I've introduced a couple of middleware components. Some of them are useful and could be enabled globally, while others might be better enabled on certain conditions. Today we'll talk about a solution to this.
Load middleware conditionally
Conditional middleware is a super (or meta) middleware that takes one middleware and enable that middleware based on a runtime condition. Let's take some examples:
- You want to enable JSONP middleware only if the path begins with /public
- You don't want to enable Basic Auth if the request comes from local IP
We investigated how they deal with situations like this in WSGI and Rack, but couldn't find a generic solution, and they mostly just implement options to individual component, which did not look cool for me.
Middleware::Conditional
The Conditional middleware is an ultimate flexible solution to this:
use Plack::Builder;
builder {
enable_if { $_[0]->{REMOTE_ADDR} !~ /^192\.168\.0\./ }
"Auth::Basic", authenticator => ...;
$app;
};
We added a new keyword to Plack::Builder enable_if, which takes a block that gets evaluated in the request time ($_[0] there is the $env hash) and if the block returns true, run the wrapped application but otherwise pass through.
This example code examines if the request comes from a local network and runs a basic authentication otherwise.
Conditional is implemented as a normal piece of middleware, and internally this is equivalent to:
use Plack::Middleware::Conditional;
use Plack::Middleware::Auth::Basic;
my $app = sub { ... };
$app = Plack::Middleware::Conditional->wrap($app,
builder => sub {
Plack::Middleware::Auth::Basic->wrap(
$_[0], authenticator => ...,
);
},
condition => sub {
my $env = shift;
$env->{REMOTE_ADDR} !~ /^192\.168\.0\./;
},
);
But it's a little boring to write, so we added a DSL version, which I recommend to use :)
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