ITEC 325 2016fall ibarland

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client-and-server-2
intro: web requests and responses

recall: So, the essence of the situation is that the server and browser are functions with the type-signatures:
server: string_url → string_html
browser: string_html → void.

Looking more closely

For this class, you'll need a browser with good debug-tools built in. For Firefox, there is an extension “Firebug”; I'll demo a couple of Chrome's built-in tools. We will not worry about supporting old browers (e.g. old versions of IE).

≡ » More Tools » Developer Tools
We'll look briefly at the "Elements" tab, but today we're mostly concerned with the "Network" tab, and clicking on particular files. In particular, viewing the Request Headers and Response Headers.

Together in class: Spend 15min looking at examples.

Btw, here are the official HTTP response codes, or the cat-picture version.

the real upshot: So, the essence of the situation is actually that the server and browser are functions with the type-signatures:
server: http-request-packet → http-response-packet (where the first packet contains the URL, and the second packet contains the html response);
browser: http-response-packet → void.

Further things to consider (if not today, then perhaps later:)

• starting up at Starbucks, when you get 'welcome to our wireless; please agree to our terms'.
• telling my phone to use RUWireless, even not in browser a page comes up w/ "please authenticate"
• Q: are URLs case-sensitive? How might you experiment, to find out?
• What is the file that gets looked up, by the www.radford.edu web server? By php.radford.edu ?
• sites that pop up 20 other windows (usually adverts)? Whose fault is that?
• Referring page is often provided, when making a request. How is this a security leak?
  An actual example: Suppose a hiring committee has a wiki with their comments, and use “privacy through obfuscation”: they don't set up a password, but they do use an un-guessable URL.
• When you start typing a google-request, it auto-completes. What's happening? (What info is being sent, and when?)

        - ACTUAL: server-side computation (via Ajax):
               on each keystroke, a transaction is happening, and google.com computes the completion
               (for *every* google visitor in the world, yikes, is that a lot of bandwidth?)
  
        - What are some other *hypothetical* was this could be handled?
          - client-side: the server includes the top 10,000 most popular searches,
              and the client javascript uses that to determine the auto-completion.
              (This wouldn't explain the .)
  
            That would be an expensive load-time on every page!  How might we use this approach but
              try to avoid having 'google.com' be a huge download every time?
  
            How about: only include that dictionary on the *first* visit to google.com,
              and have the client javascript write it to a file;
              then on subsequent visits this
  
            This requires something additional though: How does google know if this is the *first*
              time I'm visiting, or if I've visited previously and therefore I already have 
              the set of common-searches cached?
              We'll discuss cookies later, which solve this.
          
            

• How do ad blockers work? ad blockers attack, and counter-attacks

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©2016, Ian Barland, Radford University Last modified 2016.Aug.30 (Tue)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu