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Learning HTTP/2 by Javier Garza, Stephen Ludin

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HTTP/2, also called h2 for simplicity, is a major revision of the HTTP network protocol used by the World Wide Web, meant to improve the perceived performance of loading web content.

Since HTTP/1.1 (h1) was approved in 1999, the web has changed significantly from mostly text-based web pages that weighed a few kilobytes and included less than 10 objects, to today’s media-rich websites that weigh on average over 2 megabytes,1 and include an average of 140 objects. However, the HTTP protocol used to deliver the web content did not change in the intervening years, making room for a new industry of Web Performance experts who specialize in coming up with workarounds to help the aging protocol load web pages faster. People’s expectations for performance have changed too—while in the late ’90s people were willing to wait up to seven seconds for a page to load, a 2009 study by Forrester Research found that online shoppers expected pages to load under two seconds, with a large share of users abandoning sites where pages take over three seconds to load. A recent study by Google showed that a even a delay of 400 milliseconds (the blink of an eye) will cause people to search less.

That’s why h2 was created—a protocol that can better handle today’s complex pages without sacrificing speed. HTTP/2’s adoption has been increasing2 as more website administrators realize they can improve the perceived performance of their websites with little effort.

We all use h2 every day—it powers some of the most popular sites like Facebook, Twitter, Google, and Wikipedia—but many people don’t know about it. Our goal is to educate you on h2 and its performance benefits, so you can get the most out of it.

Who Should Read This Book

Regardless of your role, if you find yourself responsible for any part of the life cycle of a website, this book will be useful for you. It is intended for people building or running websites, and in general anybody considering implementing h2, or looking to understand how it works.

We expect you to be familiar with web browsers, web servers, websites, and the basics of the HTTP protocol.

What This Book Isn’t

The goal of this book is to teach you h2 and help you make the most out of the new version of the HTTP protocol. It is not a comprehensive guide for all h2 clients, servers, debug tools, performance benchmarking, etc. This book is intended for people not familiar with HTTP/2, but even experts may still find it to be a convenient resource.

Recommended Resources

h2book.com is the companion website of this book, where you will find some of the examples referenced in later chapters. In addition, we recommend the following books:

  • High Performance Websites, by Steve Souders (O’Reilly): Essential knowledge for frontend engineers

  • Even Faster Websites, by Steve Souders (O’Reilly): Performance best practices for web developers

  • High Performance Browser Networking, by Ilya Grigorik (O’Reilly): Hands-on overview about the various types of networks, transport protocols, application protocols, and APIs available in the browser

  • Using WebPageTest, by Rick Viscomi, Andy Davies, and Marcel Duran (O’Reilly): Learn basic and advanced uses of WebPagetest, a free performance measurement tool for optimizing websites

  • High Performance Mobile Web, by Maximiliano Firtman (O’Reilly): Optimize the performance of your mobile websites and webapps

  • http2 explained, by Daniel Stenberg

Conventions Used in This Book

The following typographical conventions are used in this book:


Indicates new terms, URLs, email addresses, filenames, and file extensions.

Constant width

Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords.

Constant width bold

Shows commands or other text that should be typed literally by the user.

Constant width italic

Shows text that should be replaced with user-supplied values or by values determined by context.


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Using Code Examples

Supplemental material (code examples, exercises, etc.) is available for download at https://github.com/oreillymedia/learning-http2.

This book is here to help you get your job done. In general, if example code is offered with this book, you may use it in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: “Learning HTTP/2 by Stephen Ludin and Javier Garza (O’Reilly). Copyright 2017 Stephen Ludin and Javier Garza, 978-1-491-96244-2.”

If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at .

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We would like to thank Akamai’s h2 core team and Moritz Steiner, one of Akamai’s researchers on the Foundry team who coauthored several h2 papers with Stephen; Pierre Lermant (for his good sense of humor, attention to detail, and his contribution for reviewing and contributing content for this book); Martin Flack (for his often illuminating Lisp implementation and also a member of Akamai’s Foundry team); Jeff Zitomer (for his support, encouragement, and contagious smile); Mark Nottingham (for his contributions to the h2 protocol); Pat Meenan (for all the countless contributions to Webpagetest.org, probably the best free tool for Measuring Web Performance); and Andy Davies (who created the “WebPagetest Bulk Tester,” which we used extensively across this book).

Thanks to our editors Brian Anderson, Virginia Wilson, and Dawn Schanafelt for making everything so easy, and all the h2 experts who provided feedback and ideas for this book: Ilya Grigorik, Patrick McManus, Daniel Stenberg, Ragnar Lonn, Colin Bendell, Mark Nottingham, Hooman Beheshti, Rob Trace, Tim Kadlec, and Pat Meenan.

Javier Garza

Above all, I would like to thank my wife Tina for her support, encouragement, and understanding. Thanks to my dear kids (Keona, Diego, and Lani) for still showing me their love every day even after spending countless nights, weekends, and a big chunk of our summer vacation writing this book. Thank you also to my managers Aditi and Austin for their encouragment to write this book on top of a very demanding job.

Stephen Ludin

Patience. I want to acknowledge patience. The patience of my family: Sarah, Tomas, and Liam for putting up with me and this crazy process of publishing. Their support was invaluable throughout my writing. The patience of my employer, Akamai, allowing me to make time in an always busy schedule to work on this book. The patience of O’Reilly for the practiced understanding that for their team of authors, writing a book is inevitably a third job. Lastly, the patience of my parents who gave me a leg up that I can never pay back, but can only pay forward—when my dad brought home an Atari 800 when I was nine, did he know it would propel me on a course whose destination (I like to think) still lies before me?

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