Welcome to HTTP Request and REST API. After watching this video, you will be able to explain how the HTTP protocol works, explain the role of the REST application programming interface (or API) in transporting data across the web, and perform HTTP requests and process HTTP responses using the httr package. HTTP is probably the most used communication protocol for fetching web resources for clients from servers on the Internet. A resource can include a web page, media files, including images and video clips, or even a csv file containing a dataset. Let’s look at the basic workflow of HTTP. For example, assume that you want to open the home page of IBM cloud in a browser on your mobile phone. This web page contains content and some media files. The browser uses the HTTP protocol to get all required resources and render them accordingly. First, the browser creates several requests. The requests can be distributed to a web server, which serves static or dynamic web pages, or a media file server, which serves images and videos. The servers respond to the requests by building HTTP responses and sending them back to the browser. After receiving and extracting the resources in the responses, the browser consumes the resources and renders the home page for you. The essential components of HTTP are the HTTP request and the HTTP response. Both the HTTP request and response are comprised of human-readable text called hypertext. Let’s look at some core components of a request. The HTTP method describes the operation to be performed on the resource on the server side. Some common methods are the GET method, which requests a resource, the POST method, which sends data to the server for creating or updating a resource, the PUT method, which updates a resource, and the DELETE method, which deletes a resource. The URL, which stands for Universal Resource Locator, uniquely identifies a resource on the Internet. The request header contains some extra metadata about the request, such as the accepting language or the data format. Optionally, a request may also include a body, which contains the data to be sent to the server. The HTTP response includes a status code that indicates the result of the request. Some common status codes are 200, which means the request was successful, 404, which means that the requested resource was not found, and 403, which means the current request is forbidden. The response header includes some extra metadata sent by the server about the response and the response body includes resource content, such as an HTML page or an image (in raw bytes.) HTTP is a low-level communication protocol. To help with the design and simplification of high-level distributed applications, such as web applications, Representational State Transfer (or REST) was invented. The REST API is a web service that uses the REST architecture to handle a request on a frontend web service. REST is the most popular web API design standard so most web APIs that you see today follow REST rules. REST has the following features: REST is resource-centric, meaning that the client should know the resource to be fetched but not how it will be fetched on the server side. As such, the server and client should be loosely coupled. REST is stateless, which means the server should not store any information about the connection context. Each request is independent. REST mostly uses JSON or XML to exchange data. By using JSON and XML, different applications on different platforms can communicate with each other without barriers. And REST is a high-level standard. As such, it mostly uses HTTP as the low-level data transportation implementation. In most cases, making an HTTP-based REST call is like making an HTTP request. To work with HTTP requests or REST APIs in R, you can use a popular R package called httr. httr includes functions for the most common HTTP methods, like GET, POST, DELETE, and PUT. Once you have a basic understanding of HTTP, httr is easy to use. To make a basic GET request, simply call the GET() function with a URL. The GET() function returns an HTTP response wrapped in a response object. It includes a status code, headers, and a response body. To make a POST request, you must first prepare the data to be posted. In this example, the body is a simple list with a course name and an instructor name. Then, use the POST() function with the URL and the body argument. The POST() function returns an HTTP response wrapped in a response object that includes a status code, headers, and a response body. In this video, you learned that HTTP is a communication protocol for fetching web resources for clients from servers on the Internet and that each instance is comprised of a request and response. You also learned that the REST API is a web service that uses the REST architecture to handle a request on a frontend web service. You also learned that you could perform common HTTP and REST operations using the httr package in R.
