CP3024 Lecture 3

1. CP3024 Lecture 3 Server Side Facilities

2. Lecture contents • Server side includes • Common gateway interface (CGI) • PHP Hypertext Preprocessor (PHP) pages

3. Static HTML Page • Page created and stored on server • Delivered to browser when requested • Page always remains the same

4. Dynamic Content Generated by the Server • Browser requests page • Page is generated “on the fly” • Content depends on: • Request made • Time of day • Etc.

5. “On-the-fly” Content Server Request Client HTML generated “on-the-fly”

6. 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)

7. Directive Format • <!--#command parameter=“argument”--> e.g. <!--#exec cmd=“/bin/finger”-->

8. Permitted Directives • config • echo • exec • flastmod • fsize • include • printenv • set

9. echo • echo var= “environment_variable” • Inserts the value of special side include variables into page e.g. <h1>My server is called <!--#echo var=“SERVER_NAME” --> </h1>

10. Running echo

11. 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” <!--#exec cmd=“/bin/finger” -->

12. Running exec

13. fsize • Inserts the size of a named file • Useful for warning about size of graphics etc. fsize file|virtual=“path” <!--#fsize file=“myphoto.jpeg” -->

14. 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” -->

15. Running fsize and flastmod

16. 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” -->

17. 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

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

19. 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

20. 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

21. 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 CGI Environment Variables

22. 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

23. 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

24. 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

25. 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

26. 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>

27. Switching between PHP and HTML • Can be done as and when: <? For($i=0; $i<100; $i++) { ?> <br> <?}?>

28. PHP Comments • /* C style comment */ • // C++ style comments • # Unix shell style comments

29. 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

30. 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

31. String Handling • Characters within strings can be obtained via subscripting • Subscripts start at 0 $hello = “Hello World” $hello[1] will be “e”

32. Outputting A String • The function echo() outputs a string to the standard output e.g. echo(“Hello World”); echo($astring)

33. Finding the length of a string • The function strlen() returns a string’s length $hello=“Hello World” The value of strlen($hello) is 11

34. 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

35. 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

36. Control Structures • Standard syntax for creating loops • if • switch • while • do/while • for

37. if statement • if (expression) { statements } elseif (expression) { statements } else { statements }

38. Conditional expressions • Standard comparison operators < , <=, >=, >, ==, != • Note the == • Any numeric expression which has a value of 0 is false otherwise it is true

39. 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

40. if Example if ($var==56){ echo “It’s the same”; } elseif($var<56){ echo “Less than”; } else{ echo “Greater than”; }

41. for loop • for (start_expr; cond_expr; iter_expr){ statements } • Executes the statements while the cond_expr is true

42. for example for($var=0; $var<=12; $var++){ echo($var); }

43. Getting Data From The Client • Data is often supplied to server side programs via HTML forms • Indicated by the <form> tag • Specifies HTTP method and field names • Field names become variables in PHP scripts • Field name myfield becomes $myfield

44. 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>

45. Simple Form Output

46. 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>

47. Output

48. 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

49. Other Resources • http://www.php.net • http://www.phpbuilder.com/getit/ • http://www.zend.com/ • http://www.scit.wlv.ac.uk/appdocs/php • Chapter 29 (PHP) - Internet & World Wide Web – How to Program, H.M.Deitel, P.J.Deitel & T.R.Nieto (2nd edition)

50. Summary • Dynamic pages generated by the server • Server Side Includes • Common Gateway Interface • PHP