The nature of HTTP requests

Web Scraping in R

Timo Grossenbacher

Instructor

Hypertext Transfer Protocol (HTTP)

A schema showing how browsers communicate with servers

¹ https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview

The anatomy of requests

A request is sent to the web server

An example request

Typical status codes: 200 (OK), 404 (NOT FOUND), 3xx (redirects), 5xx (server errors)

A response is received from the web server

The corresponding response

¹ https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview

Request methods: GET and POST

GET: Used to fetch a resource without submitting data (GET /index.html)
POST: Used to send data to a server, e.g. after filling out a form on a page

POST /test HTTP/1.1
Host: foo.example
Content-Type: application/x-www-form-urlencoded
Content-Length: 27

field1=value1&field2=value2

POST requests are also answered with a response!

¹ https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST

HTTP requests with httr

library(httr)
GET('https://httpbin.org')

Response [https://httpbin.org/]
  Date: 2020-09-19 13:02
  Status: 200
  Content-Type: text/html; charset=utf-8
  Size: 9.59 kB
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    ...

HTTP requests with httr

library(httr)
response <- GET('https://httpbin.org')
content(response)

{html_document}
<html lang="en">
[1] <head>\n<meta http-equiv="Content-Type" content="text/html; charset=UTF ...
[2] <body>\n    <a href="https://github.com/requests/httpbin" class="github ...

Let's practice!

Web Scraping in R