The Internet

1
The Internet

• Programming Language Design and Implementation
  (4th Edition)
• by T. Pratt and M. Zelkowitz
• Prentice Hall, 2001
• Section 12.2.2-12.2.4

2
HTML FORMS

• A method for passing information between a user
  at a Web browser and a Web server.
• This information is passed to a program on the
  server system. This is the Common Gateway
  Interface (CGI) file.
• Web servers typically have a specific cgi-bin
  directory containing these CGI programs.
• HTML forms are used
• ltform methodtype
• action location of cgi script to executegt
• text
• lt/formgt
• Perl often used as language for such scripts

3
CGI script example
4
HTML for form

• ltHTMLgt
• ltHEADgt
• ltTITLEgtcgi-testlt/TITLEgt
• lt/HEADgt
• ltBODYgt
• ltpgt This is a sample page to read
• two data items from the web page
• ltform action"cgi-bin/xaction" methodgetgt
• ltpgtFirst nameltinput typetext namexfirst
  size10gt
• ltbrgtLast nameltinput typetext namexlast
  size20gt
• ltbrgt ltinput typesubmit valueSENDgt
• ltinput typereset valueRESETgt
• lt/formgt
• lt/BODYgt
• lt/HTMLgt

Parameters passed as arguments xfirst and xlast
5
Perl - CGI script

• !/usr/bin/perl
• print Content-Type text/html\n\n
• print lthtmlgtltheadgt\n
• print lttitlegtSample PERL scriptlt/titlegt\n
• print lt/headgtltbodygt\n
• print ltpgtQuery_string is ENV'QUERY_STRING'\n
  
• foreach ( split( //, ENV'QUERY_STRING') )
• ( key, val ) split( //, _, 2 )
• tmpkey val
• print ltpgtFirst name is ltbgttmp'xfirst'lt/bgt\n
• print ltpgtLast name is ltbgttmp'xlast'lt/bgt\n
• print lt/bodygtlt/htmlgt\n
• Perl program first reads parameters as
  xfirstzlast from ENV (environment) into
  QUERY_STRING
• Output of Perl is the syntax of an HTML page that
  is displayed

6
Java applets

• Issue Many different protocols
• Solution Send program to read protocol as part
  of HTML
• (Role for Java)
• Moves processing needs from HTML server to HTML
  cllient
• Do more processing on client side of web
• import java.awt. / applet library /
• public class hello extends java.applet.Applet
• public void paint(Graphics x)
• x.drawString(Hello World, 100, 100)
• Displayed by
• lthtmlgt
• ltbodygt
• ltapplet code hello.class width200
  height200gt
• lt/appletgt
• lt/bodygt
• lt/htmlgt