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API 101 Workshop

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🍺 Code for API 101's workshop at HackNight Season I: Episode IV, a Hackers@UPC event.

Introduction

This workshop has the goal of introducing the concept of the APIs and learning how to interact with them. In order to understand the concept of how generic the APIs are, we are gonna see different examples in different programming languages such as Java, Javascript, PHP, Python or directly through the Shell.

Theory

What's an API?

APIs, also known as Application Programming Interfaces, at their most basic level, allows applications to talk to other applications, but they are so much more than this when you begin to explore the world of APIs further.

You can consider an API as a black box where given some input you have some output, indepently of which programming languange you are using. At the end, it's a box anyways.

The API is like an artist performing on stage, and its users are the audience.

RESTFul APIs are the most common in the current state of art of Computer Science. This kind of APIs uses HTTP requests to GET, PUT, POST and DELETE data. They use GET to retrieve a resource; PUT to change the state of or update a resource, which can be an object, file or block; POST to create that resource ; and DELETE to remove it.

API endpoints

You can understand an endpoint of an API as an entry point into that mentioned black box. You call to that endpoint with some parameters, and magically this endpoints returns some cool data to use for your projects.

In order to understand how to use those endpoints, we have to know how an API is properly designed.

Let’s write few endpoints for an API that has Companies which has some Employees, to understand more. /getAllEmployees is an API which will respond with the list of employees. Few more APIs around a Company will look like as follows:

  • /addNewEmployee
  • /updateEmployee
  • /deleteEmployee
  • /deleteAllEmployees
  • /promoteEmployee
  • /promoteAllEmployees

And there will be tons of other API endpoints like these for different operations. All of those will contain many redundant actions. Hence, all these API endpoints would be burdensome to maintain, when API count increases.

What is wrong? The URL should only contain resources(nouns) not actions or verbs. The API path/addNewEmployee contains the action addNew along with the resource name Employee.

Then what is the correct way?/companies endpoint is a good example, which contains no action. But the question is how do we tell the server about the actions to be performed on companies resource viz. whether to add, delete or update?

This is where the HTTP methods (GET, POST, DELETE, PUT), also called as verbs, play the role.

The resource should always be plural in the API endpoint and if we want to access one instance of the resource, we can always pass the id in the URL.

  • method GET path /companies should get the list of all companies.
  • method GET path /companies/34 should get the detail of company 34.
  • method DELETE path /companies/34 should delete company 34.

Other RESTFul APIs prefers to design these paths using query parameters instead of having the ID in the path directly. Something like:

  • method GET path /companies?id=34 should get the detail of company 34.

Query parameters / Body request / Headers

In order to specify the input of the black box, there are three ways for doing it. However, not all of them can be used in all the scenarios.

Headers

This kind of input can be used in the four HTTP methods. It's usually being used for security parameters or for configuring the request to the API.

Query parameters

This type of parameter is being used in the four types of the methods but not 100% recomended in POST. This input is always specified in the URL path directly. For example:

  • GET https://api.example.com/students?university=UPC&faculty=FIB returns all the students from UPC university and the faculty FIB.
  • DELETE https://api.example.com/subjects?code=XC deletes the subject with XC as code.

Note: See that & character in the URL path is for concatenating multiple query parameters.

Request body

This kind of input is only allowed in POST and PUT methods. This is usually useful for letting the request know which data should be added or modified. There are a bunch of different request bodies, where you can specify which one as a header using Content-Type parameter. Howerver, the most common one is application/json.

Tools

Postman

Postman is one of the most famous, if not the most, tools for firing requests to an API. It is very lightweight and fast. Requests can be organized in groups, also tests can be created with verifications for certain conditions on the response. With its features, it is very good and convenient API tool. It is possible to make different kinds of HTTP requests – GET, POST, PUT and DELETE. It is possible to add headers to the requests.

RapidAPI

RapidAPI is the biggest API markplace in the world. If you want to test a lot of APIs quickly then you are gonna find the tool very useful. With only one account you can setup thousands of APIs so much faster than doing it separetly one by one.

Free-access APIs

To find a bunch of cool APIs in general, check out this GitHub repository with an endless list of free-access APIs.

We are gonna use a bunch of them in this workshop in order to see how to interact with an API. See every programming language folder for see those examples.

Authors

License

MIT © Albert Suàrez