How HTTP response is generated - node.js

Question

I'm fairly new to programming and this question is about making sure I get the HTTP protocol correctly. My issue is that when I read about HTTP request/response, it looks like it needs to be in a very specific format with a status code, HTTP version number, headers, a blank line followed by the body.
However, after creating a web app with nodejs/express, I never once had to actually write code that made an HTTP response in this format (I'm assuming, although I don't know for sure that other frameworks like ruby on rails or python/Django are the same). In the express app, I just set up the route handlers to render the appropriate pages, when a request was made to that route.
Is this because express is actually putting the response in the correct HTTP format behind the scenes? In other words, if I looked at the expressJS code, would there be something in that code that actually makes an HTTP response in the HTTP format?
My confusion is that, it seems like the HTTP request/response format is so important but somehow I never had to write any code dealing with it for a node/express application. Maybe this is the entire point of a framework like express... to take out the details so that developers can deal with business logic. And if that is correct, does anyone ever write web apps without a framework to do this. Would you then be responsible for writing code that puts the server's response into the exact HTTP format?

Answer 1

I'm fairly new to programming and this question is about making sure I get the HTTP protocol correctly. My issue is that when I read about HTTP request/response, it looks like it needs to be in a very specific format with a status code, HTTP version number, headers, a blank line followed by the body.
Just to give you an idea, there are probably hundreds of specifications that have something to do with the HTTP protocol. They deal with not only the protocol itself, but also with the data format/encoding for everything you send including headers and all the various content types you can send, authentication schemes, caching, status codes, URL decoding, etc.... You can see some of the specifications involved just by looking here: https://www.w3.org/Protocols/.
Now a simple request and a simple text response could get away with only knowing a few of these specifications, but life is not always that simple.
Is this because express is actually putting the response in the correct HTTP format behind the scenes? In other words, if I looked at the expressJS code, would there be something in that code that actually makes an HTTP response in the HTTP format?
Yes, there would. A combination of Express and the HTTP library that is built into node.js handle all the details of the specification for you. That's the advantage of using a library/framework. They even handle different versions of the protocol and feedback from thousands of other developers have helped them to clean up edge case bugs. A good library/framework allows you to still control any detail about the response (headers, content types, status codes, etc..) without making you have to go through the detail work of actually creating the exact response. This is a good thing. It lets you write code faster and lets you ride on the shoulders of others who have already figured out minutiae details that have nothing to do with the logic of your app.
In fact, one could say the same about the TCP protocol below the HTTP protocol. No regular app developer wants to write their own TCP stack. Instead, you just want a working TCP stack that you can use that's already been tuned and debugged for you.
However, after creating a web app with nodejs/express, I never once had to actually write code that made an HTTP response in this format (I'm assuming, although I don't know for sure that other frameworks like ruby on rails or python/Django are the same). In the express app, I just set up the route handlers to render the appropriate pages, when a request was made to that route.
Yes, this is a good thing. The framework did the detail work for you. You just call res.setHeader(), res.status(), res.cookie(), res.send(), res.json(), etc... and Express makes the entire response for you.
And if that is correct, does anyone ever write web apps without a framework to do this. Would you then be responsible for writing code that puts the server's response into the exact HTTP format?
If you didn't use a framework or library of any kind and were programming at the raw TCP level, then yes you would be responsible for all the details of the HTTP protocol. But, hardly anybody other than library developers ever does this because frankly it's just a waste of time. Every single platform has at least one open source library that does this already and even if you were working on a brand new platform, you could go get an open source body of code and port it to your platform much quicker than you could write all this yourself.
Keep in mind that one of the HUGE advantages of node.js is that there's an enormous body of open source code (mostly in NPM and Github) already prepackaged to work with node.js. And, because node.js is server-side where code memory isn't usually tight and where code just comes from the local hard disk at server init time, there's little downside to grabbing a working and tested package that does what you already need, even if you're only going to use 5% of the functionality in the package. Or, worst case, clone an existing repository and modify it to perfectly suit your needs.

Answer 2

Is this because express is actually putting the response in the
correct HTTP format behind the scenes?
Yes, exactly, HTTP is so ubiquitous that almost all programming languages / frameworks handle the actual writing and parsing of HTTP behind the scenes.
Does anyone ever write web apps without a framework to do this. Would
you then be responsible for writing code that puts the server's
response into the exact HTTP format?
Never (unless you're writing code that needs very low level tweaking of HTTP code or something)