Implement the Modify a Forum option in default.pl such that individual messages can be deleted. Selecting this option should display the initial screen, but with each forum name followed by a hyperlink to a script named modForum.pl. Script modForum.pl should display the messages as in forum.pl, but each message title should be followed by a link to a script named del- Post.pl, which removes the given message from the current forum. [Hint: Look at the getElementsByTagName, removeChild, and item methods described in the XML::DOM documentation.]

Question

What will be an ideal response?

Answer 1

```
1 #!/usr/bin/perl
2 # default.pl
3 # Default page for XML forums
4
5 use warnings;
6 use strict;
7 use CGI qw( :standard );
8 use XML::Parser;
9 use Fcntl qw( :flock );
10
11 my ( $parser, $prefix, @files, @forums, @items );
12
13 open XML, "../htdocs/XML/forums.xml" or die "Could not open: $!";
14 flock XML, LOCK_UN;
15 flock XML, LOCK_SH;
16 $parser = new XML::Parser( Handlers => { Start => \&startTag,
17 Char => \&text } );
18 $parser->parse( \*XML );
19
20 print header( -expires => "-1d", -cache_control => "no-cache",
21 -pragma => "no-cache"),
22 start_html( -title => "Deitel Message Forums",
23 -style => { -src => "../XML/site.css" } );
24
25 print h1( "Deitel Message Forums" );
26
27 if ( $ENV{ "HTTP_USER_AGENT" } =~ /MSIE/i ) {
28 $prefix = "../XML/";
29 }
30 else {
31 $prefix = "forum.pl?file=";
32 }
33
34 @items = map { a( { -href => "$prefix$files[ $_ ]" }, $forums[ $_ ]
35 ) }
36 ( 0 .. $#files );
37
38 if ( param( "modify" ) )
39 {
40 my $action = param( "modify" ) eq "modify" ? "mod" : "del";
41 my $link = param( "modify" ) eq "modify" ? "Modify" : "Delete";
42
43 @items = map { $items[ $_ ] . " " .
44 a( { -href => "$action" . "Forum.pl?file=$files
45 [$_ ]",
46 -class => "modify" },
47 "[ $link ]" ) }
48 ( 0 .. $#files );
49 }
50
51 print p( strong( "Avaliable Forums" ), ul( li( \@items ) ) );
52
53 @items = ( a( { -href => "addForum.pl" }, "Add a Forum" ),
54 a( { -href => "default.pl?modify=modify" }, "Modify a
55 Forum" ),
56 a( { -href => "default.pl?modify=delete" }, "Delete a
57 Forum" ),
58 a( { -href => "default.pl" }, "Home" ) );
59
60 print p( strong( "Forum Management" ), ul( li( \@items ) ) ),
61 end_html;
62 close XML;
63
64 sub startTag
65 {
66 my ( $expat, $element, %attributes ) = @_;
67 push( @files, $attributes{ "filename" } ) if $element eq "forum";
68 }
69
70 sub text
71 {
72 my ( $expat, $string ) = @_;
73 push( @forums, $string ) if $expat->in_element( "name" );
74 }
```
```
1 #!/usr/bin/perl
2 # Sol. 17.5: modForum.pl
34
use warnings;
5 use strict;
6 use CGI qw( :standard *center *table );
7 use XML::Parser;
8 use Fcntl qw( :flock );
9 use CGI::Carp qw( fatalsToBrowser );
10
11 print redirect( "error.html" ) if not param;
12
13 my ( $file, $parser, %info );
14 my $number = 0;
15
16 if ( param ) {
17 $file = param( "file" );
18 $file =~ /^\w+\.xml$/ or die "Not a valid file: $!";
19 open FORUM, "../htdocs/XML/$file" or die "Could not open: $!";
20 flock FORUM, LOCK_SH;
21
22 $parser = new XML::Parser( Style => "Subs",
23 Handlers => { Char => \&text } );
24 $parser->parse( \*FORUM );
25 close FORUM;
26
27 }
28 else {
29 print redirect( "error.html" );
30 }
31
32 sub forum
33 {
34 print header( -cache_control => "no-cache" );
35 }
36
37 sub forum_
38 {
39 print br, start_center,
40
41 a( { -href => "../cgi-bin/addPost.pl?file=$file" },
42 "Post a Message" ),
43 br, br,
44 a( { -href => "../cgi-bin/default.pl" },
45 "Return to Main Page" ),
46
47 end_center, end_html;
48 }
49
50 sub name_
51 {
52 print start_html( -title => $info{ "name" },
53 -style => { -src => "../XML/site.css" } ),
54
55 start_table( { -width => "100%",
56 -cellspacing => "0",
57 -cellpadding => "2" } ),
58
59 Tr( td( { -class => "forumTitle" }, $info{ "name" } ) ),
60
61 end_table, br;
62 }
63
64 sub message
65 {
66 my ( $expat, $element, %attributes ) = @_;
67 $info{ "date" } = $attributes{ "timestamp" };
68 }
69
70 sub message_
71 {
72 print start_table( { -width => "100%",
73 -cellspacing => "0",
74 -cellpadding => "2" } ),
75
76 Tr( [ td( { -class => "msgTitle" },
77 $info{ "title" } . " " .
78 a( { -href => "delPost.pl?file=$file&number=$number",
79 -class => "modify" },
80 "[ Delete ]" ) ),
81
82 td( { -class => "msgInfo" },
83 " by " . em( $info{ "user" } ) . " at " .
84 span( { -class => "date" }, $info{ "date" } ) ),
85
86 td( { -class => "msgText" }, $info{ "text" } ) ] ),
87
88 end_table;
89
90 $number++;
91 }
92
93 sub text
94 {
95 my ( $expat, $string ) = @_;
96 $info{ $expat->current_element } = $string;
97 }
```
```
1 #!/usr/bin/perl
2 # Sol. 17.5: delPost.pl
34
use warnings;
5 use strict;
6 use CGI qw( :standard );
7 use XML::DOM;
8 use Fcntl qw( :flock :DEFAULT );
9 use CGI::Carp qw( fatalsToBrowser );
10
11 if ( param ) {
12 my ( $parser, $document, $forums, $forum, $name, $erase,
13 $forumList );
14
15 my $file = param( "file" );
16
17 open XML, "+< ../htdocs/XML/$file" or die "Could not open: $!";
18 flock XML, LOCK_EX;
19
20 $parser = new XML::DOM::Parser;
21 $document = $parser->parse( \*XML );
22 $forums = $document->getDocumentElement;
23
24 $forumList = $forums->getElementsByTagName( "message" );
25 $forums->removeChild( $forumList->item( param( "number" ) ) );
26
27 seek XML, 0, 0;
28 truncate XML, 0;
29 $document->print( \*XML );
30 close XML;
31 print redirect( -cache_control => "no-cache", -location =>
32 "modForum.pl?file=$file" );
33
34 }
35 else {
36 print header, start_html( -title => "Modify a Forum",
37 -style => { -src => "../XML/site.css" } );
38 print start_form,
39 "Forum Name (to modify)", br,
40 textfield( -name => "file", -size => 40 ), br,
41 submit( -name => "submit", value => "Submit" ),
42 reset, end_form,
43 a( { -href => "default.pl" }, "Return to Main Page" ),
44 end_html;
45 }
```