3 - Web Computing, Server Organization

Question 1

How does HTTP connection work for client and server?

Answer 1

1. Client opens connection, sends request to HTTP server
2. Server sends response
3. Server closes connection

Question 2

What are the 3 parts of the HTTP request?

Answer 2

1. message type (start line)
2. header lines, followed by blank line
3. body

Question 3

What are the 3 parts of the message type?

Answer 3

1. Request type (GET, POST, PUT, etc.)
2. Absolute path
3. HTTP version

Question 4

What are some useful headers?

Answer 4

content-length - required if sending a body
Content-Type - what’s in body
User-Agent - browser type
Referer[sic] - where it came from

Question 5

What are the status codes meanings? (Each 100 level)

Answer 5

100s - info
200s - success
300s - redirects
400s - client errors
500s - server error

Question 6

What is a GET?

Answer 6

Basic web server sends files in response to a request

Question 7

What is a POST?

Answer 7

Send data to server (login, forum post reply)

• Should make a NEW item

Question 8

How to parse a GET?

Answer 8

Get the text

• fetch the file, make some headers, and reply

Question 9

How to parse a POST?

Answer 9

something with JSONs - check notes

• encode content into key/value pairs
• put encoded data into body
• POST it

Question 10

How do you create “state”? in HTTP?

Answer 10

Cookies!
- server sets cookies in browser
- browser sends those cookies with every response

Question 11

What are some ways so that we don’t change pages all the time?

Answer 11

SPA - single page application

AJAX - async. Javascript and XML

• send a request “behind the scenes” update the HTML of the page (Domain Object Model)

Question 12

How do we avoid keeping username/password in our cookie and remove them?

Answer 12

• we can set the “Set-Cookie” of the password to an expiry date in the past

Question 13

For path /user/11, what would GET, POST, PUT, and DELETE do?

Answer 13

GET - fetch user info
POST - (doesnt make sense, we post a user to create one)
PUT - update user
DELETE - remove/disable user

Question 14

What is a safe method?

Answer 14

GET, HEAD, OPTIONS, TRACE

• allows for optimization, usually read only and doesn’t change anything so we can cache this info

Question 15

What does idempotent mean?

Answer 15

No matter how many times it’s done, the result is the same

• all safe methods are idempotent, but not vice versa

Question 16

Think about adding a discussion post. Write the methods + data send to create these posts:
1) Go to UMLearn
2) Log into UMLearn
3) Move to 3010 via waffle menu
4) Add a discussion thread
5) update spelling mistake in thread

Answer 16

1) GET
2) POST
3) GET
4) POST
5) POST
6) POST -> why post for 6? Gives info of what you’re changing, no guarantee if its a new post or an update

Question 17

Why aren’t Form POSTs not used as much anymore?

Answer 17

• we don’t want to see the browser completely refresh (complete changes take many resources
• replaced with XHR

Question 18

Why shouldn’t we just set the full username and password as a cookie?

Answer 18

If your session is open, someone can just check the cookies

• serverside could see this but they shouldn’t

Question 19

Why is API preferred?

Answer 19

• decouples frontend from backend
• can have multiple front-ends (app, web, watch, etc.)
• simple, lightweight, subdivide load
• better organization

Question 20

What are the pros and cons of server pages (SSR)

Answer 20

pros:
- better SEO (scraper gets everything)
- doesn’t need JS to load everything

cons:
- lots of server load
- lots of time for client to receive data

Question 21

Why is PHP good, and why is it bad?

Answer 21

Good:
- returns dynamic content precomputed by server

Bad:
- too many layers in one (scripts + front-end combined)
- adding plugins into wordpress is insecure (code you didn’t write is on your server, better trust it)