Assignment 6 HTTP Backend

HTTP Backend
So far, we have been focusing on building "front-end" applications using
JavaScript to execute within a user's browser and leveraged AJAX
requests to an HTTP server ("back-end") for some functionality. In this
assignment we will build our own backend web application
using Express to handle the monotonous details of HTTP and make us
productive quickly.
Requirements
The application will have a few disparate features so we can flex a few
different skill sets. We are going to build our very own web API (kind of
like the Weather API we used), create a dynamically generated HTML
page, and use some basic session functionality to enable the app to
hold a user's state across multiple page refreshes and navigations.
Dynamically Generated Homepage
The home page ("/") will be generated using the templated view system
in Express. The title of the page should be some made-up business
name, and there should be some text below it that incorporates the
result of the Corporate BS Generator API.
Session Data
On the home page below the title and description, there should be a
form that lets the user enter text input and click "Submit". Upon clicking
Submit, a POST request should be sent to the server with the contents
of the form input and added to the user's session state, and the
response should redirect the user back to the root page ("/") where the
items in the user's session will be displayed in a numbered list in the
order they were added.
Basic Web API
There should be an API to return the square root of a number
registered at the /sqrt route. The API has the following specifications:
• The number to find the square root for should be provided as a query
argument named num
• If the number is not provided, a 400 error response should be returned
to the user explaining the reason for the error.
• If the input number is invalid (such as a negative number), a 400 error
response should be returned to the user explaining the error.
• A successful result should return a 200 response with a JSON object
containing one key named result that maps to the number value of the
result.
Sample error output:
$ curl --verbose localhost:3000/sqrt
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 3000 (#0)
> GET /sqrt HTTP/1.1
> Host: localhost:3000
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 400 Bad Request
< X-Powered-By: Express
< Content-Type: text/html; charset=utf-8
< Content-Length: 15
< ETag: W/"f-TU573BK7UfJ7GDG0u2GT//FoCx4"
< Set-Cookie:
connect.sid=s%3AkiA1DzCN3TtaaWeR3U0P2fT53C55ULwU.9cFwdoSU7f0RuhZ%2B%2FcRucYk
cKF2S9PC%2B5Sn1pcBCOGk; Path=/; HttpOnly
< Date: Mon, 11 May 2020 03:26:28 GMT
< Connection: keep-alive
<
* Connection #0 to host localhost left intact
Number required* Closing connection 0
Implementation Notes
Start off with the home page. You can generate the express application
with any view templating system preferred, but I recommend using
Handlebars. Required reading: https://handlebarsjs.com/guide/#whatis-handlebars
Getting the corporate jargon is done similarly to how we have been
doing it on the client side. We have been using Browser
implementations of the fetch API so far, but there is an implementation
developed for Node.js on the backend as well named node-fetch.
Before starting the session work, knock out the square root API.
Register a route handler for /sqrt that behaves according to
specification. See documentation for sending a response. Test it using
your preferred tool of choice (e.g. your browser, Postman, curl,
and more.)
Finally finish the session work by setting up a route that the user can
POST their form data to. That router handler should add the user's
input to the session state. The next time the home page is requested,
the list of items in the session should be passed into the template
rendering engine to generate the numbered list. Required
Reading: express-session documentation & example at bottom.
Extra Credit
+5 points will be provided for the extra credit. The extra credit should
be submitted as a separate submission (Homework 6 - HTTP Backend
Extra Credit).
The purpose of the extra credit on this assignment is to use an external
session store instead of the default in-memory one for the basic
configuration. As discussed in the lecture, this will mean that multiple
running instances of the application behind a load balancer will function
correctly because the session will be stored in a centralized shared
database of some kind. You can choose any external database you are
comfortable with, but keep in mind that you will need to include any
set up instructions so that I can recreate the setup on my local
machine. So if you're going to be using some kind of crazy Oracle SQL
database set up... I will most likely not be able to accept the extra
credit. I recommend following the KISS principle here (keep it stupid
simple). You can use Redis, as it's simple to install and use (demo
provided at end of lecture.) Or something even simpler would be to just
use a plain old file on the filesystem
- https://www.npmjs.com/package/session-file-store
To test this, you will need to set up a load balancer. So you can set up
any HTTP load balancer you would like to distribute requests evenly
between the two running applications. Nginx was provided as an
example in class, but one could also use something like PM2 which will
probably be a lot simpler and have less configuration.
Please use Piazza to ask any questions!