X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfaq9.pod;h=d1bd593dfe7690c16f2a977b086d5e302a7eb48b;hb=2aa761807d7eac561ade382b2c66eebffcdf056f;hp=d7faca02e316951b7ebc8ab92775ff6a5eb5e7a2;hpb=bfd13ef816abf16369321d26f2f63772eff5cd21;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perlfaq9.pod b/pod/perlfaq9.pod
index d7faca0..d1bd593 100644
--- a/pod/perlfaq9.pod
+++ b/pod/perlfaq9.pod
@@ -1,40 +1,88 @@
 =head1 NAME
 
-perlfaq9 - Networking ($Revision: 1.16 $, $Date: 1997/04/23 18:12:06 $)
+perlfaq9 - Networking ($Revision: 1.26 $, $Date: 1999/05/23 16:08:30 $)
 
 =head1 DESCRIPTION
 
 This section deals with questions related to networking, the internet,
 and a few on the web.
 
-=head2 My CGI script runs from the command line but not the browser.  Can you help me fix it?
+=head2 My CGI script runs from the command line but not the browser.   (500 Server Error)
 
-Sure, but you probably can't afford our contracting rates :-)
+If you can demonstrate that you've read the following FAQs and that
+your problem isn't something simple that can be easily answered, you'll
+probably receive a courteous and useful reply to your question if you
+post it on comp.infosystems.www.authoring.cgi (if it's something to do
+with HTTP, HTML, or the CGI protocols).  Questions that appear to be Perl
+questions but are really CGI ones that are posted to comp.lang.perl.misc
+may not be so well received.
 
-Seriously, if you can demonstrate that you've read the following FAQs
-and that your problem isn't something simple that can be easily
-answered, you'll probably receive a courteous and useful reply to your
-question if you post it on comp.infosystems.www.authoring.cgi (if it's
-something to do with HTTP, HTML, or the CGI protocols).  Questions that
-appear to be Perl questions but are really CGI ones that are posted to
-comp.lang.perl.misc may not be so well received.
+The useful FAQs and related documents are:
 
-The useful FAQs are:
+    CGI FAQ
+        http://www.webthing.com/tutorials/cgifaq.html
 
-    http://www.perl.com/perl/faq/idiots-guide.html
-    http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
-    http://www.perl.com/perl/faq/perl-cgi-faq.html
-    http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
-    http://www.boutell.com/faq/
+    Web FAQ
+        http://www.boutell.com/faq/
+
+    WWW Security FAQ
+        http://www.w3.org/Security/Faq/
+
+    HTTP Spec
+        http://www.w3.org/pub/WWW/Protocols/HTTP/
+
+    HTML Spec
+        http://www.w3.org/TR/REC-html40/
+        http://www.w3.org/pub/WWW/MarkUp/
+
+    CGI Spec
+        http://www.w3.org/CGI/
+
+    CGI Security FAQ
+        http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
+
+=head2 How can I get better error messages from a CGI program?
+
+Use the CGI::Carp module.  It replaces C<warn> and C<die>, plus the
+normal Carp modules C<carp>, C<croak>, and C<confess> functions with
+more verbose and safer versions.  It still sends them to the normal
+server error log.
+
+    use CGI::Carp;
+    warn "This is a complaint";
+    die "But this one is serious";
+
+The following use of CGI::Carp also redirects errors to a file of your choice,
+placed in a BEGIN block to catch compile-time warnings as well:
+
+    BEGIN {
+        use CGI::Carp qw(carpout);
+        open(LOG, ">>/var/local/cgi-logs/mycgi-log")
+            or die "Unable to append to mycgi-log: $!\n";
+        carpout(*LOG);
+    }
+
+You can even arrange for fatal errors to go back to the client browser,
+which is nice for your own debugging, but might confuse the end user.
+
+    use CGI::Carp qw(fatalsToBrowser);
+    die "Bad error here";
+
+Even if the error happens before you get the HTTP header out, the module
+will try to take care of this to avoid the dreaded server 500 errors.
+Normal warnings still go out to the server error log (or wherever
+you've sent them with C<carpout>) with the application name and date
+stamp prepended.
 
 =head2 How do I remove HTML from a string?
 
-The most correct way (albeit not the fastest) is to use HTML::Parse
-from CPAN (part of the libwww-perl distribution, which is a must-have
-module for all web hackers).
+The most correct way (albeit not the fastest) is to use HTML::Parser
+from CPAN.  Another mostly correct
+way is to use HTML::FormatText which not only removes HTML but also
+attempts to do a little simple formatting of the resulting plain text.
 
 Many folks attempt a simple-minded regular expression approach, like
-C<s/E<lt>.*?E<gt>//g>, but that fails in many cases because the tags
+C<< s/<.*?>//g >>, but that fails in many cases because the tags
 may continue over line breaks, they may contain quoted angle-brackets,
 or HTML comment may be present.  Plus folks forget to convert
 entities, like C<&lt;> for example.
@@ -49,6 +97,29 @@ program in
 http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/striphtml.gz
 .
 
+Here are some tricky cases that you should think about when picking
+a solution:
+
+    <IMG SRC = "foo.gif" ALT = "A > B">
+
+    <IMG SRC = "foo.gif"
+	 ALT = "A > B">
+
+    <!-- <A comment> -->
+
+    <script>if (a<b && a>c)</script>
+
+    <# Just data #>
+
+    <![INCLUDE CDATA [ >>>>>>>>>>>> ]]>
+
+If HTML comments include other tags, those solutions would also break
+on text like this:
+
+    <!-- This section commented out.
+        <B>You can't see me!</B>
+    -->
+
 =head2 How do I extract URLs?
 
 A quick but imperfect approach is
@@ -62,12 +133,11 @@ A quick but imperfect approach is
     }gsix;
 
 This version does not adjust relative URLs, understand alternate
-bases, deal with HTML comments, deal with HREF and NAME attributes in
-the same tag, or accept URLs themselves as arguments.  It also runs
-about 100x faster than a more "complete" solution using the LWP suite
-of modules, such as the
-http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz
-program.
+bases, deal with HTML comments, deal with HREF and NAME attributes
+in the same tag, understand extra qualifiers like TARGET, or accept
+URLs themselves as arguments.  It also runs about 100x faster than a
+more "complete" solution using the LWP suite of modules, such as the
+http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz program.
 
 =head2 How do I download a file from the user's machine?  How do I open a file on another machine?
 
@@ -78,7 +148,7 @@ the same as the startform() method.
 
 =head2 How do I make a pop-up menu in HTML?
 
-Use the B<E<lt>SELECTE<gt>> and B<E<lt>OPTIONE<gt>> tags.  The CGI.pm
+Use the B<< <SELECT> >> and B<< <OPTION> >> tags.  The CGI.pm
 module (available from CPAN) supports this widget, as well as many
 others, including some that it cleverly synthesizes on its own.
 
@@ -90,16 +160,22 @@ on your system, is this:
     $html_code = `lynx -source $url`;
     $text_data = `lynx -dump $url`;
 
-The libwww-perl (LWP) modules from CPAN provide a more powerful way to
-do this.  They work through proxies, and don't require lynx:
+The libwww-perl (LWP) modules from CPAN provide a more powerful way
+to do this.  They don't require lynx, but like lynx, can still work
+through proxies:
 
-    # print HTML from a URL
+    # simplest version
     use LWP::Simple;
-    getprint "http://www.sn.no/libwww-perl/";
+    $content = get($URL);
 
-    # print ASCII from HTML from a URL
+    # or print HTML from a URL
     use LWP::Simple;
-    use HTML::Parse;
+    getprint "http://www.linpro.no/lwp/";
+
+    # or print ASCII from HTML from a URL
+    # also need HTML-Tree package from CPAN
+    use LWP::Simple;
+    use HTML::Parser;
     use HTML::FormatText;
     my ($html, $ascii);
     $html = get("http://www.perl.com/");
@@ -108,7 +184,30 @@ do this.  They work through proxies, and don't require lynx:
     $ascii = HTML::FormatText->new->format(parse_html($html));
     print $ascii;
 
-=head2 how do I decode or create those %-encodings on the web?
+=head2 How do I automate an HTML form submission?
+
+If you're submitting values using the GET method, create a URL and encode
+the form using the C<query_form> method:
+
+    use LWP::Simple;
+    use URI::URL;
+
+    my $url = url('http://www.perl.com/cgi-bin/cpan_mod');
+    $url->query_form(module => 'DB_File', readme => 1);
+    $content = get($url);
+
+If you're using the POST method, create your own user agent and encode
+the content appropriately.
+
+    use HTTP::Request::Common qw(POST);
+    use LWP::UserAgent;
+
+    $ua = LWP::UserAgent->new();
+    my $req = POST 'http://www.perl.com/cgi-bin/cpan_mod',
+                   [ module => 'DB_File', readme => 1 ];
+    $content = $ua->request($req)->as_string;
+
+=head2 How do I decode or create those %-encodings on the web?
 
 Here's an example of decoding:
 
@@ -116,11 +215,12 @@ Here's an example of decoding:
     $string =~ s/%([a-fA-F0-9]{2})/chr(hex($1))/ge;
 
 Encoding is a bit harder, because you can't just blindly change
-all the non-alphanumunder character (C<\W>) into their hex escapes.
+all characters that are not letters, digits or underscores (C<\W>)
+into their hex escapes.
 It's important that characters with special meaning like C</> and C<?>
 I<not> be translated.  Probably the easiest way to get this right is
 to avoid reinventing the wheel and just use the URI::Escape module,
-which is part of the libwww-perl package (LWP) available from CPAN.
+available from CPAN.
 
 =head2 How do I redirect to another page?
 
@@ -135,6 +235,26 @@ both:
 Note that relative URLs in these headers can cause strange effects
 because of "optimizations" that servers do.
 
+    $url = "http://www.perl.com/CPAN/";
+    print "Location: $url\n\n";
+    exit;
+
+To target a particular frame in a frameset, include the "Window-target:"
+in the header.
+
+    print <<EOF;
+    Location: http://www.domain.com/newpage
+    Window-target: <FrameName>
+
+    EOF
+
+To be correct to the spec, each of those virtual newlines should really be
+physical C<"\015\012"> sequences by the time you hit the client browser.
+Except for NPH scripts, though, that local newline should get translated
+by your server into standard form, so you shouldn't have a problem
+here, even if you are stuck on MacOS.  Everybody else probably won't
+even notice.
+
 =head2 How do I put a password on my web pages?
 
 That depends.  You'll need to read the documentation for your web
@@ -166,7 +286,7 @@ C<eval> or C<system> calls.  In addition to tainting, never use the
 single-argument form of system() or exec().  Instead, supply the
 command and arguments as a list, which prevents shell globbing.
 
-=head2 How do I parse an email header?
+=head2 How do I parse a mail header?
 
 For a quick-and-dirty solution, try this solution derived
 from page 222 of the 2nd edition of "Programming Perl":
@@ -182,44 +302,82 @@ the Mail::Header module from CPAN (part of the MailTools package).
 
 =head2 How do I decode a CGI form?
 
-A lot of people are tempted to code this up themselves, so you've
-probably all seen a lot of code involving C<$ENV{CONTENT_LENGTH}> and
-C<$ENV{QUERY_STRING}>.  It's true that this can work, but there are
-also a lot of versions of this floating around that are quite simply
-broken!
-
-Please do not be tempted to reinvent the wheel.  Instead, use the
-CGI.pm or CGI_Lite.pm (available from CPAN), or if you're trapped in
-the module-free land of perl1 .. perl4, you might look into cgi-lib.pl
-(available from http://www.bio.cam.ac.uk/web/form.html).
-
-=head2 How do I check a valid email address?
-
-You can't.
-
-Without sending mail to the address and seeing whether it bounces (and
-even then you face the halting problem), you cannot determine whether
-an email address is valid.  Even if you apply the email header
-standard, you can have problems, because there are deliverable
-addresses that aren't RFC-822 (the mail header standard) compliant,
-and addresses that aren't deliverable which are compliant.
-
-Many are tempted to try to eliminate many frequently-invalid email
-addresses with a simple regexp, such as
-C</^[\w.-]+\@([\w.-]\.)+\w+$/>.  However, this also throws out many
-valid ones, and says nothing about potential deliverability, so is not
-suggested.  Instead, see
+You use a standard module, probably CGI.pm.  Under no circumstances
+should you attempt to do so by hand!
+
+You'll see a lot of CGI programs that blindly read from STDIN the number
+of bytes equal to CONTENT_LENGTH for POSTs, or grab QUERY_STRING for
+decoding GETs.  These programs are very poorly written.  They only work
+sometimes.  They typically forget to check the return value of the read()
+system call, which is a cardinal sin.  They don't handle HEAD requests.
+They don't handle multipart forms used for file uploads.  They don't deal
+with GET/POST combinations where query fields are in more than one place.
+They don't deal with keywords in the query string.
+
+In short, they're bad hacks.  Resist them at all costs.  Please do not be
+tempted to reinvent the wheel.  Instead, use the CGI.pm or CGI_Lite.pm
+(available from CPAN), or if you're trapped in the module-free land
+of perl1 .. perl4, you might look into cgi-lib.pl (available from
+http://cgi-lib.stanford.edu/cgi-lib/ ).
+
+Make sure you know whether to use a GET or a POST in your form.
+GETs should only be used for something that doesn't update the server.
+Otherwise you can get mangled databases and repeated feedback mail
+messages.  The fancy word for this is ``idempotency''.  This simply
+means that there should be no difference between making a GET request
+for a particular URL once or multiple times.  This is because the
+HTTP protocol definition says that a GET request may be cached by the
+browser, or server, or an intervening proxy.  POST requests cannot be
+cached, because each request is independent and matters.  Typically,
+POST requests change or depend on state on the server (query or update
+a database, send mail, or purchase a computer).
+
+=head2 How do I check a valid mail address?
+
+You can't, at least, not in real time.  Bummer, eh?
+
+Without sending mail to the address and seeing whether there's a human
+on the other hand to answer you, you cannot determine whether a mail
+address is valid.  Even if you apply the mail header standard, you
+can have problems, because there are deliverable addresses that aren't
+RFC-822 (the mail header standard) compliant, and addresses that aren't
+deliverable which are compliant.
+
+Many are tempted to try to eliminate many frequently-invalid
+mail addresses with a simple regex, such as
+C</^[\w.-]+\@([\w.-]\.)+\w+$/>.  It's a very bad idea.  However,
+this also throws out many valid ones, and says nothing about
+potential deliverability, so is not suggested.  Instead, see
 http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz ,
 which actually checks against the full RFC spec (except for nested
-comments), looks for addresses you may not wish to accept email to
+comments), looks for addresses you may not wish to accept mail to
 (say, Bill Clinton or your postmaster), and then makes sure that the
-hostname given can be looked up in DNS.  It's not fast, but it works.
+hostname given can be looked up in the DNS MX records.  It's not fast,
+but it works for what it tries to do.
+
+Our best advice for verifying a person's mail address is to have them
+enter their address twice, just as you normally do to change a password.
+This usually weeds out typos.  If both versions match, send
+mail to that address with a personal message that looks somewhat like:
+
+    Dear someuser@host.com,
 
-Here's an alternative strategy used by many CGI script authors: Check
-the email address with a simple regexp (such as the one above).  If
-the regexp matched the address, accept the address.  If the regexp
-didn't match the address, request confirmation from the user that the
-email address they entered was correct.
+    Please confirm the mail address you gave us Wed May  6 09:38:41
+    MDT 1998 by replying to this message.  Include the string
+    "Rumpelstiltskin" in that reply, but spelled in reverse; that is,
+    start with "Nik...".  Once this is done, your confirmed address will
+    be entered into our records.
+
+If you get the message back and they've followed your directions,
+you can be reasonably assured that it's real.
+
+A related strategy that's less open to forgery is to give them a PIN
+(personal ID number).  Record the address and PIN (best that it be a
+random one) for later processing.  In the mail you send, ask them to
+include the PIN in their reply.  But if it bounces, or the message is
+included via a ``vacation'' script, it'll be there anyway.  So it's
+best to ask them to mail back a slight alteration of the PIN, such as
+with the characters reversed, one added or subtracted to each digit, etc.
 
 =head2 How do I decode a MIME/BASE64 string?
 
@@ -237,18 +395,18 @@ format after minor transliterations:
     $len = pack("c", 32 + 0.75*length);   # compute length byte
     print unpack("u", $len . $_);         # uudecode and print
 
-=head2 How do I return the user's email address?
+=head2 How do I return the user's mail address?
 
-On systems that support getpwuid, the $E<lt> variable and the
+On systems that support getpwuid, the $< variable and the
 Sys::Hostname module (which is part of the standard perl distribution),
 you can probably try using something like this:
 
     use Sys::Hostname;
-    $address = sprintf('%s@%s', getpwuid($<), hostname);
+    $address = sprintf('%s@%s', scalar getpwuid($<), hostname);
 
-Company policies on email address can mean that this generates addresses
-that the company's email system will not accept, so you should ask for
-users' email addresses when this matters.  Furthermore, not all systems
+Company policies on mail address can mean that this generates addresses
+that the company's mail system will not accept, so you should ask for
+users' mail addresses when this matters.  Furthermore, not all systems
 on which Perl runs are so forthcoming with this information as is Unix.
 
 The Mail::Util module from CPAN (part of the MailTools package) provides a
@@ -257,36 +415,90 @@ It makes a more intelligent guess than the code above, using information
 given when the module was installed, but it could still be incorrect.
 Again, the best way is often just to ask the user.
 
-=head2 How do I send/read mail?
-
-Sending mail: the Mail::Mailer module from CPAN (part of the MailTools
-package) is UNIX-centric, while Mail::Internet uses Net::SMTP which is
-not UNIX-centric.  Reading mail: use the Mail::Folder module from CPAN
-(part of the MailFolder package) or the Mail::Internet module from
-CPAN (also part of the MailTools package).
-
-   # sending mail
-    use Mail::Internet;
-    use Mail::Header;
-    # say which mail host to use
-    $ENV{SMTPHOSTS} = 'mail.frii.com';
-    # create headers
-    $header = new Mail::Header;
-    $header->add('From', 'gnat@frii.com');
-    $header->add('Subject', 'Testing');
-    $header->add('To', 'gnat@frii.com');
-    # create body
-    $body = 'This is a test, ignore';
-    # create mail object
-    $mail = new Mail::Internet(undef, Header => $header, Body => \[$body]);
-    # send it
-    $mail->smtpsend or die;
+=head2 How do I send mail?
+
+Use the C<sendmail> program directly:
+
+    open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq")
+                        or die "Can't fork for sendmail: $!\n";
+    print SENDMAIL <<"EOF";
+    From: User Originating Mail <me\@host>
+    To: Final Destination <you\@otherhost>
+    Subject: A relevant subject line
+
+    Body of the message goes here after the blank line
+    in as many lines as you like.
+    EOF
+    close(SENDMAIL)     or warn "sendmail didn't close nicely";
+
+The B<-oi> option prevents sendmail from interpreting a line consisting
+of a single dot as "end of message".  The B<-t> option says to use the
+headers to decide who to send the message to, and B<-odq> says to put
+the message into the queue.  This last option means your message won't
+be immediately delivered, so leave it out if you want immediate
+delivery.
+
+Alternate, less convenient approaches include calling mail (sometimes
+called mailx) directly or simply opening up port 25 have having an
+intimate conversation between just you and the remote SMTP daemon,
+probably sendmail.
+
+Or you might be able use the CPAN module Mail::Mailer:
+
+    use Mail::Mailer;
+
+    $mailer = Mail::Mailer->new();
+    $mailer->open({ From    => $from_address,
+                    To      => $to_address,
+                    Subject => $subject,
+                  })
+        or die "Can't open: $!\n";
+    print $mailer $body;
+    $mailer->close();
+
+The Mail::Internet module uses Net::SMTP which is less Unix-centric than
+Mail::Mailer, but less reliable.  Avoid raw SMTP commands.  There
+are many reasons to use a mail transport agent like sendmail.  These
+include queueing, MX records, and security.
+
+=head2 How do I read mail?
+
+While you could use the Mail::Folder module from CPAN (part of the
+MailFolder package) or the Mail::Internet module from CPAN (also part
+of the MailTools package), often a module is overkill, though.  Here's a
+mail sorter.
+
+    #!/usr/bin/perl
+    # bysub1 - simple sort by subject
+    my(@msgs, @sub);
+    my $msgno = -1;
+    $/ = '';                    # paragraph reads
+    while (<>) {
+        if (/^From/m) {
+            /^Subject:\s*(?:Re:\s*)*(.*)/mi;
+            $sub[++$msgno] = lc($1) || '';
+        }
+        $msgs[$msgno] .= $_;
+    }
+    for my $i (sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msgs)) {
+        print $msgs[$i];
+    }
+
+Or more succinctly,
+
+    #!/usr/bin/perl -n00
+    # bysub2 - awkish sort-by-subject
+    BEGIN { $msgno = -1 }
+    $sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m;
+    $msg[$msgno] .= $_;
+    END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msg) ] }
 
 =head2 How do I find out my hostname/domainname/IP address?
 
-A lot of code has historically cavalierly called the C<`hostname`>
-program.  While sometimes expedient, this isn't very portable.  It's
-one of those tradeoffs of convenience versus portability.
+The normal way to find your own hostname is to call the C<`hostname`>
+program.  While sometimes expedient, this has some problems, such as
+not knowing whether you've got the canonical name or not.  It's one of
+those tradeoffs of convenience versus portability.
 
 The Sys::Hostname module (part of the standard perl distribution) will
 give you the hostname after which you can find out the IP address
@@ -295,7 +507,7 @@ give you the hostname after which you can find out the IP address
     use Socket;
     use Sys::Hostname;
     my $host = hostname();
-    my $addr = inet_ntoa(scalar(gethostbyname($host || 'localhost')));
+    my $addr = inet_ntoa(scalar gethostbyname($host || 'localhost'));
 
 Probably the simplest way to learn your DNS domain name is to grok
 it out of /etc/resolv.conf, at least under Unix.  Of course, this
@@ -322,10 +534,23 @@ available from CPAN) is more complex but can put as well as fetch.
 
 A DCE::RPC module is being developed (but is not yet available), and
 will be released as part of the DCE-Perl package (available from
-CPAN).  No ONC::RPC module is known.
+CPAN).  The rpcgen suite, available from CPAN/authors/id/JAKE/, is
+an RPC stub generator and includes an RPC::ONC module.
 
 =head1 AUTHOR AND COPYRIGHT
 
-Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
-All rights reserved.  See L<perlfaq> for distribution information.
-
+Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
+All rights reserved.
+
+When included as part of the Standard Version of Perl, or as part of
+its complete documentation whether printed or otherwise, this work
+may be distributed only under the terms of Perl's Artistic License.
+Any distribution of this file or derivatives thereof I<outside>
+of that package require that special arrangements be made with
+copyright holder.
+
+Irrespective of its distribution, all code examples in this file
+are hereby placed into the public domain.  You are permitted and
+encouraged to use this code in your own programs for fun
+or for profit as you see fit.  A simple comment in the code giving
+credit would be courteous but is not required.