.. include:: <s5defs.txt>

================
 The Zen of Web
================

Anand Chitipothu
----------------

.. footer:: PyCon India 2010 / September 25-26, 2010

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
==============================

.. class:: incremental

* 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?
==========