Held: Thursday, 17 April 2014

Back to Outline 10 - Server-Side Programming with PHP. On to Outline 12 - SQL.

Summary

We continue our explorations of PHP, considering mostly conceptual issues.

Related Pages

• Examples: examples/php
• Examples: examples/cgi
• EBoard 11 (Source 11) (HTML 11) (PDF 11)

Overview

• The client-server model, revisited.
• Detour: CGI scripts.
• Why write server-side scripts, anyway?
• Dangers of server-side scripts.
• Storing and retrieving data, a simple approach.

Administrivia

• We'll look at some of the things you built.
• Remember: Pioneer Weekend is this weekend!
• Next homework: Find an online SQL Tutorial, do the tutorial, and enter a few key points you learned.

Our Model

• Server
  • Serves pages
  • Serves data
  • Holds resources
  • Does computation (with PHP or other server-side language)
  • Etc.
• Client
  • Shows content
  • Does computation (with Javascript or ...)
  • Sends requests to server (for pages

Detour: CGI Scripts

• On many servers, you can write server-side scripts in essentially any programming language.
• Issue one: You need a short header that includes at least a Content-type declaration. Follow the header with a blank line. Content-type: text/html
• Issue two: Suffix should be .cgi.
• Issue three: How do you get form data? (Do you need form data?)
  • Lots of libraries.
• We'll look at a few examples.

Server-Side vs. Client-Side, Revisited

• Why write client-side scripts?
• So far, the only thing we've come up with was "large amounts of data".
  • But an interactive client might be able to query a good database server for the subset of the data it needs.
• So why else?
• Changing a database should need password. Don't want to provide password to client.
• Some kinds of computation may be more natural.
• Other resources available on the client (what?)
  • Sam's standard search feature.

Dangers of Client-Side Scripting

• Places a burden on your servers
  • Web server: Additional computation (vector for DoS)
  • File server: Additional file requests (vector for frustration)
  • ...
• Potential security leaks
  • Can someone abuse your feature by giving unexpected input?
• MathLAN specific: Difficult (impossible) to have private passwords.
• ...

Simple Databases

• Suppose you want to store some simple data for your script. How might you do it? (No database server; all you get is the filesystem.)