REST (Representational State Transfer) APIs, sometimes also referred to as RESTful APIs, are an increasingly popular design style. REST APIs are built to take advantage of pre-existing protocols within an environment, most commonly over HTTP for a Web API. The REST API design is more lightweight and is known for its vast flexibility in enabling modern business connectivity.
What is REST API?
The most common way to describe a REST API definition is to first understand what an API is. API stands for application programming interface and is used to bring applications together with the goal of performing a designed function built around sharing data and executing pre-defined processes. Basically, it allows one piece of software to talk to another. REST APIs are one of two of the most commonly deployed forms of an API, the other being a Simple Object Access Protocol (SOAP) API.
REST is a client-service architecture that is based on a request/response design. REST APIs have become increasingly popular as part of a Web Services approach. Developers use RESTful APIs to perform requests and receive responses through HTTP functions.
How Does REST API work?
A REST API works essentially the same way that any website does. A call is made from a client to a server, and data is received back over the HTTP protocol. Facebook’s Graph API is an easy way to show the similarities between a REST API call and the loading of a webpage. Say someone wanted to pull up the Facebook page for YouTube, for example. That person would enter in the URL as normal, www.facebook.com/youtube.
If that person was a developer, instead of “www,” he or she would enter “graph.facebook.com/youtube” and would receive a response to the API request that was made through their browser. The result of the request would show structured data, organized according to key value parameters. Sticking with the YouTube page as an example, that structured data would include how many likes the page had, how many accounts were following the page, and so on.
Another concept important in the world of REST APIs is parameters. When sending a REST API request, someone can gain the ability to narrow the search request. This modifies a request with key-value pairs and filters the data that is received in a response. REST parameters specify a variable part of a resource, which is the data that is being worked with.
Some different types of API parameters include path, query (the most common kind), header, and cookie. Path parameters are a variable part of a URL path and point to a specific resource within the data. Query parameters are located at the very end of a URL path, and can be either required or optional. Header parameters are added as part of the HTTP header of an API request. Cookie parameters are needed when a REST client must authenticate themselves using cookies.
The Anatomy of a Request
Anytime a call is made to a server using a REST API, that is considered an API integration request. And while the outcome happens quickly and quite simply, there is actually a lot that goes into making that request itself.
The endpoint of a REST API is a unique URL that represents an object or group of objects of data. Each API request has its own endpoint, which is what the HTTP client is directed at in order to interact with data resources.
HTTP methods (which will be explained in further detail below) are an integral part of a RESTful API request. These methods – GET, POST, PUSH, PATCH, and DELETE – correspond to create, read, update, and delete resources.
REST headers contain information that represent metadata associated with every single REST API request. A REST header indicates the format of the request and response, and provides information about the status of the request.
A REST API request also consists of data (also referred to as a “body”) that usually works with the POST, PUT, and PATCH HTTP commands and contains the information and representation of the resource that will be created.
Guiding Principles of REST
Representational State Transfer is known for its simplistic nature, and utilizes interactions in order to communicate via HTTP protocols.
REST is a client-server architecture, where the server and the client act independently of one another as long as the interface stays the same when processing a request and a response. The server exposes the REST API, and the client makes use of it. The server stores the information and makes it available to the user, while the client takes the information and displays it to the user or uses it to perform subsequent requests for more information.
REST is designed to be stateless, meaning anytime a client and server communicate, it always includes the necessary information needed to perform the request. Stateless also means that there is no session state, and it is located squarely on the client’s side. If authentication is necessary, the client must then authenticate itself every time it performs a request.
REST is also cacheable, which means that the client, the server, and any intermediary component connected are all able to cache resources so that they will improve the performance.
In a REST architecture, a layered system has a grouping of layers, with each layer having a designed function that it needs to perform. While the layers do have their own responsibilities, they also must interact with one another, and by doing so, create a hierarchy within the REST API architecture.
A uniformed interface within a REST API architecture is designed to allow the client talk to the server in one specific language. This allows for the application to evolve independently without any of its services, models, or any other function conjoined with the API itself.
Code on Demand
Unlike the other guiding principles of REST, code on demand is the one that is actually optional in a REST architecture, not mandatory. Code on demand allows for code and applets to be transmitted through the API to use it within the application. In its simplest form, code on demand enables clients to be more flexible because the server is the one that makes the final determination of how things will be done.
REST API Examples
REST APIs have grown increasingly popular recently, as part of a Web Services approach. You might not even realize it, but many of the popular websites that you use today are in fact built using REST APIs. Some of the most common examples of REST APIs in use include Instagram, PayPal, Gmail, and Twitter. From a developer perspective, GitHub REST API, Google Developers Map APIs, and Twillio Doc REST API are popular APIs.
HTTP Request Methods
As outlined above, REST APIs are designed to perform requests and receive responses via HTTP functions. These are the five HTTP commands that REST is based on.
The GET request is a nullipotent command that safely retrieves information. No matter how many times it repeats with identical parameters, the results will always be the same.
The POST request is used to request the origin server accepts the entity enclosed in the request as a new subordinate of the resource. It can also update an existing entity.
PUT and PATCH Requests
The PUT request is an idempotent command that can create, update, or replace an entity. The PATCH request is also an idempotent command, which simply replaces an entity.
The DELETE request is an idempotent command that a resource be removed. One important detail to note is that the resource does not have to be removed immediately; it could also be asynchronous or a long-running request.
There are a few approaches when it comes to REST API authentication. It’s important to note that almost every REST API must have at least some form of authentication. Authentication verifies the credentials of a connection attempt between the sender and receiver. HTTP basic authentication is the simplest way to authenticate a REST API. In this scenario, an HTTP user agent provides a username and a password to verify its identity.
Another option for REST API authentication is using API keys. In this approach, a unique generated value is assigned to every first-time user, so that every additional time that user tries to enter the system, the unique key is used again to prove that they are in fact the same user as before.
The other method is actually a combination of authentication and authorization, called OAuth. In this scenario, a user logs into a system, and then the system requests authentication, normally in the form of a token. Next, the user’s request is forwarded to an authentication server that either allows or rejects the authentication. From there, the token goes back to the user and then to the requester. The token can be checked at any time by the requester and also over time with a specific scope and longevity.
How to Test REST API
Step #1 – Enter the URL of the API in the textbox of the tool.
Step #2 – Select the HTTP method used for this API (GET, POST, PATCH, etc).
Step #3 – Enter any headers if they are required in the Headers textbox.
Step #4 – Pass the request body of the API in a key-value pair.
Step #5 – Enter the required content type (such as application or JSON).
Step #6 – Click the send button.
After clicking Send, there will be various responses to the REST API, which details whether the API testing was a success or failure. It’s important to note the response code, response message, and response body.
APIs are critical in spanning technical and business boundaries to deliver data, capabilities, and services wherever (and whenever) they’re needed, but the design of APIs has shifted to the more lightweight and flexible varieties that are suited for mobile applications and geo-distributed networks.
Because of this approach, REST APIs continue to grow in popularity for mobile apps, social networking sites, and a variety of other offerings. Thousands of enterprises use REST APIs to generate business and grow their services, and REST API adoption will continue as one of the most efficient ways to enable the next generation of business applications.
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