Acfs - API client for services

Acfs is a library to develop API client libraries for single services within a larger service oriented application.

Acfs covers model and service abstraction, convenient query and filter methods, full middleware stack for pre-processing requests and responses on a per service level and automatic request queuing and parallel processing. See Usage for more.

Installation

Add this line to your application's Gemfile:

gem 'acfs', '~> 0.21.0'

Note: Acfs is under development. I'll try to avoid changes to the public API but internal APIs may change quite often.

And then execute:

> bundle

Or install it yourself as:

> gem install acfs

Usage

First you need to define your service(s):

class UserService < Acfs::Service
  self.base_url = 'http://users.myapp.org'

  # You can configure middlewares you want to use for the service here.
  # Each service has it own middleware stack.
  #
  use Acfs::Middleware::JsonDecoder
  use Acfs::Middleware::MessagePackDecoder
end

This specifies where the UserService is located. You can now create some models representing resources served by the UserService.

class User < Acfs::Resource
  service UserService # Associate `User` model with `UserService`.

  # Define model attributes and types
  # Types are needed to parse and generate request and response payload.

  attribute :id, :uuid # Types can be classes or symbols.
                       # Symbols will be used to load a class from `Acfs::Model::Attributes` namespace.
                       # Eg. `:uuid` will load class `Acfs::Model::Attributes::Uuid`.

  attribute :name, :string, default: 'Anonymous'
  attribute :age, ::Acfs::Model::Attributes::Integer # Or use :integer

end

The service and model classes can be shipped as a gem or git submodule to be included by the frontend application(s).

You can use the model there:

@user = User.find 14

@user.loaded? #=> false

Acfs.run # This will run all queued request as parallel as possible.
         # For @user the following URL will be requested:
         # `http://users.myapp.org/users/14`

@model.name # => "..."

@users = User.all
@users.loaded? #=> false

Acfs.run # Will request `http://users.myapp.org/users`

@users #=> [<User>, ...]

If you need multiple resources or dependent resources first define a "plan" how they can be loaded:

@user = User.find(5) do |user|
  # Block will be executed right after user with id 5 is loaded

  # You can load additional resources also from other services
  # Eg. fetch comments from `CommentSerivce`. The line below will
  # load comments from `http://comments.myapp.org/comments?user=5`
  @comments = Comment.where user: user.id

  # You can load multiple resources in parallel if you have multiple
  # ids.
  @friends  = User.find 1, 4, 10 do |friends|
    # This block will be executed when all friends are loaded.
    # [ ... ]
  end
end

Acfs.run # This call will fire all request as parallel as possible.
         # The sequence above would look similar to:
         #
         # Start                Fin
         #   |===================|       `Acfs.run`
         #   |====|                      /users/5
         #   |    |==============|       /comments?user=5
         #   |    |======|               /users/1
         #   |    |=======|              /users/4
         #   |    |======|               /users/10

# Now we can access all resources:

@user.name       # => "John
@comments.size   # => 25
@friends[0].name # => "Miraculix"

Use .find_by to get first element only. .find_by will call the index-Action and return the first resource. Optionally passed params will be sent as GET parameters and can be used for filtering in the service's controller.

@user = User.find_by age: 24

Acfs.run # Will request `http://users.myapp.org/users?age=24`

@user # Contains the first user object returned by the index action

If no object can be found, .find_by will return nil. The optional callback will then be called with nil as parameter. Use .find_by! to raise an Acfs::ResourceNotFound exception if no object can be found. .find_by! will only invoke the optional callback if an object was successfully loaded.

Acfs has basic update support using PUT requests:

@user = User.find 5
@user.name = "Bob"

@user.changed? # => true
@user.persisted? # => false

@user.save # Or .save!
           # Will PUT new resource to service synchronously.

@user.changed? # => false
@user.persisted? # => true

Singleton resources

Singletons can be used in Acfs by creating a new resource which inherits from SingletonResource:

class Single < Acfs::SingletonResource
  service UserService # Associate `Single` model with `UserService`.

  # Define model attributes and types as with regular resources

  attribute :name, :string, default: 'Anonymous'
  attribute :age, :integer

end

The following code explains the routing for singleton resource requests:

my_single = Single.new
mysingle.save # sends POST request to /single

my_single = Single.find
Acfs.run # sends GET request to /single

my_single.age = 28
my_single.save # sends PUT request to /single

my_single.delete # sends DELETE request to /single

You also can pass parameters to the find call, these will sent as GET params to the index action:

my_single = Single.find name: 'Max'
Acfs.run # sends GET request with param to /single?name=Max

Resource Inheritance

Acfs provides a resource inheritance similar to ActiveRecord Single Table Inheritance. If a type attribute exists and is a valid subclass of your resource they will be converted to you subclassed resources:

class Computer < Acfs::Resource
  ...
end

class Pc < Computer end
class Mac < Computer end

With the following response on GET /computers the collection will contain the appropriate subclass resources:

[
    { "id": 5, "type": "Computer"},
    { "id": 6, "type": "Mac"},
    { "id": 8, "type": "Pc"}
]

@computers = Computer.all

Acfs.run

@computer[0].class # => Computer
@computer[1].class # => Mac
@computer[2].class # => Pc

Stubbing

You can stub resources in applications using an Acfs service client:

# spec_helper.rb

# This will enable stabs before each spec and clear internal state
# after each spec.
require 'acfs/rspec'

before do
  @stub = Acfs::Stub.resource MyUser, :read, with: { id: 1 }, return: { id: 1, name: 'John Smith', age: 32 }
  Acfs::Stub.resource MyUser, :read, with: { id: 2 }, raise: :not_found
  Acfs::Stub.resource Session, :create, with: { ident: '[email protected]', password: 's3cr3t' }, return: { id: 'longhash', user: 1 }
  Acfs::Stub.resource MyUser, :update, with: lambda { |op| op.data.include? :my_var }, raise: 400
end

it 'should find user number one' do
  user = MyUser.find 1
  Acfs.run

  expect(user.id).to be == 1
  expect(user.name).to be == 'John Smith'
  expect(user.age).to be == 32

  expect(@stub).to be_called
  expect(@stub).to_not be_called 5.times
end

it 'should not find user number two' do
  MyUser.find 3

  expect { Acfs.run }.to raise_error(Acfs::ResourceNotFound)
end

it 'should allow stub resource creation' do
  session = Session.create! ident: '[email protected]', password: 's3cr3t'

  expect(session.id).to be == 'longhash'
  expect(session.user).to be == 1
end

By default Acfs raises an error when a non stubbed resource should be requested. You can switch of the behavior:

before do
  Acfs::Stub.allow_requests = true
end

it 'should find user number one' do
  user = MyUser.find 1
  Acfs.run             # Would have raised Acfs::RealRequestNotAllowedError
                       # Will run real request to user service instead.
end

Instrumentation

Acfs supports instrumentation via active support.

Acfs expose to following events

• acfs.operation.complete(operation, response): Acfs operation completed
• acfs.runner.sync_run(operation): Run operation right now skipping queue.
• acfs.runner.enqueue(operation): Enqueue operation to be run later.
• acfs.before_run: directly before acfs.run
• acfs.run: Run all queued operations.

Read official guide to see to to subscribe.

Roadmap

• Update
  • Better new? detection eg. storing ETag from request resources.
  • Use PATCH for with only changed attributes and If-Unmodifed-Since and If-Match header fields if resource was surly loaded from service and not created with an id (e.g User.new id: 5, name: "john").
  • Conflict detection (ETag / If-Unmodified-Since)
• High level features
  • Support for custom mime types on client and server side. (application/vnd.myservice.user.v2+msgpack)
  • Server side components
    • Reusing model definitions for generating responses?
    • Rails responders providing REST operations with integrated ETag, Modified Headers, conflict detection, ...
  • Pagination? Filtering? (If service API provides such features.)
• Documentation

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Add specs for your feature
4. Implement your feature
5. Commit your changes (git commit -am 'Add some feature')
6. Push to the branch (git push origin my-new-feature)
7. Create new Pull Request

Contributors

• Nicolas Fricke
• Tino Junge
• Malte Swart

License

MIT License

Copyright (c) 2013 Jan Graichen. MIT license, see LICENSE for more details.