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 server  Delivered to browser when requested  Page always remains the same

Dynamic Content Generated by the Server  Browser requests page  Page 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 page  When page is delivered server inserts extra information  Browser only sees final HTML version  Not supported by all server software  Pages have special suffix (normally.shtml)

Directive Format  e.g.

Permitted Directives  config  echo  exec  flastmod  fsize  include  printenv  set

echo  echo var= “environment_variable”  Inserts the value of special side include variables into page e.g. My server is called

Running echo

exec  Used to execute a command or a user program  Best if program generates HTML  Can’t send data to program exec cmd|cgi=“string”

Running exec

fsize  Inserts the size of a named file  Useful for warning about size of graphics etc. fsize file|virtual=“path”

flastmod  Inserts the last modified date for a named file  Used to indicate how up to date the information is flastmod file=“path”

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”

Common Gateway Interface  Known as CGI  One of the most misunderstood Web technologies  Allows client to pass data to programs running on server  Programs generate HTML to be returned to browser

CGI in action Program Client Server HTTP Request Data for program Generated HTML HTML

What is a CGI program?  Can be written in any language  CGI defines the format of the data passed to the program  Program reads data from an environment variable called QUERY_STRING  Program generates output prefixed by Content- type: header. E.g.: echo Content-type: text/html echo

URL encoding  Data may be sent via GET or POST  Values are encoded as variable/value pairs  Each pair is separated by & –firstname=Joe&lastname=Bloggs  CGI program must decode this string  GET 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 resources  Newer mechanisms run scripts in threads  Server designers ensure that CGI routines cannot crash the Web server

Server-side Scripting  CGI programs generate HTML  Server side script languages embed code within HTML  Server executes code before delivering to browser  Examples include PHP, ASP, JSP and XSP  Requires additional server software

PHP  PHP Hypertext Preprocessor  Server-side, HTML-embedded, cross- platform scripting language  Available as Unix Apache module  CGI version works with IIS on MS Windows  Similar to C or Perl

Embedding PHP in HTML  Between tags –  Between tags for XML –  In tags – echo “Hello World”;

Switching between PHP and HTML  Can be done as and when:

PHP Comments  /* C style comment */  // C++ style comments  # Unix shell style comments

Variables in PHP  All names begin with $ e.g. $variable  Alphabetic character or underscore (_) must follow $  Remaining chars are alphanumeric or underscore  Names are case-sensitive $A is not $a  Types 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 calculation  PHP 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 precedence  Statements separated by semi-colons  Expressions 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 ||  ($var 4) –Variable is less than 6 AND greater than 4  ($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 tag  Specifies HTTP method and field names  Field names become variables in PHP scripts –Field name myfield becomes $myfield

A Simple Form Multiply Form Enter multiplier

Simple Form Output

PHP Script Times Table <?for($i=1;$i<=12;$i++){ echo($i); ?> * =

Output

Getting It On the Server  Treat PHP scripts like ordinary HTML pages  Except save in files called.php  Suitably equipped Web Server does the rest

Other Resources      Chapter 29 (PHP) - Internet & World Wide Web – How to Program, H.M.Deitel, P.J.Deitel & T.R.Nieto (2 nd edition)

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