Zend%20Certification%20REVIEW%20Document

October 18-21, 2005
San Francisco, CA

Zend PHP Certification Tutorial

Marco Tabini
php|architect

marcot@tabini.ca
www.phparch.com

October 18, 2005

Hyatt Regency San Francisco Airport Burlingame, CA

Welcome!

• A few words about me
• A few words about what we’ll be covering
 This is not a PHP tutorial!
 I expect that you already have some PHP experience
 Goals of this tutorial
 Structure

Oct. 18, 2005 2

A bit about the exam

• We’ll talk about the exam proper at the end of
the tutorial
• The exam covers only PHP 4 — not PHP 5
• If you are taking the exam here, it will be on
paper, not on a computer
• The exam tests your knowledge of PHP, not your
knowledge of programming

Oct. 18, 2005 3

Part I - The PHP Language

• What we’ll cover in this section:
 PHP Tags
 File inclusion
 Data types & typecasting
 Variables and constants
 Operators
 Conditionals
 Iteration
 Functions
 Objects

Oct. 18, 2005 4

Tags

• Tags “drop” you out of HTML and into PHP mode
• PHP recognizes several types of tags:
 Short tags: <? ?>
 Special tags: <?= ?>
 Regular tags: <?php ?>
 ASP tags: <% %>
 HTML script tags: <script language=”PHP”> </script>

Oct. 18, 2005 5

File Inclusion

• External files can be included in a script using
either include() or require()
• Both are constructs, not functions:
 include (‘myfile.php’); or include ‘myfile.php’;
• They behave in exactly the same way, except
for how they handle failure
 include generates a warning
 require throws an error
 Upon inclusion, the parser “drops off” of PHP mode
and enters HTML mode again
• Variants: include_once()/require_once()
 Prevent multiple inclusions from within the same script
Oct. 18, 2005 6

Data Types

• PHP is not a typeless language
• It supports many different data types
• It is loosely typed
• The interpreter automatically “juggles” data
types as most appropriate
• “Most appropriate” doesn’t necessarily mean
always appropriate

Oct. 18, 2005 7

Data Types — Numeric/Boolean

• PHP recognizes two types of numeric values:
 Integers
 Floats
• Boolean values are used for logic operations
 True / False
 Easily converted to integers: non-zero / zero
• Result type of operations depends on types of
operands
 For example: int + int == int — int / float == float
int / int == int or float
• Numbers can be specified in a number of ways:
 Decimal (123), Hexadecimal (0x123) and Octal (0123)
Oct. 18, 2005 8

Data Types — Strings

• Strings are heterogeneous collections of single-
byte characters
 They don’t necessary have to be text
 They can represent Unicode as well, but cannot be
manipulated by the standard PHP functions
• PHP supports three ways of declaring strings:
 Single quotes: ‘test 1 2 3’
 Double quotes: “test 1 2 3n”
 Heredoc syntax: <<<EOT test 1 2 3
EOT;
• Main differences:
 Support for variable substitution / escape sequences
 All strings support newline characters
Oct. 18, 2005 9

Data Types — Arrays

• Arrays are ordered structures that map a key to
a value
• Values can be of any type—including other
arrays
• Keys can be either integer numeric or strings
 Keys are unique
 Negative numbers are valid keys

Oct. 18, 2005 10

Data Types — Resources / Null

• Resources are special containers that identify
external resources
 They can only be operated on directly as part of
logical operations
 They are usually passed to C-level functions to act on
external entities
 Examples: database connections, files, streams, etc.
• NULL is a special value that indicates... no value!
 NULL converts to Boolean false and Integer zero

Oct. 18, 2005 11

Data Types — Objects

• Objects are containers of data and functions
 The individual data elements are normally called
properties
 The functions are called methods
 Individual members (methods / properties) of an
object are accessed using the -> operator
 We’ll cover objects in more depth later in this section

Oct. 18, 2005 12

Typecasting

• PHP’s ability to juggle among different data
types is not entirely dependable
• There are circumstances in which you will want
to control how and when individual variables
are converted from one type to another
• This is called Typecasting

Oct. 18, 2005 13

Typecasting — Integers

• You can typecast any variable to an integer
using the (int) operator:
 echo (int) “test 1 2 3”;
• Floats are automatically truncated so that only
their integer portion is maintained
 (int) 99.99 == 99
• Booleans are cast to either one or zero:
 (int) TRUE == 1 — (int) FALSE == 0
• Strings are converted to their integer equivalent:
 (int) “test 1 2 3” == 0 , (int) “123” == 123
 (int) “123test” == 123 // String begins with integer
• Null always evaluates to 0
Oct. 18, 2005 14

Typecasting — Booleans

• Data is cast to Boolean using the (bool)
operator:
 echo (bool) “1”;
• Numeric values are always TRUE unless they
evaluate to zero
• Strings are always TRUE unless they are empty
 (bool) “FALSE” == true
• Null always evaluates to FALSE

Oct. 18, 2005 15

Typecasting — Strings

• Data is typecast to a string using the (string)
operator:
 echo (string) 123;
• Numeric values are converted to their decimal
string equivalent:
 (string) 123.1 == “123.1”;
• Booleans evaluate to either “1” (TRUE) or an
empty string (FALSE)
• NULL evaluates to an empty string
• Numeric strings are not the same as their integer
or float counterparts!

Oct. 18, 2005 16

Typecasting — Arrays / Objects

• Casting a non-array datum to an array causes a
new array to be created with a single element
whose key is zero:
 var_dump ((array) 10) == array (10);
• Casting an object to an array whose elements
correspond to the properties of the object
 Methods are discarded
• Casting a scalar value to an object creates a
new instance of stdClass with a single property
called “scalar”
 Casting an array to an object create an instance of
stdClass with properties equivalent to the array’s
elements
Oct. 18, 2005 17

Identifiers / Variables / Constants

• Identifiers are used to identify entities within a
script
 Identifiers must start with a letter or underscore and
can contain only letters, underscores and numbers
• Variables
 Containers of data
 Only one data type at any given time
 Variable names are case-sensitive identifiers prefixed
with a dollar sign ($my_var)
 Variables can contain references to other variables
• Constants
 Assigned value with declare(), cannot be modified
 User-defined constants are not case-sensitive
Oct. 18, 2005 18

Substitution / Variable variables

• Variables can be substituted directly within a
double-quoted or Heredoc string
 $a = 10;
echo “$a is: $a”; // Will output $a is: 10
• Variables values can be used to access other
variables (variable variables):
 $a = “b”;
$b = 10;
echo $$a; // will output 10

Oct. 18, 2005 19

Statements

• Statements represent individual commands that
the PHP interpreter executes
 Assignment: $a = 10;
 Construct: echo $a;
 Function call: exec ($a);
• Statements must be terminated by a semicolon
 Exception: the last statement before the end of a PHP
block

Oct. 18, 2005 20

Operations

• PHP supports several types of operations:
 Assignment
 Arithmetic
 Bitwise
 String
 Comparison
 Error control
 Logical

Oct. 18, 2005 21

Operations — Assignment

• The assignment operator ‘=’ makes it possible to
assign a value to a variable
 $a = 10;
• The left-hand operand must be a variable
 Take advantage of this to prevent mistakes by
“reversing” logical operations (as we’ll see later)
 10 = $a; // Will output error

Oct. 18, 2005 22

Operations — Arithmetic

• These operators act on numbers and include the
four basic operations:
 Addition: $a + $b
 Subtraction: $a - $b
 Multiplication: $a * $b
 Division: $a / $b
• Remember that dividing by zero is illegal
• They also include the modulus operator
 Determines the remainder of the integer division
between two numbers: 10 % 4 = 2
 Unlike proper modulus, PHP allows a negative right-
hand operand
• 10 % -4 = 2
Oct. 18, 2005 23

Operations — Bitwise

• Bitwise operations manipulate numeric values at
the bit level
 AND (&) — set bit if it is set in both operands
• 1 & 0 == 0
 OR (|) — set bit if is is set in either operand
• 1 | 0 == 1
 XOR (^) — set bit if it is set in either, but not both
• 1 ^ 1 == 0
 NOT — invert bits
• ~0 == -1
 Shift left/right (<</>>) - shift bits left or right
• 1 << 2 ==4 == 8 << 1
• Excellent shortcuts for integer multiplications by powers of
two
Oct. 18, 2005 24

Operators — Combined

• Numeric and bitwise operators can be
combined with an assignment:
 $a += 10 is equivalent to $a = $a + 10;
• This does not apply to the NOT operator, since
it’s unary

Oct. 18, 2005 25

Operators — Error Control

• PHP support several different levels of errors
• Error reporting can be tweaked either through
PHP.INI settings or by calling error_reporting().
• Remember that the exam assumes the default
“recommended” INI file
 Warning and Notices are not reported!
• Error reporting can be controlled on a
statement-by-statement basis using the @
operator:
 @fopen ($fileName, “r”);
 This only works if the underlying functionality uses PHP’s
facilities to report its errors

Oct. 18, 2005 26

Operators — Inc/Dec and String

• Incrementing and decrementing operators are
special unary operators that increment or
decrement a numeric variable:
 Postfix: $a++
 Prefix: ++$a
 You cannot perform two unary operations on the same
variable at the same time— ++$a-- will throw an error
• The only string operation is the concatentaion
(.), which “glues” together two strings into a third
one
 “a” . ‘b’ == ‘ab’

Oct. 18, 2005 27

Operators — Comparison / Logical

• Comparison operators are used to compare
values:
 Equivalence: == !=
• Equivalence operators do not require either of their
operands to be a variable
 Identity: === !==
 Relation: <, <=, >=, >
• Logical operators are used to manipulate
Boolean values:
 AND (&&) — TRUE if both operands are TRUE
 OR (||) — TRUE if either operand is TRUE
 XOR (xor) — TRUE if either operand is TRUE, but not both
 NOT (!) — Reverses expression
Oct. 18, 2005 28

Operator Precedence

• The precedence of most operators follows rules
we are used to—but not all of them
 Example: “test ” . 1 + 10 . “ 123” == “1 123”
• There are two variants of logical operators
 The “letter” operators AND, OR differ from their
“symbol” equivalents &&, || in the fact that they have
lower precedence

Oct. 18, 2005 29

Conditionals — if-then-else

• Conditionals are used to direct the execution
flow of a script
 if (condition) {

... statements ...

} else {

... statements ...

}
• Alternative short form:
 $a = (cond) ? yesvalue : novalue;

Oct. 18, 2005 30

Conditionals — case/switch

• Case/switch statements allow you to verify a
single expression against multiple expressions:
 switch (expr) {
case expr1 :
... statements ...
break;

case expr2:
... statements ...
break;

default:
... statements ...
break;
}
Oct. 18, 2005 31

Iterators — While

• While loops are the simplest form of iterator; they
allow you to repeat a set of statements while a
condition evaluates to TRUE:
 while (expr) {

... statements ...

}

Oct. 18, 2005 32

Iterators — Do...while

• Do...while loops are equivalent to while loops,
but the condition is evaluated at the end of the
loop, instead of the beginning:
 do {

... statements ...

} while (expr);
 This means that the statement block is executed at
least once

Oct. 18, 2005 33

Iterators — For and Foreach

• While and do...while are the only indispensible
iterators in any language.
• For convenience, PHP includes for loops:
 for (initial; condition; incremental) {
... statements ...
}
• Foreach loops can be used to iterate through an
aggregate value:
 foreach ($array as $k => $v) {
... statements ...
}
 Important: $k and $v are assigned by value!
 Works on objects, too!
Oct. 18, 2005 34

Iterators: continuing/breaking

• Loops can be continued using the continue
construct:
 while ($a == 1) { if ($b == 2) continue; }
• Loops can be interrupted using the break
construct:
 while ($a == 1) { if ($b == 2) break; }
• Multiple nested loops can be continued/broken
at once:
 continue 2;
 Remember the semicolon at the end of the break or
continue statement!

Oct. 18, 2005 35

Functions

• Functions allow for code isolation and reuse
 function myfunc (&$arg1, $arg2 = 10)
{
global $variable;

... statements ...
}

echo myfunc (10);
• Pay attention to variable scope!
• Functions can support variable parameters:
 func_num_args();
 fung_get_arg();

Oct. 18, 2005 36

OOP: Classes and Objects

• Classes define the structure of objects:
 class myClass {
var $myVar;

function myClass() { // constructor
$this->myVar = 10;
}
• Objects represent individual instances of a class:
 $a = new myClass;
$a->myVar = 11;
• Objects support dynamic methods and
properties:
 $obj->$var();
Oct. 18, 2005 37

OOP: Classes as Namespaces

• PHP does not support namespaces (this is true
also of PHP 5), but classes can simulate their
behaviour:
 class class encode {
    function base64($str)
    {
        return base64_encode($str);
    }
}

echo encode::base64("my string");

Oct. 18, 2005 38

OOP: Objects and References

• In PHP 4, objects receive no special treatment:
they are essentially arrays with embedded
functions
 This means that references to objects must be handled
with care.
• Passing/assigning an object is normally done by
value, not by reference, even when using new

Oct. 18, 2005 39

OOP: Objects and References

• The $this special variable cannot be passed by
reference, even if you use the & operator
 However, you can embed $this in a global array and
circumvent this problem (albeit in a horrible way):
• class obj {
var $prop;
    function obj($arg)
    {
        global $obji; // import variable into local scope
        $obji[] = $this; // get a copy of current class
        $this->prop = $arg;
    }
}
$obj = new obj(123);
var_dump($obj->prop != $obji[0]->prop); // FALSE

Oct. 18, 2005 40

OOP: Inheritance

• Inheritance makes it possible to create classes
(“subclasses”) that are based on other classes
(“superclasses”):
 class base {
    function base()
    {
    }
}

class main extends base {
    function main()
    {
        parent::base();
    }
}
Oct. 18, 2005 41

OOP: Object Serialization

• Serialization is the process of reducing an
aggregate (array or object) to a scalar (string)
• Serialization is a mostly automatic process, but
for objects it is possible to exercise a certain
amount of control:
 __sleep()
 __wakeup()
 Useful for dynamically-generated properties, such as
database connections and file descriptors
 Classes must be declared before their instances are
unserialized

Oct. 18, 2005 42

Q&A Time

• What is the difference between print and echo?

• Under what circumstance is it impossible to
assign a default value to a parameter while
declaring a function?

• How does the identity operator === compare
two values?

Oct. 18, 2005 43

Answers

• What is the difference between print and echo?

• echo is a construct
• print is a function

Oct. 18, 2005 44

Answers

• Under what circumstance is it impossible to
assign a default value to a parameter while
declaring a function?

• Always, as long as the parameter is not being
passed by reference

Oct. 18, 2005 45

Answers

• How does the identity operator === compare
two values?

• It first compares the type, then the value

Oct. 18, 2005 46

Part II — Strings and Arrays

 Comparisons
 Basic search and replace
 Regular Expressions
 String functions and formatting
 Accessing arrays
 Single- and multidimensional arrays
 Array iteration
 Array sorting
 Array functions and manipulation
 Serialization

Oct. 18, 2005 47

String Comparison

• String comparison is mostly trivial, but can
sometimes be tricky
 The equivalence operator should be used when you
know that you are comparing two strings—or when
you don’t care about cases like this:
• “123test” == 123 == TRUE!
 The identity operator should be otherwise used every
time you know that you want to compare two strings
without letting PHP juggle types
• PHP also provides function-based comparison:
 strcmp()
 strcasecmp()
 strncmp() and strncasecmp()
Oct. 18, 2005 48

Basic String Searching

• strstr() (aliased into strchr()) determines whether
a substring exists within a string:
 strstr (“PHP is a language”, “PHP”) == true
 stristr() provides a case-insensitive search
• strpos() will return the location of a substring
inside a string, optionally starting from a given
position:
 strpos ($haystack, $needle, $pos)
 Beware of zero return values!
 There is no stripos() in PHP 4!
• Reverse search is done with strrchr() / strrpos()

Oct. 18, 2005 49

Counting Strings

• The length of a string is determined with strlen()
 Do not use count()!
• You can count words inside a string using
str_word_count():
 str_word_count ($str, $n);
 $n == 1 — Returns array with words in order
 $n == 2 — Returns array with words and positions
• substr_count() can be used to count the number
of occurrences of a given substring:
 substr_count (“phpphpPHP”, “php”) == 2

Oct. 18, 2005 50

Formatting Strings

• Most of the time, strings can be formatted using
a combination of concatenations
• In some cases, however, it is necessary to use
special functions of the printf() family
 printf() — outputs formatted strings to STDOUT
• printf (“%d”, 10);
 sprintf() — returns the formatted string
• $a = sprintf (“%d”, 10);
 fprintf() — outputs formatted strings to a file descriptor
• fprintf ($f, “%d”, 10);
 vprintf(), vsprintf() — take input from array
• vprintf (“%d”, array (10));
• $a = vsprintf (“%d”, array (10));
Oct. 18, 2005 51

Formatting Strings

• % - a literal percent character.
• b – integer presented as a binary number
• c – integer (ASCII value)
• d – integer (signed decimal number)
• e – number in scientific notation (Ex. 1.2e+2)
• u – integer (unsigned decimal number)
• f – float as a floating-point number.
• o – integer (octal number).
• s – string
• x – hexadecimal number (lowercase letters).
• X – hexadecimal number (uppercase letters).
•
Oct. 18, 2005 52

Accessing Strings as Arrays

• You can access individual characters of a string
as if it were an array
 $s = “12345”;
echo $s[1]; // Outputs 2
echo $s{1}; // Outputs 2
 This works for both reading and writing
 Remember that you cannot use count() to determine
the number of characters in a string!

Oct. 18, 2005 53

Extracting and Replacing

• Substrings can be extracted using the substr()
function:
 echo substr (“Marco”, 2, 1); // Outputs r
 echo substr (“Marco”, -1); // Outputs o
 echo substr (“Marco”, 1, -1); // Outputs arc
• Substrings can be replaced using substr_replace
():
 substr_replace (‘Marco’, ‘acr’, 1, -1) == “Macro”
• The sscanf() function can be used to extract
tokens formatted à la printf() from a string:
 sscanf(“ftp://127.0.0.1”, "%3c://%d.%d.%d.%d:%d");
 Returns array (‘ftp’, ‘127’, ‘0’, ‘0’, ‘1’);
Oct. 18, 2005 54

Multiple Replacements

• str_replace() replaces instances of a substring
with another:
 str_replace (“.net”, “arch”, “php.net”) == “phparch”
• You can perform multiple replacements by
passing arrays to str_replace():
 str_replace(array('apples', 'applesauce', 'apple'),
array('oranges', 'orange-juice', 'cookie'),
“apple apples applesauce”)
 Returns “cookie oranges orangesauce”

Oct. 18, 2005 55

PCRE — Perl Regular Expressions

• Perl Regular Expressions (PCRE) make it possible
to search (and replace) variable patterns inside
a string
• PCRE is usually fast and simple to understand,
but it can also be complicated or slow (or both)
• Regular expressions are matched using the
preg_match() function:
 preg_match ($pcre, $search, &$results)
 preg_match_all ($pcre, $search, &$results)
• Search-and-replace is performed using
preg_replace():
 preg_replace ($pcre, $replace, $search)
Oct. 18, 2005 56

PCRE — Meta Characters

• Meta characters are used inside a regex to
represents a series of characters:
 d — digits 0–9
D — not a digit
w — alphanumeric character or underscor
W — opposite of w
s — any whitespace (space, tab, newline)
S — any non-whitespace character
. — any character except for a newline
• Meta characters only match one character at a time (unless
an operator is used to change this behaviour)

Oct. 18, 2005 57

PCRE — Operators / Expressions

• PCRE operators indicate repetition:
 ? — 0 or 1 time
 * — 0 or more times
 + — 1 or more times
 {,n} — at more n times
 {m,} — m or more times
 {m,n} — at least m and no more than n times
• Parentheses are used to group patterns
 (abc)+ — means “abc” one more times
• Square brackets indicate character classes
 [a-z] means “any character between a and z
 The caret negates a class: [^a-z] is the opposite of the
expression above
Oct. 18, 2005 58

PCRE — An example

• Here’s an example of a PCRE:
 $string = ‘123 abc’;
preg_match (‘/d+s[a-z]+/’, $string);

preg_match (‘/wss/’, $string);

preg_match (‘d{3}s[a-z]{3}’/, $string);

Oct. 18, 2005 59

PCRE — Another Example

• Here’s an example of how to retrieve data from
a regex:
 $email = ‘marcot@tabini.ca”;
preg_match (‘/(w+)@(w+).(w+)/’);

 Will return array (‘marcot@tabini.ca’, ‘marcot’,
‘tabini’, ‘ca’)

Oct. 18, 2005 60

String Splitting and Tokenization

• The explode() function can be used to break up
a string into an array using a common delimiter:
 explode (‘.’, ‘www.phparch.com’);
 Will return array (‘www’, ‘phparch’, ‘com’);
• The preg_split() function does the same thing,
but using a regex instead of a fixed delimiter:
 explode (‘[@.]’, ‘marcot@tabini’ca’);
 Will return array (‘marcot’, ‘tabini’, ‘ca’);

Oct. 18, 2005 61

Word Wrapping

• The wordwrap() function can be used to break a
string using a specific delimiter at a given length
 wordwrap ($string, $length, $delimiter, $break);
• If the $break parameter evaluates to TRUE, the
break occurs at the specified position, even if it
occurs in the middle of a word

Oct. 18, 2005 62

Arrays

• Arrays are created in a number of ways:
 Explicitly by calling the array() function
• array (1, 2, 3, 4);
• array (1 => 1, 2, 3, 5 => “test”);
• array (“2” => 10, “a” => 100, 30);
 By initializing a variable using the array operator:
• $x[] = 10;
• $x[-1] = 10;
• $x[‘a’] = 10;
• The count() function is used to determine the
number of elements in an array
 Executing count() against any other data type
(including objects), it will return 1 (or 0 for NULL)
Oct. 18, 2005 63

Array Contents

• Array can contain any data type supported by
PHP, including objects and other arrays
• Data can be accessed using the array operator
 $x = $array[10];
• Multiple elements can be extracted using the list
function:
 $array = (1, 2, 3);
list ($v1, $v2, $v3) = $array

Oct. 18, 2005 64

Array Iteration

• It’s possible to iterate through arrays in a number
of ways. Typically:
• for ($i = 0; $i < count ($array); $i++) // WRONG!
 $cnt = count ($array)
for ($i = 0; $i < $cnt; $i++)
 Storing the invariant array count in a separate variable
improves performance
• foreach ($array as $k => $v)
 $k and $v are assigned by value—therefore, changing
them won’t affect the values in the array
 However, you can change the array directly using $k:
 $array[$k] = $newValue;

Oct. 18, 2005 65

Array Iteration

• You can also iterate through an array using the
internal array pointer:
 $a = array(1,2,3);

while (list($k, $v) = each($a)) {
echo "{$k} => {$v} ";
  if ($k % 2) { // add entry if key is odd
   $a[] = $k + $v;
  }
} // 0 => 1 1 => 2 2 => 3 3 => 3 4 => 6
 With this approach, operations take place directly on
the array
• Finally, you can use array_callback() to iterate
through an array using a user-supplied function
Oct. 18, 2005 66

Array Keys and Values

• You can check if an element exists in one of two
ways:
 array_key_exists ($array, $key); // Better, but slower
 isset ($array[$key]); // Faster, but has pitfalls
• $a[1] = null;
echo isset ($a[1]);
• You can also check whether a value exists:
 in_array ($value, $array)
• You can extract all the keys and values from an
array using specialized functions:
 array_keys ($array);
 array_value ($array);

Oct. 18, 2005 67

Sorting Arrays

• The sort() and rsort() functions sort an array in-
place
 sort ($array); — rsort ($array)
 Key association is lost—you can use asort() and arsort()
to maintain it
• A more “natural” sorting can also be performed:
 natsort ($array);
 natcasesort ($array);
• Sorting by key is also a possibility:
 ksort();
 krsort();

Oct. 18, 2005 68

Array Functions

• Changing key case:
 array_change_key_case ($a, CASE_LOWER)
 array_change_key_case ($a, CASE_UPPER)
• Randomizing the contents of an array:
 shuffle($array)
• Extracting a random value:
 array_rand ($array, $qty);

Oct. 18, 2005 69

Merge, Diff and Sum

• Merging arrays:
 array_merge ($a, $b[, ...]);
 Later values with the same key overwrite earlier ones
• Diff’ing arrays:
 array_diff ($a, $b[, ...]);
 Returns keys that are not common to all the arrays
 Key association is lost—you can use array_diff_assoc()
to maintain it
• Intersecting:
 array_intersect ($a, $b[, ...]);
• Calculating arithmetic sum:
 array_sum ($array);
Oct. 18, 2005 70

Unique Array Values

• The array_unique() function retrieves all the
unique array values
 array_unique ($array)
 Requires traversal of entire array and therefore
hampers performance

Oct. 18, 2005 71

Arrays as stacks or queue

• The array_push() function pushes a new value at
the end of an array
 array_push ($array, $value)
 Essentially equivalent to $array[] = $value;
• The array_pop() retrieves the last value from an
array:
 $x = array_pop ($array);
• This allows you to use arrays as if they were
stacks (LIFO)
• You can also pull a value from the top of the
array, thus implementing a queue (FIFO)
 $x = array_shift ($array)
Oct. 18, 2005 72

Serializing Arrays

• Like with objects, you can serialize arrays so that
they can be conveniently stored outside your
script:
 $s = serialize ($array);

 $array = unserialize ($s);

 Unserialization will preserve references inside an array,
sometimes with odd results

Oct. 18, 2005 73

Q&A Time

• Given a comma-separated list of values in a
string, which function can create an array of
each individual value with a single call?

• The ________________ function can be used to
ensure that a string always reaches a specific
minimum length.

• Which function would you use to rearrange the
contents of the array (‘a’, ‘b’, ‘c’, ‘d’) so that they
are reversed?

Oct. 18, 2005 74

Answers

• Given a comma-separated list of values in a
string, which function can create an array of
each individual value with a single call?

• explode()
• preg_split() would have also been acceptable

Oct. 18, 2005 75

Answers

• The ________________ function can be used to
ensure that a string always reaches a specific
minimum length.

• str_pad()

Oct. 18, 2005 76

Answers

• Which function would you use to rearrange the
contents of the array (‘a’, ‘b’, ‘c’, ‘d’) so that they
are reversed?

• rsort()
• array_reverse()

Oct. 18, 2005 77

PART III — User Input / Time & Dates

 HTML form management
 File uploads
 Cookies
 Magic Quotes
 Sessions
 Times and dates in PHP
 Formatting date values
 Locale-dependent date formatting
 Date validation

Oct. 18, 2005 78

HTML Form Management

• HTML forms are submitted by the browser using
either GET or POST
 GET transaction data is sent as part of the query string
 POST data is sent as part of the HTTP transaction itself
 POST is often considered “safer” than GET—WRONG!
• POST data is made available as part of the
$_POST superglobal array
• GET data is made available as part of the $_GET
superglobal array
 Both are “superglobal”—in-context everywhere in your
scripts
 If duplicates are present, only the ones sent last end up
in the appropriate superglobal
Oct. 18, 2005 79

HTML Form Management

• Element arrays can also be sending by
postfixing the element names with []
 These are transformed into arrays by PHP
 The brackets are discarded
 A very common (and pernicious) type of security
attack
• You can also specify your own keys by placing
them inside the brackets:
 <input type=”hidden” name=”a[ts]” value=”1”>
 Will result in $a[‘ts’] = 1 being inserted in the
appropriate superglobal

Oct. 18, 2005 80

Uploading Files

• Files are uploaded through a special type of
HTML form:
 <form enctype="multipart/form-data" action="/
upload.php" method="post">
<input type="my_file" type="file" />
<input type="hidden" name="MAX_FILE_SIZE"
value="100000" />
</form>
• An arbitrary number of files can be uploaded at
the same time

Oct. 18, 2005 81

Uploading Files

• Once uploaded, file information is available
through the $_FILES superglobal array
     [my_file] => Array
    (
        [name] => php.gif
        [type] => image/gif
        [tmp_name] => /tmp/phpMJLN2g
        [error] => 0
        [size] => 4644
    )
• Uploaded file can be moved using
move_uploaded_file()
 You can also determine whether a file has been
uploaded using is_uploaded_file()
Oct. 18, 2005 82

Uploading Files

• File uploads are controlled by several PHP.INI
settings:
 file_uploads — whether or not uploads are enabled
 upload_tmp_dir — where temporary uploaded files are
stored
 upload_max_filesize — the maximum size of each
uploaded file
 post_max_size — the maximum size of a POST
transaction
 max_input_time — the maximum time allowed to
process a form

Oct. 18, 2005 83

Cookies

• Cookies are small text strings that are stored
client-side
• Cookies are sent to the client as part of the HTTP
response, and back as part of the HTTP headers
• Cookies are notoriously unreliable:
 Some browsers are set not to accept them
 Some users do not accept them
 Incorrect date/time configuration on the client’s end
can lead to cookies expiring before they are set

Oct. 18, 2005 84

Cookies

• To set a cookie:
 setcookie ($name, $value, $expires, $path, $domain);
 setcookie ($name, $value); // sets a session cookie
• Cookies are then available in the $_COOKIE
superglobal array:
 $_COOKIE[‘mycookie’]
 $_COOKIE is populated at the beginning of the script.
Therefore, it does not contain cookies you set during
the script itself (unless you update it manually)
• You cannot “delete” a cookie
 You can set it to Null or an empty string
• Remember not to use isset()!
 You can expire it explicitly
Oct. 18, 2005 85

$_REQUEST

• $_REQUEST is a superglobal populated from
other superglobals
 You have no control over how data ends up in it
 The variables_order PHP.INI setting controls how data is
loaded into it, usually Get -> Post -> Cookie
• Generally speaking, you’re better off not using it,
as it is a virtual security black hole.

Oct. 18, 2005 86

Magic Quotes

• By default, PHP will escape any “special”
characters found inside the user’s input
• You should not rely on this setting being on (as
most sysadmins turn it off anyway)
• You also (and most definitely) should not rely on
it performing proper input filtering for you
• In fact, supply your own escaping and “undo”
magic quotes if they are enabled!

Oct. 18, 2005 87

Sessions

• Sessions are mechanisms that make it possible
to create a per-visitor storage mechanism on
your site
• Sessions we born—and remain—a hack, so you
can only depend on them up to a certain point
• On the client side, sessions are just unique IDs
passed back and forth between client and
server
• On the server side, they can contain arbitrary
informaiton

Oct. 18, 2005 88

Sessions

• In order to write to a session, you must explicitly
start it
 session_start()
 This is not necessary if session.auto_start is on in your
PHP.INI fil
• You can then write directly into the $_SESSION
array, and the elements you create will be
transparently saved into the session storage
mechanism
 $_SESSION[‘test’] = $myValue

Oct. 18, 2005 89

Sessions

• By default, session data is stored in files;
however, you can specify a number of built-in
filters
• You can also define your own session handlers
in “userland”

Oct. 18, 2005 90

Date Manipulation in PHP

• For the most part, PHP handles dates in the UNIX
timestamp format
 Timestamps indicate the number of seconds from the
UNIX “epoch”, January 1st, 1970
 Not all platforms support negative timestamps (e.g.:
Windows prior to PHP 5.1)
• Timestamps are very handy because they are
just large intergers
 This makes it easy to manipulate them, but not
necessarily to represent them
 They are also handy for time calculations
 For more precision, you can use microtime()

Oct. 18, 2005 91

Date Manipulation in PHP

• Another way of representing dates is through
date arrays using getdate()
 A date array contains separate elements for each
component of a date
 [seconds] => 15 // 0 - 59
[minutes] => 15 // 0 - 59
[hours] => 9 // 0 - 23
[mday] => 4 // 1 - 31
[wday] => 3 // 0 - 6
[mon] => 8 // 1 - 12
[year] => 2004 // 1970 - 2032+
[yday] => 216 // 0 - 366
[weekday] => Wednesday // Monday - Sunday
[month] => August // January - December
[0] => 1091625315 // UNIX time stamp
Oct. 18, 2005 92

Time and Local Time

• The time() function returns the timestamp for the
current time
 time() (no parameters needed)
• Localtime performs similarly, but returns an array
 [0] => 59 // seconds 0 - 59
[1] => 19 // minutes 0 - 59
[2] => 9 // hour 0 - 23
[3] => 4 // day of month 1 - 31
[4] => 7 // month of the year, starting with 0 for January
[5] => 104 // Years since 1900
[6] => 3 // Day of the week, starting with 0 for Sunday
[7] => 216 // Day of the year
[8] => 1 // Is daylight savings time in effect

Oct. 18, 2005 93

More Local Time

• Localtime() can also return an associative array:
 var_dump (localtime(time, 1));
 Outputs:
• [tm_sec] => 1 // seconds 0 - 59
[tm_min] => 23 // minutes 0 - 59
[tm_hour] => 9 // hour 0 - 23
[tm_mday] => 4 // day of month 1 - 31
[tm_mon] => 6 // month of the year, 0 for January
[tm_year] => 104 // Years since 1900
[tm_wday] => 0 // Day of the week, 0 for Sunday
[tm_yday] => 185 // Day of the year
[tm_isdst] => 1 // Is daylight savings time in effect

Oct. 18, 2005 94

Formatting Dates

• Timestamps are great for calculations, but not
for human redability
• The date() function can be used to format a
date according to an arbitrary set of rules:
 date (“Y-m-d H:i:sn”);
 date (‘date: Y-m-d’);
• strftime() provides a printf-like, locale-
dependent formatting mechanism for date/time
values:
 strftime (“%A”, time()); // Prints weekday
 You need to use setlocale (LC_TIME, $timezone) in
order to set the timezone to a particular value

Oct. 18, 2005 95

Creating Dates

• Dates can be created using mktime():
 mktime (hour, min, sec, mon, day, year, daylight)
• Several date-related functions have GMT-
equivalents:
 gmmktime()
 gmdate()
 gmstrftime()
• It is also possible to change the timezone—just
change the TZ environment variable:
 putenv (“TZ=Canada/Toronto”);
 This will be equivalent to EST or EDT

Oct. 18, 2005 96

Interpreting Date Input

• It is also possible to create a timestamp from a
formatted string date using strtotime():
 strotime(“now”);
 strtotime(“+1 week”);
 strtotime(“November 28, 2005”);
 strtotime(“Next Monday”);
• You can also check whether a date is valid by
using the checkdate() function:
 checkdate (month, date, year)
 Automatically accounts for leap years
 Not foolproof—incapable for example, to account for
the Gregorian gap

Oct. 18, 2005 97

Q&A Time

• How would you make a cookie expire in exactly
one hour (assuming that the client machine on
which the browser is set to the correct time and
time zone—and that it resides in a time zone
different from your server’s)?

• What is the simplest way of transforming the
output of microtime() into a single numeric
value?

• If no expiration time is explicitly set for a cookie,
what happens to it?
Oct. 18, 2005 98

Answers

• How would you make a cookie expire in exactly
one hour (assuming that the client machine on
which the browser is set to the correct time and
time zone—and that it resides in a time zone
different from your server’s)?

• Pass time() + 3600 as the expiry

Oct. 18, 2005 99

Answers

• What is the simplest way of transforming the
output of microtime() into a single numeric
value?

• array_sum (explode (‘ ‘, microtime()));

Oct. 18, 2005 100

Answers

• If no expiration time is explicitly set for a cookie,
what happens to it?

• It expires at the end of the browser’s session

Oct. 18, 2005 101

PART IV: Files and E-mail

 Opening and closing files
 Reading from and writing to files
 Getting information about a file
 Copying, renaming, deleting files
 File permissions
 File locks
 Sending e-mail
 MIME
 HTML E-mails
 Multipart E-mails

Oct. 18, 2005 102

Files — Opening and Closing

• Files are open using the fopen() function:
 fopen ($filename, $mode)
 returns a file resource (not a pointer!)
• The $mode parameter indicates how the file
should be open:
 r — read only
 r+ — read/write
 w — write only and create the file
 w+ — read/write and create the file
 a — write only and position at end of file
 a+ — read/write and position at end of tile
 x — write only, fail if file already exists

Oct. 18, 2005 103

Files — Opening and Closing

• If your PHP has been compiled with URL
wrappers support, fopen() works both on local
and “remote” files via any of the supported
protocols:
 fopen (“http://www.phparch.com”, “r”);
• Files can be closed using fclose()
 This is not necessary, because PHP closes all open
handles at the end of script
 However, it’s a good idea in some cases

Oct. 18, 2005 104

Files — Reading & Writing

• Data is read from a file through a number of
functions. The most common one is fread():
 $data = fread ($file, $qty);
 Returns the maximum data available, up to $qty bytes
• The fgets() function reads data one line at a
time:
 $data = fgets ($file, $maxLen);
 Returns data up to (and including) the next newline
character or $maxLen - 1;
 May or may not work depending on how the file has
been encoded
• auto_detect_line_endings PHP.INI setting

Oct. 18, 2005 105

Files — Reading and Writing

• Writing works in a similar way:
 fwrite ($file, $data)
 Writes as much of $data as possible, returns amount
written
• You can also use fputs(), which is effectively an
alias for fwrite()

Oct. 18, 2005 106

Files — File Position

• The file position is updated as your read from or
write to a file
 ftell ($file) — Returns the current offset (in bytes) from
the beginning of the file
• You can manually alter the current position
using fseek():
 fseek ($file, $position, $from)
 $from can be one of three constants:
• SEEK_SET (beginning of file)
• SEEK_CUR (current offset)
• SEEK_END (end of file — $from should be < 0)

Oct. 18, 2005 107

Files — File Information

• The fstat() function returns several pieces of
information about a file:
 var_dump (fstat ($file))
•     [dev] => 5633            // device
    [ino] => 1059816        // inode
    [mode] => 33188            // permissions
    [nlink] => 1            // number of hard links
    [uid] => 1000            // user id of owner
    [gid] => 102            // group id of owner
    [rdev] => -1            // device type
    [size] => 106            // size of file
    [atime] => 1092665414        // time of last access
    [mtime] => 1092665412        // time of last modification
    [ctime] => 1092665412        // time of last change
    [blksize] => -1            // blocksize for filesystem I/O
    [blocks] => -1            // number of blocks allocated
Oct. 18, 2005 108


• The stat() function is a version of fstat() that does
not require you to open the file
 var_dump (stat ($fileName))
• Several functions provide only portions of the
info returned by stat() and fstat()
 file_exists ($fileName)
 fileatime ($fileName) — Last access time
 fileowner ($fileName)
 filegroup ($fileName)
• The results of these functions are cached
 This can lead to confusing results if you make changes
to a file in the same after you’ve run one of these
convenience functions
Oct. 18, 2005 109


• File permissions can be determined using either
the bitmask from fstat() or some more
convenience functions
 is_readable ($fileName);
 is_writable ($fileName);
 is_executable ($fileName);
 is_uploaded_file ($fileName);
• They can also be changed:
 chmod ($fileName, 0777);
 Note use of octal number
• The filesize() function returns the size of a file
 echo filesize ($fileName)
Oct. 18, 2005 110

Copying, Renaming & Deleting

• Files can be copied using the copy() function:
 copy ($sourcePath, $destPath)
• Renaming is done through rename():
 rename ($sourcePath, $destPath);
 Guaranteed to be atomic across the same partition
• Files are deleted using unlink():
 unlink ($fileName);
 NOT delete()!
• Files can also be “touched”:
 touch ($fileName);
• All these functions report success/failure via a
Boolean value
Oct. 18, 2005 111

Directories

• Directories cannot be removed using unlink:
 $success = rmdir ($dirName);
 The directory must be empty
 This means that you must write your own code to
empty the directory and any subdirectories

Oct. 18, 2005 112

File Locking

• File locking ensures ordered access to a file
• PHP’s locking module is collaborative
 Every application that accesses the file must use it
• Locks can be shared or exclusive
 $lock = ($file, $lockType, &$wouldBlock);
 $lockType: LOCK_SH, LOCK_EX
 To release a lock: LOCK_UN
 To prevent blocking, OR with LOCK_NB
• Several limitations:
 Doesn’t work on most networked filesystems, or on FAT
(Win98)
 Sometimes implemented per-process
Oct. 18, 2005 113

More File Fun

• Some useful file functions
• file():
 Reads an entire file in memory, splits it along newlines
• readfile():
 Reads an entire file, outputs it
• fpassthru():
 Same as readfile(), but works on file pointer and
supports partial output
• file_get_contents():
 Reads entire file in memory
 Remember that file_put_contents() is a PHP 5-only
function!

Oct. 18, 2005 114

PHP and E-mail

• PHP supports sending of e-mail through the
mail() function
 Contrary to popular belief, it’s not always available
 Relies on sendmail in UNIX, implements its own
wrappers in Windows and Netware
 Built-in wrappers do not support authentication
 The from address is set automatically under Linux
(php_user@serverdomain), must be set in PHP.ini under
Windows

Oct. 18, 2005 115

E-mail — The mail() Function

• The mail() function accepts five parameters:
 mail ($to, $subject, $body, $headers, $extra)
• mail() provides a raw interface to sending mail
 No support for attachments
 No support for MIME
 No support for HTML mail
• Extra headers can be set, including overriding
the default From:
 On UNIX machines, this may require setting -f in $extra
 This may not work if PHP user is not “trusted” by
sendmail

Oct. 18, 2005 116

E-mail — MIME

• E-mail only supports 7-bit ASCII
 Good for anglophones, not so good for the rest of the
world
 MIME provides support for sending arbitrary data over
e-mail
 MIME is supported by most MUAs, although often the
target of spam filters
• MIME headers also define the type of data that is
being sent as part of an e-mail:
 For example, HTML:
• "MIME-Version: 1.0rn" .
"Content-Type: text/html; charset="iso-8859-1"rn" .
"Content-Transfer-Encoding: 7bitrn"

Oct. 18, 2005 117

E-mail — MIME and Multipart

• Multipart e-mails make it possible to send an e-
mail that contains more than one “part”
 "MIME-Version: 1.0rn" .
"Content-Type: multipart/alternative;rn" .
" boundary="{$boundary}"rn";
 Examples:
• HTML and Text bodies (plain-text should go first)
• Attachments
• Most clients support multipart—but for those who
don’t, you always provide a plain-text message
at the beginning
 “If you are reading this, your client is too old!”

Oct. 18, 2005 118

E-mail — MIME and Multipart

• The different parts are separated by a unique
boundary
 $message .= "--" . $boundary . "rn" .
"Content-Type: text/plain; charset=us-asciirn" .
“Content-Transfer-Encoding: 7bitrnrn" .
"Plain text" .
"rnrn--" . $boundary . "--rn";
 Note the two dashes before each boundary, and after
the last boundary
• Binary attachments must be encoded:
 "Content-Transfer-Encoding: base64rn" .
‘Content-disposition: attachment; file="l.gif"rnrn"
 base64_encode ($file);

Oct. 18, 2005 119

E-mail — Getting a handle

• It’s impossible to know whether an e-mail was
successfully sent
 mail() only returns a success/failure Boolean for its end
of the deal
 E-mail can get lost at pretty much any point in the
tranmission process
 The mail protocol does not have a thoroughly-
respected feedback mechanism

Oct. 18, 2005 120

Q&A Time

• Which function(s) retrieve the entire contents of
a file in such a way that it can be used as part of
an expression?

• What does the built-in delete function do?

• Which MIME content type would be used to send
an e-mail that contains HTML, rich text, and plain
text versions of the same message so that the e-
mail client will choose the most appropriate
version?

Oct. 18, 2005 121

Answers

• Which function(s) retrieve the entire contents of
a file in such a way that it can be used as part of
an expression?

• file_get_contents()
• file()

Oct. 18, 2005 122

Answers

• What does the built-in delete function do?

• It doesn’t exist!
• Use unlink() instead

Oct. 18, 2005 123

Answers

• Which MIME content type would be used to send
an e-mail that contains HTML, rich text, and plain
text versions of the same message so that the e-
mail client will choose the most appropriate
version?

• multipart/alternative
 segment which contains sub-segments representing
multiple versions of the same content

Oct. 18, 2005 124

PART V: Databases and Networks

 Databasics
 Indices and keys
 Table manipulation
 Joins
 Aggregates
 Transactions
 File wrappers
 Streams

Oct. 18, 2005 125

Databasics

• The exam covers databases at an abstract level
 No specific implementation
 SQL-92 standards only
• Only the basics of database design and
programming are actually required
 Table creation/population/manipulation
 Data extraction
 Reference integrity
 Joins / Grouping / Aggregates

Oct. 18, 2005 126

Databasics

• Relational databases
 Called because the relationship among different
entities is its foundation
• Schemas/databases
• Tables
• Rows
 Data types
• Int
• Float
• Char/varchar
• BlOBs

Oct. 18, 2005 127

Indices

• Indices organize data
 Useful to enforce integrity
 Essential to performance
• Indices can be created on one or more columns
 More rows == bigger index
 Columns that are part of indices are called keys
• Indices can be of two types: unique or not
unique
 Unique indices make it possible to ensure that no two
combination of the same keys exist in the table
 Non-unique indices simply speed up the retrieval of
information

Oct. 18, 2005 128

Creating Schemas and Tables

• Schemas are created with CREATE DATABASE:
 CREATE DATABASE database_name
• Tables are created with CREATE TABLE:
 CREATE TABLE table_name (
column1 column1_type,
...)
• Table names are unique
 This is true on a per-schema basis
• Each table must contain at least one column
 Most DBMSs implement some sort of limits to the size of
a row, but that is not part of the standard

Oct. 18, 2005 129

Creating Indices

• Indices are created using CREATE INDEX:
 CREATE [UNIQUE] INDEX index_name (
column1,
...)
• Index names must be unique
 On a per-schema basis
• Primary keys are special unique indices that
indicate the “primary” method of accessing a
table
 There can only be one primary key per table
 Generally, the primary key indicates the way the data
is physically sorted in storage

Oct. 18, 2005 130

Creating Good Indices

• A good index provides maximum performance
at minimum cost
 Create only indices that reflect database usage
 Implement the minimum number of columns per index
 Create as few indices as possible
• Many DBMSs can only use one index per query
 Make sure you understand how your DBMS uses indices
 Analyze, analyze, analyze
 Continue analyzing once you’re done!

Oct. 18, 2005 131

Foreign Keys

• A foreign key establishes a relationship between
two tables:
 CREATE TABLE A (ID INT NOT NULL PRIMARY KEY)
 CREATE TABLE B (A_ID INT NOT NULL REFERENCES A(ID))
• Foreign keys enforce referential integrity
 They ensure that you cannot add rows to table B with
values for A_ID that do not exist in table A
 It also ensures that you cannot delete from table A if
there are TABLE B rows that still reference it
• Some DBMSs do not support foreign keys
 Notably, MySQL until version 5.0

Oct. 18, 2005 132

Inserting, Updating and Deleting

• Rows are inserted in a table using the INSERT
INTO statement:
 INSERT INTO TABLE A (ID) VALUES (123)
 INSERT INTO TABLE A VALUES (123)
• Updates are performed using UPDATE:
 UPDATE A SET ID = 124
• Deletions are performed using DELETE:
 DELETE FROM A
• Both additions and deletion can be limited by a
WHERE clause:
 UPDATE A SET ID = 124 WHERE ID = 123

Oct. 18, 2005 133

Retrieving Data

• Data is retrieved using the SELECT FROM
statement:
 SELECT * FROM A
 SELECT ID FROM A
• SELECT statements can also be limited by a
WHERE clause
 SELECT * FROM A WHERE ID = 123
 SELECT ID FROM A WHERE ID = 123
 Where clauses are what makes indices so important

Oct. 18, 2005 134

Joins

• A join makes it possible to... join together the
results from two tables:
 SELECT * FROM A INNER JOIN B ON A.ID = B.A_ID
• Inner Joins require that both tables return rows
for a particular set of keys
• Outer Joins require that either table return rows
for a particular set of keys
 SELECT * FROM A LEFT JOIN B
ON A.ID = B.A_ID
 SELECT A.ID, B.* FROM A RIGHT JOIN B
ON A.ID = B.A_ID

Oct. 18, 2005 135

Joins

• Joins don’t always work the way you expect
them to
 SELECT * FROM A INNER JOIN B
WHERE A.ID <> B.A_ID
 This won’t return a list of the rows that A and B do not
have in common
 It will return a list of all the rows that each row of A
does not have in common with B!
• Joins also rely on indices
• Joins can be stacked, and they are executed
from left to right

Oct. 18, 2005 136

Grouping and Aggregates

• The GROUP BY clause can be used to group
return sets according to one or more columns:
 SELECT A_ID FROM B GROUP BY A_ID
• Grouped result sets can then be used with
aggregates to perform statistical analysis on
data:
 SELECT A_ID, COUNT(A_ID) FROM B GROUP BY A_ID
• When using GROUP BY, only aggregates and
columns that appear in the GROUP BY clause
can be extracted
 This is the standard, but it’s not always respect (notably
by MySQL)

Oct. 18, 2005 137

Aggregates

• Sum of all rows
 SUM(column_name)
• Count of rows returned
 COUNT(column_name)
 COUNT(*)
• Arithmetic average:
 AVG(column_name)
• Maximum / minimum
 MAX (column_name)
 MIN (column_name)
• Not all aggregates can be sped up by proper
indexing
Oct. 18, 2005 138

Sorting

• Result sets can be sorted using the ORDER BY
clause
 SELECT * FROM A ORDER BY ID
• This is superfluous — ID is the primary key!
 SELECT * FROM A ORDER BY ID DESC
 SELECT * FROM B ORDER BY A_ID DESC, ID
• Sorting performance is affected by indexing

Oct. 18, 2005 139

Transactions

• Transaction create atomic sets of operations that
can be committed or rolled back without any
chaange to the underlying data
 BEGIN TRANSACTION
DELETE FROM A
DELETE FROM B
ROLLBACK TRANSACTION
 BEGIN TRANSACTION
UPDATE A SET ID = 124 WHERE ID = 123
UPDATE B SET A_ID = 124 WHERE ID = 123
COMMIT TRANSACTION
• Not all DBMSs support transactions
 For example, MySQL only supports them with InnoDB

Oct. 18, 2005 140

SQL and Dates

• Most DBMSs can handle dates much better than
PHP
 Extended range
 Higher resolution
• Therefore, you should keep all date operations
within your DBMS for as long as possible

Oct. 18, 2005 141

File Wrappers

• File wrappers extend PHP’s file handling
 use fopen(), fread() and all other file functions with
something other than files
 For example, access HTTP, FTP, ZLIB and so on
• Built-in wrappers, or your own
 Simply define your own wrapper class:
• class wrap {
function stream_open($path, $mode, $options, &$opened_path) {}
function stream_read($count) {}
function stream_write($data) {}
function stream_tell() {}
function stream_eof() {}
function stream_seek($offset, $whence) {}
}
stream_wrapper_register("wrap", "wrap"); // register wrapper
$fp = fopen("wrap://some_file", "r+"); // open file via new wrapper

Oct. 18, 2005 142

File Wrappers

• Not all file wrappers support all operations
 For example, HTTP is read-only
• Remote file access may be turned off
 Use the allow_furl_open PHP.INI directive
• Some wrappers are write-only
 For example: php://stdout and php://stderr
• Some wrappers do not support appending
 For example ftp://
• Only the “file://” wrapper allows simultaneous
read and write operations

Oct. 18, 2005 143

File Wrappers

• File wrappers support information retrieval via
stat() and fstat()
 This is only implemented for file://
 Remember, however, that SMB and NFS files are “local”
as far as the operating system is concerned
• Deleting and renaming is also supported
 Renaming only supported for local file (but see above)
 Both require write access
• You can also access and manipulate directories
 Supported only for local files
• Remember to close unused wrapper instance
 Not necessary, but often a good idea
Oct. 18, 2005 144

Streams

• Streams represent access to network services
 File wrapper
 One or two pipelines
 Context
 Metadata
• Pipelines
 Established to allow for the actual streaming of data
 Can be one only (read or write) or two (read and
write)
• Context
 Provides access to advanced options
• For example, under HTTP you can set additional headers

Oct. 18, 2005 145

Streams

• Metadata
 Contains “out-of-band” information provided by the
stream
• print_r(stream_get_meta_data(fopen("http://www.php.net", "r")));
/* Array (
    [wrapper_data] => Array (
        [0] => HTTP/1.1 200 OK
        [1] => Date: Wed, 25 Aug 2004 22:19:57 GMT
[2] => Server: Apache/1.3.26 (Unix) mod_gzip/1.3.26.1a PHP/4.3.3-dev
[3] => X-Powered-By: PHP/4.3.3-dev
        [4] => Last-Modified: Wed, 25 Aug 2004 21:12:17 GMT
        [5] => Content-language: en
        [8] => Content-Type: text/html;charset=ISO-8859-1
    )
    [wrapper_type] => HTTP
    [stream_type] => socket
    [unread_bytes] => 1067
    [timed_out] =>
    [blocked] => 1
    [eof] =>
Oct. 18, 2005 146

Sockets

• Sockets provide the lowest-level form of network
communication
 Because of this, you should use them only when strictly
necessary
• Several transports are supported:
 TCP/UPD
 SSL
 TLS
 UNIX
 UDG
• You can’t switch transports mid-stream
 Sometimes problematic for TLS

Oct. 18, 2005 147

Sockets

• Opening:
 $fp = fsockopen ($location, $port, &$errno, &$errstr)
 You can then use fwrite, fread(), fgets(), etc.
• Opening persistend sockets:
 $fp = pfsockopen ($location, $port, &$errno, &$errstr)
 Persistent sockets will only work for persistent APIs, like
mod_php on Apache and FastCGI
 Connections can also be terminated from the remote
host because of lack of network activity
 Use with care—lots of potential pitfalls!

Oct. 18, 2005 148

Socket Timeout

• An optional fifth parameter to fsockopen()
indicates timeout
 $fp = fsockopen("www.php.net", 80, $errno, $errstr, 30);
 Timeout is in seconds
 Default is stored in default_socket_timeout PHP.INI
setting
• Timeout must be set separately for network
activity:
 socket_set_timeout ($socket, $timeout)
• Sockets can be blocking or non-blocking
 stream_set_blocking ($socket, FALSE);
 This needs a pre-existing socket!

Oct. 18, 2005 149

Q&A Time

• What does an “inner join” construct do?

• What function would you use to open a socket
connection manually with the purpose of
communicating with a server not supported by a
file wrapper?

• When dealing with timeout values in sockets, the
connection timeout can be changed
independently of the read/write time out. Which
function must be used for this purpose?

Oct. 18, 2005 150

Answers

• What does an “inner join” construct do?

• It creates a result set based on the rows in
common between two tables

Oct. 18, 2005 151

Answers

• What function would you use to open a socket
connection manually with the purpose of
communicating with a server not supported by a
file wrapper?

• fsockopen()
• pfsockopen() for persistent connections

Oct. 18, 2005 152

Answers

• When dealing with timeout values in sockets, the
connection timeout can be changed
independently of the read/write time out. Which
function must be used for this purpose?

• stream_set_timeout()

Oct. 18, 2005 153

PART VI: Secure, Optimize, Debug

 Data filtering
 SQL injection
 Command injection
 XSS
 Safe mode
 Coding Standards
 Error logging
 Debugging and optimization

Oct. 18, 2005 154

Data Filtering

• Users are evil
 And sometimes they don’t even know it
• You should always “taint” and filter data
 PHP provides lots of functions that can help here
 Never rely on register_globals
• In fact, if you’re writing for redistribution, undo its effects if
it is on
• Data filtering depends on what you need to do
with it
 You will rarely need “raw” data
 Most of the time, it needs to be escaped to do
something or other—e.g.: display, insert into db, and so
on
Oct. 18, 2005 155

SQL Injection

• SQL injection occurs when improperly filtered
data ends up in a database query
 “SELECT * FROM USER WHERE ID = $id”
 $id = “1; DELETE FROM USER;”
• Most DBMS modules have their own escaping
mechanisms
 mysql_real_escape_string()
 addslashes() — The swiss army knife approach

Oct. 18, 2005 156

Command Injection

• Command injection takes place when
improperly filtered input ends up in a shell
command
• Both commands and parameters should be
escaped:
 escapeshellcmd ($cmd)
 escapeshellarg ($arg)
 shell_exec ($cmd . ‘ ‘ . $arg)

Oct. 18, 2005 157

Cross-site Scripting

• XSS happens when improperly escaped input is
outputted to the client
 XSS can be used for all sorts of nasty purposes
 Often underrated, it is an extremely serious security
problem
 It’s often easy to implement on the attacker’s side
• User input should be properly escaped before
being outputted back to the browser
 htmlspecialchars()
 htmlentities()
 strip_tags()

Oct. 18, 2005 158

Safe Mode

• Safe mode implements certain restrictions to
help prevent security problems
 UID matching
 open_basedir restrictions
• Safe mode and open_basedir have several
drawbacks
 PHP is not the right place for implementing security at
this level
 Files created in safe_mode may not be readable by
your scripts!
 Add noticeable overhead to the system

Oct. 18, 2005 159

Coding Standards

• Coding standards help writing good code
 There is no “official” standard connected with the
exam
• A few ideas:
 Flattening if statements
 Splitting long statements across multiple lines
 Using substitution instead of concatenation
• Watch out for performance hits
 Comparison vs. Assignment
• Reverse comparisons
 Use type-sensitive comparisons when possible
 Validate resources

Oct. 18, 2005 160

Error Management

• PHP has an impressive array of error
management facilities—use them!
• Report all errors during development
• Keep error reporting on in production, but shift to
logging
• Implement your own error handlers

Oct. 18, 2005 161

Debugging

• Debugging can be very difficult
• “Echo” debugging is the simplest form
 Output status throughout the script’s execution
• Complex logic is better handled through
external debuggers
 Lots available—from open source (Xdebug) to
commercial (e.g.: Zend Studio IDE)
 IDEs support both local and remote debugging

Oct. 18, 2005 162

Optimization

• Optimization can be as simple as installing a
bytecode cache
 No changes to codebase
 Immediate (but limited) benefits
• Proper optimization requires good analysis
 Finding bottlenecks
• Optimization can take place on multiple levels:
 Write faster code
 Remove external bottlenecks
 Use caching for internal bottlenecks
 Improve web server configuration

Oct. 18, 2005 163

Q&A Time

• Although the best practice is to disable
register_globals entirely, if it must be enabled,
what should your scripts do to prevent malicious
users from compromising their security?

• When uploading a file, is there a way to ensure
that the client browser will disallow sending a
document larger than a certain size?

• Can you turn off all error reporting from within a
script with a single PHP function call?

Oct. 18, 2005 164

Answers

• Although the best practice is to disable
register_globals entirely, if it must be enabled,
what should your scripts do to prevent malicious
users from compromising their security?

• Filter all data
• Initialize all variables

Oct. 18, 2005 165

Answers

• When uploading a file, is there a way to ensure
that the client browser will disallow sending a
document larger than a certain size?

• No.
 You can check a file size after it’s been uploaded
 The server can ignore files above a certain size
 But you can’t prevent the user from trying to send the
data across the network

Oct. 18, 2005 166

Answers

• Can you turn off all error reporting from within a
script with a single PHP function call?

• No.
 error_reporting() will not silence parse errors

Oct. 18, 2005 167

Conclusion

• A few quick words about the exam
• Pay close attention to the code
 Pay close attention to the code
 Are you paying close attention yet???
• You have 90 minutes—use them all
• Use the booklet to mark your questions before
you transfer them over to the answer sheet
• Remember that you’re working with PHP 4, not
PHP 5—and 4.3, not 4.4!
• Don’t forget to sign up for your exam at the
registration desk

Oct. 18, 2005 168

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