Swagger

Swagger is a specification for describing REST APIs. The main aim of Swagger is to provide a REST API definition format that is readable by both machines and humans.

You can think of two entities in a REST API: One the provider of API, and another the client using the API. Swagger essentially covers the gap between them by providing a format that is easy to use by the client and easy for the provider to define.

If not using Swagger, one would most certainly be creating the API first, writing the documentation (human-readable) with it. The client developer would read the documentation and use APIs as required. With Swagger, the specification can be considered as the document itself, helping both the client developer and the provider.

Here’s an example spec I wrote for our GET APIs at Organizer Server: https://gist.github.com/shivamMg/dacada0b45585bcd9cd0fbe4a722eddf

The format, although readable doesn’t really look what a client developer would be asking for.

Remember that the format is machine readable? What does it mean exactly?

Since the Swagger spec is a defined format, the provider can document it and people can write programs that understand the Swagger specification. Swagger itself comes with a set of tools (http://swagger.io/tools/) that use Swagger definitions created by the API provider to create SDKs for the clients to use.

Swagger-UI

One of our most used tools at our server is the Swagger UI (http://swagger.io/swagger-ui/).

It reads an API spec written in Swagger to generate corresponding UI that people can use to explore the APIs. Every API endpoint can have responses and parameters associated with it. For instance our Event endpoint at Server (“/events/:event_id”).

You can see how the UI displays the Model Schema, required parameters and possible response message.

Screenshot from 2016-06-07 19:08:21

Apart from documentation, Swagger UI provides the “Try it out!” tool that lets you make requests to the server for the corresponding API. This feature is incredibly useful for POST requests. No need for long curl commands in the terminal.

Here’s the Swagger config from our demo application: https://open-event.herokuapp.com/api/v2/swagger.json

The Swagger UI for this config can be found at https://open-event.herokuapp.com/api/v2

The UI for the example spec (gist) I linked before can be browsed here.

Swagger-js

https://github.com/swagger-api/swagger-js

Swagger-js is JS library that reads an API spec written in Swagger and provides an interface to the client developer to interact with the API. We will be using Swagger-js for Open Event Webapp.

Here’s an example to show you how it works. Let’s say the following endpoint returns (json) a list of events.

/events

The client developer can create a GET request and render the list with HTML.

$.getJSON("http://example.com/api/v2/events", function(data) {

  var events = "";
  $.each(data, function(i, event) {
    events += "<li id='event_" + i + "'>" + event.name + "</li>";
  });

  $("ul#events").html(events);
});

What if the provider moves the endpoint to “/event/all”? The client developer would need to change every instance of the URL to http://example.com/event/all.

Let’s now take the case of Swagger-js. With Swagger-js the client developer would essentially be writing programs to interact with the API Swagger spec defined by the provider, instead of directly consuming the API.

window.client = new SwaggerClient({
    url: "http://example.com/api/v2/swagger.json",
    success: function() {
      client.event.getEvents({
        responseContentType: 'application/json'
      }, function(data) {

        /* Create `events` string same as before */

        $("ul#events").html(events);
      });
    }
  });

 

The APIs at the Organizer server are getting more complex. Swagger helps in keeping the spec well defined.

That’s all for now. Hope you enjoyed the read.