10/20/1998

The plan for today:

Perl review
Using Java applets
Review of HTML
Review of Apache installation
Introducing Web Security

1. Perl Review ^*

Perl Data Structures
Perl Control Structures
I/O using Perl
Special variables, expressions and functions
Perl shortcuts
Builtin perl functions
Perl Regular Expressions

Perl Data Structures

Scalars: Number, strings...
$name = "John Doe"; $salary = 500.00;
Lists (Arrays): A list of scalars
$#listname : last index of a list
@teams = ("Bulls", "Rockets", "Pacers"); @scores = (42, 45, 50, 35, 40); @weird1 = ("Age", 50, "income", 50000); $scores[3] = 42;
Hash (Associative Arrays)
%weird2 = ("Age", 50, "income", 50000); $weird2{"Age"} = 65;
Inter-structure assignments:
$foo = @scores; %weird3 = @weird1; @weird4 = $weird2

Operations

Scalar arithmetic:
```
+ - ++ -- * /
```
Scalar comparisons:
> < >= <= == !=
Spaceship operator: <=>
String comparisons:
gt lt ge le eq ne
String representations:
- Single-quoted strings: verbatim
  print 'Single quoted: hello$foo@weird1\n';
- Double-quoted strings: replaced
  print "Double-quoted: hello$foo@weird1\n";
Hash operations:
- List of all keys: keys(%weird2)
- Next pair: each(%weird2)

Perl Control Structures (non-repeating)

Blocks: statements within { ... } separated by semicolons

if statements:

if (condition) block
elsif (condition) block
...
else block

Unless statement:
unless (false-condition) block block unless (false-condition)

More Control Structures (Repeating)

While statement:
while (true-condition) block do block while (true-condition)
Until statement:
until (false-condition) block do block until (false-condition)
For statement:
for (initialize; true-condition; update) block
Foreach statement
foreach var (list) block

Perl I/O

I/O (File) Handles: usually all capitals
Special file handles: STDIN, STDOUT, STDERR
Reading:
$foo = <STDIN>; # Read one line from keyboard @jumbo = <STDIN>; # Read all lines into a list
Writing:
print STDERR "This is an error message\n"; printf STDOUT "A formatted Error message: %d: %s\n", $code, $mesg;

Dealing with files

opening files: (using "open")
open(INPUTFILE, "/u/asengupt/apache/logs/access_log"); # Read open(OUTPUTFILE, ">test.out"); # Write
reading and writing:
sampleline = <INPUTFILE>; print OUTPUTFILE "This goes to a file\n";
DBM files:
dbmopen(%a "file", 0644); print $a{$mykey}, "\n"; dbmclose(%a);

Special variables and functions

@ARGV: list of command-line arguments
$0: Name of the perl script
$!: Last error message
chomp(string): chops the last character
shift, unshift take out/put in element in a list (from the left)
push, pop use list as a stack (from the right)
See man perlfunc(1)

Perl shortcuts

The "implied" variable _
As a scalar, $_ represents the "default" scalar:
- The default input and pattern searching space:
  while (<>) { print $_; }
- As default in foreach:
  foreach (@names) { print $_; }
- As default pattern search:
  if /pattern/ { print $_; }
As a list, @_ represents function parameters, etc.
$_ can be omitted: while(<>) { print; }

Perl builtin functions

As described earlier, see man perlfunc
Some useful functions:
- Math functions: abs,sqrt,log,rand,srand
- list functions: push, pop, shift, unshift
- String functions: chomp, index, length, substr
- Advanced string functions: split, join

Perl Regular Expressions

Pattern matching: Does the input match a specific pattern?
Extraction of components from a string based on a specific pattern: Does the input match a specific pattern? If so, extract individual components of the input.
Highly useful in text-based data processing - e.g., dealing with flat-file data, logfiles, system files (such as /etc/passwd), simple data storage and retrieval

Basic use of REs

#!/usr/local/bin/perl

# Open some file for reading, could be STDIN
open(INFILE, "some/filename");

while($line = <INFILE>) {
  if ($line =~ /some_pattern/) {
    # ok, this line matches the pattern.
  }
  else {
    # this line does not match the pattern
  }
}

RE operators

The /pattern/ operator: includes a pattern against which matching is to be performed
The =~ operator: compares a variable with the given pattern.
The s/pattern/string/ operator: can be used with =~ to replace pattern with string.

Types of matches

Simple pattern: /hello/ matches if the given string contains "hello" anywhere. e.g., "hello world", "Joe says hello"
Case insensitive pattern: /hello/i - as above, but the pattern is case insensitive. Matches "hello", "Hello", "hElLo", etc.
Positioned pattern: /^hello/ matches the pattern only if it appears in the beginning of the string. /hello$/ matches at the end.

Single Character Patterns

Any character matches itself e.g., /x/ matches an 'x'
The character . matches any character except a newline (\n)
Character sets: [abcdefgh] matches one of the given characters.
Named lists: [0-9] is the same as [0123456789
Negated set: [^abcdef] matches a character not in the given set
Special characters (any special perl or RE character): \/  \{ \} \[ \] \$ \\ \? \* \+
Predefined character classes: \d (digit), \s (white space character), \D non-digits, \S non-space characters

Multipliers

(p) matches one p - useful for multiplying a complex pattern
p? matches 0 or 1 p
p* matches 0 or more p's
p+ matches 1 or more p's
p{m,n} matches at least m p's, no more than n p's

Exercises From Schwartz:

at least one a followed by any number of b's
any number of backslashes followed by any number of asterisks (any number may be zero)
three consecutive copies of whatever is contained in $whatever
any five characters, including newline

Remembering what matched

It is often necessary to retrieve portions of patterns if they match. (example?)
In Perl REs, this is simply done using "Parenthesis memory variables"
Anything within parenthesis gets automatically assigned to a variable sequentially named as $1, $2, etc..
Example:
if /(pat1)...(pat2)...(pat3)/ { print $1, $2, $3; }

Note: Materials from last year's A348 have been used in this Perl review.

2. Using Java applets (Chapter 12)

Java Basics

The Life of a Java Applet

Obtaining and Installing Applets

Installing Precompiled Applets

Getting Applets

Installing Applets Distributed as Source Code

Embedding Remote Applets in Your Pages
Example from O'Reilly

Testing Applets

The <APPLET> and <PARAM> Tags

<APPLET
  CODE     = name of applet (.class file)
  WIDTH    = width of applet (pixels) 
  HEIGHT   = height of applet (pixels) 
  CODEBASE = URL of applet 
  ALT      = alternate text to display 
  NAME     = applet's name 
  ALIGN    = alignment 
  VSPACE   = extra whitespace above and below the applet 
  HSPACE   = extra whitespace to either side of applet 
>
<PARAM NAME="param 1" VALUE="value 1">
<PARAM NAME="param 2" VALUE="value 2">
  
  ...
  Alternative HTML code to display 
  
</APPLET>

Attributes of the <APPLET> Tag
- CODE (required)
- WIDTH, HEIGHT (required)
- CODEBASE (optional)
- ALT (optional)
- NAME (optional)
- ALIGN (optional)
- VSPACE, HSPACE (optional)
The <PARAM> Tag
Unpaired and contains two required attributes, NAME and VALUE:
```
<PARAM NAME=score VALUE=120>
```
Each PARAM corresponds to a named parameter.
Alternative HTML Content

Useful Java Applets
- Decorations
  - Dynamic Rules
  - Scrolling Marquees
  - Animation
- Navigational Enhancements
  - Button PLUS
  - Image Maps
- Business Graphics
- Slide Shows and Presentations
Boxes
- Interfacing Java with JavaScript
- Debugging Applets
- Are Java Applets Safe?

We also covered writing applets:

The Scribble Applet
The Feedback Applet

3. Review of Basic HTML (Chapter 5)

An HTML document consists of text interspersed with markup tags. Tags never appear in the printed text, but silently guide the browser behind the scenes. Tags are surrounded by left and right angle brackets and often, but not always, occur in pairs.

Escaping: < is used to produce <

Basic HTML Tags

A complete HTML document always begins with the tag <HTML> and ends with the tag </HTML>. Within the document there are two sections: the head, bracketed by <HEAD> and </HEAD> (contains identifying and control information that isn't part fo the displayed text) and the body bracketed by <BODY> and </BODY> (the user readable text)

Header Tags
<H1> through <H6> paired
Paragraphs and Line Breaks
<P> paired or not
Creating HyperText Links
- Using <A> to Create a Link
  <a href="/images/pic1.gif">Relative Link</a>
  <a href="#name">Local Link</a>
- Using <A> to Create a Link target
  <a name="here">Some text</a>
- Using URLs in Links
  <a href="http://www.cc.columbia.edu">External Link</a>
Adding In-Line Images to Pages
<IMG SRC="http://www.cc.columbia.edu/low3.gif">
The ALT Attribute
<IMG SRC="http://www.cc.columbia.edu/low3.gif" ALT="Columbia U">

Combining Links with Images

<A HREF="http://www.cc.columbia.edu"> 
  <IMG SRC="http://www.cc.columbia.edu/low3.gif">
</A>

Boxes:

HTML and SGML
A Brief History of HTML

Advanced Tags

Controlling Text Styles
- EM (emphasis)
- STRONG (strong emphasis)
- VAR (a variable)
- DFN (a definition)
- CITE (a citation)
- ADDRESS (an address)
- CODE (computer code)
- SAMP (sample computer output)
- KBD (a key from the keyboard)
Physical
- I (italic font)
- B (bold font)
- U (underline)
- TT (typewriter font, monospaced)
- STRIKE (strike-through text)
- BIG (big font)
- SMALL (small font)
- SUB (subscript)
- SUP (superscript)
Related Tags
- BASEFONT
- FONT
Special Text Characters
Y is Y (ASCII code between # and ;).
Control over Paragraph Formatting
- Alignment
- Special-Purpose Paragraph Styles
  - <BLOCKQUOTE>
  - <PRE>
  - <HR>

Lists

Ordered, unordered.

<ul> 
  <li> Item 1 
  <li> Item 2 
  <li> Item 3 
</ul>

Definition lists:

<DL>
  <DT> Term 1
  <DD> Definition of term 1

  <DT> Term 2
  <DD> Definition of term 2
</DL>

Controlling the Size and Position of In-Line Images
- HEIGHT, WIDTH
- ALIGN (TOP, MIDDLE, LEFT, RIGHT, TEXTTOP, ABSMIDDLE etc).
Controlling the Global Appearance of a Document
- <BODY BGCOLOR=white>
- <BODY BACKGROUND="http://www.cc.columbia.edu/low3.gif">
Tables
All tags are paired and have params.
- TABLE (BORDER, CELLPADDING etc.)
- TR (begin/end row)
- TD (begin/end cell)
- TH (cell with header text)
- CAPTION (define a caption for the table)
Miscellaneous HTML Tags
- Comments
- ISINDEX (simplest form)
- BASE (base URL)
- META (varia, HTTP_EQUIV)
Putting It All Together

Frames

There's a similarity between frames and images and applets in some sense.

<FRAMESET ROWS="45%,45%,10%">
  <FRAME SRC="text.html" NAME="text">
  <FRAME SRC="figure1.gif" NAME="figure">
</FRAMESET>

4. Review of Apache Installation

Setting Up the Server ad Document Roots
We've covered this in the lab and in lecture 3
Also inthe same lecture:
Basic Configuration
Starting and Stopping Apache
Also protecting the server against machine reboots with Steve Kinzler's starthttpd and crontab
Customizing Apache

5. Introducing Web Security

The Problem
The Aproaches