Is there a way to throw a 414 and avoid this behavior when Dancer running under Starman?

Sure, add a check for URI size first in line :) http://search.cpan.org/dist/Dancer/lib/Dancer/Cookbook.pod#Default_route

(untested)

any qr{.{8190}.*} => sub { 
    status '414'; # 414 - Request-URI Too Long
};
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Or make a Plack::Middleware to do the check

(untested)

  package Plack::Middleware::ProhibitRequestUri8190;
  use parent qw(Plack::Middleware);
  use Plack::Util;
  sub call {
      my($self, $env) = @_;
      my $res  = $self->app->($env);
      if( length $res->{REQUEST_URI} > 8190 ){
        Plack::Util::response_cb($res, sub {
            my $res = shift;
            $res->[0] = 414;
            return;
        });
      }
  }
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plack middleware 414 request uri too large

Thanks.

The default route doesn't appear to do the trick (see the updated question).

So far I've had no luck with the plack middleware, although http://advent.perldancer.org/2010/22 looks promising (towards the bottom where they wrap the app).

Although I have used Dancer, I definitely don't consider myself to be an "expert" on Dancer.

Looking through the Dancer documentation, here's one (untested) idea that might work.

use Dancer;
my $max_url_length = 100; # change this to what you want

# first route handler
any ['get', 'post'] => '.*' => sub {
  if ((length request->request_uri) > $max_url_length) {
    # do the 414 error page
  }
  else {pass(...);}
};

# create other routes

dance;
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The basic idea that I was trying to do in the above code was to have the first route handler that will catch everything and check the URL length. If it's above the max limit, give the 414 error page. Otherwise, pass the request on to the next matching route handler. Again, I haven't tested that code, so I can't guarantee that I'm reading documentation correctly.

Thanks for the suggestion. It appears that, because of how things are written, I can't rely on the first route handler being the first one processed... at least it doesn't appear to work that way (see the updated question).

Solved.

I was able to get the desired behavior by wrapping things in app.pl

#!/usr/bin/env perl
use Dancer;
use REST_App;
#dance;

use Plack::Builder;

my $app = sub {
    my $env = shift;

    if (length ($env->{REQUEST_URI}) > 1000) {
        return [
            '414',
            [ 'Content-Type' => 'text/html' ],
            [ get_414_page() ], # HTML for the error page
        ];
    }

    my $request = Dancer::Request->new(env => $env);
    Dancer->dance($request);
};

builder {
    $app;
};
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