don't lookup at table when table isn't inited

apps/explorer/lib/explorer/exchange_rates/exchange_rates.ex

@@ -90,7 +90,7 @@ defmodule Explorer.ExchangeRates do
   """
   @spec lookup(String.t()) :: Token.t() | nil
   def lookup(symbol) do
-    if store() == :ets do
+    if store() == :ets and enabled?() do
       case :ets.lookup(table_name(), symbol) do
         [tuple | _] when is_tuple(tuple) -> Token.from_tuple(tuple)
         _ -> nil
@@ -133,4 +133,10 @@ defmodule Explorer.ExchangeRates do
   defp store do
     config(:store) || :ets
   end
+
+  defp enabled? do
+    :explorer
+    |> Application.fetch_env!(__MODULE__)
+    |> Keyword.fetch!(:enabled)
+  end
 end

apps/explorer/lib/explorer/known_tokens/known_tokens.ex

@@ -81,7 +81,11 @@ defmodule Explorer.KnownTokens do
   """
   @spec list :: [{String.t(), Hash.Address.t()}]
   def list do
+    if enabled?() do
       list_from_store(store())
+    else
+      []
+    end
   end
 
   @doc """
@@ -89,7 +93,7 @@ defmodule Explorer.KnownTokens do
   """
   @spec lookup(String.t()) :: {:ok, Hash.Address.t()} | :error | nil
   def lookup(symbol) do
-    if store() == :ets do
+    if store() == :ets && enabled?()do
       case :ets.lookup(table_name(), symbol) do
         [{_symbol, address} | _] -> Hash.Address.cast(address)
         _ -> nil
@@ -128,4 +132,10 @@ defmodule Explorer.KnownTokens do
   defp store do
     config(:store) || :ets
   end
+
+  defp enabled? do
+    :explorer
+    |> Application.fetch_env!(__MODULE__)
+    |> Keyword.fetch!(:enabled)
+  end
 end

apps/explorer/test/explorer/exchange_rates/exchange_rates_test.exs

@@ -19,6 +19,7 @@ defmodule Explorer.ExchangeRatesTest do
 
     Application.put_env(:explorer, Explorer.ExchangeRates.Source, source: TestSource)
     Application.put_env(:explorer, Explorer.ExchangeRates, table_name: :rates)
+    Application.put_env(:explorer, Explorer.ExchangeRates, enabled: true)
 
     on_exit(fn ->
       Application.put_env(:explorer, Explorer.ExchangeRates.Source, source_configuration)
@@ -135,4 +136,10 @@ defmodule Explorer.ExchangeRatesTest do
     assert z == ExchangeRates.lookup("z")
     assert nil == ExchangeRates.lookup("nope")
   end
+
+  test "lookup when desibled" do
+    Application.put_env(:explorer, Explorer.ExchangeRates, enabled: false)
+
+    assert nil == ExchangeRates.lookup("z")
+  end
 end

apps/explorer/test/explorer/known_tokens/known_tokens_test.exs

@@ -21,6 +21,7 @@ defmodule Explorer.KnownTokensTest do
 
     Application.put_env(:explorer, Explorer.KnownTokens.Source, source: TestSource)
     Application.put_env(:explorer, Explorer.KnownTokens, table_name: :known_tokens)
+    Application.put_env(:explorer, Explorer.KnownTokens, enabled: true)
 
     on_exit(fn ->
       Application.put_env(:explorer, Explorer.KnownTokens.Source, source_configuration)
@@ -128,4 +129,10 @@ defmodule Explorer.KnownTokensTest do
     assert Hash.Address.cast("0x0000000000000000000000000000000000000001") == KnownTokens.lookup("TEST1")
     assert nil == KnownTokens.lookup("nope")
   end
+
+  test "lookup when desibled" do
+    Application.put_env(:explorer, Explorer.KnownTokens, enabled: false)
+
+    assert nil == KnownTokens.lookup("z")
+  end
 end