1Mojolicious::Guides::FAUQs(e3r)Contributed Perl DocumentMaotjioolnicious::Guides::FAQ(3)
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6 Mojolicious::Guides::FAQ - Frequently Asked Questions
7
9 This document contains answers for the most frequently asked questions
10 about Mojolicious.
11
13 We hope these answers are to your satisfaction.
14 How does Mojolicious compare to other Perl web frameworks?
16 The short answer is "it doesn't", because we interpret the term "web
17 framework" much more literally than others. With the emergence of the
18 real-time web and new technologies such as WebSockets, we are facing
19 new challenges that go way beyond what commonly used modules like LWP
20 were designed for. Because of this, Mojolicious contains a whole new
21 HTTP client/server stack called Mojo, which was heavily inspired by the
22 original LWPng effort and carefully designed with these new
23 requirements in mind. So while some of the higher abstraction layers
24 might look similar to other web frameworks, it is more of a web toolkit
25 and can even be used as the foundation for more advanced web
26 frameworks.
27 Why doesn't Mojolicious have any dependencies?
29 We are optimizing Mojolicious for user-friendliness and development
30 speed, without compromises. While there are no rules in
31 Mojolicious::Guides::Contributing that forbid dependencies, we do
32 currently discourage adding non-optional ones in favor of a faster and
33 more painless installation process. And we do in fact already use
34 several optional CPAN modules such as Cpanel::JSON::XS, EV,
35 IO::Socket::Socks, IO::Socket::SSL, Net::DNS::Native, Plack and
36 Role::Tiny to provide advanced functionality if possible.
37 Why reinvent wheels?
39 Because we can make them rounder. Components specifically designed for
40 user-friendliness and development speed are not easy to come by. We are
41 strong believers of the Perl mantra "There is more than one way to do
42 it", and our quest is to develop the best possible solutions for these
43 two criteria.
44 What about backwards compatibility?
46 In conformance with Mojolicious::Guides::Contributing, we will always
47 deprecate a feature for 3 months, before removing or changing it in
48 incompatible ways between major releases. New features can however be
49 marked as experimental to explicitly exclude them from these rules.
50 This gives us the necessary freedom to ensure a healthy future for
51 Mojolicious. So, as long as you are not using anything marked
52 experimental, untested or undocumented, you can always count on
53 backwards compatibility, everything else would be considered a bug.
54 However, to completely avoid any risk of accidental breakage, we do
55 recommend following current best practices for version pinning with
56 Carton for production setups.
57 Why not split up Mojolicious into many smaller distributions?
59 Because there are no advantages, it drastically increases maintenance
60 costs and installation times without giving us anything in return. It
61 would only make sense if we wanted to pass ownership of a module to a
62 new maintainer, which we already have done in the past.
63 Where can i discuss my patches for Mojolicious?
65 We'd love to discuss your contributions to Mojolicious on our official
66 IRC channel "#mojo" on "irc.freenode.net" (chat now!
67 <https://kiwiirc.com/nextclient/#irc://irc.freenode.net/mojo?nick=guest-?>).
68 Which versions of Perl are supported by Mojolicious?
70 First of all, you need to be aware that according to the perlpolicy,
71 only the two most recent stable release series of Perl are supported by
72 the community and receive bug fixes, which are currently 5.30.x and
73 5.28.x. Mojolicious follows this model and fully supports these two
74 release series. In addition we will also keep the distribution
75 installable (and that means passing all tests) up to a certain legacy
76 version that the core team deems worthy of supporting, but not
77 specifically optimize for it, this is currently 5.10.1.
78 Note that Perl versions 5.10.x and 5.12.x are known to work very poorly
80 with Mojolicious, and we strongly suggest you do not use them, to avoid
81 stability and security issues. If it wasn't for a very vocal minority
82 within the community we would not support these versions at all.
83 How well is Windows supported by Mojolicious?
85 Windows is not officially supported by Mojolicious, even though we try
86 to keep the distribution installable. There may be serious security
87 and/or reliability issues. Some of the more advanced features, such as
88 subprocesses and the Hypnotoad web server, will also require the use of
89 the Windows Subsystem for Linux
90 <https://msdn.microsoft.com/commandline/wsl/>.
91 Do I need to clean my environment before testing Mojolicious?
93 Mojolicious uses many environment variables both internally and
94 externally, notably (but not exclusively) those starting with the
95 prefix "MOJO_*" and "PLACK_ENV". The test suite expects a clean
96 environment; testing with a non-standard environment is unsupported and
97 is unlikely to succeed. Therefore when installing or upgrading
98 Mojolicious and when running its tests, we highly recommend using an
99 environment which does not set these variables.
100 Where did my file extension go?
102 Standard route placeholders will not match the "." character, however
103 Mojolicious routes automatically take file extensions like ".html",
104 remove the leading ".", and store the result in the "format" stash
105 value. This can be useful for URL-based content negotiation, such as
106 automatically rendering different templates based on the file
107 extension. See "Formats" in Mojolicious::Guides::Routing for
108 information on customizing format detection, or consider using relaxed
109 placeholders to allow matching of the "." character.
110 Can I configure Hypnotoad from the command line?
112 No, you can't, Hypnotoad is a bit special in this regard. Because when
113 you initiate a zero downtime software upgrade (hot deployment), you are
114 only really sending a "USR2" signal to the already running server, and
115 no other information can be passed along. What you can do instead, is
116 to use a Mojolicious::Plugin::Config or Mojolicious::Plugin::JSONConfig
117 configuration file.
118 # myapp.conf
120 {
121 hypnotoad => {
122 listen => ['http://*:8080'],
123 workers => 10
124 }
125 };
126 Or if you don't actually need zero downtime software upgrades, just use
128 Mojolicious::Command::prefork instead, which is otherwise almost
129 identical to Hypnotoad.
130 $ ./myapp.pl prefork -m production -l http://*:8080 -w 10
132 What does the error "...certificate verify failed" mean?
134 There are many variations of this error, but most of them mean that TLS
135 certificate verification in Mojo::UserAgent failed. This usually
136 happens for two reasons. The most common one is that the peer
137 certificate is simply invalid. If that's the case and you are certain
138 that no MITM attack is being attempted, you can use the attribute
139 "insecure" in Mojo::UserAgent or "MOJO_INSECURE" environment variable
140 to disable certificate verification. And if that's not the case you
141 might be missing the Mozilla::CA module, which is often required by
142 IO::Socket::SSL to be able to verify certificates.
143 What does the error "Maximum message size exceeded" mean?
145 To protect your applications from excessively large requests and
146 responses, our HTTP parser has a cap after which it will automatically
147 stop accepting new data, and in most cases force the connection to be
148 closed. The limit is 16MiB for requests, and 2GiB for responses by
149 default. You can use the attributes "max_request_size" in Mojolicious
150 and "max_response_size" in Mojo::UserAgent to change these values.
151 What does the error "Maximum start-line size exceeded" mean?
153 This is a very similar protection mechanism to the one described in the
154 previous answer, but a little more specific. It limits the maximum
155 length of the start-line for HTTP requests and responses. The limit is
156 8KiB by default, you can use the attribute "max_line_size" in
157 Mojo::Message or "MOJO_MAX_LINE_SIZE" environment variable to change
158 this value.
159 What does the error "Maximum header size exceeded" mean?
161 Almost the same as the previous answer, but this protection mechanism
162 limits the number and maximum length of HTTP request and response
163 headers. The limits are 100 headers with 8KiB each by default, you can
164 use the attributes "max_lines" in Mojo::Headers and "max_line_size" in
165 Mojo::Headers or the "MOJO_MAX_LINES" and "MOJO_MAX_LINE_SIZE"
166 environment variables to change these values.
167 What does the error "Maximum buffer size exceeded" mean?
169 This protection mechanism limits how much content the HTTP parser is
170 allowed to buffer when parsing chunked, compressed and multipart
171 messages. The limit is around 256KiB by default, you can use the
172 attribute "max_buffer_size" in Mojo::Content or "MOJO_MAX_BUFFER_SIZE"
173 environment variable to change this value.
174 What does "Your secret passphrase needs to be changed" mean?
176 Mojolicious uses secret passphrases for security features such as
177 signed cookies. It defaults to using "moniker" in Mojolicious, which is
178 not very secure, so we added this log message as a reminder. You can
179 change the passphrase with the attribute "secrets" in Mojolicious.
180 Since some plugins also depend on it, you should try changing it as
181 early as possible in your application.
182 $app->secrets(['My very secret passphrase.']);
184 What does "Nothing has been rendered, expecting delayed response" mean?
186 Mojolicious has been designed from the ground up for non-blocking I/O
187 and event loops. So when a new request comes in and no response is
188 generated right away, it will assume that this was intentional and
189 return control to the web server, which can then handle other requests
190 while waiting for events such as timers to finally generate a response.
191 What does "Inactivity timeout" mean?
193 To protect your applications from denial-of-service attacks, all
194 connections have an inactivity timeout which limits how long a
195 connection may be inactive before being closed automatically. It
196 defaults to 20 seconds for the user agent and 15 seconds for all built-
197 in web servers, and can be changed with the attributes
198 "inactivity_timeout" in Mojo::UserAgent and "inactivity_timeout" in
199 Mojo::Server::Daemon or the "MOJO_INACTIVITY_TIMEOUT" environment
200 variable. In Mojolicious applications you can also use the helper
201 "inactivity_timeout" in Mojolicious::Plugin::DefaultHelpers to change
202 it on demand for each connection individually. This timeout always
203 applies, so you might have to tweak it for applications that take a
204 long time to process a request.
205 What does "Premature connection close" mean?
207 This error message is often related to the one above, and means that
208 the web server closed the connection before the user agent could
209 receive the whole response or that the user agent got destroyed, which
210 forces all connections to be closed immediately.
211 # The variable $ua goes out of scope and gets destroyed too early
213 Mojo::IOLoop->timer(5 => sub {
214 my $ua = Mojo::UserAgent->new;
215 $ua->get('https://mojolicious.org' => sub {
216 my ($ua, $tx) = @_;
217 say $tx->result->dom->at('title')->text;
218 });
219 });
220 What does "Worker 31842 has no heartbeat (30 seconds), restarting" mean?
222 As long as they are accepting new connections, worker processes of all
223 built-in pre-forking web servers send heartbeat messages to the manager
224 process at regular intervals, to signal that they are still responsive.
225 A blocking operation such as an infinite loop in your application can
226 prevent this, and will force the affected worker to be restarted after
227 a timeout. This timeout defaults to 30 seconds and can be extended with
228 the attribute "heartbeat_timeout" in Mojo::Server::Prefork if your
229 application requires it.
230 What does "Transaction already destroyed" mean?
232 This error message usually appears after waiting for the results of a
233 non-blocking operation for longer periods of time, because the
234 underlying connection has been closed in the meantime and the value of
235 the attribute "tx" in Mojolicious::Controller is no longer available.
236 While there might not be a way to prevent the connection from getting
237 closed, you can try to avoid this error message by keeping a reference
238 to the transaction object that is not weakened.
239 # Keep a strong reference to the transaction object
241 my $tx = $c->render_later->tx;
242 $c->ua->get_p('https://mojolicious.org')->then(sub {
243 $c->render(text => 'Visited mojolicious.org');
244 })->catch(sub {
245 my $err = shift;
246 $tx;
247 $c->reply->exception($err);
248 });
249
251 You can continue with Mojolicious::Guides now or take a look at the
252 Mojolicious wiki <http://github.com/mojolicious/mojo/wiki>, which
253 contains a lot more documentation and examples by many different
254 authors.
255
257 If you have any questions the documentation might not yet answer, don't
258 hesitate to ask on the mailing list
259 <http://groups.google.com/group/mojolicious> or the official IRC
260 channel "#mojo" on "irc.freenode.net" (chat now!
261 <https://kiwiirc.com/nextclient/#irc://irc.freenode.net/mojo?nick=guest-?>).
262perl v5.30.1 2020-01-30 Mojolicious::Guides::FAQ(3)