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What happens when you type 'google.com' into a browser and press Enter?

Anton Frattaroli on July 19, 2018

My most favorite interview question I've come across yet was "You type 'google.com' into a browser address bar and hit <Enter>, what happens ...

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Daniel Lo Nigro • Jul 21 '18 • Edited

You could go on for much longer if you also talk about hardware interrupts from the keyboard, and the handling of the WM_KEYDOWN window messages. That is, when you type "google.com" on the keyboard, where do those key presses go? How does the computer read and process them?

For every abstraction layer, there's always a deeper layer that you could explain in more detail. :)

Max Cerrina • Jul 22 '18

That is, when you type "google.com" on the keyboard, where do those key presses go? How does the computer read and process them?

welp, guess know what rabbithole I'm falling down next

Shaurya • Jul 21 '18

You can answer this question for infinitely long -

keyboard and typing physics > brain signals to make you type > psychology about why you typed > your great grandfather's marriage and the quadrillion possibilities and detail since then that made you come to that interview > Infinite ∞ stuff about the creation of the universe. 😵😵😵😵

Oscar • Jul 20 '18

There is a Github repository that deals with that question and tries to be really specific.

alex / what-happens-when

An attempt to answer the age old interview question "What happens when you type google.com into your browser and press enter?"

What happens when...

This repository is an attempt to answer the age-old interview question "What happens when you type google.com into your browser's address box and press enter?"

Except instead of the usual story, we're going to try to answer this question in as much detail as possible. No skipping out on anything.

This is a collaborative process, so dig in and try to help out! There are tons of details missing, just waiting for you to add them! So send us a pull request, please!

This is all licensed under the terms of the Creative Commons Zero license.

Read this in 简体中文 (simplified Chinese), 日本語 (Japanese), 한국어 (Korean) and Spanish. NOTE: these have not been reviewed by the alex/what-happens-when maintainers.

View on GitHub

alamnr • Jul 20 '18

thanks for your nice comment , what happen if you copy n paste following address into your browser and press enter -- alamnr.github.io/profile.html?user...

Adrian B.G. • Jul 19 '18

As an addition, if you get into the google internal infrastructure, with their multi-layered DNS LB and service LB and front-end proxies you can talk for a few hours, at least :))

A good question indeed. I also realized that I lack in the TLS knowledge, I'll put it in the 1000 long TOREAD list.

Anton Frattaroli • Jul 20 '18

I thought about including a section on browser mechanics - parse, evaluate, paint. But I didn't originally say anything about that so I deemed it to be out of scope.

Hiroto Fukui 🐶 • Jul 24 '18

I often ask this question to figure out which layer they have strength of technical knowledge.

If the interviewee talks about network layer longer than others, he probably have great skill on that layer.

d3rrila • Jul 21 '18

The question is so incredibly broad and can be answered in so many (correct) ways that I can't see how it would be useful

Pascal Bourguignon • Sep 4 '18 • Edited

Ah, but it is a perfect question to learn about the candidate, what he knows, how he thinks, etc. It’s a kind of Rorschach test. Also, a good sieve for two “interesting” categories of people: “I don’t know”, and “the browse displays the google search box”.

Antony Garand • Jul 20 '18 • Edited

The nonce attribute on a script tag is a CSP-related attribute:

developers.google.com/web/fundamen...

To use a nonce, give your script tag a nonce attribute. Its value must match one in the list of trusted sources. For example:
<script nonce=EDNnf03nceIOfn39fn3e9h3sdfa>
  //Some inline code I cant remove yet, but need to asap.
</script>
Now, add the nonce to your script-src directive appended to the nonce- keyword.
Content-Security-Policy: script-src 'nonce-EDNnf03nceIOfn39fn3e9h3sdfa'
Remember that nonces must be regenerated for every page request and they must be unguessable.

It does prevent unsafe script from being executed on the webpage if you have an XSS vulnerability. As the nonce must be present in the CSP header, even if you could inject a script tag it wouldn't be executed.

Also note that it does not always default to http and port 80: If your website is in a HSTS preload list. In the case of google.com, it isn't, but many big websites will.

If a website enforces HSTS, it will only default to HTTPS.

Anton Frattaroli • Jul 20 '18

I like how that's nested under "fundamentals".

Bobby Towers • Jul 23 '18 • Edited

The tech equivalent of Subway's "How do you make a PB&J sandwich" interview test.

Both are obviously impossible to answer in full detail, so the question then becomes, what details do you choose to focus on?

Daniel Golant • Jul 20 '18

Every time I see a breakdown of this question I am pleasantly surprised about where the author digs in vs skims over. I liked your approach here of writing out an answer off the top of your head and then digging in on what actually happens. I did my own take on this a while back, but I am afraid it came across waaaay more stiff :).