Plack::Builder(3) User Contributed Perl Documentation Plack::Builder(3)NAMEPlack::Builder - OO and DSL to enable Plack Middlewares
SYNOPSIS
# in .psgi
use Plack::Builder;
my $app = sub { ... };
builder {
enable "Deflater";
enable "Session", store => "File";
enable "Debug", panels => [ qw(DBITrace Memory Timer) ];
enable "+My::Plack::Middleware";
$app;
};
# use URLMap
builder {
mount "/foo" => builder {
enable "Foo";
$app;
};
mount "/bar" => $app2;
mount "http://example.com/" => builder { $app3 };
};
# using OO interface
my $builder = Plack::Builder->new();
$builder->add_middleware('Foo', opt => 1);
$app = $builder->mount('/app' => $app);
$app = $builder->to_app($app);
DESCRIPTIONPlack::Builder gives you a quick domain specific language (DSL) to wrap
your application with Plack::Middleware subclasses. The middleware
you're trying to use should use Plack::Middleware as a base class to
use this DSL, inspired by Rack::Builder.
Whenever you call "enable" on any middleware, the middleware app is
pushed to the stack inside the builder, and then reversed when it
actually creates a wrapped application handler. "Plack::Middleware::"
is added as a prefix by default. So:
builder {
enable "Foo";
enable "Bar", opt => "val";
$app;
};
is syntactically equal to:
$app = Plack::Middleware::Bar->wrap($app, opt => "val");
$app = Plack::Middleware::Foo->wrap($app);
In other words, you're supposed to "enable" middleware from outer to
inner.
INLINE MIDDLEWAREPlack::Builder allows you to code middleware inline using a nested code
reference.
If the first argument to "enable" is a code reference, it will be
passed an $app and should return another code reference which is a PSGI
application that consumes $env at runtime. So:
builder {
enable sub {
my $app = shift;
sub {
my $env = shift;
# do preprocessing
my $res = $app->($env);
# do postprocessing
return $res;
};
};
$app;
};
is equal to:
my $mw = sub {
my $app = shift;
sub { my $env = shift; $app->($env) };
};
$app = $mw->($app);
URLMap supportPlack::Builder has a native support for Plack::App::URLMap via the
"mount" method.
use Plack::Builder;
my $app = builder {
mount "/foo" => $app1;
mount "/bar" => builder {
enable "Foo";
$app2;
};
};
See Plack::App::URLMap's "map" method to see what they mean. With
"builder" you can't use "map" as a DSL, for the obvious reason :)
NOTE: Once you use "mount" in your builder code, you have to use
"mount" for all the paths, including the root path ("/"). You can't
have the default app in the last line of "builder" like:
my $app = sub {
my $env = shift;
...
};
builder {
mount "/foo" => sub { ... };
$app; # THIS DOESN'T WORK
};
You'll get warnings saying that your mount configuration will be
ignored. Instead you should use "mount "/" => ..." in the last line to
set the default fallback app.
builder {
mount "/foo" => sub { ... };
mount "/" => $app;
}
Note that the "builder" DSL returns a whole new PSGI application, which
means
· "builder { ... }" should normally the last statement of a ".psgi"
file, because the return value of "builder" is the application that
is actually executed.
· You can nest your "builder" blocks, mixed with "mount" statements
(see "URLMap support" above):
builder {
mount "/foo" => builder {
mount "/bar" => $app;
}
}
will locate the $app under "/foo/bar", since the inner "builder"
block puts it under "/bar" and it results in a new PSGI application
which is located under "/foo" because of the outer "builder" block.
CONDITIONAL MIDDLEWARE SUPPORT
You can use "enable_if" to conditionally enable middleware based on the
runtime environment. See Plack::Middleware::Conditional for details.
SEE ALSO
Plack::Middleware Plack::App::URLMap Plack::Middleware::Conditional
perl v5.14.2 2012-08-13 Plack::Builder(3)
