Action Web Service – Serving APIs on rails

Action Web Service provides a way to publish interoperable web service APIs with Rails without spending a lot of time delving into protocol details.

Features

  • SOAP RPC protocol support

  • Dynamic WSDL generation for APIs

  • XML-RPC protocol support

  • Clients that use the same API definitions as the server for easy interoperability with other Action Web Service based applications

  • Type signature hints to improve interoperability with static languages

  • Active Record model class support in signatures

Defining your APIs

You specify the methods you want to make available as API methods in an ActionWebService::API::Base derivative, and then specify this API definition class wherever you want to use that API.

The implementation of the methods is done separately from the API specification.

Method name inflection

Action Web Service will camelcase the method names according to Rails Inflector rules for the API visible to public callers. What this means, for example, is that the method names in generated WSDL will be camelcased, and callers will have to supply the camelcased name in their requests for the request to succeed.

If you do not desire this behaviour, you can turn it off with the ActionWebService::API::Base inflect_names option.

Inflection examples

:add       => Add
:find_all  => FindAll

Disabling inflection

class PersonAPI < ActionWebService::API::Base
  inflect_names false
end

API definition example

class PersonAPI < ActionWebService::API::Base
  api_method :add, :expects => [:string, :string, :bool], :returns => [:int]
  api_method :remove, :expects => [:int], :returns => [:bool]
end

API usage example

class PersonController < ActionController::Base
  web_service_api PersonAPI

  def add
  end

  def remove
  end
end

Publishing your APIs

Action Web Service uses Action Pack to process protocol requests. There are two modes of dispatching protocol requests, Direct, and Delegated.

Direct dispatching

This is the default mode. In this mode, public controller instance methods implement the API methods, and parameters are passed through to the methods in accordance with the API specification.

The return value of the method is sent back as the return value to the caller.

In this mode, a special api action is generated in the target controller to unwrap the protocol request, forward it on to the relevant method and send back the wrapped return value. This action must not be overridden.

Direct dispatching example

class PersonController < ApplicationController
  web_service_api PersonAPI

  def add
  end

  def remove
  end
end

class PersonAPI < ActionWebService::API::Base
  ...
end

For this example, protocol requests for Add and Remove methods sent to /person/api will be routed to the controller methods add and remove.

Delegated dispatching

This mode can be turned on by setting the web_service_dispatching_mode option in a controller to :delegated.

In this mode, the controller contains one or more web service objects (objects that implement an ActionWebService::API::Base definition). These web service objects are each mapped onto one controller action only.

Delegated dispatching example

class ApiController < ApplicationController
  web_service_dispatching_mode :delegated

  web_service :person, PersonService.new
end

class PersonService < ActionWebService::Base
  web_service_api PersonAPI

  def add
  end

  def remove
  end
end

class PersonAPI < ActionWebService::API::Base
  ...
end

For this example, all protocol requests for PersonService are sent to the /api/person action.

The /api/person action is generated when the web_service method is called. This action must not be overridden.

Other controller actions (actions that aren't the target of a web_service call) are ignored for ActionWebService purposes, and can do normal action tasks.

Layered dispatching

This mode can be turned on by setting the web_service_dispatching_mode option in a controller to :layered.

This mode is similar to delegated mode, in that multiple web service objects can be attached to one controller, however, all protocol requests are sent to a single endpoint.

Use this mode when you want to share code between XML-RPC and SOAP clients, for APIs where the XML-RPC method names have prefixes. An example of such a method name would be blogger.newPost.

Layered dispatching example

class ApiController < ApplicationController
  web_service_dispatching_mode :layered

  web_service :mt, MovableTypeService.new
  web_service :blogger, BloggerService.new
  web_service :metaWeblog, MetaWeblogService.new
end

class MovableTypeService < ActionWebService::Base
  ...
end

class BloggerService < ActionWebService::Base
  ...
end

class MetaWeblogService < ActionWebService::API::Base
  ...
end

For this example, an XML-RPC call for a method with a name like mt.getCategories will be sent to the getCategories method on the :mt service.

Customizing WSDL generation

You can customize the names used for the SOAP bindings in the generated WSDL by using the wsdl_service_name option in a controller:

class WsController < ApplicationController
  wsdl_service_name 'MyApp'
end

You can also customize the namespace used in the generated WSDL for custom types and message definition types:

class WsController < ApplicationController
  wsdl_namespace 'http://my.company.com/app/wsapi'
end

The default namespace used is 'urn:ActionWebService', if you don't supply one.

ActionWebService and UTF-8

If you're going to be sending back strings containing non-ASCII UTF-8 characters using the :string data type, you need to make sure that Ruby is using UTF-8 as the default encoding for its strings.

The default in Ruby is to use US-ASCII encoding for strings, which causes a string validation check in the Ruby SOAP library to fail and your string to be sent back as a Base-64 value, which may confuse clients that expected strings because of the WSDL.

Two ways of setting the default string encoding are:

  • Start Ruby using the -Ku command-line option to the Ruby executable

  • Set the $KCODE flag in config/environment.rb to the string 'UTF8'

Testing your APIs

Functional testing

You can perform testing of your APIs by creating a functional test for the controller dispatching the API, and calling #invoke in the test case to perform the invocation.

Example:

class PersonApiControllerTest < Test::Unit::TestCase
  def setup
    @controller = PersonController.new
    @request    = ActionController::TestRequest.new
    @response   = ActionController::TestResponse.new
  end

  def test_add
    result = invoke :remove, 1
    assert_equal true, result
  end
end

This example invokes the API method test, defined on the PersonController, and returns the result.

If you're not using SOAP (or you're having serialisation difficulties), you can test XMLRPC like this:

class PersonApiControllerTest < Test::Unit::TestCase
  def setup
    @controller = PersonController.new
    @request    = ActionController::TestRequest.new
    @response   = ActionController::TestResponse.new

    @protocol   = :xmlrpc # can also be :soap, the default
  end

  def test_add
    result = invoke :remove, 1 # no change here
    assert_equal true, result
  end
end

Scaffolding

You can also test your APIs with a web browser by attaching scaffolding to the controller.

Example:

class PersonController
  web_service_scaffold :invocation
end

This creates an action named invocation on the PersonController.

Navigating to this action lets you select the method to invoke, supply the parameters, and view the result of the invocation.

Using the client support

Action Web Service includes client classes that can use the same API definition as the server. The advantage of this approach is that your client will have the same support for Active Record and structured types as the server, and can just use them directly, and rely on the marshaling to Do The Right Thing.

Note: The client support is intended for communication between Ruby on Rails applications that both use Action Web Service. It may work with other servers, but that is not its intended use, and interoperability can't be guaranteed, especially not for .NET web services.

Web services protocol specifications are complex, and Action Web Service client support can only be guaranteed to work with a subset.

Factory created client example

class BlogManagerController < ApplicationController
  web_client_api :blogger, :xmlrpc, 'http://url/to/blog/api/RPC2', :handler_name => 'blogger'
end

class SearchingController < ApplicationController
  web_client_api :google, :soap, 'http://url/to/blog/api/beta', :service_name => 'GoogleSearch'
end

See ActionWebService::API::ActionController::ClassMethods for more details.

Manually created client example

class PersonAPI < ActionWebService::API::Base
  api_method :find_all, :returns => [[Person]]
end

soap_client = ActionWebService::Client::Soap.new(PersonAPI, "http://...")
persons = soap_client.find_all

class BloggerAPI < ActionWebService::API::Base
  inflect_names false
  api_method :getRecentPosts, :returns => [[Blog::Post]]
end

blog = ActionWebService::Client::XmlRpc.new(BloggerAPI, "http://.../xmlrpc", :handler_name => "blogger")
posts = blog.getRecentPosts

See ActionWebService::Client::Soap and ActionWebService::Client::XmlRpc for more details.

Dependencies

Action Web Service requires that the Action Pack and Active Record are either available to be required immediately or are accessible as GEMs.

It also requires a version of Ruby that includes SOAP support in the standard library. At least version 1.8.2 final (2004-12-25) of Ruby is recommended; this is the version tested against.

Download

The latest Action Web Service version can be downloaded from rubyforge.org/projects/actionservice

Installation

You can install Action Web Service with the following command.

% [sudo] ruby setup.rb

License

Action Web Service is released under the MIT license.

Support

The Ruby on Rails mailing list

Or, to contact the author, send mail to bitserf@gmail.com