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What happens when you make an HTTP request?

Last updated: June 25, 2022

Thoughts about an additional resource.

We’ll have to clarify what a “server” is…

https://developer.mozilla.org/en-US/docs/Learn/Getting_started_with_the_web/How_the_Web_works
  • Assuming Browser with well-formed Uniform Resource Identifier/URL.
  • A Domain Name is a human-readable address but it is not the actual address of the resource.
  • The URL is an alias that acts as a pointer to the true Internet Protocol address and location of the requested resource.
    • Has the browser recently visited this address and already determined the IP?
    • If not, it will as the operating system if another program has (there’s a host file where they are saved).
    • If it has the IP address already – then great.
    • If not, it will ask the Internet Service Provider.
      • This means that other people may have already requested this and it’s saving all of those connections (scary!)
    • If it has the IP address already – then great.
    • If not, then it will ask the global authority DNS (look into these details). It will know how to find it (But is the most work)
      • that will come back and the ISP will get a taste(for other users), and the OS(for other programs), and the browser etc. those things will all keep that info for next time
  • With the IP address in hand, the browser can properly make its HTTP request
    • That will go to the ISP
    • A range of other intermediate computers along the routing
  • The web server will note the request (this is a computer)
    • This has a program that will run (“The web server”) / dedicated to serving the files that are requested
      • The physical computer is often called a “server” / but it’s just a computer. The program is the server.
      • Clarify that…  (apache / nginx) (we can build a simple one) (check curl) (create one with PHP)
    • It’s waiting for requests.
    • It has a bunch of rules
  • The HTML could be a file sitting on the file system of that computer
    • Or / it could be being created on the fly – based on a set of data/request – or other things – and it will create an HTML file from that
  • The browser will receive that HTML file
  • It will read the HTML file and create a tree-like structure called the Document Object Model.
    • It might be complete
    • but it’s likely to reference separate images, CSS, JS – and all other sorts of files
      • It will start building the website
      • and then – will start requesting the other files
      • WHEN does the final paint happen? (look at these details)
    • At this point, the website is all loaded – and it will just exist
      • But it’s also likely to have lots of scripts that are waiting to see if there will be any input
      • At that point, the user can interact with the program in whatever way it’s designed to work
      • Clicking a regular link might load a new page just like we’ve described above.
      • Clicking a button or adding some text to an input might create new pieces of HTML and insert it into the DOM and update the page
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