CP3024 Lecture 3

Server Side Facilities

Lecture contents

Server side includes Common gateway interface (CGI)PHP Hypertext Preprocessor (PHP) pages

Static HTML Page

Page created and stored on serverDelivered to browser when requestedPage always remains the same

Dynamic Content Generated by the Server

Browser requests pagePage is generated “on the fly”Content depends on:

– Request made– Time of day– Etc.

“On-the-fly” Content

Server

Client

Request

HTML generated “on-the-fly”

Server Side Includes(SSI)

Directives placed in an HTML pageWhen page is delivered server inserts extra

informationBrowser only sees final HTML versionNot supported by all server softwarePages have special suffix (normally .shtml)

Directive Format

<!--#command parameter=“argument”-->

e.g.

<!--#exec cmd=“/bin/finger”-->

Permitted Directives

config echo exec flastmod fsize includeprintenv set

echo

echo var= “environment_variable”Inserts the value of special side include

variables into pagee.g.

<h1>My server is called

<!--#echo var=“SERVER_NAME” -->

</h1>

Running echo

exec

Used to execute a command or a user program

Best if program generates HTMLCan’t send data to program

exec cmd|cgi=“string”

<!--#exec cmd=“/bin/finger” -->

Running exec

fsize

Inserts the size of a named fileUseful for warning about size of graphics

etc.

fsize file|virtual=“path”

<!--#fsize file=“myphoto.jpeg” -->

flastmod

Inserts the last modified date for a named file

Used to indicate how up to date the information is

flastmod file=“path”

<!--#flastmod file=“index.html” -->

Running fsize and flastmod

include

Use to include text (normally html) into a file

Can be used to add standard text to pages

include file|virtual=“path”

<!--#include file=“disclaim.html” -->

Common Gateway Interface

Known as CGIOne of the most misunderstood Web

technologiesAllows client to pass data to programs

running on serverPrograms generate HTML to be returned to

browser

CGI in action

ProgramClient

Server

HTTP Request

Data for program

Generated HTML

HTML

What is a CGI program?

Can be written in any languageCGI defines the format of the data passed to the

programProgram reads data from an environment variable

called QUERY_STRINGProgram generates output prefixed by Content-

type: header. E.g.:echo Content-type: text/html echo

URL encoding

Data may be sent via GET or POSTValues are encoded as variable/value pairsEach pair is separated by &

– firstname=Joe&lastname=Bloggs

CGI program must decode this stringGET strings go into the server logs but

POST strings are not logged

CGI Environment Variables

AUTH_TYPE CONTENT_LENGTH CONTENT_TYPE DOCUMENT_ROOT GATEWAY_INTERFACE HTTP_ACCEPT HTTP_COOKIE HTTP_FROM HTTP_REFERER PATH_INFO PATH_TRANSLATED

QUERY_STRING REMOTE_ADDR REMOTE_HOST REMOTE_IDENT REMOTE_USER REQUEST_METHOD SCRIPT_NAME SERVER_NAME SERVER_PORT SERVER_PROTOCOL SERVER_SOFTWARE

Identifying CGI Scripts

Some server set-ups require script to be stored in /cgi-bin

Other set-ups allow scripts anywhere– Script names have format ????.cgi

Scripts should be made executable for the server username

Apache server username is nobody

Load On Server

Originally each CGI script ran as a separate process

Very costly on server resourcesNewer mechanisms run scripts in threadsServer designers ensure that CGI routines

cannot crash the Web server

Server-side Scripting

CGI programs generate HTMLServer side script languages embed code

within HTMLServer executes code before delivering to

browserExamples include PHP, ASP, JSP and XSPRequires additional server software

PHP

PHP Hypertext PreprocessorServer-side, HTML-embedded, cross-

platform scripting languageAvailable as Unix Apache moduleCGI version works with IIS on MS

WindowsSimilar to C or Perl

Embedding PHP in HTML

Between <? And ?> tags– <?echo “Hello World”;?>

Between <?php and ?> tags for XML– <?php echo “Hello World”; ?>

In <script> tags– <script language=“php”>

echo “Hello World”; </script>

Switching between PHP and HTML

Can be done as and when:<? For($i=0; $i<100; $i++) { ?>

<br>

<?}?>

PHP Comments

/* C style comment */// C++ style comments# Unix shell style comments

Variables in PHP

All names begin with $ e.g. $variableAlphabetic character or underscore (_)

must follow $Remaining chars are alphanumeric or

underscoreNames are case-sensitive $A is not $aTypes determined by first assignment

Data Types in PHP

Integer– Whole numbers –2,147,483,648 to 2,147,483,647

Floating Point– Decimal values in the range 1.7E-308 to 1.7E308

String– Sequence of characters e.g. “Hello World”

Can convert using setype() function or by casting:– settype($myInt, “string”)– (integer) $myString

String Handling

Characters within strings can be obtained via subscripting

Subscripts start at 0

$hello = “Hello World”

$hello[1] will be “e”

Outputting A String

The function echo() outputs a string to the standard output

e.g. echo(“Hello World”);

echo($astring)

Finding the length of a string

The function strlen() returns a string’s length

$hello=“Hello World”

The value of strlen($hello) is 11

Getting a number from a string

Use the string in a calculationPHP converts as much as it can to a number

$var=“1234”

$num=$var[2] + 5

$num contains the number 8

Expressions

Includes normal arithmetic operations– $i=$i+1 or $i++– $i=$i-1 or $i--– Also / (divide) and * (multiply)– % is the modulo operation

May use brackets to specify precedenceStatements separated by semi-colonsExpressions evaluate to true or false

Control Structures

Standard syntax for creating loops– if– switch– while– do/while– for

if statement

if (expression) {statements

}elseif (expression) {

statements}else {

statements}

Conditional expressions

Standard comparison operators< , <=, >=, >, ==, !=

Note the ==Any numeric expression which has a value

of 0 is false otherwise it is true

Can combine conditiond

Logical connectors && and ||($var<6) && ($var>4)

– Variable is less than 6 AND greater than 4

($var==6) || ($var==4)– Variable is equal to 4 OR equal to 6

if Example

if ($var==56){echo “It’s the same”;

}elseif($var<56){echo “Less than”;

}else{echo “Greater than”;

}

for loop

for (start_expr; cond_expr; iter_expr){

statements

}Executes the statements while the

cond_expr is true

for example

for($var=0; $var<=12; $var++){

echo($var);

}

Getting Data From The Client

Data is often supplied to server side programs via HTML forms

Indicated by the <form> tagSpecifies HTTP method and field namesField names become variables in PHP

scripts– Field name myfield becomes $myfield

A Simple Form

<html><head><title>Multiply Form</title></head><body><h1>Enter multiplier</h1><form action="multiply.php" method="POST">

<input type="text" name="multiplier"></form></body></html>

Simple Form Output

PHP Script

<html><head><title>Times Table</title></head><body><?for($i=1;$i<=12;$i++){ echo($i); ?> * <?echo($multiplier);?> = <?echo($multiplier*$i);?> <br><?}?></body></html>

Output

Getting It On the Server

Treat PHP scripts like ordinary HTML pages

Except save in files called .phpSuitably equipped Web Server does the

rest

Other Resources

http://www.php.net http://www.phpbuilder.com/getit/ http://www.zend.com/ http://www.scit.wlv.ac.uk/appdocs/phpChapter 29 (PHP) - Internet & World

Wide Web – How to Program, H.M.Deitel, P.J.Deitel & T.R.Nieto (2nd edition)

Summary

Dynamic pages generated by the server– Server Side Includes– Common Gateway Interface– PHP