Evolution of HTTP — HTTP/0.9, HTTP/1.0, HTTP/1.1, Keep-Alive, Upgrade, and HTTPS

Understanding how HTTP works in the real world

Thilina Ashen Gamage
Platform Engineer
Published in
6 min readNov 17, 2017


Photo by Nate Grant on Unsplash

Disclaimer: This article focuses on explaining some underlying implementation details of HTTP, which will be helpful for readers to better understand my blog article — “Web API Design with HTTP and Websockets

Invented by Tim Berners-Lee at CERN in the years 1989–1991, HTTP (Hypertext Transfer Protocol) is the underlying communication protocol of World Wide Web. HTTP functions as a request–response protocol in the client–server computing model. HTTP standards are developed by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C), culminating in the publication of a series of Requests for Comments (RFCs). HTTP has four versions — HTTP/0.9, HTTP/1.0, HTTP/1.1, and HTTP/2.0. Today the version in common use is HTTP/1.1 and the future will be HTTP/2.0.

HTTP/0.9 — The One-line Protocol

  • Initial version of HTTP — a simple client-server, request-response, telenet-friendly protocol
  • Request nature: single-line (method + path for requested document)
  • Methods supported: GET only
  • Response type: hypertext only
  • Connection nature: terminated immediately after the response
  • No HTTP headers (cannot transfer other content type files), No status/error codes, No URLs, No versioning
$> telnet ashenlive.com 80(Connection 1 Establishment - TCP Three-Way Handshake)
Connected to xxx.xxx.xxx.xxx
GET /my-page.html
(Response in hypertext)
A very simple HTML page
(Connection 1 Closed - TCP Teardown)

Popular web servers (Apache, Nginx) still supports HTTP/0/9. Try opening up a Telnet session and accessing google.com



Thilina Ashen Gamage
Platform Engineer

Advocate of Cloud, Microservices, & Clean Code | 1.5M+ Reach | For more exciting content, stay in touch: https://medium.com/@ThilinaAshenGamage