WebFund 2013F Lecture 7

Audio from the lecture given on September 30, 2013 is available here.

Note

September 30

• cookies
  • text document
  • saves info on what you were doing on site
• stateless
  • HTTPS
  • SSH
• what can server do to keep track of client?
  • Cookies!
    • Something the server sets
    • sent along later
  • Encode information in the url itself
    • that will say what this session identifier is
• Server can't trust anything the client sends
• webrequests are stateless
• How to make sure the user doesn't mess with your cookies
  • have to be encoded
    • cookies should look like garbage
    • if you can hand edit the cookie you are doing something really dumb
• state is being passed around in url
• remote procedure calls
  • a program calling another and passing stuff around
  • ie. like buttons on webpages
• File:Http://homeostasis.scs.carleton.ca/wiki/index.php/File:Sept30.jpg
• block
  • running (on a 4 core processor you could have 4 processes running simultaneously)
  • ready (waiting for a free processor)
  • waiting on I/O (blocked until something has happened)
• synchonous I/O
  • read (b)
  • what happens here?
    • Program went to sleep and is woken up
    • could be doing other things here instead of giving up the CPU!
    • Not efficient to switch between processes
  • scanf(b)
    • only makes sense after read is completed
• in node when you do any I/O code it returns immediately
  • asynchronous
  • callbacks solve asynchronous promblem
    • read(s, b, callback)
      • do the read request, and when it's done, here is the code to run encoded in this callback
• node acts like a dispatcher
  • constantly routing data
• classic callback in node
  • listen line
    • has a port number + callback function