ch06_04.htm

用perl编写CGI的好书。本书从解释CGI和底层HTTP协议如何工作开始

<p><a href="ch06_04.htm#ch06-83567">Example 6-14</a> contains the
<tt class="function">get_story</tt> function from the News module.</p>



<a name="ch06-83567" /><div class="example">
<h4 class="objtitle">Example 6-14. News.pm (part 2 of 3) </h4>

<blockquote><pre class="code">sub get_story {
    my( $filename ) = shift(  ) =~ /^(\d+)$/;
    my( $headline, $article );
    
    unless ( defined( $filename ) and -T "$NEWS_DIR/$filename" ) {
        return "Story Not Found", &lt;&lt;END_NOT_FOUND, get_time( time );
&lt;P&gt;Oops, the story you requested was not found.&lt;/P&gt;
&lt;P&gt;If a link on our What's New page brought you here, please
notify the &lt;A HREF="mailto:$ENV{SERVER_ADMIN}"&gt;webmaster&lt;/A&gt;.&lt;/P&gt;
END_NOT_FOUND
    }
    
    open STORY, "$NEWS_DIR/$filename" or
      die "Cannot open $NEWS_DIR/$filename: $!";
    flock STORY, LOCK_SH;
    $headline = &lt;STORY&gt;;
    chomp $headline;
    local $/ = undef;
    $article = &lt;STORY&gt;;
    
    return $headline, $article, get_date( $filename );
}</pre></blockquote>
</div>


<p>This function takes the story number as a parameter, and the first
thing this function does is verify that it is the expected format.
The <a name="INDEX-1478" />regular expression assignment
followed by the <tt class="function">defined</tt> test may seem like a
roundabout way to test this, but we do this in order to untaint the
<a name="INDEX-1479" />filename;
we explain tainting and why it's important in <a href="ch08_04.htm#ch08-28640">Section 8.4, "Perl's Taint Mode"</a>. Finally we make sure that this story exists
and is a text file.</p>


<p>If any of our checks fail, we return an error to the user formatted
like a standard story. Otherwise, we open the file read the headline
and contents, get its date, and return this to the page.</p>


<p>Now let's look at the administrative pages. The administrative
pages should be placed in a subdirectory beneath the other files. For
example, the files could be installed in the following locations:</p>


<blockquote><pre class="code">.../news/news.epl
.../news/article.epl
.../news/admin/edit_news.epl
.../news/admin/edit_article.epl</pre></blockquote>


<p>This enables us to configure the web server to restrict access to the
<em class="emphasis">admin</em> subdirectory. <a href="ch06_04.htm#ch06-70774">Example 6-15</a>
shows the main administrative page,
<em class="filename">admin_news.epl</em>.</p>



<a name="ch06-70774" /><div class="example">
<h4 class="objtitle">Example 6-15. admin_news.epl </h4>

<blockquote><pre class="code">&lt;HTML&gt;

[!
    use lib "/usr/local/apache/lib-perl";
    use News;
!]

[-  
    if ( my( $input ) = keys %fdat ) {
        my( $command, $story ) = split ":", $input;
        
        $command eq "new" and do {
            $http_headers_out{Location} = "edit_article.epl";
            exit;
        };
        $command eq "edit" and do {
            $http_headers_out{Location} = "edit_article.epl?story=$story";
            exit;
        };
        $command eq "delete" and
            News::delete_story( $story );
    }
    
    @stories = News::get_stories(  )
-]

&lt;HEAD&gt;
  &lt;TITLE&gt;What's New Administration&lt;/TITLE&gt;
&lt;/HEAD&gt;

&lt;BODY BGCOLOR="white"&gt;
  &lt;FORM METHOD="POST"&gt;
    &lt;H2&gt;What's New Administration&lt;/H2&gt;
    
    &lt;P&gt;Here you can edit and delete existing stories as well as create
      new stories. Clicking on a headline will take you to that article
      in the public area; you will need to use your browser's Back button
      to return.&lt;/P&gt;
    &lt;HR&gt;
    
    &lt;TABLE BORDER=1&gt;
    &lt;TR&gt;
      [- ( $story, $headline, $date ) = @{ $stories[$row] } if $stories[$row] -]
      &lt;TD&gt;
        &lt;INPUT TYPE="submit" NAME="edit:[+ $story +]" VALUE="Edit"&gt;
        &lt;INPUT TYPE="submit" NAME="delete:[+ $story +]" VALUE="Delete"
          onClick="return confirm('Are you sure you want to delete this?')"&gt;
      &lt;/TD&gt;
      &lt;TD&gt;
        &lt;A HREF="../article.epl?story=[+ $story +]"&gt;[+ $headline +]&lt;/A&gt;
        &lt;I&gt;[+ $date +]&lt;/I&gt;
      &lt;/TD&gt;
    &lt;/TR&gt;
    &lt;/TABLE&gt;
    
    &lt;INPUT TYPE="submit" NAME="new" VALUE="Create New Story"&gt;  
  &lt;/FORM&gt;

  &lt;HR&gt;
  &lt;P&gt;Go to &lt;A HREF="../news.epl"&gt;What's New&lt;/A&gt;.&lt;/P&gt;

&lt;/BODY&gt;
&lt;/HTML&gt;</pre></blockquote>
</div>


<p>The result looks like <a href="ch06_04.htm#ch06-53377">Figure 6-5</a>.</p>


<a name="ch06-53377" /><div class="figure"><img width="478" src="figs/cgi2.0605.gif" height="288" alt="Figure 6-5" /></div><h4 class="objtitle">Figure 6-5. Main administrative page for "What's New"</h4>

<p>This page must handle a few different requests. If it receives a
parameter, it uses a series of conditions to determine how to handle
the request. Let's return to these statements after looking at
the rest of the file because when the administrator first visits this
page, there are no parameters.</p>


<p>Like <em class="filename">news.epl</em>, we fetch an array of stories from
<tt class="function">get_stories</tt>, but instead of creating an ordered
list and looping over list items, we output a table and loop over
rows in this table. For each story, we output a corresponding Edit
and Delete button as well as a link to the story. Note that the name
of the Edit and Delete buttons contain the command as well as the
number of the story separated by a colon. This allows us to pass both
pieces of information when the administrator clicks on a button,
without restricting us from changing the label of the button.
Finally, we add a submit button to the bottom of the page to allow
the administrator to add a new story.</p>


<p>All the form elements on these page are submit buttons, and they will
only send a name-value pair if they are clicked. Thus, if the
administrator clicks a button, the browser will request the same page
again, passing a parameter for the selected button. Returning to the
conditions at the top of the file, if there is a parameter passed to
this file, it is split by colon into <tt class="literal">$command</tt> and
<tt class="literal">$story</tt>.</p>


<p>You may have noticed that if the administrator selects the button to
create a new story, then the supplied parameter will not include a
colon. That's okay because in this case,
<tt class="function">split</tt> will set <tt class="literal">$command</tt> to
"new" and <tt class="literal">$story</tt> to
<tt class="literal">undef</tt>. If <tt class="literal">$command</tt> is set to
"new", we forward the user to the
<em class="filename">edit_article.epl</em> file. To do this, we assign
Embperl's special <tt class="literal">%http_headers_out</tt>
variable. Setting the "Location" key to a value outputs a
<em class="emphasis">Location</em> HTTP header; we can then exit this
page.</p>


<p>If the administrator edits an existing story, we also forward to the
<em class="filename">edit_article.epl</em> file and exit, but in this case
we pass the story number as part of the query string. If the
administrator deletes a story, we invoke the
<tt class="function">delete_story</tt> function from our News module and
continue processing. Because we gather the list of stories after this
deletion, this page will display the updated list of headers.</p>


<p>We also add a JavaScript handler to the delete button to prevent
stray mouse clicks from deleting the wrong file. Even if you have
decided not to use JavaScript on your public site, it can be very
useful for administrative pages with limited access such as this,
where you typically can be more restrictive about the browsers
supported.</p>


<p>Finally, <a href="ch06_04.htm#ch06-90891">Example 6-16</a> presents
<em class="firstterm">edit_article.epl</em>, the page that allows the
administrator to create or edit articles.</p>



<a name="ch06-90891" /><div class="example">
<h4 class="objtitle">Example 6-16. edit_article.ep </h4>

<blockquote><pre class="code">&lt;HTML&gt;

[!
    use lib "/usr/local/apache/lib-perl";
    use News;
!]

[-
    if ( $fdat{story} ) {
        ( $fdat{headline}, $fdat{article} ) =
            News::get_story( $fdat{story} );
    }
    elsif ( $fdat{save} ) {
        News::save_story( $fdat{story}, $fdat{headline}, $fdat{article} );
        $http_headers_out{Location} = "edit_news.epl";
        exit;
    }
-]

&lt;HEAD&gt;
  &lt;TITLE&gt;Edit Article&lt;/TITLE&gt;
&lt;/HEAD&gt;

&lt;BODY BGCOLOR="white"&gt;
  &lt;H2&gt;Edit Article&lt;/H2&gt;
  
  &lt;HR&gt;
  &lt;FORM METHOD="POST"&gt;
    &lt;P&gt;&lt;B&gt;Headline: &lt;/B&gt;&lt;INPUT TYPE="text" NAME="headline" SIZE="50"&gt;&lt;/P&gt;
    
    &lt;P&gt;&lt;B&gt;Article:&lt;/B&gt; (HTML formatted)&lt;BR&gt;
      &lt;TEXTAREA NAME="article" COLS=60 ROWS=20&gt;&lt;/TEXTAREA&gt;&lt;/P&gt;
    
    &lt;INPUT TYPE="reset" VALUE="Reset Form"&gt;
    &lt;INPUT TYPE="submit" NAME="save" VALUE="Save Article"&gt;
    [$ hidden $]
  &lt;/FORM&gt;

  &lt;HR&gt;
  &lt;P&gt;Return to &lt;A HREF="edit_news.epl"&gt;What's New Administration&lt;/A&gt;.
    &lt;I&gt;Warning, you will lose your changes!&lt;/I&gt;&lt;/P&gt;

&lt;/BODY&gt;
&lt;/HTML&gt;</pre></blockquote>
</div>


<p>The result looks like <a href="ch06_04.htm#ch06-86259">Figure 6-6</a>.</p>


<a name="ch06-86259" /><div class="figure"><img width="473" src="figs/cgi2.0606.gif" height="375" alt="Figure 6-6" /></div><h4 class="objtitle">Figure 6-6. Article editing page</h4>

<p>If the administrator is editing a page, then the story number will be
supplied in the query string. We get this from
<tt class="literal">%fdat</tt> and fetch the headline and article contents
using <tt class="function">get_story</tt>. We then set these fields in
<tt class="literal">%fdat</tt> so that when Embperl encounters the
<em class="emphasis">headline</em> and <em class="emphasis">article</em> form
elements later in this file, it will pre-fill these defaults values
for us automatically. The hidden command in the form below will be
replaced with the story number if it was supplied. This is all we
need to do in order to have the form handle new stories as well as
edits.</p>


<p>When the administrator submits these changes, the story number (which
will be present for edits and undefined for additions), the headline
text, and the article text are supplied to the
<tt class="function">save_story</tt> function and the administrator is
redirected back to the main administrative page.</p>


<p>The administrative functions from <a name="INDEX-1480" />
<a name="INDEX-1481" />News are shown in <a href="ch06_04.htm#ch06-74481">Example 6-17</a>.</p>



<a name="ch06-74481" /><div class="example">
<h4 class="objtitle">Example 6-17. News.pm (part 3 of 3) </h4>

<blockquote><pre class="code">sub save_story {
    my( $story, $headline, $article ) = @_;
    local *STORY;
    
    $story ||= time;                        # name new files based on time in secs
    $article =~ s/\015\012|\015|\012/\n/g;  # make line endings consistent
    $headline =~ tr/\015\012//d;            # delete any line endings just in case
    
    my( $file ) = $story =~ /^(\d+)$/ or die "Illegal filename: '$story'";
    
    open STORY, "&gt; $NEWS_DIR/$file";
    flock STORY, LOCK_EX;
    seek STORY, 0, 0;
    print STORY $headline, "\n", $article;
    close STORY;
}

sub delete_story {
    my $story = shift;    
    my( $file ) = $story =~ /^(\d+)$/ or die "Illegal filename: '$story'";
    unlink "$NEWS_DIR/$file" or die "Cannot remove story $NEWS_DIR/$file: $!";
}</pre></blockquote>
</div>


<p>The <tt class="function">save_story</tt> function takes an optional story
file number, a headline, and article contents. If a number is not
provided for the story, <tt class="function">save_story</tt> assumes that
this is a new story and generates a new number from
<tt class="function">date</tt>. We convert line endings from browsers on
other platforms to the standard line ending for our web server and
trim any line-ending characters from the headline because these would
corrupt our data.</p>


<p>Again, we test the story number to make sure it is valid and then
open this file and write to it, replacing any previous version if
this is an update. We get an exclusive lock while we are writing so
someone else does not try to read it before we finish (and get a
partial news story). The <tt class="function">delete_story</tt> function
simply tests that the filename is <a name="INDEX-1482" /> <a name="INDEX-1,483" />valid and removes it.</p>
</div>
</div>




<a name="ch06-22-fm2xml" /><div class="sect2">
<h3 class="sect2">6.4.6. Summary</h3>


<p>As we have seen, Embperl presents a very different approach to
generating dynamic output with Perl. We've covered what you
need to know in order to develop most Embperl pages, but Embperl has
many features and options that we simply do not have room to present.
Fortunately, Embperl has extensive documentation, so if you want to
learn more about HTML::Embperl, you can download it from CPAN
<a name="INDEX-1484" />
<a name="INDEX-1485" />
<a name="INDEX-1486" />and visit
the <a name="INDEX-1487" />
<a name="INDEX-1488" />Embperl
website at <a href="http://perl.apache.org/embperl/">http://perl.apache.org/embperl/</a>.</p>
</div>


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