15 ms·

What happens when you load a URL? (2015)

170 points by caiobegotti 6y ago

nickelpro 6y ago
I find I run into similar discussions whenever a beginner programmer decides they want to capture input from the arrow keys. They've worked through the bog standard Python tutorials using input() to capture from stdin, so it should be trivial to design a simple game that uses the arrow keys right? And suddenly this gulf of complexity opens up of event polling, keycodes, integrating third party modules, and they're left wondering why moving one key over on the keyboard is so hard.
- Spivak 6y ago
  Having never really had a needed to do this I'm a little confused -- isn't this just a matter of putting the tty into cbreak or raw mode and then just reading keys from stdin? Like keycodes are annoying but "special keys have this weird text representation, here's a table" doesn't seem like a huge gap to cross.
  - tmpz22 6y ago
    For games you also have to decipher what a keystroke should do physics wise which isn’t always simple, ie acceleration and deceleration, including what happens when multiple arrows are held down. You now are polling multiple events concurrently and processing them outside of that loop. And so on and so on.
    - deleted 6y ago
      [deleted]
  - divingdragon 6y ago
    > putting the tty into cbreak or raw mode and then just reading keys from stdin You're saying this like most beginners even have an idea what a tty is. An anecdote: When I wrote my first C++ program that reads an input (using `cin`, hello-world style), I immediately wondered how to read single keys including arrow keys. The book I was following had nothing about this. I don't remember the exact details but a bit of Internet search got me to `conio.h` (I was using Dev-C++ on Windows) which did work. But getting it to work was so confusing to me at the time. And I didn't even get to understand what it's actually doing under the hood. I imagine it would be a bit easier in Python given the right libraries, but the dependency management probably adds to the complexity for a beginner.
  - sokoloff 6y ago
    For games, I usually want to handle at the level of keydown and keyup rather than keystrokes. What’s the keystroke for right-arrow, spacebar, left-shift, and W all being held down? (Think of an Asteroids arcade game where w is thrust, spacebar is fire, left-shift is shields, and right arrow is rotate. Those are up/down, not strokes, that the player is giving you.)
- qertistick 6y ago
  You use a game library for this and then it becomes as simple as pushing a key handler onto the event loop and usually the keycodes are already processed for you as well. I don't get the false dilemma people are creating that somehow this is complicated or that people who use the easy way are less knowledgable than others. If you make a game engine from scratch by yourself it's going to be a logical disaster, whether you've learned c++ or python.
  - Gravityloss 6y ago
    Yeah, it's surprisingly simple. It took little time with a game library to get the key polling to work. I was experimenting with chorded keyboard ideas back then.
  - saagarjha 6y ago
    But then you might end up talking about event loops and routing…
  - MaxBarraclough 6y ago
    > You use a game library for this If it's a command-line application, they might use curses. edit Apparently curses isn't available by default in Python3 for Windows. Is there a nice way to do this?
aronpye 6y ago
Reminds me of when Richard Feynman analysed the question of “how do magnets work?”. There are so many levels to it, coupled with assumed knowledge, that the question itself is shown to be improperly bounded.
- nitrix 6y ago
  A fascinating man and video. Link for the interested: https://www.youtube.com/watch?v=36GT2zI8lVA https://www.youtube.com/watch?v=36GT2zI8lVA
  - serniebanders 6y ago
    I don't find the video fascinating, quite the opposite actually. Richard Feynman could have just explained the electrical force and left out the rest. When someone asks, `why does x work`, its a sign that they are curious and ready to explore and learn. Its an opportunity to teach and educate. The whole video (to his credit, Richard did explain the concept well) focuses on how little the questioner know. It is a little belittling. If someone talked like that to me I'd have gone home and accepted the fact that I just would never understand electromagnetism and moved on. A better approach instead of actually capitalizing on this curiosity and teaching the questioner, giving them just a bit more than the normally accepted answer so the curiosity lives on.
    - aronpye 6y ago
      I think in this example Feynman was using the question to illustrate the levels of complexity in answering a scientific question. If you watch his actual lectures, Feynman does break the concepts down in order to teach them. Also, documentaries and popular science books tend to dumb down and over simplify theories to such an extent, such as by removing all mathematics, that they just become either wrong, inaccurate, or misleading. I think it was Einstein which said make things as simple as possible, but not simpler.
klodolph 6y ago
I was given this as an interview question once, it was fun. I was told to go into “as much breadth and depth as possible” but I did get stopped a couple times when I started talking about things like debouncing.
- abfan1127 6y ago
  breadth and depth as possible seems like they are just asking for as many rabbit hole as possible!
- borgchick 6y ago
  I've asked this question a number of times in interviews. Sadly, not one person has ever talked about debouncing. I think I would've instantly hired the person, if they talked about debouncing :P To clarify, I would ask this question as a wrap up, a sort of final probe of depth test. If they don't go into much detail, no big deal. If they were good in the rest of the interview, they'd still get hired. If they were good elsewhere but also went into depth on this question, then it really boosts their likeliness of getting hired. I find that people who are curious about how things work, especially when it is outside of their main domain, are usually people interesting to work with.
  - kamyarg 6y ago
    can you link to a resource for reading about debouncing?
    - kens 6y ago
      The Art of Electronics has a good section on debouncing switches. There are various analog and digital ways of doing it, from R-C smoothing to latches to debounce ICs to microcontrollers. If you want a thoroughly obsolete look at debouncing, I got a debouncing module from an IBM 705 computer (1954). This module was built from 8 vacuum tubes and a pile of resistors and other components. I powered it up with an inconvenient set of voltages (+140V, -60V, -130V) and actually got it to work: http://www.righto.com/2018/01/ibm-mainframe-tube-module-part-ii.html http://www.righto.com/2018/01/ibm-mainframe-tube-module-part...
bookmarkable 6y ago
Interesting, but couldn't you ask this of any existing technology with years of development and realize you don't know how we arrived at a function we take for granted? What happens when you press the accelerator on your car?
- canadian_tired 6y ago
  Indeed. I have realized 2 things: First, technical specialization is increasingly more fine-grained; second, assumptions that anything outside of the specialization will magically just work. To extend your example, 30 years ago you could easily find someone who understood the whole chain...from the pedal all the way to the rubber on the road. Today? the pedal itself likely has a microcontroller in it... designed by a pedal expert, who knows what the various I/O requirements are and has little or no concern with what the car actually does. Probably leads to better pedal designs, but you need an army of people to tell you why the car might not move.
- bluetomcat 6y ago
  > What happens when you press the accelerator on your car? No single automotive engineer can answer that question to the level of detail that the original post wants to approach. A car is a collection of separately engineered mechanical devices meeting some power/torque/thermal requirements, electronic units which, to a mechanical engineer are essentially black boxes with inputs and outputs. Abstraction is in every field of engineering and it helps people reason about a complex system in terms of abstract interconnected parts, not in terms of bits, bytes, cogs or bearings. In a similar vein, a web developer, a browser developer, a kernel developer, a network driver developer each use different levels of abstraction and paradigms in order to achieve their thing.
  - mcguire 6y ago
    There is another way of asking this question: "Someone types the URL of your application in their browser and doesn't get the application page. How do you figure out what went wrong?"
- amelius 6y ago
canadian_tired 6y ago
Asked of Cliff Stoll for his PhD defense: "Why is the sky blue?"
davidhyde 6y ago
Your browser tries to guess if what you have typed is is a url or a search query. If you’re using chrome then there is a chance that your request will hit a root domain name server so that the browser can check if you are connected to a scammy Internet service provider or some other ad serving intermediary. https://arstechnica.com/gadgets/2020/08/a-chrome-feature-is-creating-enormous-load-on-global-root-dns-servers/ https://arstechnica.com/gadgets/2020/08/a-chrome-feature-is-...
fortran77 6y ago
This used to be a standard interview question I'd ask potential junior candidates. I'd see how far down I can get them to go.
mattlondon 6y ago
This is why I love this question as a phone-screener for onsite interviews and stuff. Sounds so easy, but there is so much depth in so many areas that people can drill into. If someone starts talking convincingly about the OS handling keyboard interrupts or about HTTPS certificate revocation during the TLS handshake explanation etc, you know they are probably worth bringing in for a face to face. Someone bluffing will usually fail this really hard - "The browser connects to example.com and downloads the page." or something. Uh-huh. Maybe they talk about DNS ... Maybe they talk about a TCP connection ... Maybe they talk about retrieving the HTML and parsing it ... but even then, if they get that far that will be better than a lot of bluffers. If they have simply revised anticipating this question and can answer everything then congrats - they've just educated themselves in a lot of the core fundamentals :) As an interviewer this question can easily take up a whole 30 min phone screener as good candidates get deeper and deeper.
- ceejayoz 6y ago
  > Sounds so easy, but there is so much depth in so many areas that people can drill into. If someone starts talking convincingly about the OS handling keyboard interrupts or checking for HTTPS certificate revocation during the TLS handshake etc, you know they are probably worth bringing in for a face to face. If I ask you "what happens when you load a URL" and you start talking about the operating system's handling of keyboard events, I might get the impression you're hopelessly prone to bizarre and useless digressions.
  - mattlondon 6y ago
    I usually say something like "What happens if I type 'example.com' in my browser's address bar and hit enter?" If someone goes wildly off-track and starts talking about the design of the mechanical switches in the keyboard or I am specifically interested in one area vs another then you can easily tailor it "Ok cool - lets skip ahead to the network aspects" or "lets say I've found the server and downloaded the HTML - now what?" etc. That said, I often like to let people just talk in interviews unless I am really specifically trying to drill into one area and get specific evidence of specific skills. I might jump in with a "Ah - interesting. Tell me more about DNS" or whatever, but usually I find that the good candidates will have a lot to say, and the less-good candidates either say hardly anything, bullshit, or talk a lot but are not good communicators (confusing explanations/hand-waving/etc) ... or a combination of those things :)
thecrumb 6y ago
A bit dated as well. It's assuming I'm using a physical keyboard. Today I might be using my phone. Might be using voice recognition. It might be my fridge hitting a URL using IoT to order me some more beer.
colinrand 6y ago
I ask this question from time to time and look for different responses depending on the type of candidate. When I ask an engineer, I am looking to see if they can grasp the problem space and ask clarifying questions about what I'm looking for. When I'm interviewing for an engineering manager I am looking to see if they can grasp the problem space and ask clarifying questions about what I'm looking for. Since I tend to work on technical products, when I interview a product manager I tend to look for... So much of the engineering mindset jumps to solutions instead of clarifying problems. I'm guilty of this constantly.
- MichaelMoser123 6y ago
  What is more important to you - the clarifying questions of the candidate or the actual answer?
- TurkishPoptart 6y ago
  Can you clarify as to what kinds of clarifying questions you're looking for? Not trying to be ironic here, just need help with interviewing.
  - rendaw 6y ago
    For example, what does "load" mean? Type it into a browser url bar and press enter? Or just what happens when you press enter (excluding the typing)? Via curl? Or does load refer to just a single HTTP request?
  - colinrand 6y ago
    Certainly. I like to have the candidate ask follow ups like, are you interested in the networking aspects? the brower's behaviors? the way the website handles the request? all of these above? If I phrased the question slightly differently, engineers would have a very different reaction. Q: Can you write a test for me that demonstrates I can load a URL successfully? That could drive the engineer down a different mode of thought. Business stakeholders won't ask for a requirement to implement a test, and the engineer needs to translate the business request into an engineering solution. From what I've seen, different levels of experience in engineer will have different responses and illustrate for me where they are in the engineering journey. A young engineer, perhaps a new college grad or intern, will tend to react to this with a very open mind and lean on their recent academic background, showing excitement with the question and identifying the challenges in it. They usually do pretty well. The mid career programmer often stumbles. They want to show the expertise so latch on to the part of the problem they are most familiar with do show technical prowess. They can often lose the forest for the trees. The senior engineer, will want to know why you're asking and what you're trying to accomplish. Perhaps I'm looking to optimize one part of the problem, perhaps make a step more resilient, more extensible, etc. They will want to know why this question is important for the problems at hand, and hopefully they'll ask about that directly! Hope this gives some insight for you.
qertistick 6y ago
I was once curious about this sort of thing. I hate that I didn't know how a computer worked from the ground up, it made them feel like magic when I knew they were just clever machines. I wasn't satisfied with learning about circuits so I went even lower and asked how transistors work. I spent a long time in a deep rabbit hole learning chemistry so I could understand why capacitors keep charge and etc. That's when I realise to learn every layer of a computer to a level of expert proficiency is a lifetime's work, not something you can expect one person to be able to do off the top of their head. This is why we work together, we are not swiss army knives.
deleted 6y ago
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athenot 6y ago
I really like this question. What I get out of it is where the candidate focuses on, and where they gloss over. I find it useful to prefix the question with a statement about there being no "right" answer, and "go in as much detail as you want or know". Since I'm not hiring for hardware, when they get into minute details about keyboard and USB, I smile and gently interrupt to move to the browser making the request. Come to think of it, I may rephrase the question to "What happens when you click on a link?" since that covers browser events, CORS and all that fun; and does away with the keyboard.
- toast0 6y ago
  If you don't want to hear about USB details, beware, clicking often involves USB mice. More importantly, telling someone there is no right answer, and go into as much detail as they want, and then cutting them off when they do is a bad interview experience. At least guide them on where you want to focus. Or let them take you on an adventure through USB. The point of this as an interview question is to demonstrate broad knowledge as well as some detailed knowledge --- it doesn't particularly matter which knowledge. If someone can figure out USB, they can figure out TCP, etc. You're looking for people who can figure things out. It's all distributed state management. Maybe a little different if you're hiring a contractor than a staff member.
tester756 6y ago
I think it lacks of: Parsing and js execution TLS Handshake / algo negotation Cache
loa_in_ 6y ago
I appreciate author's quest for bottom-up understanding of all the things we depend on daily. The quote "We are standing on shoulders of giants" really shines here, and we all do a great service to them by trying to understand.
lxe 6y ago
Another interesting thought exercise would be "can you accomplish X with as few layers/infrastructure/historical context/complexity as possible?" Knowing what you need to accomplish, can you design a system from the ground up that sheds some of the traditionally expected layers and idioms and see what you can come up with.
yarone 6y ago
Reminds me of "I, pencil": "A charming story which explains how something as apparently simple as a pencil is in fact the product of a very complex economic process based upon the division of labor, international trade, and comparative advantage." https://oll.libertyfund.org/titles/read-i-pencil-my-family-tree-as-told-to-leonard-e-read-dec-1958/simple https://oll.libertyfund.org/titles/read-i-pencil-my-family-t...
kaycebasques 6y ago
> How does the browser know to try to load a webpage? I guess it sees an "http://" http://" or just assumes that anything with no prefix is a URL? Question #7 seems related to that Chromium DNS lookup algorithm [1] that has been getting attention recently [1] https://news.ycombinator.com/item?id=24231857 https://news.ycombinator.com/item?id=24231857
kaycebasques 6y ago
Another great resource similar to How Browsers Work [1] is Mariko's Inside look at modern browsers series [2] [1] https://www.html5rocks.com/en/tutorials/internals/howbrowserswork/ https://www.html5rocks.com/en/tutorials/internals/howbrowser... [2] https://developers.google.com/web/updates/2018/09/inside-browser-part1 https://developers.google.com/web/updates/2018/09/inside-bro... Disclosure: Mariko and I are on the same team; I didn't work on that series
kaycebasques 6y ago
There seems to be a need for resources about browser internals. This is something we could potentially pursue on web.dev. However, it's a big field. Can you all help me by: * Providing examples of existing resources that explain browser internals which has made you a better developer * Listing situations in which you needed to go deeper into how browser internals work and didn't find good resources
zoomablemind 6y ago
A nice why-and-why journey. Yet as an interviewing approach this seems to lack an initial premise, the need. For example. * I want to know what does a URL represent. Is it a porn site? Am I gonna be hacked/tracked? * I need to check if this domain name is not/taken. * I want to know if URL can contain spaces, or emojis. * I want to know if I get a reasonably fast response. * My phone tells me the site access is Forbidden. Basically, a reasonable answer needs to be also a "Why?". This sets up a logical context for drilling down with an intention to locate something, not just for the drilling down sake. "Computer, what happens...?" "Why do you need to load a URL, Dave?"
AndrewStephens 6y ago
I tried writing an answer to (almost) this exact question in non-technical language[0], starting from packets and working upwards. The document ended up much longer than I intended and I am still not sure my answer is that helpful. [0] https://sheep.horse/2017/10/how_you_are_reading_this_page.html https://sheep.horse/2017/10/how_you_are_reading_this_page.ht...
1vuio0pswjnm7 6y ago
Interesting that he skipped the part about parsing the URL and generating the HTTP (httpMethod, path, headers), assuming that is the protocol. It seems relatively simple but unless one is careful there are some gotchas. Perhaps that is why this particular part of the process ends up in so many "web security" write-ups; many people, including the author, just do not think it is significant. He also asssumes that the client is a "browser".

170 points by caiobegotti 6y ago

I find I run into similar discussions whenever a beginner programmer decides they want to capture input from the arrow keys. They've worked through the bog standard Python tutorials using input() to capture from stdin, so it should be trivial to design a simple game that uses the arrow keys right? And suddenly this gulf of complexity opens up of event polling, keycodes, integrating third party modules, and they're left wondering why moving one key over on the keyboard is so hard.

Spivak 6y ago
Having never really had a needed to do this I'm a little confused -- isn't this just a matter of putting the tty into cbreak or raw mode and then just reading keys from stdin? Like keycodes are annoying but "special keys have this weird text representation, here's a table" doesn't seem like a huge gap to cross.
- tmpz22 6y ago
  For games you also have to decipher what a keystroke should do physics wise which isn’t always simple, ie acceleration and deceleration, including what happens when multiple arrows are held down. You now are polling multiple events concurrently and processing them outside of that loop. And so on and so on.
  - deleted 6y ago
    [deleted]
- divingdragon 6y ago
  > putting the tty into cbreak or raw mode and then just reading keys from stdin You're saying this like most beginners even have an idea what a tty is. An anecdote: When I wrote my first C++ program that reads an input (using `cin`, hello-world style), I immediately wondered how to read single keys including arrow keys. The book I was following had nothing about this. I don't remember the exact details but a bit of Internet search got me to `conio.h` (I was using Dev-C++ on Windows) which did work. But getting it to work was so confusing to me at the time. And I didn't even get to understand what it's actually doing under the hood. I imagine it would be a bit easier in Python given the right libraries, but the dependency management probably adds to the complexity for a beginner.
- sokoloff 6y ago
  For games, I usually want to handle at the level of keydown and keyup rather than keystrokes. What’s the keystroke for right-arrow, spacebar, left-shift, and W all being held down? (Think of an Asteroids arcade game where w is thrust, spacebar is fire, left-shift is shields, and right arrow is rotate. Those are up/down, not strokes, that the player is giving you.)
qertistick 6y ago
You use a game library for this and then it becomes as simple as pushing a key handler onto the event loop and usually the keycodes are already processed for you as well. I don't get the false dilemma people are creating that somehow this is complicated or that people who use the easy way are less knowledgable than others. If you make a game engine from scratch by yourself it's going to be a logical disaster, whether you've learned c++ or python.
- Gravityloss 6y ago
  Yeah, it's surprisingly simple. It took little time with a game library to get the key polling to work. I was experimenting with chorded keyboard ideas back then.
- saagarjha 6y ago
  But then you might end up talking about event loops and routing…
- MaxBarraclough 6y ago
  > You use a game library for this If it's a command-line application, they might use curses. edit Apparently curses isn't available by default in Python3 for Windows. Is there a nice way to do this?

aronpye 6y ago

Reminds me of when Richard Feynman analysed the question of “how do magnets work?”. There are so many levels to it, coupled with assumed knowledge, that the question itself is shown to be improperly bounded.

nitrix 6y ago
A fascinating man and video. Link for the interested: https://www.youtube.com/watch?v=36GT2zI8lVA https://www.youtube.com/watch?v=36GT2zI8lVA
- serniebanders 6y ago
  I don't find the video fascinating, quite the opposite actually. Richard Feynman could have just explained the electrical force and left out the rest. When someone asks, `why does x work`, its a sign that they are curious and ready to explore and learn. Its an opportunity to teach and educate. The whole video (to his credit, Richard did explain the concept well) focuses on how little the questioner know. It is a little belittling. If someone talked like that to me I'd have gone home and accepted the fact that I just would never understand electromagnetism and moved on. A better approach instead of actually capitalizing on this curiosity and teaching the questioner, giving them just a bit more than the normally accepted answer so the curiosity lives on.
  - aronpye 6y ago
    I think in this example Feynman was using the question to illustrate the levels of complexity in answering a scientific question. If you watch his actual lectures, Feynman does break the concepts down in order to teach them. Also, documentaries and popular science books tend to dumb down and over simplify theories to such an extent, such as by removing all mathematics, that they just become either wrong, inaccurate, or misleading. I think it was Einstein which said make things as simple as possible, but not simpler.

klodolph 6y ago

I was given this as an interview question once, it was fun. I was told to go into “as much breadth and depth as possible” but I did get stopped a couple times when I started talking about things like debouncing.

abfan1127 6y ago
breadth and depth as possible seems like they are just asking for as many rabbit hole as possible!
borgchick 6y ago
I've asked this question a number of times in interviews. Sadly, not one person has ever talked about debouncing. I think I would've instantly hired the person, if they talked about debouncing :P To clarify, I would ask this question as a wrap up, a sort of final probe of depth test. If they don't go into much detail, no big deal. If they were good in the rest of the interview, they'd still get hired. If they were good elsewhere but also went into depth on this question, then it really boosts their likeliness of getting hired. I find that people who are curious about how things work, especially when it is outside of their main domain, are usually people interesting to work with.
- kamyarg 6y ago
  can you link to a resource for reading about debouncing?
  - kens 6y ago
    The Art of Electronics has a good section on debouncing switches. There are various analog and digital ways of doing it, from R-C smoothing to latches to debounce ICs to microcontrollers. If you want a thoroughly obsolete look at debouncing, I got a debouncing module from an IBM 705 computer (1954). This module was built from 8 vacuum tubes and a pile of resistors and other components. I powered it up with an inconvenient set of voltages (+140V, -60V, -130V) and actually got it to work: http://www.righto.com/2018/01/ibm-mainframe-tube-module-part-ii.html http://www.righto.com/2018/01/ibm-mainframe-tube-module-part...

bookmarkable 6y ago

Interesting, but couldn't you ask this of any existing technology with years of development and realize you don't know how we arrived at a function we take for granted? What happens when you press the accelerator on your car?

canadian_tired 6y ago
Indeed. I have realized 2 things: First, technical specialization is increasingly more fine-grained; second, assumptions that anything outside of the specialization will magically just work. To extend your example, 30 years ago you could easily find someone who understood the whole chain...from the pedal all the way to the rubber on the road. Today? the pedal itself likely has a microcontroller in it... designed by a pedal expert, who knows what the various I/O requirements are and has little or no concern with what the car actually does. Probably leads to better pedal designs, but you need an army of people to tell you why the car might not move.
bluetomcat 6y ago
> What happens when you press the accelerator on your car? No single automotive engineer can answer that question to the level of detail that the original post wants to approach. A car is a collection of separately engineered mechanical devices meeting some power/torque/thermal requirements, electronic units which, to a mechanical engineer are essentially black boxes with inputs and outputs. Abstraction is in every field of engineering and it helps people reason about a complex system in terms of abstract interconnected parts, not in terms of bits, bytes, cogs or bearings. In a similar vein, a web developer, a browser developer, a kernel developer, a network driver developer each use different levels of abstraction and paradigms in order to achieve their thing.
- mcguire 6y ago
  There is another way of asking this question: "Someone types the URL of your application in their browser and doesn't get the application page. How do you figure out what went wrong?"
amelius 6y ago

canadian_tired 6y ago

Asked of Cliff Stoll for his PhD defense: "Why is the sky blue?"

davidhyde 6y ago

Your browser tries to guess if what you have typed is is a url or a search query. If you’re using chrome then there is a chance that your request will hit a root domain name server so that the browser can check if you are connected to a scammy Internet service provider or some other ad serving intermediary. https://arstechnica.com/gadgets/2020/08/a-chrome-feature-is-creating-enormous-load-on-global-root-dns-servers/ https://arstechnica.com/gadgets/2020/08/a-chrome-feature-is-...

fortran77 6y ago

This used to be a standard interview question I'd ask potential junior candidates. I'd see how far down I can get them to go.

mattlondon 6y ago

This is why I love this question as a phone-screener for onsite interviews and stuff. Sounds so easy, but there is so much depth in so many areas that people can drill into. If someone starts talking convincingly about the OS handling keyboard interrupts or about HTTPS certificate revocation during the TLS handshake explanation etc, you know they are probably worth bringing in for a face to face. Someone bluffing will usually fail this really hard - "The browser connects to example.com and downloads the page." or something. Uh-huh. Maybe they talk about DNS ... Maybe they talk about a TCP connection ... Maybe they talk about retrieving the HTML and parsing it ... but even then, if they get that far that will be better than a lot of bluffers. If they have simply revised anticipating this question and can answer everything then congrats - they've just educated themselves in a lot of the core fundamentals :) As an interviewer this question can easily take up a whole 30 min phone screener as good candidates get deeper and deeper.

ceejayoz 6y ago
> Sounds so easy, but there is so much depth in so many areas that people can drill into. If someone starts talking convincingly about the OS handling keyboard interrupts or checking for HTTPS certificate revocation during the TLS handshake etc, you know they are probably worth bringing in for a face to face. If I ask you "what happens when you load a URL" and you start talking about the operating system's handling of keyboard events, I might get the impression you're hopelessly prone to bizarre and useless digressions.
- mattlondon 6y ago
  I usually say something like "What happens if I type 'example.com' in my browser's address bar and hit enter?" If someone goes wildly off-track and starts talking about the design of the mechanical switches in the keyboard or I am specifically interested in one area vs another then you can easily tailor it "Ok cool - lets skip ahead to the network aspects" or "lets say I've found the server and downloaded the HTML - now what?" etc. That said, I often like to let people just talk in interviews unless I am really specifically trying to drill into one area and get specific evidence of specific skills. I might jump in with a "Ah - interesting. Tell me more about DNS" or whatever, but usually I find that the good candidates will have a lot to say, and the less-good candidates either say hardly anything, bullshit, or talk a lot but are not good communicators (confusing explanations/hand-waving/etc) ... or a combination of those things :)

thecrumb 6y ago

A bit dated as well. It's assuming I'm using a physical keyboard. Today I might be using my phone. Might be using voice recognition. It might be my fridge hitting a URL using IoT to order me some more beer.

colinrand 6y ago

I ask this question from time to time and look for different responses depending on the type of candidate. When I ask an engineer, I am looking to see if they can grasp the problem space and ask clarifying questions about what I'm looking for. When I'm interviewing for an engineering manager I am looking to see if they can grasp the problem space and ask clarifying questions about what I'm looking for. Since I tend to work on technical products, when I interview a product manager I tend to look for... So much of the engineering mindset jumps to solutions instead of clarifying problems. I'm guilty of this constantly.

MichaelMoser123 6y ago
What is more important to you - the clarifying questions of the candidate or the actual answer?
TurkishPoptart 6y ago
Can you clarify as to what kinds of clarifying questions you're looking for? Not trying to be ironic here, just need help with interviewing.
- rendaw 6y ago
  For example, what does "load" mean? Type it into a browser url bar and press enter? Or just what happens when you press enter (excluding the typing)? Via curl? Or does load refer to just a single HTTP request?
- colinrand 6y ago
  Certainly. I like to have the candidate ask follow ups like, are you interested in the networking aspects? the brower's behaviors? the way the website handles the request? all of these above? If I phrased the question slightly differently, engineers would have a very different reaction. Q: Can you write a test for me that demonstrates I can load a URL successfully? That could drive the engineer down a different mode of thought. Business stakeholders won't ask for a requirement to implement a test, and the engineer needs to translate the business request into an engineering solution. From what I've seen, different levels of experience in engineer will have different responses and illustrate for me where they are in the engineering journey. A young engineer, perhaps a new college grad or intern, will tend to react to this with a very open mind and lean on their recent academic background, showing excitement with the question and identifying the challenges in it. They usually do pretty well. The mid career programmer often stumbles. They want to show the expertise so latch on to the part of the problem they are most familiar with do show technical prowess. They can often lose the forest for the trees. The senior engineer, will want to know why you're asking and what you're trying to accomplish. Perhaps I'm looking to optimize one part of the problem, perhaps make a step more resilient, more extensible, etc. They will want to know why this question is important for the problems at hand, and hopefully they'll ask about that directly! Hope this gives some insight for you.

qertistick 6y ago

I was once curious about this sort of thing. I hate that I didn't know how a computer worked from the ground up, it made them feel like magic when I knew they were just clever machines. I wasn't satisfied with learning about circuits so I went even lower and asked how transistors work. I spent a long time in a deep rabbit hole learning chemistry so I could understand why capacitors keep charge and etc. That's when I realise to learn every layer of a computer to a level of expert proficiency is a lifetime's work, not something you can expect one person to be able to do off the top of their head. This is why we work together, we are not swiss army knives.

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athenot 6y ago

I really like this question. What I get out of it is where the candidate focuses on, and where they gloss over. I find it useful to prefix the question with a statement about there being no "right" answer, and "go in as much detail as you want or know". Since I'm not hiring for hardware, when they get into minute details about keyboard and USB, I smile and gently interrupt to move to the browser making the request. Come to think of it, I may rephrase the question to "What happens when you click on a link?" since that covers browser events, CORS and all that fun; and does away with the keyboard.

toast0 6y ago
If you don't want to hear about USB details, beware, clicking often involves USB mice. More importantly, telling someone there is no right answer, and go into as much detail as they want, and then cutting them off when they do is a bad interview experience. At least guide them on where you want to focus. Or let them take you on an adventure through USB. The point of this as an interview question is to demonstrate broad knowledge as well as some detailed knowledge --- it doesn't particularly matter which knowledge. If someone can figure out USB, they can figure out TCP, etc. You're looking for people who can figure things out. It's all distributed state management. Maybe a little different if you're hiring a contractor than a staff member.

tester756 6y ago

I think it lacks of: Parsing and js execution TLS Handshake / algo negotation Cache

loa_in_ 6y ago

I appreciate author's quest for bottom-up understanding of all the things we depend on daily. The quote "We are standing on shoulders of giants" really shines here, and we all do a great service to them by trying to understand.

lxe 6y ago

Another interesting thought exercise would be "can you accomplish X with as few layers/infrastructure/historical context/complexity as possible?" Knowing what you need to accomplish, can you design a system from the ground up that sheds some of the traditionally expected layers and idioms and see what you can come up with.

yarone 6y ago

Reminds me of "I, pencil": "A charming story which explains how something as apparently simple as a pencil is in fact the product of a very complex economic process based upon the division of labor, international trade, and comparative advantage." https://oll.libertyfund.org/titles/read-i-pencil-my-family-tree-as-told-to-leonard-e-read-dec-1958/simple https://oll.libertyfund.org/titles/read-i-pencil-my-family-t...

kaycebasques 6y ago

> How does the browser know to try to load a webpage? I guess it sees an "http://" http://" or just assumes that anything with no prefix is a URL? Question #7 seems related to that Chromium DNS lookup algorithm [1] that has been getting attention recently [1] https://news.ycombinator.com/item?id=24231857 https://news.ycombinator.com/item?id=24231857

kaycebasques 6y ago

Another great resource similar to How Browsers Work [1] is Mariko's Inside look at modern browsers series [2] [1] https://www.html5rocks.com/en/tutorials/internals/howbrowserswork/ https://www.html5rocks.com/en/tutorials/internals/howbrowser... [2] https://developers.google.com/web/updates/2018/09/inside-browser-part1 https://developers.google.com/web/updates/2018/09/inside-bro... Disclosure: Mariko and I are on the same team; I didn't work on that series

kaycebasques 6y ago

There seems to be a need for resources about browser internals. This is something we could potentially pursue on web.dev. However, it's a big field. Can you all help me by: * Providing examples of existing resources that explain browser internals which has made you a better developer * Listing situations in which you needed to go deeper into how browser internals work and didn't find good resources

zoomablemind 6y ago

A nice why-and-why journey. Yet as an interviewing approach this seems to lack an initial premise, the need. For example. * I want to know what does a URL represent. Is it a porn site? Am I gonna be hacked/tracked? * I need to check if this domain name is not/taken. * I want to know if URL can contain spaces, or emojis. * I want to know if I get a reasonably fast response. * My phone tells me the site access is Forbidden. Basically, a reasonable answer needs to be also a "Why?". This sets up a logical context for drilling down with an intention to locate something, not just for the drilling down sake. "Computer, what happens...?" "Why do you need to load a URL, Dave?"

AndrewStephens 6y ago

I tried writing an answer to (almost) this exact question in non-technical language[0], starting from packets and working upwards. The document ended up much longer than I intended and I am still not sure my answer is that helpful. [0] https://sheep.horse/2017/10/how_you_are_reading_this_page.html https://sheep.horse/2017/10/how_you_are_reading_this_page.ht...

1vuio0pswjnm7 6y ago

Interesting that he skipped the part about parsing the URL and generating the HTTP (httpMethod, path, headers), assuming that is the protocol. It seems relatively simple but unless one is careful there are some gotchas. Perhaps that is why this particular part of the process ends up in so many "web security" write-ups; many people, including the author, just do not think it is significant. He also asssumes that the client is a "browser".