Poet::Manual::Intro - A gentle introduction to 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.
If you don't yet have cpanminus (cpanm), get it here. Then run
cpanm
cpanm -S --notest Poet
Omit the "-S" if you don't have root, in which case cpanminus will install Poet and prereqs into ~/perl5.
~/perl5
Omit the "--notest" if you want to run all the installation tests. Note that this will take about four times as long.
You should now have a poet app installed:
poet
% 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.
CamelCase
MyApp
TLA
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.
conf
comps
lib
bin - executable scripts
bin
comps - Mason components (templates)
conf - configuration files
data - transient data such as cache files
data
db - database related files such as your schema
db
lib - app-specific libraries and Poet subclasses
logs - logs from web server and from explicit logging statements
logs
static - static web files - css, images, js
static
t - unit tests
t
Any web server or script must initialize Poet before it can use any of Poet's features. This is accomplished by with Poet::Script:
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:
bin/run.pl
use Poet::Script
Searches upwards from the script for the environment root (as marked by the .poet_root file).
.poet_root
Reads and parses your configuration.
Unshifts onto @INC the lib/ subdirectory of your environment, so that you can use your application modules.
use
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.
$conf
$poet
Ideally your environment will be relocatable -- if you move your environment to a different root, or checkout a second copy of it in a different root, things should just work.
To achieve this you should never refer to exact environment directory paths in your code; instead you'll call Poet methods that return them. e.g. instead of this:
system("/path/to/environment/bin/myscript.pl");
you'll do this:
system($poet->bin_path("myscript.pl"));
(More information about this $poet variable below.)
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.
MyApp::Schema
lib/MyApp/Schema.pm
The app name is also where Poet will look for subclasses of its own classes.
Poet configuration files are kept in the conf subdirectory. The files are in YAML 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
layer
local
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.
conf/global.cfg
conf/global/*.cfg
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.
conf/layer/*.cfg
Note: layer is analagous to Plack's environment concept. And in fact, bin/run.pl passes the layer to plackup's <-E> option.
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.
conf/local.cfg
You can also specify an extra local file via $ENV{POET_EXTRA_CONF_FILE}.
$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.
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.
poet new generates bin/run.pl and bin/app.psgi for you.
poet new
bin/app.psgi
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:
conf/.htpasswd
enable "Auth::Htpasswd", file => $poet->conf_path('.htpasswd');
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.
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.
$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.
$m->res
Calls $interp->run with the URL and the GET/POST parameters. So for example, a URL like
$interp->run
/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.
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
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.
text/html
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.
$m->redirect
$m->not_found
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:
ArrayRef
/foo/bar.mc
<%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
$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.
$m->request_args
my $hmv = $m->request_args; # get all values for 'e' $hmv->get_all('e');
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.
logs/poet.log
See Poet::Log for more information.
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.
data/chi
See Poet::Cache for more information.
Poet
Jonathan Swartz <swartz@pobox.com>
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.
To install Poet, copy and paste the appropriate command in to your terminal.
cpanm Poet
CPAN shell
perl -MCPAN -e shell install Poet
For more information on module installation, please visit the detailed CPAN module installation guide.