Swagger / YAML and self documenting RESTful API’s

Get your Swagger on with Delphi

So you want to build a new REST server (using Delphi or C++) and want it to become really popular and easily used by other developers. Imagine….

  • Your building a new REST server,
  • You have to document the API’s
  • You have to keep the documentation updated
  • To aid adoption of your services you want to create examples for other developers to connect into your server quickly

With the release of RAD Studio 10.1 Berlin, it is now possible to do all the above thanks to the new documentation attributes used in EMS packages that create YAML documentation that can be used with Swagger.

What is YAML?

YAML: (rhymes with “camel”) YAML Ain’t Markup Language

In short, YAML is a human friendly data serialization standard for all programming languages that is a subset of JSON.

Both JSON and YAML aim to be human readable data interchange formats. However, JSON and YAML have different priorities. JSON’s foremost design goal is simplicity and universality. Thus, JSON is trivial to generate and parse, at the cost of reduced human readability. It also uses a lowest common denominator information model, ensuring any JSON data can be easily processed by every modern programming environment.

In contrast, YAML’s foremost design goals are human readability and support for serializing arbitrary native data structures. Thus, YAML allows for extremely readable files, but is more complex to generate and parse. In addition, YAML ventures beyond the lowest common denominator data types, requiring more complex processing when crossing between different programming environments.

YAML can therefore be viewed as a natural superset of JSON, offering improved human readability and a more complete information model. This is also the case in practice; every JSON file is also a valid YAML file. This makes it easy to migrate from JSON to YAML if/when the additional features are required.

What is Swagger?

Swagger is a simple yet powerful representation of your RESTful API, and as part of the open tools initiative (joining November 2015) it is backed by members such as Microsoft, Google, PayPal and IBM.

Using a YAML document, you can create Swagger instance of your API.

With the largest ecosystem of API tooling on the planet, thousands of developers are supporting Swagger in almost every modern programming language and deployment environment making it a great choice to make your REST server easily integrated and used by others.

With a Swagger-enabled API, you get interactive documentation, client SDK generation and discoverability.

Creating YAML with Delphi / C++ Builder

To gain the benefits of Swagger you need to create the YAML documentation; this is achieved using a number of new attributes defined on the custom API’s you are creating. The three core Custom API Documentation attributes are:

In addition there are two additional documentation elements that allow you to define EndPointObjects that are used by your API. This way you define structures that are returned, rather than just returning simple types.

Custom API Documentation Sample

With Rad Studio 10.1 Berlin, in the samples, there is a new demo that covers the above custom api documentation attributes. If you want to open it in the IDE, choose “Open a sample project” and browse to the following folder and open the APIDocDelphiAttributes.bpl package (cpp equivalents also available, swap Delphi for CPP in names).

 \Samples\Delphi\Database\EMS\APIDocAttributes

As this sample uses InterBase, you need to make sure you have started InterBase. If its not running, use the IBServerManager to make sure its running. 

Rather than cover each of the attributes here, and repeat the documentation, I’ll leave you explore the links above to read up on these attributes, instead I want to use this sample to explore the YAML using Swagger UI, but first lets get the YAML document by running the sample.

Getting YAML from EMS Sample

Compile and run (F9) the sample project and choose Open Browser. You should now see a call to http://localhost:8080/version showing version 2.1 or higher.EMS Version

To get the documentation from the server, navigate to http://localhost:8080/api where you will see the different documentation types supported. EMS API

This shows 2 currently. apidoc.yaml and apidoc.json. Add these to the end of the API url to see how they look. e.g. http://localhost:8080/api/apidoc.yaml

EMS APIDoc YAML
http://localhost:8080/api/apidoc.yaml returning YAML from use with Swagger from EMS

YAML to Swagger UI

So you have a YAML document.. now what? Swagger UI is a great tool for reading the YAML document and giving you interactive HTML documentation for your RESTful API.

You can download the latest Swagger UI from GitHub onto your development machine https://github.com/swagger-api/swagger-ui

Download Swagger UI
Download Swagger UI

Unzip the download on your development machine / vm. In there locate the dist folder and open the index.html

A note on CORS

Now before we go any further, your need to be aware of CORS – Cross Origin Resource Sharing. In short, because we will want to enable PUT, POST, DELETE from outside the core domain, we need to allow CORS (or you will not be able to call EMS)

You can either update the EMS configuration to allow CORS or install the following google chrome plugin. If you install the plugin, once you have the SwaggerUI index.html page open, you need to make sure its enabled. (i’ve sometimes found I’ve had to disable and re-enable it to get it to work).

Enabling CORS using Google Chrome Plugin
Enabling CORS using Google Chrome Plugin

Loading the YAML into Swagger

Copy the URL for the YAML document and post it into your SwaggerUI/dist/index.html page, and choose Explore.

The sample (pet store) documentation in SwaggerUI will now be replaced with the documentation form the EMS server.

You can now browse and invoke the API calls directly from the SwaggerUI interface. The example creates a category called Sample Tag (which you can see listed) All the other categories cover the default features of EMS, including User security, and the new ThingPoint EdgeModule API’s

Visualising YAML in Swagger UI
Visualising YAML in Swagger UI

You can now explore the categories, review the documentation model that defines the structure being return (thanks to the EndPointObjectXXX attributes)Viewing Swagger UI exposed Methods

… and once you fill in any defined parameters you can “Try It Out”. This shows the URL called, and also the response body!

Trying out Swagger UI
Trying out Swagger UI

That is it! How simple to test you RESTful API than by using YAML and Swagger UI.

You can now explore Swagger.IO and learn about the other languages that you can create connections into your EMS server with 🙂

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