Waffle GCS

Google Cloud Storage for Waffle

What's Waffle?

Waffle (formerly Arc) is a file uploading library for Elixir. It's main goal is to provide "plug and play" file uploading and retrieval functionality for any storage provider (e.g. AWS S3, Google Cloud Storage, etc).

What's Waffle GCS?

Waffle GCS provides an integration between Waffle and Google Cloud Storage. It is (in my opinion) the spiritual successor to arc_gcs. If you want to easily upload and retrieve files using Google Cloud Storage as your provider, and you also use Waffle, then this library is for you.

What's different from arc_gcs?

The major three differences are:

1. Transitions from Arc to Waffle.
2. Uses the official Google Cloud API client for Elixir rather than constructing XML requests and sending them over HTTP.
3. (In Progress) Implements the v4 URL signing process in addition to the existing v2 process.

Because Google now officially builds client libraries for Elixir, it is more maintainable to use those libraries rather than relying on the older XML API. The v2 URL signing process is also being deprecated in favor of the v4 process. Although Google will give plenty of advance notice if/when the v2 process is becoming unsupported, it's again more maintainable to use Google best practices to ensure future compatibility.

Installation

Add it to your mix dependencies:

defp deps do
  [
    ...,
    {:waffle_gcs, "~> 0.1"}
  ]
end

Configuration

All configuration values are stored under the :waffle app key. E.g.

config :waffle,
  storage: Waffle.Storage.Google,
  bucket: "gcs-bucket",
  storage_dir: "uploads/waffle"

Note: a valid bucket name is a required config. This can either be a hard-coded string (e.g. "gcs-bucket") or a system env tuple (e.g. {:system, "WAFFLE_BUCKET"}). You can also override this in your definition module (e.g. def bucket(), do: "my-bucket").

Authentication is done through Goth which requires credentials (https://github.com/peburrows/goth#installation).

Custom Token Generation

By default, the credentials provided to Goth will be used to generate tokens. If you have multiple sets of credentials in Goth or otherwise need more control over token generation, you can define your own module:

defmodule MyCredentials do
  @behaviour Waffle.Storage.Google.TokenFetcher

  @impl Waffle.Storage.Google.TokenFetcher
  def get_token(scopes) when is_list(scopes), do: get_token(Enum.join(scopes, " "))

  @impl Waffle.Storage.Google.TokenFetcher
  def get_token(scope) when is_binary(scope) do
    {:ok, token} = Goth.Token.for_scope({"[email protected]", scope})
    token.token
  end
end

And configure it to use this new module instead of the default token generation:

config :waffle,
  storage: Waffle.Storage.Google,
  bucket: "gcs-bucket-name",
  token_fetcher: MyCredentials

URL Signing

If your bucket/object permissions do not allow for public access, you will need to use signed URLs to give people access to the uploaded files. This is done by either passing signed: true to CloudStorage.url/4 or by setting it in the configs (config :waffle, signed: true). The default expiration time is one hour but can be changed by setting the :expires_in config/option value. The value is the number of seconds the URL should remain valid for after generation.

GCS object headers

You can specify custom object headers by defining gcs_object_headers/2 in your definition which returns keyword list or map. E.g.

def gcs_object_headers(_version, {_file, _scope}) do
  [contentType: "image/jpeg"]
end

The list of all the supported attributes can be found here: https://hexdocs.pm/google_api_storage/GoogleApi.Storage.V1.Model.Object.html.