Plack::Middleware::Lint(3pm) User Contributed Perl Documentation Plack::Middleware::Lint(3pm)NAME
Plack::Middleware::Lint - Validate request and response
SYNOPSIS
use Plack::Middleware::Lint;
my $app = sub { ... }; # your app or middleware
$app = Plack::Middleware::Lint->wrap($app);
# Or from plackup
plackup -e 'enable "Lint"' myapp.psgi
DESCRIPTION
Plack::Middleware::Lint is a middleware component to validate request and response environment formats. You are strongly suggested to use
this middleware when you develop a new framework adapter or a new PSGI web server that implements the PSGI interface.
This middleware is enabled by default when you run plackup or other launcher tools with the default environment development value.
DEBUGGING
Because of how this middleware works, it may not be easy to debug Lint errors when you encounter one, unless you're writing a PSGI web
server or a framework.
For example, when you're an application developer (user of some framework) and see errors like:
Body should be an array ref or filehandle at lib/Plack/Middleware/Lint.pm line XXXX
there's no clue about which line of your application produces that error.
We're aware of the issue, and have a plan to spit out more helpful errors to diagnose the issue. But until then, currently there are some
workarounds to make this easier. For now, the easiest one would be to enable Plack::Middleware::REPL outside of the Lint middleware, like:
plackup -e 'enable "REPL"; enable "Lint"' app.psgi
so that the Lint errors are caught by the REPL shell, where you can inspect all the variables in the response.
AUTHOR
Tatsuhiko Miyagawa
Tokuhiro Matsuno
SEE ALSO
Plack
perl v5.14.2 2011-09-22 Plack::Middleware::Lint(3pm)
Check Out this Related Man Page
Plack::Middleware(3pm) User Contributed Perl Documentation Plack::Middleware(3pm)NAME
Plack::Middleware - Base class for easy-to-use PSGI middleware
SYNOPSIS
package Plack::Middleware::Foo;
use parent qw( Plack::Middleware );
sub call {
my($self, $env) = @_;
# Do something with $env
# $self->app is the original app
my $res = $self->app->($env);
# Do something with $res
return $res;
}
# then in app.psgi
use Plack::Builder;
my $app = sub { ... } # as usual
builder {
enable "Plack::Middleware::Foo";
enable "Plack::Middleware::Bar", %options;
$app;
};
DESCRIPTION
Plack::Middleware is a utility base class to write PSGI middleware. All you have to do is to inherit from Plack::Middleware and then
implement the callback "call" method (or "to_app" method that would return the PSGI code reference) to do the actual work. You can use
"$self->app" to call the original (wrapped) application.
Your middleware object is created at a PSGI application compile time and is persistent during the web server life cycle (unless it is a
non-persistent environment such as CGI), so you should never set or cache per-request data like $env in your middleware object. See also
"OBJECT LIFECYCLE" in Plack::Component.
See Plack::Builder how to actually enable middleware in your .psgi application file using the DSL. If you do not like our builder DSL, you
can also use "wrap" method to wrap your application with a middleware:
use Plack::Middleware::Foo;
my $app = sub { ... };
$app = Plack::Middleware::Foo->wrap($app, %options);
$app = Plack::Middleware::Bar->wrap($app, %options);
RESPONSE CALLBACK
The typical middleware is written like this:
package Plack::Middleware::Something;
use parent qw(Plack::Middleware);
sub call {
my($self, $env) = @_;
# pre-processing $env
my $res = $self->app->($env);
# post-processing $res
return $res;
}
The tricky thing about post processing the response is that it could either be an immediate 3 element array ref, or a code reference that
implements the delayed (streaming) interface.
Dealing with these two types of response in each piece of middleware is pointless, so you're recommended to use the "response_cb" wrapper
function in Plack::Util when implementing a post processing middleware.
my $res = $app->($env);
Plack::Util::response_cb($res, sub {
my $res = shift;
# do something with $res;
});
The callback function gets a PSGI response as a 3 element array reference, and you can update the reference to implement the post
processing.
package Plack::Middleware::Always500;
use parent qw(Plack::Middleware);
use Plack::Util;
sub call {
my($self, $env) = @_;
my $res = $self->app->($env);
Plack::Util::response_cb($res, sub {
my $res = shift;
$res->[0] = 500;
return;
});
}
In this example, the callback gets the $res and updates its first element (status code) to 500. Using "response_cb" makes sure that this
works with the delayed response too.
You're not required (and not recommended either) to return a new array reference - they will be simply ignored. You're suggested to
explicitly return, unless you fiddle with the content filter callback (see below).
Similarly, note that you have to keep the $res reference when you swap the entire response.
Plack::Util::response_cb($res, sub {
my $res = shift;
$res = [ $new_status, $new_headers, $new_body ]; # THIS DOES NOT WORK
return;
});
This does not work, since assigning a new anonymous array to $res doesn't update the original PSGI response value. You should instead do:
Plack::Util::response_cb($res, sub {
my $res = shift;
@$res = ($new_status, $new_headers, $new_body); # THIS WORKS
return;
});
The third element of PSGI response array ref is a body, and it could be either array ref or IO::Handle-ish object. The application could
also make use of $writer object if "psgi.streaming" is in effect. Dealing with these variants is again really painful, and "response_cb"
can take care of that too, by allowing you to return a content filter as a code reference.
# replace all "Foo" in content body with "Bar"
Plack::Util::response_cb($res, sub {
my $res = shift;
return sub {
my $chunk = shift;
return unless defined $chunk;
$chunk =~ s/Foo/Bar/g;
return $chunk;
}
});
The callback takes one argument $chunk and your callback is expected to return the updated chunk. If the given $chunk is undef, it means
the stream has reached the end, so your callback should also return undef, or return the final chunk and return undef when called next
time.
SEE ALSO
Plack Plack::Builder Plack::Component
perl v5.14.2 2011-06-22 Plack::Middleware(3pm)