support specifying asset host for local storage

README.md

@@ -50,6 +50,7 @@ Arc expects certain properties to be configured at the application level:
 config :arc,
   storage: Arc.Storage.S3, # or Arc.Storage.Local
   bucket: {:system, "AWS_S3_BUCKET"}, # if using Amazon S3
+  asset_host: "http://static.example.com" # or {:system "ASSET_HOST"}
 ```
 
 Along with any configuration necessary for ExAws.

lib/arc/storage/local.ex

@@ -16,10 +16,10 @@ defmodule Arc.Storage.Local do
   def url(definition, version, file_and_scope, _options \\ []) do
     local_path = build_local_path(definition, version, file_and_scope)
 
-    if String.starts_with?(local_path, "/") do
-      local_path
+    if host() == "" do
+      Path.join "/", local_path
     else
-      "/" <> local_path
+      Path.join [host(), "/", local_path]
     end
   end
 
@@ -34,4 +34,13 @@ defmodule Arc.Storage.Local do
       Arc.Definition.Versioning.resolve_file_name(definition, version, file_and_scope)
     ])
   end
+
+  defp host do
+    host_url = Application.get_env(:arc, :asset_host, "")
+
+    case host_url do
+      {:system, env_var} when is_binary(env_var) -> System.get_env(env_var)
+      url -> url
+    end
+  end
 end

test/storage/local_test.exs

@@ -1,6 +1,7 @@
 defmodule ArcTest.Storage.Local do
   use ExUnit.Case
   @img "test/support/image.png"
+  @custom_asset_host "http://static.example.com"
 
   setup_all do
     File.mkdir_p("arctest/uploads")
@@ -10,6 +11,18 @@ defmodule ArcTest.Storage.Local do
     end
   end
 
+  def with_env(app, key, value, fun) do
+    previous = Application.get_env(app, key, :nothing)
+
+    Application.put_env(app, key, value)
+    fun.()
+
+    case previous do
+      :nothing -> Application.delete_env(app, key)
+      _ -> Application.put_env(app, key, previous)
+    end
+  end
+
 
   defmodule DummyDefinition do
     use Arc.Definition.Storage
@@ -41,6 +54,24 @@ defmodule ArcTest.Storage.Local do
     refute File.exists?("arctest/uploads/1/thumb-image.png")
   end
 
+  test "get, delete with :asset_host set" do
+    with_env :arc, :asset_host, @custom_asset_host, fn ->
+
+      assert {:ok, "original-image.png"} == Arc.Storage.Local.put(DummyDefinition, :original, {Arc.File.new(%{filename: "original-image.png", path: @img}), nil})
+      assert {:ok, "1/thumb-image.png"} == Arc.Storage.Local.put(DummyDefinition, :thumb, {Arc.File.new(%{filename: "1/thumb-image.png", path: @img}), nil})
+
+      assert File.exists?("arctest/uploads/original-image.png")
+      assert File.exists?("arctest/uploads/1/thumb-image.png")
+      assert @custom_asset_host <> "/arctest/uploads/original-image.png" == DummyDefinition.url("image.png", :original)
+      assert @custom_asset_host <> "/arctest/uploads/1/thumb-image.png" == DummyDefinition.url("1/image.png", :thumb)
+
+      :ok = Arc.Storage.Local.delete(DummyDefinition, :original, {%{file_name: "image.png"}, nil})
+      :ok = Arc.Storage.Local.delete(DummyDefinition, :thumb, {%{file_name: "image.png"}, nil})
+      refute File.exists?("arctest/uploads/original-image.png")
+      refute File.exists?("arctest/uploads/1/thumb-image.png")
+    end
+  end
+
   test "save binary" do
     Arc.Storage.Local.put(DummyDefinition, :original, {Arc.File.new(%{binary: "binary", filename: "binary.png"}), nil})
     assert true == File.exists?("arctest/uploads/binary.png")