[Eiffel-Loop News] Update on Amazon Instant Access API

[Finnian Reilly]

Amazon Instant Access API

Amazon Instant Access (AIA) is a fulfilment technology for digital content that is purchased on the Amazon website and is delivered by a third party vendor.

Motivation

My motivation for developing this API is so I can advertise my software on the thousands of books sold by Amazon relevant to the software. But do this I need to become a vendor. It could be worth it despite the 30% cut Amazon take on the software.

Progress Update

Work on this API is now substantially finished although I have yet to test against a live server.  I have inserted links to the integration guide in the class descriptions. I have not bothered to implement the subscription activation part of the API since I have my own software subscription system. But will be happy to implement it for anyone who requests it. There is very little in it.

http://www.eiffel-loop.com/library/network/amazon/class-index.html

Test Suite

The code for the test suite can be found here.

New Reflective Classes

It's a fairly simple API and the reason it has been taking so long is I have been using it as a test ground for some new Eiffel-Loop classes that provide some powerful reflective capabilities. If you examine the AIA code you will find many classes are curiously absent of code that does anything. For example you won't find any JSON related strings, and you won't find any code to translate between the JSON camel case and the Eiffel snake case naming conventions, and you won't find any code that defines object equality by attribute comparison. All the heavy lifting is done by the reflective parent. Here is the reflective class hierarchy as pertaining to the AIA api.

EL_REFLECTION

   EL_STATUS_CODE_REFLECTION* [N -> {NUMERIC, HASHABLE}]

      AIA_RESPONSE_CODE

      AIA_REASON_CODE

   EL_REFLECTIVELY_SETTABLE* [S -> STRING_GENERAL create make_empty end]

      EL_STORABLE*

         AIA_CREDENTIAL

      EL_REFLECTIVELY_JSON_SETTABLE*

         AIA_REQUEST*

            AIA_GET_USER_ID_REQUEST

            AIA_PURCHASE_REQUEST

               AIA_REVOKE_REQUEST

         AIA_RESPONSE

            AIA_GET_USER_ID_RESPONSE

            AIA_PURCHASE_RESPONSE

               AIA_REVOKE_RESPONSE

      AIA_AUTHORIZATION_HEADER

      EL_REFLECTIVELY_SETTABLE_STRINGS* [S -> STRING_GENERAL create make_empty end]

         AIA_CREDENTIAL_ID

      FCGI_REQUEST_PARAMETERS

      FCGI_HTTP_HEADERS

Source Code

The code is not yet part of an Eiffel-Loop release but is available by cloning or checking out the github repository.

https://github.com/finnianr/Eiffel-Loop/

The AIA code is located here

https://github.com/finnianr/Eiffel-Loop/tree/master/library/network/amazon

[Finnian Reilly]

Reflection Notes

I forgot to mention about one cool new feature of the template substitution class  EL_SUBSTITUTION_TEMPLATE that is demonstrated in class AIA_AUTHORIZATION_HEADER. You can use `set_variables_from_object' to reflectively set the variables in the template from an object that implements EL_REFLECTIVELY_SETTABLE.

feature -- Access

   as_string: STRING

      local

         template: like Signed_string_template

      do

         template := Signed_string_template

         template.wipe_out_variables

         template.set_variables_from_object (Current)

         template.set_variables_from_object (credential)

         Result := template.substituted

      end

feature {NONE} -- Constants

   Signed_string_template: EL_SUBSTITUTION_TEMPLATE [STRING]

      once

         create Result.make ("$algorithm SignedHeaders=$signed_headers, Credential=$key/$date, Signature=$signature")

      end

A Note on Efficiency

It is worth pointing out that class EL_REFLECTIVELY_SETTABLE removes a major source of inefficiency from the underlying Eiffel reflection API. I am referring to calls to {REFLECTED_OBJECT}.field_name which creates a new string every time it's called. Class EL_REFLECTIVELY_SETTABLE caches field names in a table `field_index_table' which is generated only once per each reflectively settable type.