Provided by: libpoet-perl_0.16-1_all 
NAME
Poet::Manual::Intro - A gentle introduction to Poet
WHAT IS POET?
Poet is a modern Perl web framework for Mason developers. It uses PSGI/Plack for server
integration, Mason for request routing and templating, and a selection of best-of-breed
CPAN modules for caching, logging and configuration.
INSTALLATION
If you don't yet have cpanminus ("cpanm"), get it here
<http://search.cpan.org/perldoc?App::cpanminus#INSTALLATION>. Then run
cpanm -S --notest Poet
Omit the "-S" if you don't have root, in which case cpanminus will install Poet and
prereqs into "~/perl5".
Omit the "--notest" if you want to run all the installation tests. Note that this will
take about four times as long.
SETUP
You should now have a "poet" app installed:
% which poet
/usr/local/bin/poet
Run this to create your initial environment:
% poet new MyApp
my_app/.poet_root
my_app/bin/app.psgi
my_app/bin/get.pl
...
Now run 'my_app/bin/run.pl' to start your server.
The app name must be a valid Perl class name, generally either "CamelCase" ("MyApp") or an
all-uppercase acronym ("TLA"). The directory, if not specified with -d, will be formed
from the app name, but lowercased and underscored.
ENVIRONMENT
In Poet, your entire web site lives within a single directory hierarchy called the
environment. It contains subdirectories for configuration, libraries, Mason components
(templates), static files, etc.
Here are the subdirectories that are generated for you. If you don't need some of these
directories, feel free to delete them. The only ones really required by Poet are "conf",
"comps" and "lib".
• "bin" - executable scripts
• "comps" - Mason components (templates)
• "conf" - configuration files
• "data" - data not checked into version control, such as cache and object files
• "db" - database related files such as your schema
• "lib" - app-specific libraries and Poet subclasses
• "logs" - logs from web server and from explicit logging statements
• "static" - static web files - css, images, js
• "t" - unit tests
Initializing Poet
Any web server or script must initialize Poet before it can use any of Poet's features.
This is accomplished by with "Poet::Script":
#!/usr/local/bin/perl
use Poet::Script qw($conf $poet);
You'll see this in "bin/run.pl", for example, the script you use to start your webserver.
The "use Poet::Script" line does several things:
• Searches upwards from the script for the environment root (as marked by the
".poet_root" file).
• Reads and parses your configuration.
• Unshifts onto @INC the lib/ subdirectory of your environment, so that you can "use"
your application modules.
• Imports the specified quick vars - in this case $conf and $poet - as well as some
default utilities into the script namespace. More information about these below.
Relocatable environments
Ideally your environment will be relocatable -- if you move your environment to a
different root, or checkout a second copy of it in a different root, things should just
work.
To achieve this you should never refer to exact environment directory paths in your code;
instead you'll call Poet methods that return them. e.g. instead of this:
system("/path/to/environment/bin/myscript.pl");
you'll do this:
system($poet->bin_path("myscript.pl"));
(More information about this $poet variable below.)
App name
Your app name, e.g. "MyApp", is where you are expected to put app-specific subclasses. For
example if you have a DBIx::Class schema, you'd create it under "MyApp::Schema" in the
file "lib/MyApp/Schema.pm".
The app name is also where Poet will look for subclasses of its own classes.
CONFIGURATION AND LAYERS
Poet configuration files are kept in the "conf" subdirectory. The files are in YAML
<http://www.yaml.org/> form and are merged in a particular order to create a single
configuration hash. (If you want to use something other than YAML you can customize this.)
Configuration files come in three varieties: "global", "layer", and "local", in order from
least to highest precedence.
Global
Global configuration applies to all instances of your environment, and is typically
checked into version control.
Your generated environment includes a "conf/global.cfg". This is simplest to start
out with, but as a site scales in size and number of developers, you can split out
your global configuration into multiple files in "conf/global/*.cfg".
Layer
Layers allow you to have different configuration for different contexts. With all but
the simplest site you'll have at least two layers: development (the internal
environment where you develop) and production (the live site). Later on, you might
want a staging environment (which looks like production except for a different data
source, etc.).
In general you can have as many layers as you like. Each layer has a corresponding
configuration file in "conf/layer/*.cfg"; only one layer file will be loaded per
environment. We recommend that these files all be checked into version control as
well, so that changes to each layer are tracked.
Note: layer is analagous to Plack's environment concept. And in fact, "bin/run.pl"
passes the layer to plackup's <-E> option.
Local
"conf/local.cfg" contains configuration local to this specific environment instance.
This is where the current layer must be defined. It is also the only configuration
file that must exist, and the only one that should not be checked into version
control.
You can also specify an extra local file via $ENV{POET_EXTRA_CONF_FILE}.
There are a variety of ways to access configuration:
my $value = $conf->get('key', 'default');
my $value = $conf->get_or_die('key');
my $listref = $conf->get_list('key', ['default']);
my $hashref = $conf->get_hash('key', {'default' => 5});
my $bool = $conf->get_boolean('key');
See below for more information about this $conf variable, and see Poet::Conf for more
information on specifying and accessing configuration.
Development versus live mode
Although you may have as many layers as you like, Poet also maintains a more limited
binary notion of development mode versus live mode. By default, you're in development mode
iff layer equals 'development', and in live mode otherwise.
You can use these boolean methods to determine which mode you're in at runtime:
$conf->is_development
$conf->is_live
These are mutually exclusive (exactly one is always true).
Poet uses development/live mode to determine things like
• whether to turn on automatic server restarting
• whether to display errors in the browser
• whether to enable debugging utilities
You can customize how mode is determined by subclassing Poet::Conf.
SERVER RUNNER AND MIDDLEWARE
"poet new" generates "bin/run.pl" and "bin/app.psgi" for you.
"bin/run.pl" is a wrapper around plackup, which starts your server. It has a few sensible
defaults, such as setting up autorestart in development mode and using an access log in
live mode. It will also take a few options from configuration, e.g.
server:
host: 127.0.0.1
port: 5000
If you are using something other than plackup (e.g. Server::Starter) then you'll have to
adapt this into your own startup script.
"bin/app.psgi" defines your PSGI app. It's the place to add Plack middleware, or change
the configuration of the default middleware. For example, to enable basic authentication
with an "conf/.htpasswd" file, add this to app.psgi:
enable "Auth::Htpasswd", file => $poet->conf_path('.htpasswd');
QUICK VARS AND UTILITIES
Poet makes it easy to import certain variables (known as "quick vars") and utility sets
into any module or script in your environment. You've seen two examples of quick vars
above: $conf, the global configuration variable, and $poet, the global environment object.
In a script, this looks like:
#!/usr/local/bin/perl
use Poet::Script qw($conf :file);
In a module, this looks like:
package MyApp::Foo;
use Poet qw($cache $poet);
And every Mason component automatically gets this on top:
use Poet qw($conf $poet :web);
Debug utilities are automatically imported without having to specify a tag.
See Poet::Import for a complete list of quick vars and utility sets.
HANDLING HTTP REQUESTS
HTTP requests are handled with PSGI/Plack and Mason.
A persistent Mason interpreter is created at server startup, with component root set to
the "comps" subdirectory. (See Poet::Mason for other default settings and how to configure
them.)
When an HTTP request comes in, Poet
• Constructs a Poet::Plack::Request object from the plack environment. This is a thin
subclass of Plack::Request and provides information such as the URL and incoming HTTP
headers. It is made available in Mason components as "$m->req".
• Constructs an empty Poet::Plack::Response object. This is a thin subclass of
Plack::Response, and you may use it to set things such as the HTTP status and headers.
It is made available in Mason components as "$m->res".
• Calls "$interp->run" with the URL and the GET/POST parameters. So for example, a URL
like
/foo/bar?a=5&b=6
would result in
$interp->run("/foo/bar", a=>5, b=>6);
From there Mason will choose a component to dispatch to - see
Mason::Manual::RequestDispatch and Mason::Plugin::RouterSimple.
Generating content with Mason
Mason is a full-featured templating system and beyond our ability to summarize here.
Recommended reading:
• Poet::Manual::Tutorial, especially starting here
• Mason::Manual::Components
• Mason::Manual::Syntax
Success and failure results
If the Mason request finishes successfully, the Mason output becomes the plack response
body, the status code is set to 200 if it hasn't already been set, and the content type is
set to "text/html" (or the specified default content type) if it hasn't already been set.
If the top-level component path cannot be found, the status code is set to 404.
If any other kind of runtime error occurs in development mode, it will be nicely displayed
in the browser via StackTrace middleware. Outside of development it will be logged and
sent as a 500 error response.
You can call "$m->redirect" and "$m->not_found" to generate redirect and not_found results
from a component. These are documented in Poet::Mason.
Multiple values for parameters
If there are multiple values for a GET or POST parameter, generally only the last value
will be kept, as per Hash::MultiValue. However, if the corresponding attribute in the page
component is declared an "ArrayRef", then all values will be kept and passed in as an
arrayref. For example, if the page component "/foo/bar.mc" has these declarations:
<%class>
has 'a';
has 'b' => (isa => "Int");
has 'c' => (isa => "ArrayRef");
has 'd' => (isa => "ArrayRef[Int]");
</%class>
then this URL
/foo/bar?a=1&a=2&b=3&b=4&c=5&c=6&d=7&d=8
would result in
$interp->run("/foo/bar", a=>2, b=>4, c=>[5,6], d => [7,8]);
You can always get the original Hash::MultiValue object from "$m->request_args". e.g.
my $hmv = $m->request_args;
# get all values for 'e'
$hmv->get_all('e');
LOGGING
Poet uses the Log::Log4perl engine for logging, but with a much simpler configuration for
the common cases. (If you want to use something other than Log4perl you can customize
this.)
Once you have a $log variable, logging looks like:
$log->error("an error occurred");
$log->debugf("arguments are: %s", \@_)
if $log->is_debug();
By default, all logs go to "logs/poet.log" with a reasonable set of metadata such as
timestamp.
See Poet::Log for more information.
CACHING
Poet uses CHI for caching, providing access to a wide variety of cache backends (memory,
files, memcached, etc.) You can configure caching differently for different namespaces.
Once you have a $cache variable, caching looks like:
my $customer = $cache->get($name);
if ( !defined $customer ) {
$customer = get_customer_from_db($name);
$cache->set( $name, $customer, "10 minutes" );
}
or
my $customer2 = $cache->compute($name2, "10 minutes", sub {
get_customer_from_db($name2)
});
By default, everything is cached in files under "data/chi".
See Poet::Cache for more information.
SEE ALSO
Poet
AUTHOR
Jonathan Swartz <swartz@pobox.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2012 by Jonathan Swartz.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.