ch09_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

$message
END_OF_MESSAGE
    close MAIL or die "Error closing sendmail: $!";
}

sub send_receipt {
    my $email = shift;
    
    open MAIL, "| /usr/lib/sendmail -t -F'$from_name' -f'$from_email'"
        or die "Could not open sendmail: $!";
    print MAIL <<END_OF_MESSAGE;
To: $email
Subject: Your feedback

Your message has been sent and someone should be responding to you 
shortly. Thanks for taking the time to provide us with your feedback!
END_OF_MESSAGE
    close MAIL or die "Error closing sendmail: $!";
}</pre></blockquote>
</div>


<p>We collect two pieces of information from the user: an email address
and a message to send to customer service. We validate the email
address according to the subroutine earlier in this chapter, but we
don't include the code for that subroutine here. The script
then composes two messages and forwards users to a static page to
thank them.</p>


<p>The first message goes to customer service. It uses the
<em class="emphasis">-t</em>
<a name="INDEX-1877" /> option as well as the
<em class="emphasis">-i</em> option. The<a name="INDEX-1878" /> <em class="emphasis">-i</em> option is a
good idea if the message includes any dynamic information. It
prevents a single dot from prematurely ending the email message.</p>


<p>The <em class="emphasis">-t</em> option is the most important of these
options. It tells <tt class="command">sendmail</tt> to read the routing
information for the recipient from the message itself. Otherwise you
have to provide the recipient's email address on the command
line. Generally, you call <tt class="command">sendmail</tt> like this:</p>


<blockquote><pre class="code">/usr/lib/sendmail [e-mail]</pre></blockquote>


<p><tt class="command">sendmail</tt> then reads the message including the
headers and body from its STDIN and sends the message on to Mary,
even if the <em class="emphasis">To</em>, <em class="emphasis">Cc</em>, or
<em class="emphasis">Bcc</em> fields say it should go elsewhere! This can
get confusing.</p>


<p>You should always use the
<em class="emphasis">-t</em>
<a name="INDEX-1879" />
flag. First, it makes your life easier, since it automatically
handles the <em class="emphasis">To</em>, <em class="emphasis">Cc</em>, and
<em class="emphasis">Bcc</em> fields. Second, it lets you avoid that awful
<a name="INDEX-1880" />security risk of passing user data
through the <a name="INDEX-1881" />shell. Many times you will be
sending email to an address that was entered into an HTML form, so
being able to simply include the email address in the body of the
message instead is another big win.</p>


<p>Once this message has been sent, the script sends a
<a name="INDEX-1882" />confirmation to the user. It also uses the
<em class="emphasis">-t</em> option here, and here we see the security
benefit. The email address comes from the user, but we don't
have to worry about passing it through the shell.</p>


<p>In this second email, we also use two other
<a name="INDEX-1883" />fields to override the sender's
<a name="INDEX-1884" />routing information.
<tt class="command">sendmail</tt> will not automatically read the
sender's email address from the headers as it does for the
<em class="emphasis">-t</em> option. This must be specified with the
<em class="emphasis">-f</em>
<a name="INDEX-1885" /> and <em class="emphasis">-F</em> options.
There are two options in order to support the extended address
notation including a name and an email address in this form:</p>


<blockquote><pre class="code">The Webmaster &lt;[e-mail]&gt;</pre></blockquote>


<p>It is important to override the sender's routing information
because if the message to Mary bounces, it will come back to the
original sender, and if the
<a name="INDEX-1886" /> <a name="INDEX-1,887" />user that the web server runs as has a
standard account with a mail box, bounced messages will collect
there. If it has no mail account, then they'll bounce back and
forth either until they time out or some system administrator gets
annoyed at the increased network traffic and steps in. Ideally, your
system should be configured so that any mail addressed to
<em class="emphasis">nobody</em> (the user your web server runs as) is
automatically forwarded to the webmaster. If this hasn't been
done, or you aren't sure, then it's a good idea to set
the <em class="emphasis">-f</em> option to a real email address that
someone monitors or that is processed automatically. We'll see
how to set up a process to handle mail like this at the end of this
chapter.</p>


<p>Note that if you do <a name="INDEX-1888" />override the sender's email
address with the <em class="emphasis">-f</em> option,
<tt class="command">sendmail</tt> will add an extra
<a name="INDEX-1889" />header to the email message unless you
are a <a name="INDEX-1890" />
<a name="INDEX-1891" />trusted user. This extra header
typically looks like the following:</p>


<blockquote><pre class="code">X-Authentication-Warning: scripted.com: sguelich set sender to [e-mail] using -f</pre></blockquote>


<p>By default, the users who have permission to use the
<em class="emphasis">-f</em> option without generating this warning are
<em class="emphasis">root</em>, <em class="emphasis">daemon</em>, and
<em class="emphasis">uucp</em>. Most mail agents do not actually pay
attention to this header, so it is rare that recipients will see it.
However, you can avoid sending it by adding
<em class="emphasis">nobody</em> to the trusted users section in
<em class="filename">/etc/sendmail.cf</em>.</p>
</div>




<a name="ch09-6-fm2xml" /><div class="sect2">
<h3 class="sect2">9.4.2. Mail Queue</h3>


<p>The remaining option <a name="INDEX-1892" />
<a name="INDEX-1893" /> <a name="INDEX-1,894" /> <a name="INDEX-1,895" />we haven't discussed is the
<em class="emphasis">-odq</em> option. It is useful if you are sending out
many messages at the same time. For example, you may run a web site
that connects job hunters with available positions. You have the job
hunters record keywords describing the types of positions they are
looking for in a database along with their email addresses. Then,
when the new positions available today have been entered, you start a
CGI script which matches the job hunters' keywords against the
positions. The script generates and sends out customized messages to
the job hunters notifying them if there are any matches. In this
example, you would want to use the <em class="emphasis">-odq</em> option.
It takes sendmail time to find remote servers and deliver messages,
so your script runs much, much faster if you simply add them to the
queue to be processed separately and don't wait for sendmail to
try to deliver each message.</p>


<p>You do need to make sure that <em class="emphasis">sendmail</em> is
configured on your system to process the queue or the messages may
just sit around indefinitely. If you aren't sure, ask your
system administrator.</p>


<p>Also note that queuing messages this way is only a good idea if each
message you are sending out is unique. If you are sending the same
message to multiple people, don't queue a separate message
addressed to each person, 
<a name="INDEX-1896" /> <a name="INDEX-1,897" /> <a name="INDEX-1,898" />use the
<em class="emphasis">Bcc</em>
<a name="INDEX-1899" /> field instead.</p>
</div>


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