| perlfaq9 - Web, Email and Networking |
perlfaq9 - Web, Email and Networking
version 5.20190126
This section deals with questions related to running web sites, sending and receiving email as well as general networking.
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 or the Plack::Middleware::TemplateToolkit manpage so maintenance of your HTML files (and other assets) is easier.
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.
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).
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 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 Plack) is a better option.
Use the HTML::Strip manpage, or the HTML::FormatText manpage which not only removes HTML but also attempts to do a little simple formatting of the resulting plain text.
the HTML::SimpleLinkExtor manpage 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 the HTML::LinkExtor manpage or the HTML::Parser manpage. You might even use the HTML::SimpleLinkExtor manpage as an example for something specifically suited to your needs.
You can use the URI::Find manpage to extract URLs from an arbitrary text document.
(contributed by brian d foy)
Use the libwww-perl distribution. The the LWP::Simple manpage module can fetch web resources and give their content back to you as a string:
use LWP::Simple qw(get);
my $html = get( "http://www.example.com/index.html"; );
It can also store the resource directly in a file:
use LWP::Simple qw(getstore);
getstore( "http://www.example.com/index.html";, "foo.html" );
If you need to do something more complicated, you can use the LWP::UserAgent manpage module to create your own user-agent (e.g. browser) to get the job done. If you want to simulate an interactive web browser, you can use the the WWW::Mechanize manpage module.
If you are doing something complex, such as moving through many pages and forms or a web site, you can use the WWW::Mechanize manpage. 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 query_form method:
use LWP::Simple;
use URI::URL;
my $url = url('L<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;
my $ua = LWP::UserAgent->new();
my $req = POST 'L<http://www.perl.com/cgi-bin/cpan_mod'>,
[ module => 'DB_File', readme => 1 ];
my $content = $ua->request($req)->as_string;
Most of the time you should not need to do this as your web framework, or if you are making a request, the the LWP manpage or other module would handle it for you.
To encode a string yourself, use the the URI::Escape manpage 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.
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 the Plack::Middleware::Rewrite manpage is worth looking at if you are migrating from Apache or have URL's you want to always redirect.
See if the web framework you are using has an authentication system and if that fits your needs.
Alternativly look at the Plack::Middleware::Auth::Basic manpage, or one of the other Plack authentication options.
(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 the LWP manpage 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 the perlsec manpage documentation has general advice about data security.
If you are using the the DBI manpage 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.
Use the the Email::MIME manpage 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 the Email::Abstract manpage and then using its cast method to get an the Email::MIME manpage object:
my $abstract = Email::Abstract->new($mail_message_object);
my $email_mime_object = $abstract->cast('Email::MIME');
(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 the Email::Valid manpage 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.
The the MIME::Base64 manpage 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 the Email::MIME manpage module can decode base 64-encoded email message parts transparently so the developer doesn't need to worry about it.
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.
Use the the Email::MIME manpage and the Email::Sender::Simple manpage modules, like so:
# first, create your message
my $message = Email::MIME->create(
header_str => [
From => 'you@example.com',
To => 'friend@example.com',
Subject => 'Happy birthday!',
],
attributes => {
encoding => 'quoted-printable',
charset => 'utf-8',
},
body_str => "Happy birthday to you!\n",
);
use Email::Sender::Simple qw(sendmail); sendmail($message);
By default, the Email::Sender::Simple manpage 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:
Telling the Email::Sender::Simple manpage to use your transport is straightforward.
sendmail(
$message,
{
transport => $email_sender_transport_object,
}
);
the Email::MIME manpage directly supports multipart messages. the Email::MIME manpage objects themselves are parts and can be attached to other the Email::MIME manpage objects. Consult the the Email::MIME manpage documentation for more information, including all of the supported methods and examples of their use.
Use the the Email::Folder manpage 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 the Email::Folder manpage namespace for supporting various mailbox types. Note that these modules are generally rather limited and only support reading rather than writing.
(contributed by brian d foy)
The the Net::Domain manpage 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 the Sys::Hostname manpage module, part of the Standard Library, can also get the hostname:
use Sys::Hostname;
$host = hostname();
The the Sys::Hostname::Long manpage 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 the Socket manpage module, which also comes with perl.
use Socket;
my $address = inet_ntoa(
scalar gethostbyname( $host || 'localhost' )
);
the Net::FTP manpage, and the Net::SFTP manpage allow you to interact with FTP and SFTP (Secure FTP) servers.
Use one of the RPC modules( https://metacpan.org/search?q=RPC ).
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.
| perlfaq9 - Web, Email and Networking |