> Transaction.changeset(extract_transaction(block, changes))
+    |> Repo.insert_or_update!
+    |> create_from_address(changes["from"])
+    |> create_to_address(changes["to"] || changes["creates"])
   end
 
   def extract_transaction(block, transaction) do
@@ -77,28 +78,31 @@ defmodule Explorer.Fetcher  do
 
   def create_to_address(transaction, hash) do
     address = Address.find_or_create_by_hash(hash)
-    attrs = %{transaction_id: transaction.id, address_id: address.id}
+    changes = %{transaction_id: transaction.id, address_id: address.id}
 
-    %ToAddress{}
-    |> ToAddress.changeset(attrs)
-    |> Repo.insert
+    to_address = Repo.get_by(ToAddress, changes) || %ToAddress{}
+    to_address
+    |> ToAddress.changeset(changes)
+    |> Repo.insert_or_update!
 
     transaction
   end
 
   def create_from_address(transaction, hash) do
     address = Address.find_or_create_by_hash(hash)
-    attrs = %{transaction_id: transaction.id, address_id: address.id}
+    changes = %{transaction_id: transaction.id, address_id: address.id}
 
-    %FromAddress{}
-    |> FromAddress.changeset(attrs)
-    |> Repo.insert
+    from_address = Repo.get_by(FromAddress, changes) || %FromAddress{}
+    from_address
+    |> FromAddress.changeset(changes)
+    |> Repo.insert_or_update!
 
     transaction
   end
 
-  def prepare_block(block) do
-    Block.changeset(%Block{}, block)
+  def prepare_block(changes) do
+    block = Repo.get_by(Block, hash: changes.hash) || %Block{}
+    Block.changeset(block, changes)
   end
 
   def decode_integer_field(hex) do
diff --git a/lib/explorer/latest_block.ex b/lib/explorer/latest_block.ex
deleted file mode 100644
index 6add7487fd..0000000000
--- a/lib/explorer/latest_block.ex
+++ /dev/null
@@ -1,16 +0,0 @@
-defmodule Explorer.LatestBlock do
-  alias Explorer.Fetcher
-  import Ethereumex.HttpClient, only: [eth_block_number: 0]
-
-  @moduledoc false
-
-  @dialyzer {:nowarn_function, fetch: 0}
-  def fetch do
-    get_latest_block() |> Fetcher.fetch
-  end
-
-  def get_latest_block do
-    {:ok, block_number} = eth_block_number()
-    block_number
-  end
-end
diff --git a/lib/explorer/skipped_blocks.ex b/lib/explorer/skipped_blocks.ex
index b735dea09f..a3f904d538 100644
--- a/lib/explorer/skipped_blocks.ex
+++ b/lib/explorer/skipped_blocks.ex
@@ -1,38 +1,29 @@
 defmodule Explorer.SkippedBlocks do
-  alias Explorer.Fetcher
   alias Explorer.Block
   alias Explorer.Repo
   alias Ecto.Adapters.SQL
-  import Ecto.Query
+
+  import Ecto.Query, only: [limit: 2]
 
   @moduledoc false
 
   @query """
   SELECT missing_numbers.number AS missing_number
-  FROM generate_series($1, 1, -1) missing_numbers(number)
+  FROM generate_series($1, 0, -1) missing_numbers(number)
   LEFT OUTER JOIN blocks ON (blocks.number = missing_numbers.number)
-  WHERE blocks.id IS NULL;
+  WHERE blocks.id IS NULL
+  LIMIT $2;
   """
 
-  @dialyzer {:nowarn_function, fetch: 0}
-  def fetch do
-    get_skipped_blocks()
-    |> Enum.map(&Integer.to_string/1)
-    |> Enum.map(&Fetcher.fetch/1)
-  end
-
-  def get_skipped_blocks do
-    last_block_number = get_last_block_number()
-    SQL.query!(Repo, @query, [last_block_number]).rows
+  def first, do: first(1)
+  def first(count) do
+    SQL.query!(Repo, @query, [latest_block_number(), count]).rows
     |> Enum.map(&List.first/1)
+    |> Enum.map(&Integer.to_string/1)
   end
 
-  def get_last_block_number do
-    block = Block
-    |> order_by(desc: :number)
-    |> limit(1)
-    |> Repo.all
-    |> List.first || %{number: 0}
-    block.number
+  def latest_block_number do
+    (Block |> Block.latest |> limit(1) |> Repo.one || Block.null)
+    |> Map.fetch!(:number)
   end
 end
diff --git a/lib/explorer/workers/import_block.ex b/lib/explorer/workers/import_block.ex
new file mode 100644
index 0000000000..b6a5c2485e
--- /dev/null
+++ b/lib/explorer/workers/import_block.ex
@@ -0,0 +1,17 @@
+defmodule Explorer.Workers.ImportBlock do
+  alias Explorer.Fetcher
+
+  @moduledoc "Imports blocks by web3 conventions."
+
+  @dialyzer {:nowarn_function, perform: 1}
+  def perform(number) do
+    Fetcher.fetch("#{number}")
+  end
+
+  @dialyzer {:nowarn_function, perform: 0}
+  def perform, do: perform("latest")
+
+  def perform_later(number) do
+    Exq.enqueue(Exq.Enqueuer, "default", __MODULE__, [number])
+  end
+end
diff --git a/lib/explorer/workers/import_skipped_blocks.ex b/lib/explorer/workers/import_skipped_blocks.ex
new file mode 100644
index 0000000000..fcc397dedd
--- /dev/null
+++ b/lib/explorer/workers/import_skipped_blocks.ex
@@ -0,0 +1,16 @@
+defmodule Explorer.Workers.ImportSkippedBlocks do
+  alias Explorer.SkippedBlocks
+  alias Explorer.Workers.ImportBlock
+
+  @moduledoc "Imports skipped blocks."
+
+  def perform, do: perform(1)
+  def perform(count) do
+    count |> SkippedBlocks.first |> Enum.map(&ImportBlock.perform_later/1)
+  end
+
+  def perform_later, do: perform_later(1)
+  def perform_later(count) do
+    Exq.enqueue(Exq.Enqueuer, "default", __MODULE__, [count])
+  end
+end
diff --git a/lib/explorer_web/router.ex b/lib/explorer_web/router.ex
index 61bd4c2aaf..08ad78cf88 100644
--- a/lib/explorer_web/router.ex
+++ b/lib/explorer_web/router.ex
@@ -15,21 +15,51 @@ defmodule ExplorerWeb.Router do
         font-src 'self' 'unsafe-inline' 'unsafe-eval' data:;\
       "
     }
-    if Mix.env != :prod, do: plug Jasmine, js_files: ["js/test.js"], css_files: ["css/test.css"]
+  end
+
+  pipeline :set_locale do
     plug SetLocale, gettext: ExplorerWeb.Gettext, default_locale: "en"
   end
 
+  pipeline :exq do
+    plug :accepts, ["html"]
+    plug :fetch_session
+    plug :fetch_flash
+    plug :put_secure_browser_headers, %{
+      "content-security-policy" => "\
+        default-src 'self';\
+        script-src 'self' 'unsafe-inline';\
+        font-src 'self' fonts.gstatic.com;\
+        style-src 'self' 'unsafe-inline' fonts.googleapis.com;\
+      "
+    }
+    plug ExqUi.RouterPlug, namespace: "exq"
+  end
+
+  pipeline :jasmine do
+    if Mix.env != :prod, do: plug Jasmine, js_files: ["js/test.js"], css_files: ["css/test.css"]
+  end
+
   pipeline :api do
     plug :accepts, ["json"]
   end
 
+  scope "/exq", ExqUi do
+    pipe_through :exq
+    forward "/", RouterPlug.Router, :index
+  end
+
   scope "/", ExplorerWeb do
     pipe_through :browser
+    pipe_through :jasmine
+    pipe_through :set_locale
     resources "/", ChainController, only: [:show], singleton: true, as: :chain
   end
 
   scope "/:locale", ExplorerWeb do
-    pipe_through :browser # Use the default browser stack
+    pipe_through :browser
+    pipe_through :jasmine
+    pipe_through :set_locale
     resources "/", ChainController, only: [:show], singleton: true, as: :chain
     resources "/blocks", BlockController, only: [:index, :show]
     resources "/transactions", TransactionController, only: [:index, :show]
diff --git a/lib/mix/tasks/backfill.ex b/lib/mix/tasks/backfill.ex
deleted file mode 100644
index b4e52b3105..0000000000
--- a/lib/mix/tasks/backfill.ex
+++ /dev/null
@@ -1,12 +0,0 @@
-defmodule Mix.Tasks.Backfill do
-  use Mix.Task
-  alias Explorer.SkippedBlocks
-
-  @shortdoc "Backfill blocks from the chain."
-  @moduledoc false
-
-  def run(_) do
-    Mix.Task.run("app.start")
-    SkippedBlocks.fetch()
-  end
-end
diff --git a/lib/mix/tasks/exq.start.ex b/lib/mix/tasks/exq.start.ex
new file mode 100644
index 0000000000..5f20ccb3fc
--- /dev/null
+++ b/lib/mix/tasks/exq.start.ex
@@ -0,0 +1,18 @@
+defmodule Mix.Tasks.Exq.Start do
+  alias Explorer.Repo
+  alias Explorer.Scheduler
+
+  use Mix.Task
+
+  @moduledoc "Starts the Exq worker"
+
+  def run(_args) do
+    [:postgrex, :ecto, :ethereumex, :tzdata]
+    |> Enum.each(&Application.ensure_all_started/1)
+    Repo.start_link()
+    Exq.start_link(mode: :default)
+    Scheduler.start_link()
+    IO.puts "Started Exq"
+    :timer.sleep(:infinity)
+  end
+end
diff --git a/lib/mix/tasks/scrape.ex b/lib/mix/tasks/scrape.ex
deleted file mode 100644
index 09223f1354..0000000000
--- a/lib/mix/tasks/scrape.ex
+++ /dev/null
@@ -1,13 +0,0 @@
-defmodule Mix.Tasks.Scrape do
-  use Mix.Task
-  alias Explorer.LatestBlock
-
-  @shortdoc "Scrape the blockchain."
-  @moduledoc false
-
-  @dialyzer {:nowarn_function, run: 1}
-  def run(_) do
-    Mix.Task.run("app.start")
-    LatestBlock.fetch()
-  end
-end
diff --git a/mix.exs b/mix.exs
index 9d9e315995..c69f3b6842 100644
--- a/mix.exs
+++ b/mix.exs
@@ -35,11 +35,12 @@ defmodule Explorer.Mixfile do
   defp elixirc_paths,        do: ["lib"]
 
   # Specifies extra applications to start per environment
-  defp extra_applications(:prod), do: [:phoenix_pubsub_redis, :new_relixir | extra_applications()]
+  defp extra_applications(:prod), do: [:phoenix_pubsub_redis, :new_relixir, :exq, :exq_ui | extra_applications()]
+  defp extra_applications(:dev), do: [:exq, :exq_ui | extra_applications()]
   defp extra_applications(_), do: extra_applications()
   defp extra_applications, do: [
     :scrivener_ecto, :scrivener_html, :ex_cldr, :ex_jasmine, :ethereumex,
-    :timex, :timex_ecto, :set_locale, :logger, :runtime_tools
+    :timex, :timex_ecto, :crontab, :set_locale, :logger, :runtime_tools
   ]
 
   # Specifies your project dependencies.
@@ -49,16 +50,20 @@ defmodule Explorer.Mixfile do
     [
       {:cowboy, "~> 1.0"},
       {:credo, "~> 0.8", only: [:dev, :test], runtime: false},
+      {:crontab, "~> 1.1"},
       {:dialyxir, "~> 0.5", only: [:dev, :test], runtime: false},
       {:ethereumex, github: "exthereum/ethereumex", commit: "262f1d81ae163ffb46e127283658249dac1c8318"}, # Waiting for this version to be pushed to Hex.
       {:ex_cldr_numbers, "~> 1.0"},
       {:ex_cldr_units, "~> 1.0"},
+      {:ex_jasmine, github: "minifast/ex_jasmine", branch: "master"},
       {:ex_machina, "~> 2.1", only: [:test]},
+      {:exq, "~> 0.9.1"},
+      {:exq_ui, "~> 0.9.0"},
       {:exvcr, "~> 0.8", only: :test},
       {:gettext, "~> 0.11"},
-      {:ex_jasmine, github: "minifast/ex_jasmine", branch: "master"},
-      {:junit_formatter, ">= 0.0.0"},
+      {:junit_formatter, ">= 0.0.0", only: [:test], runtime: false},
       {:math, "~> 0.3.0"},
+      {:mock, "~> 0.3.0", only: [:test], runtime: false},
       {:new_relixir, "~> 0.4.0", only: [:prod]},
       {:phoenix, "~> 1.3.0"},
       {:phoenix_ecto, "~> 3.2"},
diff --git a/mix.lock b/mix.lock
index be9cd4444b..aa5a0bdc39 100644
--- a/mix.lock
+++ b/mix.lock
@@ -19,6 +19,8 @@
   "ex_machina": {:hex, :ex_machina, "2.1.0", "4874dc9c78e7cf2d429f24dc3c4005674d4e4da6a08be961ffccc08fb528e28b", [:mix], [{:ecto, "~> 2.1", [hex: :ecto, repo: "hexpm", optional: true]}], "hexpm"},
   "exactor": {:hex, :exactor, "2.2.4", "5efb4ddeb2c48d9a1d7c9b465a6fffdd82300eb9618ece5d34c3334d5d7245b1", [:mix], [], "hexpm"},
   "exjsx": {:hex, :exjsx, "4.0.0", "60548841e0212df401e38e63c0078ec57b33e7ea49b032c796ccad8cde794b5c", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, repo: "hexpm", optional: false]}], "hexpm"},
+  "exq": {:hex, :exq, "0.9.1", "77ee12c117411ddddd9810aec714eaa704fb8f327949551d9efaea19606122c3", [:mix], [{:poison, ">= 1.2.0 or ~> 2.0", [hex: :poison, repo: "hexpm", optional: false]}, {:redix, ">= 0.5.0", [hex: :redix, repo: "hexpm", optional: false]}, {:uuid, ">= 1.1.0", [hex: :uuid, repo: "hexpm", optional: false]}], "hexpm"},
+  "exq_ui": {:hex, :exq_ui, "0.9.0", "e97e9fa9009f30d2926b51a166e40a3a521e83f61f3f333fede8335b2aa57f09", [:mix], [{:cowboy, "~> 1.0", [hex: :cowboy, repo: "hexpm", optional: false]}, {:exq, "~> 0.9", [hex: :exq, repo: "hexpm", optional: false]}, {:plug, ">= 0.8.1 and < 2.0.0", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
   "exvcr": {:hex, :exvcr, "0.9.1", "31e3936a790a14bf56b31b6b276577076a5ef8afd9b2d53ba3ff8bb647d45613", [:mix], [{:exactor, "~> 2.2", [hex: :exactor, repo: "hexpm", optional: false]}, {:exjsx, "~> 4.0", [hex: :exjsx, repo: "hexpm", optional: false]}, {:httpoison, "~> 0.13", [hex: :httpoison, repo: "hexpm", optional: true]}, {:httpotion, "~> 3.0", [hex: :httpotion, repo: "hexpm", optional: true]}, {:ibrowse, "~> 4.4", [hex: :ibrowse, repo: "hexpm", optional: true]}, {:meck, "~> 0.8.8", [hex: :meck, repo: "hexpm", optional: false]}], "hexpm"},
   "file_system": {:hex, :file_system, "0.2.4", "f0bdda195c0e46e987333e986452ec523aed21d784189144f647c43eaf307064", [:mix], [], "hexpm"},
   "gen_stage": {:hex, :gen_stage, "0.12.2", "e0e347cbb1ceb5f4e68a526aec4d64b54ad721f0a8b30aa9d28e0ad749419cbb", [:mix], [], "hexpm"},
@@ -33,6 +35,7 @@
   "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], [], "hexpm"},
   "mime": {:hex, :mime, "1.2.0", "78adaa84832b3680de06f88f0997e3ead3b451a440d183d688085be2d709b534", [:mix], [], "hexpm"},
   "mimerl": {:hex, :mimerl, "1.0.2", "993f9b0e084083405ed8252b99460c4f0563e41729ab42d9074fd5e52439be88", [:rebar3], [], "hexpm"},
+  "mock": {:hex, :mock, "0.3.1", "994f00150f79a0ea50dc9d86134cd9ebd0d177ad60bd04d1e46336cdfdb98ff9", [:mix], [{:meck, "~> 0.8.8", [hex: :meck, repo: "hexpm", optional: false]}], "hexpm"},
   "new_relixir": {:hex, :new_relixir, "0.4.0", "32e15de5dc21bd9823040d3d7fe62cd931755a06de2163e02b79a703179ea102", [:mix], [{:ecto, "~> 2.0", [hex: :ecto, repo: "hexpm", optional: false]}, {:hackney, "~> 1.10", [hex: :hackney, repo: "hexpm", optional: false]}, {:phoenix, "~> 1.3", [hex: :phoenix, repo: "hexpm", optional: false]}], "hexpm"},
   "phoenix": {:hex, :phoenix, "1.3.0", "1c01124caa1b4a7af46f2050ff11b267baa3edb441b45dbf243e979cd4c5891b", [:mix], [{:cowboy, "~> 1.0", [hex: :cowboy, repo: "hexpm", optional: true]}, {:phoenix_pubsub, "~> 1.0", [hex: :phoenix_pubsub, repo: "hexpm", optional: false]}, {:plug, "~> 1.3.3 or ~> 1.4", [hex: :plug, repo: "hexpm", optional: false]}, {:poison, "~> 2.2 or ~> 3.0", [hex: :poison, repo: "hexpm", optional: false]}], "hexpm"},
   "phoenix_ecto": {:hex, :phoenix_ecto, "3.3.0", "702f6e164512853d29f9d20763493f2b3bcfcb44f118af2bc37bb95d0801b480", [:mix], [{:ecto, "~> 2.1", [hex: :ecto, repo: "hexpm", optional: false]}, {:phoenix_html, "~> 2.9", [hex: :phoenix_html, repo: "hexpm", optional: true]}, {:plug, "~> 1.0", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
@@ -59,4 +62,5 @@
   "timex_ecto": {:hex, :timex_ecto, "3.2.1", "461140751026e1ca03298fab628f78ab189e78784175f5e301eefa034ee530aa", [:mix], [{:ecto, "~> 2.2", [hex: :ecto, repo: "hexpm", optional: false]}, {:timex, "~> 3.1", [hex: :timex, repo: "hexpm", optional: false]}], "hexpm"},
   "tzdata": {:hex, :tzdata, "0.5.16", "13424d3afc76c68ff607f2df966c0ab4f3258859bbe3c979c9ed1606135e7352", [:mix], [{:hackney, "~> 1.0", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm"},
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.3.1", "a1f612a7b512638634a603c8f401892afbf99b8ce93a45041f8aaca99cadb85e", [:rebar3], [], "hexpm"},
+  "uuid": {:hex, :uuid, "1.1.8", "e22fc04499de0de3ed1116b770c7737779f226ceefa0badb3592e64d5cfb4eb9", [:mix], [], "hexpm"},
   "wallaby": {:hex, :wallaby, "0.19.2", "358bbff251e3555e02566280d1795132da792969dd58ff89963536d013058719", [:mix], [{:httpoison, "~> 0.12", [hex: :httpoison, repo: "hexpm", optional: false]}, {:poison, ">= 1.4.0", [hex: :poison, repo: "hexpm", optional: false]}, {:poolboy, "~> 1.5", [hex: :poolboy, repo: "hexpm", optional: false]}], "hexpm"}}
diff --git a/test/explorer/block_test.exs b/test/explorer/block_test.exs
index 3c5ec3e3d5..4b1f93c496 100644
--- a/test/explorer/block_test.exs
+++ b/test/explorer/block_test.exs
@@ -2,6 +2,7 @@ defmodule Explorer.BlockTest do
   use Explorer.DataCase
 
   alias Explorer.Block
+  import Ecto.Query, only: [order_by: 2]
 
   describe "changeset/2" do
     test "with valid attributes" do
@@ -28,4 +29,18 @@ defmodule Explorer.BlockTest do
       assert changeset.errors == [hash: {"has already been taken", []}]
     end
   end
+
+  describe "null/0" do
+    test "returns a block with a number of 0" do
+      assert Block.null.number === -1
+    end
+  end
+
+  describe "latest/1" do
+    test "returns the blocks sorted by number" do
+      insert(:block, number: 1)
+      insert(:block, number: 5)
+      assert Block |> Block.latest |> Repo.all == Block |> order_by(desc: :number) |> Repo.all
+    end
+  end
 end
diff --git a/test/explorer/latest_block_test.exs b/test/explorer/latest_block_test.exs
deleted file mode 100644
index 63034935e8..0000000000
--- a/test/explorer/latest_block_test.exs
+++ /dev/null
@@ -1,31 +0,0 @@
-defmodule Explorer.LatestBlockTest do
-  use Explorer.DataCase
-
-  alias Explorer.Block
-  alias Explorer.Repo
-  alias Explorer.LatestBlock
-
-  describe "fetch/0" do
-    test "the latest block is copied over from the blockchain" do
-      use_cassette "latest_block_fetch" do
-        LatestBlock.fetch()
-
-        last_block = Block
-          |> order_by(desc: :inserted_at)
-          |> limit(1)
-          |> Repo.all
-          |> List.first
-
-        assert(last_block.number)
-      end
-    end
-  end
-
-  describe "get_latest_block/0" do
-    test "returns the number of the latest block" do
-      use_cassette "fetcher_get_latest_block" do
-        assert LatestBlock.get_latest_block() == "0x89923"
-      end
-    end
-  end
-end
diff --git a/test/explorer/skipped_blocks_test.exs b/test/explorer/skipped_blocks_test.exs
index 5d0efa6f59..8a0141525b 100644
--- a/test/explorer/skipped_blocks_test.exs
+++ b/test/explorer/skipped_blocks_test.exs
@@ -1,53 +1,76 @@
 defmodule Explorer.SkippedBlocksTest do
   use Explorer.DataCase
 
-  alias Explorer.Block
-  alias Explorer.Repo
   alias Explorer.SkippedBlocks
 
-  describe "fetch/0" do
-    test "inserts a missing block into the database" do
-      insert(:block, %{number: 2})
-      use_cassette "skipped_block_fetch" do
-        SkippedBlocks.fetch()
+  describe "first/0 when there are no blocks" do
+    test "returns no blocks" do
+      assert SkippedBlocks.first() == []
+    end
+  end
 
-        blocks = Block |> order_by(asc: :number) |> Repo.all |> Enum.map(fn(block) -> block.number end)
+  describe "first/0 when there are no skipped blocks" do
+    test "returns no blocks" do
+      insert(:block, %{number: 0})
+      assert SkippedBlocks.first() == []
+    end
+  end
 
-        assert blocks == [1, 2]
-      end
+  describe "first/0 when a block has been skipped" do
+    test "returns the first skipped block number" do
+      insert(:block, %{number: 0})
+      insert(:block, %{number: 2})
+      assert SkippedBlocks.first() == ["1"]
     end
   end
 
-  describe "get_skipped_blocks/0 when there are no blocks" do
+  describe "first/1 when there are no blocks" do
     test "returns no blocks" do
-      assert SkippedBlocks.get_skipped_blocks() == []
+      assert SkippedBlocks.first(1) == []
     end
   end
 
-  describe "get_skipped_blocks/0 when there are no skipped blocks" do
+  describe "first/1 when there are no skipped blocks" do
     test "returns no blocks" do
-      insert(:block, %{number: 1})
-      assert SkippedBlocks.get_skipped_blocks() == []
+      insert(:block, %{number: 0})
+      assert SkippedBlocks.first(1) == []
     end
   end
 
-  describe "get_skipped_blocks/0 when a block has been skipped" do
-    test "returns no blocks" do
-      insert(:block, %{number: 2})
-      assert SkippedBlocks.get_skipped_blocks() == [1]
+  describe "first/1 when a block has been skipped" do
+    test "returns the skipped block number" do
+      insert(:block, %{number: 1})
+      assert SkippedBlocks.first(1) == ["0"]
+    end
+
+    test "returns up to the requested number of skipped block numbers in reverse order" do
+      insert(:block, %{number: 1})
+      insert(:block, %{number: 3})
+      assert SkippedBlocks.first(1) == ["2"]
+    end
+
+    test "returns only the skipped block number" do
+      insert(:block, %{number: 1})
+      assert SkippedBlocks.first(100) == ["0"]
+    end
+
+    test "returns all the skipped block numbers in descending order" do
+      insert(:block, %{number: 1})
+      insert(:block, %{number: 3})
+      assert SkippedBlocks.first(100) == ["2", "0"]
     end
   end
 
-  describe "get_last_block_number/0 when there are no blocks" do
-    test "returns zero" do
-      assert SkippedBlocks.get_last_block_number() == 0
+  describe "latest_block_number/0 when there are no blocks" do
+    test "returns -1" do
+      assert SkippedBlocks.latest_block_number() == -1
     end
   end
 
-  describe "get_last_block_number/0 when there is a block" do
+  describe "latest_block_number/0 when there is a block" do
     test "returns the number of the block" do
       insert(:block, %{number: 1})
-      assert SkippedBlocks.get_last_block_number() == 1
+      assert SkippedBlocks.latest_block_number() == 1
     end
   end
 end
diff --git a/test/explorer/workers/import_block_test.exs b/test/explorer/workers/import_block_test.exs
new file mode 100644
index 0000000000..e785ee07d2
--- /dev/null
+++ b/test/explorer/workers/import_block_test.exs
@@ -0,0 +1,38 @@
+defmodule Explorer.Workers.ImportBlockTest do
+  use Explorer.DataCase
+  alias Explorer.Block
+  alias Explorer.Repo
+
+  test "perform/1 imports the requested block number as an integer" do
+    use_cassette "import_block_perform_1_integer" do
+      Explorer.Workers.ImportBlock.perform(1)
+      last_block = Block |> order_by(asc: :number) |> Repo.one
+      assert last_block.number == 1
+    end
+  end
+
+  test "perform/1 imports the requested block number as a string" do
+    use_cassette "import_block_perform_1_string" do
+      Explorer.Workers.ImportBlock.perform("1")
+      last_block = Block |> order_by(asc: :number) |> Repo.one
+      assert last_block.number == 1
+    end
+  end
+
+  test "perform/1 imports the earliest block" do
+    use_cassette "import_block_perform_1_earliest" do
+      Explorer.Workers.ImportBlock.perform("earliest")
+      last_block = Block |> order_by(asc: :number) |> Repo.one
+      assert last_block.number == 0
+    end
+  end
+
+  test "perform/1 when there is alaready a block with the requested hash" do
+    use_cassette "import_block_perform_1_duplicate" do
+      insert(:block, hash: "0x52c867bc0a91e573dc39300143c3bead7408d09d45bdb686749f02684ece72f3")
+      Explorer.Workers.ImportBlock.perform("1")
+      block_count = Block |> Repo.all |> Enum.count
+      assert block_count == 1
+    end
+  end
+end
diff --git a/test/explorer/workers/import_skipped_blocks_test.exs b/test/explorer/workers/import_skipped_blocks_test.exs
new file mode 100644
index 0000000000..4a8aae66f4
--- /dev/null
+++ b/test/explorer/workers/import_skipped_blocks_test.exs
@@ -0,0 +1,23 @@
+defmodule Explorer.Workers.ImportSkippedBlocksTest do
+  alias Explorer.Block
+  alias Explorer.Repo
+  alias Explorer.Workers.ImportBlock
+  alias Explorer.Workers.ImportSkippedBlocks
+
+  import Mock
+
+  use Explorer.DataCase
+
+  describe "perform/1" do
+    test "imports the requested number of skipped blocks" do
+      insert(:block, %{number: 2})
+      use_cassette "import_skipped_blocks_perform_1" do
+        with_mock ImportBlock, [perform_later: fn (number) -> insert(:block, number: number) end] do
+          ImportSkippedBlocks.perform(1)
+          last_block = Block |> order_by(asc: :number) |> limit(1) |> Repo.one
+          assert last_block.number == 1
+        end
+      end
+    end
+  end
+end
diff --git a/test/explorer_web/features/exq_test.exs b/test/explorer_web/features/exq_test.exs
new file mode 100644
index 0000000000..45990690c9
--- /dev/null
+++ b/test/explorer_web/features/exq_test.exs
@@ -0,0 +1,11 @@
+defmodule ExplorerWeb.ExqTest do
+  use ExplorerWeb.FeatureCase, async: true
+
+  import Wallaby.Query, only: [css: 2]
+
+  test "views the exq dashboard", %{session: session} do
+    session
+    |> visit("/exq")
+    |> assert_has(css(".navbar-brand", text: "Exq"))
+  end
+end
diff --git a/test/mix/tasks/backfill_test.exs b/test/mix/tasks/backfill_test.exs
deleted file mode 100644
index 7c321cc8f0..0000000000
--- a/test/mix/tasks/backfill_test.exs
+++ /dev/null
@@ -1,21 +0,0 @@
-defmodule Scrape.Backfill do
-  use Explorer.DataCase
-  alias Explorer.Block
-  alias Explorer.Repo
-
-  test "backfills previous blocks" do
-    insert(:block, %{number: 2})
-
-    use_cassette "backfill" do
-      Mix.Tasks.Backfill.run([])
-
-      last_block = Block
-        |> order_by(asc: :number)
-        |> limit(1)
-        |> Repo.all
-        |> List.first
-
-      assert last_block.number == 1
-    end
-  end
-end
diff --git a/test/mix/tasks/scrape_test.exs b/test/mix/tasks/scrape_test.exs
deleted file mode 100644
index 059f0b9f32..0000000000
--- a/test/mix/tasks/scrape_test.exs
+++ /dev/null
@@ -1,19 +0,0 @@
-defmodule Scrape.Test do
-  use Explorer.DataCase
-  alias Explorer.Block
-  alias Explorer.Repo
-
-  test "it downloads a new block" do
-    use_cassette "scrape" do
-      Mix.Tasks.Scrape.run([])
-
-      last_block = Block
-        |> order_by(desc: :inserted_at)
-        |> limit(1)
-        |> Repo.all
-        |> List.first
-
-      assert(last_block.number)
-    end
-  end
-end
diff --git a/test/support/fixture/vcr_cassettes/backfill_skipped_blocks_perform_1.json b/test/support/fixture/vcr_cassettes/backfill_skipped_blocks_perform_1.json
new file mode 100644
index 0000000000..0637a088a0
--- /dev/null
+++ b/test/support/fixture/vcr_cassettes/backfill_skipped_blocks_perform_1.json
@@ -0,0 +1 @@
+[]
\ No newline at end of file
diff --git a/test/support/fixture/vcr_cassettes/import_block_perform_1_duplicate.json b/test/support/fixture/vcr_cassettes/import_block_perform_1_duplicate.json
new file mode 100644
index 0000000000..5c27841c1d
--- /dev/null
+++ b/test/support/fixture/vcr_cassettes/import_block_perform_1_duplicate.json
@@ -0,0 +1,30 @@
+[
+  {
+    "request": {
+      "body": "{\"params\":[\"1\",true],\"method\":\"eth_getBlockByNumber\",\"jsonrpc\":\"2.0\",\"id\":3}",
+      "headers": {
+        "Content-Type": "application/json"
+      },
+      "method": "post",
+      "options": [],
+      "request_body": "",
+      "url": "https://sokol.poa.network:443"
+    },
+    "response": {
+      "binary": false,
+      "body": "{\"jsonrpc\":\"2.0\",\"result\":{\"author\":\"0xe8ddc5c7a2d2f0d7a9798459c0104fdf5e987aca\",\"difficulty\":\"0xffffffffffffffffffffffffedf58e45\",\"extraData\":\"0xd5830108048650617269747986312e32322e31826c69\",\"gasLimit\":\"0x66556d\",\"gasUsed\":\"0x0\",\"hash\":\"0x52c867bc0a91e573dc39300143c3bead7408d09d45bdb686749f02684ece72f3\",\"logsBloom\":\"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\",\"miner\":\"0xe8ddc5c7a2d2f0d7a9798459c0104fdf5e987aca\",\"number\":\"0x1\",\"parentHash\":\"0x5b28c1bfd3a15230c9a46b399cd0f9a6920d432e85381cc6a140b06e8410112f\",\"receiptsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"sealFields\":[\"0x84120a71ba\",\"0xb8417a5887662f09ac4673af5850d28f3ad6550407b9c814ef563a13320f881b55ef03754f48f2dde027ad4a5abcabcc42780d9ebfc645f183e5252507d6a25bc2ec01\"],\"sha3Uncles\":\"0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347\",\"signature\":\"7a5887662f09ac4673af5850d28f3ad6550407b9c814ef563a13320f881b55ef03754f48f2dde027ad4a5abcabcc42780d9ebfc645f183e5252507d6a25bc2ec01\",\"size\":\"0x240\",\"stateRoot\":\"0xc196ad59d867542ef20b29df5f418d07dc7234f4bc3d25260526620b7958a8fb\",\"step\":\"302674362\",\"timestamp\":\"0x5a3438a2\",\"totalDifficulty\":\"0xffffffffffffffffffffffffedf78e45\",\"transactions\":[],\"transactionsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"uncles\":[]},\"id\":3}\n",
+      "headers": {
+        "Date": "Sun, 04 Feb 2018 07:41:06 GMT",
+        "Content-Type": "application/json",
+        "Transfer-Encoding": "chunked",
+        "Connection": "keep-alive",
+        "Set-Cookie": "__cfduid=d9be038a0189dadf6dd2c0f72a4626d271517730066; expires=Mon, 04-Feb-19 07:41:06 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": "3e7bfc51196092e8-SJC"
+      },
+      "status_code": 200,
+      "type": "ok"
+    }
+  }
+]
\ No newline at end of file
diff --git a/test/support/fixture/vcr_cassettes/import_block_perform_1_earliest.json b/test/support/fixture/vcr_cassettes/import_block_perform_1_earliest.json
new file mode 100644
index 0000000000..cb57985af6
--- /dev/null
+++ b/test/support/fixture/vcr_cassettes/import_block_perform_1_earliest.json
@@ -0,0 +1,30 @@
+[
+  {
+    "request": {
+      "body": "{\"params\":[\"earliest\",true],\"method\":\"eth_getBlockByNumber\",\"jsonrpc\":\"2.0\",\"id\":2}",
+      "headers": {
+        "Content-Type": "application/json"
+      },
+      "method": "post",
+      "options": [],
+      "request_body": "",
+      "url": "https://sokol.poa.network:443"
+    },
+    "response": {
+      "binary": false,
+      "body": "{\"jsonrpc\":\"2.0\",\"result\":{\"author\":\"0x0000000000000000000000000000000000000000\",\"difficulty\":\"0x20000\",\"extraData\":\"0x\",\"gasLimit\":\"0x663be0\",\"gasUsed\":\"0x0\",\"hash\":\"0x5b28c1bfd3a15230c9a46b399cd0f9a6920d432e85381cc6a140b06e8410112f\",\"logsBloom\":\"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\",\"miner\":\"0x0000000000000000000000000000000000000000\",\"number\":\"0x0\",\"parentHash\":\"0x0000000000000000000000000000000000000000000000000000000000000000\",\"receiptsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"sealFields\":[\"0x80\",\"0xb8410000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\"],\"sha3Uncles\":\"0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347\",\"signature\":\"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\",\"size\":\"0x215\",\"stateRoot\":\"0xfad4af258fd11939fae0c6c6eec9d340b1caac0b0196fd9a1bc3f489c5bf00b3\",\"step\":\"0\",\"timestamp\":\"0x0\",\"totalDifficulty\":\"0x20000\",\"transactions\":[],\"transactionsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"uncles\":[]},\"id\":2}\n",
+      "headers": {
+        "Date": "Sun, 04 Feb 2018 01:09:56 GMT",
+        "Content-Type": "application/json",
+        "Transfer-Encoding": "chunked",
+        "Connection": "keep-alive",
+        "Set-Cookie": "__cfduid=ddc1b2cd399b32475cbc191f806ff29d61517706596; expires=Mon, 04-Feb-19 01:09:56 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": "3e79bf530a669601-SJC"
+      },
+      "status_code": 200,
+      "type": "ok"
+    }
+  }
+]
\ No newline at end of file
diff --git a/test/support/fixture/vcr_cassettes/import_block_perform_1_integer.json b/test/support/fixture/vcr_cassettes/import_block_perform_1_integer.json
new file mode 100644
index 0000000000..4f70538688
--- /dev/null
+++ b/test/support/fixture/vcr_cassettes/import_block_perform_1_integer.json
@@ -0,0 +1,30 @@
+[
+  {
+    "request": {
+      "body": "{\"params\":[\"1\",true],\"method\":\"eth_getBlockByNumber\",\"jsonrpc\":\"2.0\",\"id\":0}",
+      "headers": {
+        "Content-Type": "application/json"
+      },
+      "method": "post",
+      "options": [],
+      "request_body": "",
+      "url": "https://sokol.poa.network:443"
+    },
+    "response": {
+      "binary": false,
+      "body": "{\"jsonrpc\":\"2.0\",\"result\":{\"author\":\"0xe8ddc5c7a2d2f0d7a9798459c0104fdf5e987aca\",\"difficulty\":\"0xffffffffffffffffffffffffedf58e45\",\"extraData\":\"0xd5830108048650617269747986312e32322e31826c69\",\"gasLimit\":\"0x66556d\",\"gasUsed\":\"0x0\",\"hash\":\"0x52c867bc0a91e573dc39300143c3bead7408d09d45bdb686749f02684ece72f3\",\"logsBloom\":\"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\",\"miner\":\"0xe8ddc5c7a2d2f0d7a9798459c0104fdf5e987aca\",\"number\":\"0x1\",\"parentHash\":\"0x5b28c1bfd3a15230c9a46b399cd0f9a6920d432e85381cc6a140b06e8410112f\",\"receiptsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"sealFields\":[\"0x84120a71ba\",\"0xb8417a5887662f09ac4673af5850d28f3ad6550407b9c814ef563a13320f881b55ef03754f48f2dde027ad4a5abcabcc42780d9ebfc645f183e5252507d6a25bc2ec01\"],\"sha3Uncles\":\"0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347\",\"signature\":\"7a5887662f09ac4673af5850d28f3ad6550407b9c814ef563a13320f881b55ef03754f48f2dde027ad4a5abcabcc42780d9ebfc645f183e5252507d6a25bc2ec01\",\"size\":\"0x240\",\"stateRoot\":\"0xc196ad59d867542ef20b29df5f418d07dc7234f4bc3d25260526620b7958a8fb\",\"step\":\"302674362\",\"timestamp\":\"0x5a3438a2\",\"totalDifficulty\":\"0xffffffffffffffffffffffffedf78e45\",\"transactions\":[],\"transactionsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"uncles\":[]},\"id\":0}\n",
+      "headers": {
+        "Date": "Sun, 04 Feb 2018 01:09:55 GMT",
+        "Content-Type": "application/json",
+        "Transfer-Encoding": "chunked",
+        "Connection": "keep-alive",
+        "Set-Cookie": "__cfduid=dd200d77362e268d446c7df8154111eac1517706595; expires=Mon, 04-Feb-19 01:09:55 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": "3e79bf4df8849601-SJC"
+      },
+      "status_code": 200,
+      "type": "ok"
+    }
+  }
+]
\ No newline at end of file
diff --git a/test/support/fixture/vcr_cassettes/import_block_perform_1_string.json b/test/support/fixture/vcr_cassettes/import_block_perform_1_string.json
new file mode 100644
index 0000000000..08556b962b
--- /dev/null
+++ b/test/support/fixture/vcr_cassettes/import_block_perform_1_string.json
@@ -0,0 +1,30 @@
+[
+  {
+    "request": {
+      "body": "{\"params\":[\"1\",true],\"method\":\"eth_getBlockByNumber\",\"jsonrpc\":\"2.0\",\"id\":1}",
+      "headers": {
+        "Content-Type": "application/json"
+      },
+      "method": "post",
+      "options": [],
+      "request_body": "",
+      "url": "https://sokol.poa.network:443"
+    },
+    "response": {
+      "binary": false,
+      "body": "{\"jsonrpc\":\"2.0\",\"result\":{\"author\":\"0xe8ddc5c7a2d2f0d7a9798459c0104fdf5e987aca\",\"difficulty\":\"0xffffffffffffffffffffffffedf58e45\",\"extraData\":\"0xd5830108048650617269747986312e32322e31826c69\",\"gasLimit\":\"0x66556d\",\"gasUsed\":\"0x0\",\"hash\":\"0x52c867bc0a91e573dc39300143c3bead7408d09d45bdb686749f02684ece72f3\",\"logsBloom\":\"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\",\"miner\":\"0xe8ddc5c7a2d2f0d7a9798459c0104fdf5e987aca\",\"number\":\"0x1\",\"parentHash\":\"0x5b28c1bfd3a15230c9a46b399cd0f9a6920d432e85381cc6a140b06e8410112f\",\"receiptsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"sealFields\":[\"0x84120a71ba\",\"0xb8417a5887662f09ac4673af5850d28f3ad6550407b9c814ef563a13320f881b55ef03754f48f2dde027ad4a5abcabcc42780d9ebfc645f183e5252507d6a25bc2ec01\"],\"sha3Uncles\":\"0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347\",\"signature\":\"7a5887662f09ac4673af5850d28f3ad6550407b9c814ef563a13320f881b55ef03754f48f2dde027ad4a5abcabcc42780d9ebfc645f183e5252507d6a25bc2ec01\",\"size\":\"0x240\",\"stateRoot\":\"0xc196ad59d867542ef20b29df5f418d07dc7234f4bc3d25260526620b7958a8fb\",\"step\":\"302674362\",\"timestamp\":\"0x5a3438a2\",\"totalDifficulty\":\"0xffffffffffffffffffffffffedf78e45\",\"transactions\":[],\"transactionsRoot\":\"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421\",\"uncles\":[]},\"id\":1}\n",
+      "headers": {
+        "Date": "Sun, 04 Feb 2018 01:09:56 GMT",
+        "Content-Type": "application/json",
+        "Transfer-Encoding": "chunked",
+        "Connection": "keep-alive",
+        "Set-Cookie": "__cfduid=dd200d77362e268d446c7df8154111eac1517706595; expires=Mon, 04-Feb-19 01:09:55 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": "3e79bf4fa9299601-SJC"
+      },
+      "status_code": 200,
+      "type": "ok"
+    }
+  }
+]
\ No newline at end of file
diff --git a/test/support/fixture/vcr_cassettes/import_skipped_blocks_perform_1.json b/test/support/fixture/vcr_cassettes/import_skipped_blocks_perform_1.json
new file mode 100644
index 0000000000..0637a088a0
--- /dev/null
+++ b/test/support/fixture/vcr_cassettes/import_skipped_blocks_perform_1.json
@@ -0,0 +1 @@
+[]
\ No newline at end of file