5 HTTP

To retrieve data from the Web, we have to enable our software to communicate with servers and web services. The lingua franca of communication on the Web is HTTP, the Hypertext Transfer Protocol. HTTP dates back to the late 1980s when it was invented by Tim Berners-Lee, Roy Fielding and others at the CERN near Geneva, Switzerland (Berners-Lee 2000; Berners-Lee et al. 1996). It is the most common protocol for communication between web clients (e.g., browsers) and servers, that is, computers that respond to requests from the network. Virtually every HTML page we open, every image we view in a browser, every video we watch is delivered by HTTP. When we type a URL into the address bar, we usually do not even start with http:// anymore, but with the hostname directly (e.g., r-datacollection.com) as a request via HTTP is taken for granted and automatically processed by the browser. HTTP's current official version 1.1 dates back to 1999 (Fielding et al. 1999), a fact that nicely illustrates its reliability over the years—in the same time period, other web standards such as HTML have changed a lot more often.

We hardly ever come into direct contact with HTTP. Constructing and sending HTTP requests and processing servers’ HTTP responses are tasks that are automatically processed by our browsers and email clients. Imagine how exhausting it would be if we had to formulate requests like “Hand me a document called index.html from the host www.nytimes.com/ in the directory pages/science/ ...

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