JoshCheek/webserver.md

## webserver.md

      
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              webserver.md
            
          
    I'll move this over to curriculum when it's more legitimate :)


Due Tuesday, we'll have a fun lunch at the Vault
and "evaluate" the solutions all together!
Your pairs are: ["pat", "jason"], ["shannon", "robbie"], ["chad", "charissa"], ["ryan", "tyler"], ["matt", "emily"], ["ross"]

Project Overview

Goals


Demystify servers, the internet, http, and everything else that is ultimately just these...
AJAX, sessions, cookies, APIs, Service Oriented Architectures, Oauth
Show you that the things you've learned can be used to accomplish real goals and write real programs
Show you that all the things that seem like magic... are not magic
Don't spend forever on this thing

What is it?

The internet... how does that work?
It's really just strings going back and forth across the internet.
Something like a browser will send a string called a "request"
which will hit a server, which will send back a string called a "response".
You can make your own server if you can accept a request,
parse the request (which means turn the string into something more useful, like a hash),
and write the response.
The format of the request and response is defined by something called "http",
which probably stands for something, but who cares.
The HTTP Request

Anatomy:

The first line
the method aka verb ("POST")
the path ("/to_braille")
version or protocol, something ("HTTP/1.1")
Headers


Any number of "Key: Value" pairs
Some headers have meaning, eg Content-Length tells you how long the body is


Body

View an HTTP request by starting a server, in order to see http
$ nc -l 9292

And now click this link: http://localhost:9292/this/is/the/path
The HTTP Response

Anatomy:

The first line
version or protocol, something "HTTP/1.1"
The status code (eg 404)
The status code for humans (eg "Not Found")
Headers


any number of "Key: Value" pairs
Ending when you find a blank line


Body

Make a request from the command line, and see the response
$ curl -i http://google.com

Accepting a request

# Tell my computer that web requests to http://localhost:9292 should be sent to me
require 'socket'
port       = 9292
tcp_server = TCPServer.new(port)

# Wait for a request
client = tcp_server.accept

# Read the request
first_line = client.gets
puts "The first line is: #{first_line}"

# Write the response
client.print("HTTP/1.1 302 Found\r\n")
client.print("Location: http://turing.io\r\n")
client.print("Content-Type: text/html; charset=UTF-8\r\n")
client.print("Content-Length: 219\r\n")
client.print("\r\n")
client.print("<HTML><HEAD></HEAD><BODY></BODY>\r\n")
client.close

# I'm done now, computer ^_^
tcp_server.close_read
tcp_server.close_write
A successful Ruby webserver

Does this:


Receive the request


Parse it into a Hash


Give it to Sinatra or whatever (called the "app")


Receive the instructions for what to put in the response,
an array with the status code, headers, body, eg:
[302, {'Location' => 'http://turing.io'}, ["<h1>hi</h1>"]]


Write the response


Getting Feedback

See what a real server parses a request as:

Install server stuff:
$ gem install rack puma

In a file called "config.ru"
class LetsGoExploring
  def call(hash)
    status_code = 200
    headers     = {'Content-Type' => 'text/html;', 'Content-Length' => '15'}
    body        = ["<h1>Hello!</h1>"]

    require "pry"
    binding.pry

    [status_code, headers, body]
  end
run
Then run it with
$ rackup config.ru -p 9292

And now click this link: http://localhost:9292/this/is/the/path
Getting comfortable

To familiarize yourself with this stuff, try using nc -l 9292
to start servers, and type the responses by hand. Can you do these things?

Redirect the browser (status code and Location header)
Return some JSON (Content-Type, Content-Length headers, body)
Try starting the server on a couple of different ports
Set a cookie (forgot what the header is, I think it's "Set-Cookie", then make a second request and see that the browser sends you back the cookie you set)
See how the path comes in (any request from the browser)
See how query params come in (any request from the browser)
See a form submission (edit any form on any page to point at your server -- another way is to start your Rails server, request the form, stop the server, start nc on that port, and then submit it)
Decrypt a Rails session -- We can get the session from the cookie, and the secret_key_base from config/secrets.yml, these should be all we need, but I'd have to look into how the encryption is done.
Render your own http response (probably have them write it independently, set the status, and the headers (Content-Type and Content-Length), and then paste the body in)
Render arbitrary other headers and see that they are present in the browser (Network tab from dev Webkit's dev tools)
Start nc on two different ports and redirect the browser from the one to the other, then you can see it come in twice.
Often, a redirect url will be sent.