Multiverse

This plug helps to manage multiple API versions based on request and response gateways. This is an awesome practice to hide your backward compatibility. It allows to have your code in a latest possible version, without duplicating controllers or models. We use it in production.

Inspired by Stripe API. Read more at MOVE FAST, DON'T BREAK YOUR API or API versioning.

Goals

reduce changes required to support multiple API versions;
provide a way to test and schedule API version releases;
to have minimum dependencies and low performance hit;
to be flexible enough for most of projects to adopt it.

Adapters

Multiverse allows you to use a custom adapter which can, for eg.:

store consumer version upon his first request and re-use it as default each time consumer is using your API, eliminating need of passing version headers for them (a.k.a. version pinning). Change this version when consumer has explicitly set it;
use other than ISO date version types, eg. incremental counters (v1, v2);
handle malformed versions by responding with JSON errors.

Default adapter works with ISO-8601 date from x-api-version header (configurable). For malformed versions it would log a warning and fallback to the default date (configured via :default_version setting):

:first - apply all gates by default. This option is useful when you integrate Multiverse in existing project and API consumers are not ready to accept latest changes by default;
:latest - user current date as default version. This option is useful when there are no legacy clients or there was no breaking changes before those clients started to send API version.

ISO date adapter allows API clients to use channel name instead of date:

latest channel would fallback to the current date;
edge channel would disable all changes altogether.

Channels allow you to plan version releases upfront and test them without affecting users, just set future date for a change and pass it explicitly or use edge channel to test latest application version.

Installation

The package (take look at hex.pm) can be installed as:

Add multiverse to your list of dependencies in mix.exs:

def deps do
  [{:multiverse, "~> 2.0.0"}]
end

Make sure that multiverse is available at runtime in your production:

def application do
  [applications: [:multiverse]]
end

How to use

Insert this plug into your API pipeline (in your router.ex):

pipeline :api do
  plug :accepts, ["json"]
  plug :put_secure_browser_headers

  plug Multiverse, default_version: :latest
end

Define module that handles change

defmodule AccountTypeChange do
  @behaviour Multiverse.Change

  def handle_request(%Plug.Conn{} = conn) do
    # Mutate your request here
    IO.inspect "AccountTypeChange.handle_request applied to request"
    conn
  end

  def handle_response(%Plug.Conn{} = conn) do
    # Mutate your response here
    IO.inspect "AccountTypeChange.handle_response applied to response"
    conn
  end
end

Enable the change:

pipeline :api do
  plug :accepts, ["json"]
  plug :put_secure_browser_headers

  plug Multiverse,
    default_version: :latest,
    gates: %{
      ~D[2016-07-21] => [AccountTypeChange]
    }
end

Send your API requests with X-API-Version header with version lower or equal to 2016-07-20.

Overriding version header

You can use any version headers by passing option to Multiverse:

pipeline :api do
  plug :accepts, ["json"]
  plug :put_secure_browser_headers

  plug Multiverse,
    default_version: :latest,
    version_header: "x-my-version-header",
    gates: %{
      ~D[2016-07-21] => [AccountTypeChange]
    }
end

Using custom adapters

You can use your own adapter which implements Multiverse.Adapter behaviour:

pipeline :api do
  plug :accepts, ["json"]
  plug :put_secure_browser_headers

  plug Multiverse,
    default_version: :latest,
    adapter: MyApp.SmartMultiverseAdapter,
    gates: %{
      ~D[2016-07-21] => [AccountTypeChange]
    }
end

Structuring your tests

Split your tests into versions:

$ ls -l test/acceptance
total 0
drwxr-xr-x  2 andrew  staff  68 Aug  1 19:23 AccountTypeChange
drwxr-xr-x  2 andrew  staff  68 Aug  1 19:24 OlderChange

Avoid touching request or response in old tests. Create API gates and matching folder in acceptance tests.

Other things you might want to do

Store Multiverse configuration in config.ex:

use Mix.Config

config :my_app, MyApp.Endpoint,
  default_version: :latest,
  gates: %{
    ~D[2016-07-21] => [AccountTypeChange]
  }

plug Multiverse, otp_app: :my_app, endpoint: __MODULE__

Generate API documentation from changes @moduledoc's.
Other awesome stuff. Open an issue and tell me about it! :).

License

See LICENSE.md.

cmedley/multiverse