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Document Sample
Chapter 16 – Session Tracking and
Cookies
Outline
16.1 Introduction
16.2 Uses of Storing Data
16.3 Methods of Storing Data
16.4 Query Strings
16.5 Hidden Fields
16.6 Cookies
16.7 Server-side Files
16.8 Example: Shopping Cart
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16.1 Introduction
• HTTP
– After server sends reply connection is closed
• Client can send data only once
• Client can receive data only once per request
– Multiple interactions require linked pages
• Series of calls
• Store data between calls
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16.2 Uses of Storing Data
• e-commerce
– Online stores
– User information needs to be maintained
• Interactive
• Customization
– Features
– Colors
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16.3 Methods of Storing Data
• Storing data
– Client
• Cookies
– Store small amounts of text
– Can be disabled
– Server
• Store files on server
– Best way
– May require large amounts of space on the server
– Browser
• Can store data
• Can pass data from one to another
• Only non vital data
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16.4 Query Strings
• Query String
– Sent to the server attached to the request
• Same as a get request
– Question mark at end of URL followed by information being
sent in key-value pairs
– Security issue
• Anyone can change the query string manually
– Change the URL arguments
• Someone could input values that do not make sense
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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
2 <!-- Fig. 16.1: fig16_01.html -->
Outline
3 <!-- Web page offering different color options. -->
4 fig16_01.html
5 <html>
6 <head>
7 <title>Preserving State Through Query Strings</title>
8 </head>
9
10 <body>
11 <p>Which Style do you Prefer?</p>
12 <table bgcolor = "#ffffff">
13 <tbody> Outputs the Perl program
14 <tr> with normal style
15 <td>
16 <font color = "#000000">Normal Style</font>
17 </td>
18 <td>
19 <a href = "/cgi-bin/fig16_02.pl?type=normal">
20 <font color = "#0000ff">Click here</font>
21 </td>
22 </tr>
23 </tbody>
24 </table>
25 <br/>
26 <table bgcolor = "#dddddd">
27 <tbody>
28 <tr>
29 <td>
30 <font color = "#000000">Dark Style</font>
31 </td>
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32 <td> Outline
33 <a href = "/cgi-bin/fig16_02.pl?type=dark">
34 <font color = "#002060">Click here</font>
35 </td>
fig16_01.html
36 </tr>
37 </tbody>
Outputs the Perl program
38 </table>
39 <br/>
with dark style
40 <table bgcolor = "#5555ff">
41 <tbody>
42 <tr>
43 <td>
44 <font color = "#ee3333">Bright Style</font>
45 </td>
46 <td>
47 <a href = "/cgi-bin/fig16_02.pl?type=bright">
48 <font color = "#ffff00">Click here</font>
49 </td>
50 </tr>
51 </tbody>
Outputs the Perl program
52 </table> in a bright style
53 <br/>
54 <table bgcolor = "#ffffc0">
55 <tbody>
56 <tr>
57 <td>
58 <font color = "#ee82ee">Another Style</font>
59 </td>
60 <td>
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61 <a href = "/cgi-bin/fig16_02.pl?type=another"> Outline
62 <font color = "#3cb371">Click here</font>
63 </td> fig16_01.html
64 </tr>
65 </tbody> Outputs the perl program
66 </table> in a another style
67 <br/>
68 </body>
69 </html>
Program Output
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1 #!/usr/bin/perl Outline
2 # Fig. 16.2: fig16_02.pl
3 # Create a page with a specified style.
4
fig16_02.pl
5 use strict;
6 use warnings;
7 use CGI qw( :standard );
8
9 print( header() );
10
Used to retrieve the chosen style
11 my $type = param( "type" );
12
13 my %colors = ( "normal" => [ "#ffffff", "#000000", "#0000ff" ],
14 "dark" => [ "#dddddd", "#000000", "#002060" ],
15 "bright" => [ "#5555ff", "#ee3333", "#ffff00" ], A hash with the style as a key and
16 "another" => [ "#ffffc0", "#ee82ee", "#3cb371" ] ); the value as an array of colors to
17 that style
18 my $style = $colors{ $type };
19 my @style = @{ $style }; The desired list of colors is
20 then stored into @style
21 print <<HTML;
22 <html><head><title>Your Style Page</title></head>
23 <body bgcolor = "$style[ 0 ]" text = "$style[ 1 ]"
24 link = "$style[ 2 ]" vlink = "$style[ 2 ]">
25 <p>This is your style page.</p> Uses the @style array to set the
26 <p>You chose the colors.</p> colors of the background, text,
27 <a href = "/fig16_01.html">Choose a new style.</a> link, and vlink
28 </body></html>
29 HTML
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Outline
fig16_02.pl
Program Output
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16.5 Hidden Fields
• Hidden fields
– Used to keep track of user information through the browser
– Not useful for vital or important data
• Easy to mimic or change
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1 #!/usr/bin/perl Outline
2 # Fig. 16.3: fig16_03.pl
3 # Use hidden form fields to keep track of data.
4
fig16_03.pl
5 use warnings;
6 use strict;
7 use CGI qw( :standard );
8
9 my $data = param( "HIDDEN" );
Uses the CGI.pm’s param method
10 my $name = param( "NAME" );
11 my $value = param( "VALUE" ); to get the values that were passed
12
13 $data .= "$name ";
14 $data .= "$value ";
Adds the new data to the old data
15
16 print( header() );
17 print( start_html( -title => 'Using Hidden Fields' ) );
18
19 print <<Form;
20 <form method = "post" action = "fig16_03.pl">
21 <strong>Please enter the fields name: </strong> Transfers all old data
22 <input type = "TEXT" name = "NAME"><br>
through a hidden field
23 <strong>Please enter the fields value: </strong>
24 <input type = "TEXT" name = "VALUE"><br>
25 <input type = "HIDDEN" name = "HIDDEN" value = "$data">
26 <input type = "SUBMIT" value = "enter your data">
27 </form>
28 Form
29
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30 my %values = split( ' ', $data ); Outline
31
32 foreach ( keys( %values ) ) { Formats the information in $data
fig16_03.pl
33 print( p( "$_: $values{ $_ }" ) ); so it is output in a readable style
34 }
35
36 print( end_html() );
Program Output
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Outline
fig16_03.pl
Program Output
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16.6 Cookies
• Cookies
– Small text file sent by Web server
– Written to user’s computer
– Keep track of data
• How many times visited
• What purchased
• Personal data
– Can be disabled
• Some see it as a security and privacy concern
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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
2 <!-- Fig. 16.4: fig16_04.html -->
Outline
3 <!-- Web page to read in some data from the user. -->
4 fig16_04.html
5 <html>
6 <head>
7 <title>Writing a cookie to the client computer</title>
8 </head>
9 Creates a Web form that
10 <body>
takes data from the user and
11 <font face = "arial,sans-serif" size = 2>
12 then passes it to another form
13 <font size = +2>
14 <b>Click Write Cookie to save your cookie data.</b>
15 </font><br>
16
17 <form method = "post" action = "/cgi-bin/fig16_05.pl">
18 <strong>Name:</strong><br>
19 <input type = "text" name = "name"><br>
20
21 <strong>Height:</strong><br> Sends the data to fig16_05.pl
22 <input type = "text" name = "height"><br>
23
24 <strong>Favorite Color</strong><br>
25 <input type = "text" name = "color"><br>
26
27 <input type = "SUBMIT" value = "Write Cookie">
28 </form>
29
30 </body>
31 </html>
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Outline
fig16_04.html
Program Output
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1 #!/usr/bin/perl Outline
2 # Fig. 16.5: fig16_05.pl
3 # Program to write a cookie to a client’s machine.
4 fig16_05.pl
5 use strict;
6 use warnings;
7 use CGI qw( :standard );
8
9 my $name = param( "name" );
10 my $height = param( "height" );
11 my $color = param( "color" );
12
13 my $expires = "Monday, 11-JUN-01 16:00:00 GMT"; Contains the expiration
14 date of the cookie
15 print( "Set-Cookie: Name=$name; expires=$expires; path=\n" );
16 print( "Set-Cookie: Height=$height; expires=$expires; path=\n"
);
17 print( "Set-Cookie: Color=$color; expires=$expires; path=\n" );
18
19 print( header(), start_html( "Cookie Saved" ) ); Creates 3 cookies to store
20 the user entered data.
21 print <<End_Data;
22 <font face = "arial,sans-serif" size = 3>
23 The cookie has been set with the following data:<br><br>
24
Indicates that the cookie was written
25 <font color = blue>Name:</font> $name<br>
26 <font color = blue>Height:</font> $height<br>
27 <font color = blue>Favorite Color:</font>
28 <font color = $color> $color<br></font><br>
29
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30 Click <a href = "fig16_06.pl">here</a> Outline
31 to read saved cookie.
32 End_Data
fig16_05.pl
33
34 print( end_html() );
Program Output
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1 #!/usr/bin/perl Outline
2 # Fig. 16.6: fig16_06.pl
3 # Program to read cookies from the client's computer.
4
fig16_06.pl
5 use strict;
6 use warnings;
7 use CGI qw( :standard );
8
9 print( header(), start_html( "Read cookies" ) );
10 print( "<font face = \"arial,sans-serif\" size = 3>" );
11 print( strong( "The following data is saved in a cookie " ) );
12 print( strong( "on your computer." ) );
13 print( br(), br() );
14
15 my %cookies = readCookies(); Calls the readCookies function
16
17 print( "<table border = \"5\" cellspacing = \"0\" " );
18 print( "cellpadding = \"10\">" );
19 Goes through all the keys printing
20 foreach ( "Name", "Height", "Color" ) { each value into an HTML table
21 print( "<tr>" );
22 print( " <td bgcolor = #aaaaff>$_</td>" );
23 print( " <td bgcolor = #aaaaaa>$cookies{ $_ }</td>" );
24 print( "</tr>" );
25 }
26
27 print( "</table>" );
28 print( end_html() );
29
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30 sub readCookies Outline
31 {
32 my @cookieArray = split( "; ", $ENV{ 'HTTP_COOKIE' } );
33 my $cookieName;
fig16_06.pl
34 my $cookieValue;
35 my %cookieHash; Split is used to get the original
36 name and value of the pair
37 foreach ( @cookieArray ) {
38 ( $cookieName, $cookieValue ) = split( "=", $_ );
39 $cookieHash{ $cookieName } = $cookieValue;
40 }
41
42 return %cookieHash;
43 }
The pairs are then stored into a
hash and returned
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Outline
fig16_06.pl
Program Output
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16.7 Server-side Files
• Server-side files
– Store user files on the server machine
– Most secure way of storing files
– One downside is the requirement of large amounts of disk
space
– Need a way to distinguish from anonymous users
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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> Outline
2 <!-- Fig. 16.7: fig16_07.html -->
3 <!-- Web page to read in some data that will be -->
4 <!-- entered into a file. -->
fig16_07.pl
5
6 <html>
7 <head>
8 <title>
9 Please enter your contact information.
10 </title>
11 </head>
12
13 <body>
14 <p>
Calls the program fig16_08.pl
15 Please enter your information in the form below:
16 </p>
17 <form method = "post" action = "/cgi-bin/fig16_08.pl">
18 <strong>
19 <p>
20 First name:
21 <input type = "text" name = "first" size = "10">
22 Last name:
23 <input type = "text" name = "last" size = "15">
24 </p>
25 <p>
26 Address:
27 <input type = "text" name = "address" size = "25">
28 <br/>
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29 Town: Outline
30 <input type = "text" name = "town" size = "10">
31 State:
32 <input type = "text" name = "state" size = "2">
fig16_07.pl
33 <br/>
34 Zip Code:
35 <input type = "text" name = "zip" size = "5">
36 Country:
37 <input type = "text" name = "country" size = "10">
38 </p>
39 <p>
40 E-mail Address:
41 <input type = "text" name = "email">
42 </p>
43 <input type = "submit" value = "Enter">
44 <input type = "reset" value = "Clear">
45 </form>
46 </body>
47 </html>
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_07.pl
Program Output
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1 #!/usr/bin/perl Outline
2 # Fig. 16.8: fig16_08.pl
3 # Program to enter user's contact information into a
4 # server-side file. fig16_08.pl
5
6 use strict;
7 use warnings;
8 use CGI qw( :standard );
9 use Fcntl;
10
11 my $first = param( 'first' );
12 my $last = param( 'last' );
13 my $address = param( 'address' );
14 my $town = param( 'town' ); Reads all the parameters that
15 my $state = param( 'state' ); were posted by the client
16 my $zip = param( 'zip' );
17 my $country = param( 'country' );
18 my $email = param( 'email' );
19
20 my $name;
21 my @characters = ( 'a' .. 'z', '0' .. '9' );
22
23 do {
24
25 for ( 1 .. 10 ) { Creates a randomly generated file name
26 my $number = rand( 36 );
27 $name .= $characters[ $number ]; Loops until an original file name is
28 } generated, and then makes the file
29 }
30 until sysopen( FILE, "$name.txt", O_WRONLY | O_EXCL | O_CREAT );
2001 Prentice Hall, Inc. All rights reserved.
31 Outline
32 print( FILE "$first $last\n" );
33 print( FILE "$address\n" );
34 print( FILE "$town $state $country $zip\n" );
fig16_08.pl
35 print( FILE "$email\n" );
36 close( FILE ) or die( "Cannot close file: $!" );
Outputs the information of the file
37
38 print( header() );
39 print( start_html( -title => 'Contact Information is entered' ) );
40 print( strong( "The following information has been stored:\n" ));
41
42 print( "<table><tbody>" );
43
44 print( Tr( td( "First Name: " ), td( $first ) ) );
45 print( Tr( td( "Last Name: " ), td( $last ) ) );
46 print( Tr( td( "Address: " ), td( $address ) ) );
47 print( Tr( td( "Town: " ), td( $town ) ) );
48 print( Tr( td( "State: " ), td( $state ) ) );
49 print( Tr( td( "Zip Code: " ), td( $zip ) ) );
50 print( Tr( td( "Country: " ), td( $country ) ) );
51 print( Tr( td( "E-mail: " ), td( $email ) ) );
52
53 print( "</tbody></table>" );
54 Displays the file name for the user
55 print( p( "Your ID number is $name" ) );
56
57 print( end_html() );
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Outline
fig16_08.pl
Program Output
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16.7 Server-side Files
Jane Doe
123 Main Street
Boston MA USA 12345
jane@doe.com
Fig. 16.9 Contents of rnvonpq849.txt.
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16.8 Example: Shopping Cart
• Shopping Carts
– Allow users to store items the want to buy
– The user pays for them when they “check out”
2001 Prentice Hall, Inc. All rights reserved.
1 #!/usr/bin/perl Outline
2 # Fig. 16.10: fig16_10.pl
3 # Script to login to a Web page.
4 fig16_10.pl
5 use strict;
6 use warnings;
7 use CGI qw( :standard );
8 use Digest::MD5;
9 use Digest::MD5 qw( md5_hex );
10
11 # parameters are read in from the previous Web page
12 my $password = param( "password" );
13 my $user = param( "user" );
14 my $new = param( "new" );
15
16 if ( param( "new" ) ) { Checks to see if the new parameter exists
17 my @search1;
18
19 # Write nothing to the cookie ---
20 cart
# Users just logging in will not have aanew cookie for
Creates the
21 writeCookie(); user, clears cart if empty
22
23 # Encryption of password so that it is protected
24 my $encrypt;
25 my $digestObject = Digest::MD5->new();
26 $digestObject->add( "$password" ); Encrypts the user’s password
27 $encrypt = $digestObject->digest();
28
29 print( header() );
30 print( start_html() );
2001 Prentice Hall, Inc. All rights reserved.
31 Outline
32 open( LOG, "<log.txt" ) or die( "Cannot open: $!" );
33
34 while ( <LOG> ) {
Checks for duplications fig16_10.pl
35 @search1 = split( "\t" );
The file that contains all the
36 usernames and passwords
37 # If this username is found in the log,
38 # it has already been taken
39 if ( $search1[ 0 ] eq $user ) {
40 print( "This name has already been taken.<br>" );
41 print( "<a href = \"fig16_10.pl\">Try again</a>." );
42 print( end_html() );
43 exit;
44 }
45 }
46 close( LOG ) or die( "Cannot close: $!" );
47
48 # Add new user to the file
49 open( LOG, ">>log.txt" ) or die( "Cannot open: $!" );
50 print( LOG "$user\t$encrypt\n" );
51 close( LOG ) or die( "Cannot close: $!" );
52 Brings the user to a page
53 print( i( "Your information has been processed." ) ); to begin shopping
54 print( br() );
55 print( "<a href = \"fig16_11.pl\">Start Shopping!</a>" );
56 print( end_html() );
57 }
Checks to see if the
58 elsif ( param( "password" ) ) {
59 my $found = 0; password parameter exists
60 my @search2;
61
2001 Prentice Hall, Inc. All rights reserved.
62 writeCookie(); Outline
63 print( header(), start_html() );
64
fig16_10.pl
65 my $digestObject = Digest::MD5->new();
Encrypt the password
66 $digestObject->add( "$password" );
67 my $encrypt = $digestObject->digest();
68
69 # Search the log for this person
70 open( LOG, "<log.txt" ) or die( "Cannot open: $!" );
71
72 while ( <LOG> ) { Find the user name in the log file
73 @search2 = split( "\t" );
74 chomp( $search2[ 1 ] );
75
76 if ( $search2[ 0 ] eq $user ) {
77
78 # The password entered is correct
79 if ( $search2[ 1 ] eq $encrypt ) {
80 print( "Thank you for returning, $user!" );
81 print( br() );
82 print( "<a href = \"fig16_11.pl\">Start Shopping!" );
83 print( "</a>" );
84 $found = 1; Lets the user shop after
85 last; verifying the password
86 }
2001 Prentice Hall, Inc. All rights reserved.
87 else { Outline
88 print( i( "You have entered an incorrect " ) );
89 print( i( "password. Please try again." ) );
90 print( br() ); fig16_10.pl
91 print( "<a href = \"fig16_10.pl\">Back to login" );
92 print( "</a>" );
93 $found = 1;
94 last;
95 } Returns the user to the login
96 } for an incorrect password
97 }
98 close( LOG );
99
100 # This person is not found in the log
101 # They are new or have entered an incorrect username
102 if ( $found == 0 ) {
103 print( "You are not a registered user.<br>" );
104 print( "<a href = \"fig16_10.pl\">Register</a>" );
If the user is not found the
105 } program registers them
106 print( end_html() );
107 }
108 else { Executed when the program is first started
109 print( header() );
110 print( start_html( -title => 'Please login' ) );
111
112 print <<" FORM";
113
114 <p>Please login.</p>
115
116 <form method = "post" action = "fig16_10.pl"><p>
117
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118 User Name: <input type = "text" name = "user"><br/> Outline
119 Password: <input type = "password" name = "password"><br/>
120 New? <input type = "checkbox" name = "new" value = "1"></p>
121 fig16_10.pl
122 <input type = "submit" value = "login">
123 </form>
124 Creates an HTML form that
125 FORM
allows the user to enter a name
126
127 print( end_html() );
and password or check the ‘new’
128 } box
129
130 # Function writeCookie creates a cookie containing
131 # the array that was passed in during the function call
132 sub writeCookie
133 { Creates a new cookie
134 my $expires = "Monday, 11-JUN-01 16:00:00 GMT";
135 print( "Set-Cookie: " );
136 print( "CART=", join( "\t", @_ ), "; expires=$expires\n" );
137 return;
138 }
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_10.pl
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_10.pl
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_10.pl
2001 Prentice Hall, Inc. All rights reserved.
1 #!/usr/bin/perl Outline
2 # Fig. 16.11: fig16_11.pl
3 # Add or remove a book from cart and print cart contents
4 fig16_11.pl
5 use warnings;
6 use strict;
7 use CGI qw( :standard );
8
9 my @cart = readCookie();
10 my $remove = param( "remove" );
11 my @book;
12
13 if ( $remove ) { Removing an item from the cart
14 my $number = param( "number" );
15
16 # The book is removed from the cart array
17 @book = splice( @cart, 4 * ( $number - 1 ), 4 );
18
19 # The new array is written to the cookie
20 writeCookie( @cart );
21 print( header() );
22 print( start_html( "Book removed" ) );
23
24 print <<" End_Remove";
25 <center><p>The book <i>$book[0]</i> has been removed.</p>
26 <a href = "fig16_11.pl">Return to cart</a>
27 <br>
28 <a href = "fig16_13.pl">Sign Out</a>
29 End_Remove
30
31 }
2001 Prentice Hall, Inc. All rights reserved.
32 else { Outline
33 @book = param( "newbook" ); When adding an item to the cart
34
35 # Add the book the user wants to the cart array fig16_11.pl
36 push( @cart, @book );
37 Creates a new book to be
38 # If there is nothing in the cart, added to the cart
39 # simply show the items for sale
40 if ( !@cart ) {
41 print( redirect( "fig16_12.pl" ) );
42 exit;
43 }
If the cart is empty the user is
44 directed to fig16_12.pl
45 # Change cookie so it has the new entry
46 writeCookie( @cart );
47 print( header() ); Update the cookie
48 print( start_html( "Shopping Cart" ) );
49
50 print <<" End_Add";
51 <center><p>Here is your current order.</p> Displays the book for the user
52 <table border = "1" cellpadding = "7">
53 <tr>
54 <th>Item</th>
55 <th>Name</th>
56 <th>Year</th>
57 <th>ISBN</th>
58 <th>Price</th>
59 <th></th>
60 </tr>
61 End_Add
62
2001 Prentice Hall, Inc. All rights reserved.
63 my $counter = 1; Outline
64 my $total = 0;
65 my @cartCopy = @cart;
fig16_11.pl
66
67 # print out the cart for the user
68 while ( @book = splice( @cartCopy, 0, 4 ) ) {
69 print( "<tr><form method = \"post\"" );
70 print( "action = \"fig16_11.pl\">" );
71 print( "<td>$counter</td>" ); Displays the cart for the user
72 print( "<td>$book[ 0 ]</td>" );
73 print( "<td>$book[ 1 ]</td>" );
74 print( "<td>$book[ 2 ]</td>" );
75 print( "<td>$book[ 3 ]</td>" );
76 print( "<td>", submit( "Remove" ), "</td>" );
77
78 param( "remove", 1 ); # set "remove" variable to true
79 param( "number", $counter ); # book number to remove
80 print( hidden( "remove" ) );
81 print( hidden( "number" ) );
82 print( "</form></tr>" );
83
84 $book[ 3 ] =~ s/\$//; # remove $ sign
85 $total += $book[ 3 ]; # add price Takes a tally of the total price
86 $counter++;
87 }
88
89 print( "<tr><th colspan = \"4\">Total Order</th><th>" );
90 printf( "\$%0.2f", $total ); # print the total
2001 Prentice Hall, Inc. All rights reserved.
91 Outline
92 print( "</tr>" );
93 print( "</table><br>" );
fig16_11.pl
94 print( "<a href = \"fig16_12.pl\">Buy more books</a>" );
95 print( br() );
96 print( "<a href = \"fig16_13.pl\">Sign out</a>" );
97 }
98 print( end_html() );
99
100 sub writeCookie
101 { Creates a cookie
102 my $expires = "Monday, 11-JUN-01 16:00:00 GMT";
103 print( "Set-Cookie: " );
104 print( "CART=", join( "\t", @_ ), "; expires=$expires\n" );
105 return;
106 }
107
108 # Read the user's cookies
109 # Return the information from the CART cookie
110 sub readCookie
111 { Reads the cookie
112 my @cookieValues = split( "; ", $ENV{ 'HTTP_COOKIE' } );
113 my $name;
114 my $value;
115 my @data;
116
2001 Prentice Hall, Inc. All rights reserved.
117 foreach ( @cookieValues ) { Outline
118 ( $name, $value ) = split ( "=" );
119
fig16_11.pl
120 if ( $name eq "CART" ) {
121 @data = split( "\t", $value );
122 last;
123 }
124 }
125 return @data;
126 }
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_11.pl
2001 Prentice Hall, Inc. All rights reserved.
1 #!/usr/bin/perl Outline
2 # Fig. 16.12: fig16_12.pl
3 # Reads books from a database and prints them in a table
4 fig16_12.pl
5 use warnings;
6 use strict;
7 use CGI qw( :standard );
8
9 my @data;
10
11 print( header(), start_html( "Book List" ) );
12
13 open( BOOKS, "catalog.txt" ) or
14 die( "The database could not be opened." );
15
16 print <<End_Begin;
Opens the catalog, which contains
17
18 <center>Books available for sale<br>
the books the user can buy
19
20 <a href = "fig16_13.pl">Sign Out</a><br>
21
22 <table border = "1" cellpadding = "7">
23 <tr>
24 <th>Name</th>
25 <th>Year</th>
26 <th>ISBN</th>
27 <th>Price</th>
28 </tr>
29
30 End_Begin
2001 Prentice Hall, Inc. All rights reserved.
31 Outline
32 # print books the user can buy
33 while ( <BOOKS> ) {
Outputs a table that fig16_12.pl
34
35 @data = split( "\t" ); # Variable items
contains all the $_ assumed
36
37 print( "<form method = \"post\" action = \"fig16_11.pl\">"
);
38 param( "remove" , 0 ); # The user is not removing a book,
39 param( "newbook", @data ); # They are adding a book
40 print( hidden( "remove" ) );
41 print( hidden( "newbook"), "\n<tr>" );
42
43 foreach ( @data ) {
44 print( "<td>$_</td>" ); # print data item within a cell
45 }
46
47 print( "<td>", submit( "Buy" ), "</td></tr></form>\n" );
48 }
49
A button the user can
50 print( "</table>" );
click on to buy the book
51
52 print( end_html() );
53 close( BOOKS ) or die( "Cannot close: $!" );
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_12.pl
2001 Prentice Hall, Inc. All rights reserved.
1 #!/usr/bin/perl Outline
2 # Fig. 16.13: fig16_13.pl
3 # Web page used to sign user out.
fig16_13.pl
4
5 use strict;
6 use warnings;
7 use CGI qw( :standard );
8
9 # Erase the user's cart information
10 writeCookie(); Clears the cookie thus
11 emptying the users cart
12 print( header() );
13 print( start_html( -title => 'Logged out' ) );
14 print( "You are now logged out." ); Logs the user out of the program
15 print( br(), "You will be billed accordingly." );
16
17 print( br(), "To login again, " );
18 print( "<a href = \"fig16_10.pl\">click here</a>." );
19
20 print( end_html() );
21
22 sub writeCookie
23 {
24 my $expires = "Monday, 11-JUN-01 16:00:00 GMT";
25 print( "Set-Cookie: " );
26 print( "CART=", join( "\t", @_ ), "; expires=$expires\n" );
27 return;
28 }
2001 Prentice Hall, Inc. All rights reserved.
Outline
fig16_13.pl
2001 Prentice Hall, Inc. All rights reserved.
16.8 Example: Shopping Cart
Visual Basic 6 How to Program 1999 0-13-456955-5 $50.00
C++ How to Program 1997 0-13-528910-6 $49.95
C How to Program 1994 0-13-226119-7 $50.00
Java How to Program 1997 0-13-899394-7 $39.95
Java How to Program 2e 1999 0-13-012507-5 $50.00
Fig. 16.14 Contents of catalog.txt.
2001 Prentice Hall, Inc. All rights reserved.
