NAME

       perlfaq9 - Web, Email and Networking

VERSION

       version 5.20210411

DESCRIPTION

       This section deals with questions related to running web sites, sending and receiving
       email as well as general networking.

   Should I use a web framework?
       Yes. If you are building a web site with any level of interactivity (forms / users /
       databases), you will want to use a framework to make handling requests and responses
       easier.

       If there is no interactivity then you may still want to look at using something like
       Template Toolkit <https://metacpan.org/module/Template> or
       Plack::Middleware::TemplateToolkit so maintenance of your HTML files (and other assets) is
       easier.

   Which web framework should I use?
       There is no simple answer to this question. Perl frameworks can run everything from basic
       file servers and small scale intranets to massive multinational multilingual websites that
       are the core to international businesses.

       Below is a list of a few frameworks with comments which might help you in making a
       decision, depending on your specific requirements. Start by reading the docs, then ask
       questions on the relevant mailing list or IRC channel.

       Catalyst
           Strongly object-oriented and fully-featured with a long development history and a
           large community and addon ecosystem. It is excellent for large and complex
           applications, where you have full control over the server.

       Dancer2
           Free of legacy weight, providing a lightweight and easy to learn API.  Has a growing
           addon ecosystem. It is best used for smaller projects and very easy to learn for
           beginners.

       Mojolicious
           Self-contained and powerful for both small and larger projects, with a focus on HTML5
           and real-time web technologies such as WebSockets.

       Web::Simple
           Strongly object-oriented and minimal, built for speed and intended as a toolkit for
           building micro web apps, custom frameworks or for tieing together existing Plack-
           compatible web applications with one central dispatcher.

       All of these interact with or use Plack which is worth understanding the basics of when
       building a website in Perl (there is a lot of useful Plack::Middleware
       <https://metacpan.org/search?q=plack%3A%3Amiddleware>).

   What is Plack and PSGI?
       PSGI is the Perl Web Server Gateway Interface Specification, it is a standard that many
       Perl web frameworks use, you should not need to understand it to build a web site, the
       part you might want to use is Plack.

       Plack is a set of tools for using the PSGI stack. It contains middleware
       <https://metacpan.org/search?q=plack%3A%3Amiddleware> components, a reference server and
       utilities for Web application frameworks.  Plack is like Ruby's Rack or Python's Paste for
       WSGI.

       You could build a web site using Plack and your own code, but for anything other than a
       very basic web site, using a web framework (that uses <https://plackperl.org>) is a better
       option.

   How do I remove HTML from a string?
       Use HTML::Strip, or HTML::FormatText which not only removes HTML but also attempts to do a
       little simple formatting of the resulting plain text.

   How do I extract URLs?
       HTML::SimpleLinkExtor will extract URLs from HTML, it handles anchors, images, objects,
       frames, and many other tags that can contain a URL.  If you need anything more complex,
       you can create your own subclass of HTML::LinkExtor or HTML::Parser. You might even use
       HTML::SimpleLinkExtor as an example for something specifically suited to your needs.

       You can use URI::Find or URL::Search to extract URLs from an arbitrary text document.

   How do I fetch an HTML file?
       (contributed by brian d foy)

       The core HTTP::Tiny module can fetch web resources and give their content back to you as a
       string:

           use HTTP::Tiny;

           my $ua = HTTP::Tiny->new;
           my $html = $ua->get( "http://www.example.com/index.html" )->{content};

       It can also store the resource directly in a file:

           $ua->mirror( "http://www.example.com/index.html", "foo.html" );

       If you need to do something more complicated, the HTTP::Tiny object can be customized by
       setting attributes, or you can use LWP::UserAgent from the libwww-perl distribution or
       Mojo::UserAgent from the Mojolicious distribution to make common tasks easier. If you want
       to simulate an interactive web browser, you can use the WWW::Mechanize module.

   How do I automate an HTML form submission?
       If you are doing something complex, such as moving through many pages and forms or a web
       site, you can use WWW::Mechanize. See its documentation for all the details.

       If you're submitting values using the GET method, create a URL and encode the form using
       the "www_form_urlencode" method from HTTP::Tiny:

           use HTTP::Tiny;

           my $ua = HTTP::Tiny->new;

           my $query = $ua->www_form_urlencode([ q => 'DB_File', lucky => 1 ]);
           my $url = "https://metacpan.org/search?$query";
           my $content = $ua->get($url)->{content};

       If you're using the POST method, the "post_form" method will encode the content
       appropriately.

           use HTTP::Tiny;

           my $ua = HTTP::Tiny->new;

           my $url = 'https://metacpan.org/search';
           my $form = [ q => 'DB_File', lucky => 1 ];
           my $content = $ua->post_form($url, $form)->{content};

   How do I decode or create those %-encodings on the web?
       Most of the time you should not need to do this as your web framework, or if you are
       making a request, the LWP or other module would handle it for you.

       To encode a string yourself, use the URI::Escape module. The "uri_escape" function returns
       the escaped string:

           my $original = "Colon : Hash # Percent %";

           my $escaped = uri_escape( $original );

           print "$escaped\n"; # 'Colon%20%3A%20Hash%20%23%20Percent%20%25'

       To decode the string, use the "uri_unescape" function:

           my $unescaped = uri_unescape( $escaped );

           print $unescaped; # back to original

       Remember not to encode a full URI, you need to escape each component separately and then
       join them together.

   How do I redirect to another page?
       Most Perl Web Frameworks will have a mechanism for doing this, using the Catalyst
       framework it would be:

           $c->res->redirect($url);
           $c->detach();

       If you are using Plack (which most frameworks do), then Plack::Middleware::Rewrite is
       worth looking at if you are migrating from Apache or have URL's you want to always
       redirect.

   How do I put a password on my web pages?
       See if the web framework you are using has an authentication system and if that fits your
       needs.

       Alternativly look at Plack::Middleware::Auth::Basic, or one of the other Plack
       authentication <https://metacpan.org/search?q=plack+auth> options.

   How do I make sure users can't enter values into a form that causes my CGI script to do bad
       things?
       (contributed by brian d foy)

       You can't prevent people from sending your script bad data. Even if you add some client-
       side checks, people may disable them or bypass them completely. For instance, someone
       might use a module such as LWP to submit to your web site. If you want to prevent data
       that try to use SQL injection or other sorts of attacks (and you should want to), you have
       to not trust any data that enter your program.

       The perlsec documentation has general advice about data security.  If you are using the
       DBI module, use placeholder to fill in data.  If you are running external programs with
       "system" or "exec", use the list forms. There are many other precautions that you should
       take, too many to list here, and most of them fall under the category of not using any
       data that you don't intend to use. Trust no one.

   How do I parse a mail header?
       Use the Email::MIME module. It's well-tested and supports all the craziness that you'll
       see in the real world (comment-folding whitespace, encodings, comments, etc.).

         use Email::MIME;

         my $message = Email::MIME->new($rfc2822);
         my $subject = $message->header('Subject');
         my $from    = $message->header('From');

       If you've already got some other kind of email object, consider passing it to
       Email::Abstract and then using its cast method to get an Email::MIME object:

         my $abstract = Email::Abstract->new($mail_message_object);
         my $email_mime_object = $abstract->cast('Email::MIME');

   How do I check a valid mail address?
       (partly contributed by Aaron Sherman)

       This isn't as simple a question as it sounds. There are two parts:

       a) How do I verify that an email address is correctly formatted?

       b) How do I verify that an email address targets a valid recipient?

       Without sending mail to the address and seeing whether there's a human on the other end to
       answer you, you cannot fully answer part b, but the Email::Valid module will do both part
       a and part b as far as you can in real-time.

       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. 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, include a link to your site with the PIN included. If the mail bounces, you
       know it's not valid. If they don't click on the link, either they forged the address or
       (assuming they got the message) following through wasn't important so you don't need to
       worry about it.

   How do I decode a MIME/BASE64 string?
       The MIME::Base64 package handles this as well as the MIME/QP encoding.  Decoding base 64
       becomes as simple as:

           use MIME::Base64;
           my $decoded = decode_base64($encoded);

       The Email::MIME module can decode base 64-encoded email message parts transparently so the
       developer doesn't need to worry about it.

   How do I find the user's mail address?
       Ask them for it. There are so many email providers available that it's unlikely the local
       system has any idea how to determine a user's email address.

       The exception is for organization-specific email (e.g. foo@yourcompany.com) where policy
       can be codified in your program. In that case, you could look at $ENV{USER},
       $ENV{LOGNAME}, and getpwuid($<) in scalar context, like so:

         my $user_name = getpwuid($<)

       But you still cannot make assumptions about whether this is correct, unless your policy
       says it is. You really are best off asking the user.

   How do I send email?
       Use the Email::Stuffer module, like so:

         # first, create your message
         my $message = Email::Stuffer->from('you@example.com')
                                     ->to('friend@example.com')
                                     ->subject('Happy birthday!')
                                     ->text_body("Happy birthday to you!\n");

         $message->send_or_die;

       By default, Email::Sender::Simple (the "send" and "send_or_die" methods use this under the
       hood) will try "sendmail" first, if it exists in your $PATH. This generally isn't the
       case. If there's a remote mail server you use to send mail, consider investigating one of
       the Transport classes. At time of writing, the available transports include:

       Email::Sender::Transport::Sendmail
           This is the default. If you can use the mail(1) or mailx(1) program to send mail from
           the machine where your code runs, you should be able to use this.

       Email::Sender::Transport::SMTP
           This transport contacts a remote SMTP server over TCP. It optionally uses TLS or SSL
           and can authenticate to the server via SASL.

       Telling Email::Stuffer to use your transport is straightforward.

         $message->transport($email_sender_transport_object)->send_or_die;

   How do I use MIME to make an attachment to a mail message?
       Email::MIME directly supports multipart messages. Email::MIME objects themselves are parts
       and can be attached to other Email::MIME objects. Consult the Email::MIME documentation
       for more information, including all of the supported methods and examples of their use.

       Email::Stuffer uses Email::MIME under the hood to construct messages, and wraps the most
       common attachment tasks with the simple "attach" and "attach_file" methods.

         Email::Stuffer->to('friend@example.com')
                       ->subject('The file')
                       ->attach_file('stuff.csv')
                       ->send_or_die;

   How do I read email?
       Use the Email::Folder module, like so:

         use Email::Folder;

         my $folder = Email::Folder->new('/path/to/email/folder');
         while(my $message = $folder->next_message) {
           # next_message returns Email::Simple objects, but we want
           # Email::MIME objects as they're more robust
           my $mime = Email::MIME->new($message->as_string);
         }

       There are different classes in the Email::Folder namespace for supporting various mailbox
       types. Note that these modules are generally rather limited and only support reading
       rather than writing.

   How do I find out my hostname, domainname, or IP address?
       (contributed by brian d foy)

       The Net::Domain module, which is part of the Standard Library starting in Perl 5.7.3, can
       get you the fully qualified domain name (FQDN), the host name, or the domain name.

           use Net::Domain qw(hostname hostfqdn hostdomain);

           my $host = hostfqdn();

       The Sys::Hostname module, part of the Standard Library, can also get the hostname:

           use Sys::Hostname;

           $host = hostname();

       The Sys::Hostname::Long module takes a different approach and tries harder to return the
       fully qualified hostname:

         use Sys::Hostname::Long 'hostname_long';

         my $hostname = hostname_long();

       To get the IP address, you can use the "gethostbyname" built-in function to turn the name
       into a number. To turn that number into the dotted octet form (a.b.c.d) that most people
       expect, use the "inet_ntoa" function from the Socket module, which also comes with perl.

           use Socket;

           my $address = inet_ntoa(
               scalar gethostbyname( $host || 'localhost' )
           );

   How do I fetch/put an (S)FTP file?
       Net::FTP, and Net::SFTP allow you to interact with FTP and SFTP (Secure FTP) servers.

   How can I do RPC in Perl?
       Use one of the RPC modules( <https://metacpan.org/search?q=RPC> ).

AUTHOR AND COPYRIGHT

       Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other authors as noted.
       All rights reserved.

       This documentation is free; you can redistribute it and/or modify it under the same terms
       as Perl itself.

       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.