
=encoding utf8

=head1 NAME

Mojolicious::Guides::FAQ - Frequently Asked Questions

=head1 OVERVIEW

This document contains answers for the most frequently asked questions about
L<Mojolicious>.

=head1 QUESTIONS

We hope these answers are to your satisfaction.

=head2 How does Mojolicious compare to other Perl web frameworks?

The short answer is "it doesn't", because we interpret the term "web framework"
much more literally than others. With the emergence of the real-time web and
new technologies such as WebSockets, we are facing new challenges that go way
beyond what commonly used modules like L<LWP> were designed for. Because of
this, L<Mojolicious> contains a whole new HTTP client/server stack called
L<Mojo>, which was heavily inspired by the original LWPng effort and carefully
designed with these new requirements in mind. So while some of the higher
abstraction layers might look similar to other web frameworks, it is more of a
web toolkit and can even be used as the foundation for more advanced web
frameworks.

=head2 Why doesn't Mojolicious have any dependencies?

We are optimizing L<Mojolicious> for user-friendliness and development speed,
without compromises. While there are no rules in
L<Mojolicious::Guides::Contributing> that forbid dependencies, we do currently
discourage adding non-optional ones in favor of a faster and more painless
installation process. And we do in fact already use several optional CPAN
modules such as L<Cpanel::JSON::XS>, L<EV>, L<IO::Socket::Socks>,
L<IO::Socket::SSL>, L<Net::DNS::Native>, L<Plack> and L<Role::Tiny> to provide
advanced functionality if possible.

=head2 Why reinvent wheels?

Because we can make them rounder. Components specifically designed for
user-friendliness and development speed are not easy to come by. We are strong
believers of the Perl mantra "There is more than one way to do it", and our
quest is to develop the best possible solutions for these two criteria.

=head2 What about backwards compatibility?

In conformance with L<Mojolicious::Guides::Contributing>, we will always
deprecate a feature for 3 months, before removing or changing it in
incompatible ways between major releases. New features can however be marked as
experimental to explicitly exclude them from these rules. This gives us the
necessary freedom to ensure a healthy future for L<Mojolicious>. So, as long as
you are not using anything marked experimental, untested or undocumented, you
can always count on backwards compatibility, everything else would be
considered a bug. However, to completely avoid any risk of accidental breakage,
we do recommend following current best practices for version pinning with
L<Carton> for production setups.

=head2 Why not split up Mojolicious into many smaller distributions?

Because there are no advantages, it drastically increases maintenance costs and
installation times without giving us anything in return. It would only make
sense if we wanted to pass ownership of a module to a new maintainer, which we
already have done in the past.

=head2 Where can i discuss my patches for Mojolicious?

We'd love to discuss your contributions to L<Mojolicious> on our official IRC
channel C<#mojo> on C<irc.freenode.net> (L<chat
now!|https://kiwiirc.com/nextclient/#irc://irc.freenode.net/mojo?nick=guest-?>).

=head2 Which versions of Perl are supported by Mojolicious?

First of all, you need to be aware that according to the L<perlpolicy>, only
the two most recent stable release series of Perl are supported by the
community and receive bug fixes, which are currently 5.30.x and 5.28.x.
L<Mojolicious> follows this model and fully supports these two release series.
In addition we will also keep the distribution installable (and that means
passing all tests) up to a certain legacy version that the core team deems
worthy of supporting, but not specifically optimize for it, this is currently
5.10.1.

Note that Perl versions 5.10.x and 5.12.x are known to work very poorly with
L<Mojolicious>, and we strongly suggest you do not use them, to avoid stability
and security issues. If it wasn't for a very vocal minority within the community
we would not support these versions at all.

=head2 How well is Windows supported by Mojolicious?

Windows is not officially supported by L<Mojolicious>, even though we try to
keep the distribution installable. There may be serious security and/or
reliability issues. Some of the more advanced features, such as
L<subprocesses|Mojo::IOLoop/"subprocess"> and the
L<Hypnotoad|Mojo::Server::Hypnotoad> web server, will also require the use of
the L<Windows Subsystem for Linux|https://msdn.microsoft.com/commandline/wsl/>.

=head2 Do I need to clean my environment before testing Mojolicious?

L<Mojolicious> uses many environment variables both internally and externally,
notably (but not exclusively) those starting with the prefix C<MOJO_*> and
C<PLACK_ENV>. The test suite expects a clean environment; testing with a
non-standard environment is unsupported and is unlikely to succeed. Therefore
when installing or upgrading L<Mojolicious> and when running its tests, we
highly recommend using an environment which does not set these variables.

=head2 Where did my file extension go?

Standard route placeholders will not match the C<.> character, however
L<Mojolicious> routes automatically take file extensions like C<.html>, remove
the leading C<.>, and store the result in the C<format> stash value. This can
be useful for URL-based content negotiation, such as automatically rendering
different templates based on the file extension. See
L<Mojolicious::Guides::Routing/"Formats"> for information on customizing format
detection, or consider using
L<relaxed placeholders|Mojolicious::Guides::Routing/"Relaxed placeholders"> to
allow matching of the C<.> character.

=head2 Can I configure Hypnotoad from the command line?

No, you can't, L<Hypnotoad|Mojo::Server::Hypnotoad> is a bit special in this
regard. Because when you initiate a zero downtime software upgrade (hot
deployment), you are only really sending a C<USR2> signal to the already running
server, and no other information can be passed along. What you can do instead,
is to use a L<Mojolicious::Plugin::Config> or L<Mojolicious::Plugin::JSONConfig>
configuration file.

  # myapp.conf
  {
    hypnotoad => {
      listen  => ['http://*:8080'],
      workers => 10
    }
  };

Or if you don't actually need zero downtime software upgrades, just use
L<Mojolicious::Command::prefork> instead, which is otherwise almost identical to
Hypnotoad.

  $ ./myapp.pl prefork -m production -l http://*:8080 -w 10

=head2 What does the error "...certificate verify failed" mean?

There are many variations of this error, but most of them mean that TLS
certificate verification in L<Mojo::UserAgent> failed. This usually happens for
two reasons. The most common one is that the peer certificate is simply invalid.
If that's the case and you are certain that no MITM attack is being attempted,
you can use the attribute L<Mojo::UserAgent/"insecure"> or C<MOJO_INSECURE>
environment variable to disable certificate verification. And if that's not the
case you might be missing the L<Mozilla::CA> module, which is often required by
L<IO::Socket::SSL> to be able to verify certificates.

=head2 What does the error "Maximum message size exceeded" mean?

To protect your applications from excessively large requests and responses, our
HTTP parser has a cap after which it will automatically stop accepting new
data, and in most cases force the connection to be closed. The limit is 16MiB
for requests, and 2GiB for responses by default. You can use the attributes
L<Mojolicious/"max_request_size"> and L<Mojo::UserAgent/"max_response_size"> to
change these values.

=head2 What does the error "Maximum start-line size exceeded" mean?

This is a very similar protection mechanism to the one described in the
previous answer, but a little more specific. It limits the maximum length of
the start-line for HTTP requests and responses. The limit is 8KiB by default,
you can use the attribute L<Mojo::Message/"max_line_size"> or
C<MOJO_MAX_LINE_SIZE> environment variable to change this value.

=head2 What does the error "Maximum header size exceeded" mean?

Almost the same as the previous answer, but this protection mechanism limits
the number and maximum length of HTTP request and response headers. The limits
are 100 headers with 8KiB each by default, you can use the attributes
L<Mojo::Headers/"max_lines"> and L<Mojo::Headers/"max_line_size"> or the
C<MOJO_MAX_LINES> and C<MOJO_MAX_LINE_SIZE> environment variables to change
these values.

=head2 What does the error "Maximum buffer size exceeded" mean?

This protection mechanism limits how much content the HTTP parser is allowed to
buffer when parsing chunked, compressed and multipart messages. The limit is
around 256KiB by default, you can use the attribute
L<Mojo::Content/"max_buffer_size"> or C<MOJO_MAX_BUFFER_SIZE> environment
variable to change this value.

=head2 What does "Your secret passphrase needs to be changed" mean?

L<Mojolicious> uses secret passphrases for security features such as signed
cookies. It defaults to using L<Mojolicious/"moniker">, which is not very
secure, so we added this log message as a reminder. You can change the
passphrase with the attribute L<Mojolicious/"secrets">. Since some plugins also
depend on it, you should try changing it as early as possible in your
application.

  $app->secrets(['My very secret passphrase.']);

=head2 What does "Nothing has been rendered, expecting delayed response" mean?

L<Mojolicious> has been designed from the ground up for non-blocking I/O and
event loops. So when a new request comes in and no response is generated right
away, it will assume that this was intentional and return control to the web
server, which can then handle other requests while waiting for events such as
timers to finally generate a response.

=head2 What does "Inactivity timeout" mean?

To protect your applications from denial-of-service attacks, all connections
have an inactivity timeout which limits how long a connection may be inactive
before being closed automatically. It defaults to C<40> seconds for the user
agent and C<30> seconds for all built-in web servers, and can be changed with
the attributes L<Mojo::UserAgent/"inactivity_timeout"> and
L<Mojo::Server::Daemon/"inactivity_timeout"> or the C<MOJO_INACTIVITY_TIMEOUT>
environment variable. In L<Mojolicious> applications you can also use the helper
L<Mojolicious::Plugin::DefaultHelpers/"inactivity_timeout"> to change it on
demand for each connection individually. This timeout always applies, so you
might have to tweak it for applications that take a long time to process a
request.

=head2 What does "Premature connection close" mean?

This error message is often related to the one above, and means that the web
server closed the connection before the user agent could receive the whole
response or that the user agent got destroyed, which forces all connections to
be closed immediately.

  # The variable $ua goes out of scope and gets destroyed too early
  Mojo::IOLoop->timer(5 => sub {
    my $ua = Mojo::UserAgent->new;
    $ua->get('https://mojolicious.org' => sub {
      my ($ua, $tx) = @_;
      say $tx->result->dom->at('title')->text;
    });
  });

=head2 What does "Worker 31842 has no heartbeat (50 seconds), restarting" mean?

As long as they are accepting new connections, worker processes of all built-in
pre-forking web servers send heartbeat messages to the manager process at
regular intervals, to signal that they are still responsive. A blocking
operation such as an infinite loop in your application can prevent this, and
will force the affected worker to be restarted after a timeout. This timeout
defaults to C<50> seconds and can be extended with the attribute
L<Mojo::Server::Prefork/"heartbeat_timeout"> if your application requires it.

=head2 What does "Transaction already destroyed" mean?

This error message usually appears after waiting for the results of a
non-blocking operation for longer periods of time, because the underlying
connection has been closed in the meantime and the value of the attribute
L<Mojolicious::Controller/"tx"> is no longer available. While there might not be
a way to prevent the connection from getting closed, you can try to avoid this
error message by keeping a reference to the transaction object that is not
weakened.

  # Keep a strong reference to the transaction object
  my $tx = $c->render_later->tx;
  $c->ua->get_p('https://mojolicious.org')->then(sub {
    $c->render(text => 'Visited mojolicious.org');
  })->catch(sub {
    my $err = shift;
    $tx;
    $c->reply->exception($err);
  });

=head1 MORE

You can continue with L<Mojolicious::Guides> now or take a look at the
L<Mojolicious wiki|http://github.com/mojolicious/mojo/wiki>, which contains a lot more
documentation and examples by many different authors.

=head1 SUPPORT

If you have any questions the documentation might not yet answer, don't
hesitate to ask on the
L<mailing list|http://groups.google.com/group/mojolicious> or the official IRC
channel C<#mojo> on C<irc.freenode.net> (L<chat
now!|https://kiwiirc.com/nextclient/#irc://irc.freenode.net/mojo?nick=guest-?>).

=cut
