The Zen of Web

Anand Chitipothu

World Wide Web

Key Concepts:

• Uniform Resource Locators
• Hyper Text
• Hyper Text Transfer Protocol

Uniform Resource Locators

http://in.pycon.org/2010/talks/44-the-zen-of-web

http://docs.python.org/tutorial/

http://en.wikipedia.org/wiki/Guido_van_Rossum

Hyper Text

The <a href="http://python.org">Python
programming language</a> was created by
<a href="http://en.wikipedia.org/wiki/Guido_van_Rossum">
Guido vas Rossum</a>.

HTTP: Sample Request

GET /helloworld.txt HTTP/1.1
User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
Host: anandology.com
Accept: */*

HTTP: Sample Response

HTTP/1.1 200 OK
Content-Type: text/plain
Accept-Ranges: bytes
ETag: "2838438748"
Last-Modified: Fri, 24 Sep 2010 18:28:17 GMT
Content-Length: 14
Date: Fri, 24 Sep 2010 18:29:34 GMT
Server: lighttpd/1.4.19

Hello, world!

How to Build Web Applications?

Let There be Resources

• Design your webapp around resources, not actions.
• Give an URL for each resource.

Design Beautiful URLs

Beautuful URLs:

• never change
• readable
• recognizable
• rememberable (?)

Understand HTTP Methods

• GET - Requests a resource.
• POST - Submits data to a resource.
• PUT - Updates a resource.
• DELETE - Deletes a resource.

GET should not have side-effects and PUT and DELETE should be idempotent.

Avoid Server-Side Sessions

HTTP is designed to be stateless.

Stateful Conversation

client: This is Anand and my password is secret.
        Do I have any new emails.
server: Hello Anand, you have 2 new emails.
client: please show me the first one.
server: blah blah blah!
client: and the next one please!
server: blee blee blee!
client: Thank you server, I'm leaving now.
server: bye!

Stateless Conversation

client: This is Anand and my password is secret.
        Do I have any new emails.
server: Hello Anand, you have 2 new emails,
        email-x and email-y.
client: This is Anand and my password is secret,
        please show me email-x.
server: blah blah blah!
client: This is Anand and my password is secret,
        please show me email-y.
server: blee blee blee!
client: Thank you server, I'm leaving now.
server: bye!

Shopping Cart without Sessions

• Make shopping cart a resource
• Give it a URL
• Link it with user account

Support Multiple Formats

Request:

GET / HTTP/1.1
Accept: application/json
...

Response:

HTTP/1.1 200 OK
Content-Type: application/json
...

Support Multiple Languages

Request:

GET /hello HTTP/1.1
Accept-Language: te,kn;q=0.8,en;q=0.5
...

Response:

HTTP/1.1 200 OK
Content-Language: te
...

Compress When Possible

Request:

GET / HTTP/1.1
Accept-Encoding: gzip, deflate
....

Response:

HTTP/1.1 200 OK
Content-Encoding: gzip
Vary: Accept-Encoding
...

Provide Caching Info

Request:

GET / HTTP/1.1
...

Response:

HTTP/1.1 200 OK
Cache-Control: public
Last-Modified: ...
E-Tag: "..."

Summary

• Let there be resources
• Design beautiful URLs
• Understand HTTP methods
• Avoid server-side sessions
• Support multiple formats
• Support multiple languages
• Compress when possible
• Provide caching info

Questions?