Basic Networking & Infastructure

HTTP

hyper-text transfer protocol; This is what defines how two computers structure their data to talk to each other (it's the http or https at the beginning of a URL)

HTTP Diagram

Imagine bobby wants to get the shulich ignite beginner sessions page (https://schulichignite.com/beginner)

This whole interaction and how it works is defined by the HTTP protocol

HTTP Headers

HTTP requests and responses both have headers. Headers are key-value pairs that tell the client & host the details they need to interact properly

Mail analogy

Imagine you're sending mail, you need 3 things

That is what HTTP needs

Additionally like how you would add FRAGILE to mail to tell the post service how to handle your message, headers can also contain information about how to handle the request/response

How to examine headers in browser

First open your browser dev tools, go to the network tab and then either refresh or navigate to a webpage

HTTP Requests

The first part of HTTP communication is to request a URL

HTTP Request Example

We're going to request https://schulichignite.com/beginner

GET /beginner HTTP/1.1
Host: schulichignite.com
User-Agent:... Removed for readability

HTTP Request types (GET/HEAD)

A GET request asks for a response that includes a header and some content, a HEAD request asks for just a header response without any content

HTTP Request types (POST)

A POST request POSTs some content to a server. This is usually done for forms to submit the data

HTTP Request types (PUT)

A PUT request tells the server to PUT whatever is being sent at the location specified. This might be used on a photo sharing service to indicate replacing a photo with a new version.

HTTP Request types (DELETE)

A DELETE request is used to ask a server to DELETE a resource (i.e. a photo)

Other HTTP Request types

Breaking down the headers

This won't cover everything, just the things that are useful

First line

The first line tells the browser the request type, slug, protocol and version

GET /beginner HTTP/1.1

Host

This tells the server & browser the domain you're trying to access

Host: schulichignite.com

User Agent

This tells the server information about your browser. This is used by developers often to patch compatability if a browser doesn't support a feature (usually REALLY long)

User-Agent: Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.5060.53 Mobile Safari/537.36 Edg/103.0.1264.37 

HTTP Response

The response is comprised of a header, and the response content (the HTML or file contents of the resource) Example

HTTP/1.x 200 OK
Content-Type: text/html; charset=UTF-8
Cache-Control: max-age=3600, public
Content-Encoding: gzip

<title> Schulich Ignite </title><!--More HTML here-->

HTTP Response header example

Like requests the response headers provide additional details. Usually about the type of content being sent and other information

HTTP/1.x 200 OK
Content-Type: text/html; charset=UTF-8
Cache-Control: max-age=3600, public
Content-Encoding: gzip

Breaking down HTTP Response header

Again this isn't everything, just things that are often useful

First line

First line is always the response protocol, version and status code

HTTP/1.x 200 OK

HTTP Response status codes 2xx

These codes means everything is working as intended. Examples:

200 OK; Successful response
201 Created; A new file was created successfully
202 Accepted; The request has been accepted, but isn't done yet

HTTP Response status codes 3xx

These codes are called redirect codes. Examples:

300 Multiple choices; Means there are a few options (like various image or file formats the browser can choose from)
301 Moved permanantly; This request and any future requests should look to a provided URL instead of the one they requested
302 Moved Temporarily; Temporarily go to a different provided URL, but next time check back here again

HTTP Response status codes 4xx

These are Client error codes (meaning you made a mistake). Examples:

400 Bad Request; You broke something, probably a syntax error or request size is too big
403 Forbidden; You need permissions the server thinks you don't have
404 Not found; The slug you provided has no valid response on the server
418 I'm a teapot; :)

HTTP Response status codes 5xx

These are server errors (meaning the host made a mistake)

500 Internal Server Error; Something broke, but the server won't give specifics (like a web segfault)
502 Bad Gateway; Server couldn't get a valid response when trying to generate one from another server's data
503 Service Unavailable; Server is borked and completely down (hopefully it's not yours)

Other HTTP Response codes

Content-Type

This is used to tell the browser the type of info you recieved. Not everything we do is going to have an html file as a response (can have images, pdfs, file downloads etc.). This will have the file's MIME type (type of file it is) & encoding (the type of characters it supports)

Content-Type: text/html; charset=UTF-8

Cache Control

The cache control sets how long a page should be considered 'fresh' by the browser before asking the server to update it

Cache-Control: max-age=3600, public

Content Encoding

Web pages aren't usually sent as plaintext that is human readable. They often use an encoding to save space. This header tells you which encoding is used so you know how to decode it

Content-Encoding: gzip

Great, so we know about domains & HTTP let's go

So we should be able to just connect to the domain and send HTTP requests and get responses, right?