A tl;dr overview of an API ?

In this article Im going to discuss the following topics related to an API.

• What is an API ?
• What is the use of an API ?
• What are the different types of API ?
• What is a Restful API ?
• What are the HTTP verbs related to an API ?
• What are the HTTP status code related to an API ?

What is an API ?

API is more like an agreement or a contract of services between any application with distinct functions. Here, the contract of service referred as an application INTERFACE and application with distinct functions referred as an application PROGRAMS, and thats how API stands for APPLICATION PROGRAMMING INTERFACE.

What is the use of an API ?

API is mostly used for interaction( by transferring data ) between more than two applications followed by a request-response behavior.

What are the different types of API ?

There are two ways you can categorized an API.

1.Based on architecture, for example

• RPC ( Remote Procedure Call ), there are two variation XML-RPC, JSON-RPC

• SOAP ( Simple Object Access Protocol )

• REST ( Representational State Transfer )

• GraphQL

2.Based on availability, for example

• Open API / Public API

• Partner API

• Internal API / Private API

• Composite API

In todays world most of the APIs are REST Driven or RESTful ( based on REST architecture ).

What is a Restful API ?

There are six constraints in a REST API or a RESTful API. Any API can be a RESTful API if it follows those six constrains.

• Uniform Interface - An agreement that separates clients from the server. A resource( information that returned by an API ) in the system should have only one logical URI but it should contain links (known as HATEOAS) pointing to relative URIs to fetch related information.

• Client-Server - Client and the Server must be able to evolve separately without depending upon each other.

• Stateless- The server will not store anything about the latest request that the client made. It will treat every request as a new one. Here the client is responsible for managing the state of the application.

• Layered System - A application architecture should be distributed in multiple layers but each layer doesn't need to know anything about any other layer other than the intermediate one.

• Cacheable - The main function of that constraint is to increase the performance of the application by storing frequently used data either in the client-side or the server side.

• Code on demand(optional) - Most of the cases its optional. But it works by returning a executable code to support a part of your application.

What are the HTTP verbs related to an API ?

HTTP verbs mainly use to tell the server what to do with the data identified by the url. There are 5 most common HTTP verbs and there uses as follows.

• POST - Create new resource ( C )
• GET - Read resources ( R )
• PUT - Update/Replace existing resource ( E )
• PATCH - Update/Modify existing resource
• DELETE - Delete resources ( D )

It almost similar to the CRUD functionality with different verbs.

What are the HTTP status code related to an API ?

HTTP status code divided into 4 segment and each segment has their own functionality.

2xx series related to Successful Request.

• 200 - Successful

• 201 - Resource Created

• 204 - Resource Updated

3xx series related to Redirection

• 301 - Permanent redirection ( possible to change HTTP verb )

• 307 - Temporary redirection ( cant change HTTP verb )

• 308 - Permanent redirection ( cant change HTTP verb )

4xx series related to Client Error

• 400 - Bad request

• 401 - Wrong credentials ( unauthorized )

• 403 - Lack of authorization ( forbidden )

• 404 - Resource not exist

• 405 - HTTP verb mismatch

• 422 - Send data in valid

5xx series related to Server Error

• 500 - Internal Server error

• 501 - If server dont know how to handle the request

• 502 - Bad Gateway

• 503 - Service is down for maintenance

• 504 - Gateway timeout