print IP address to error_log for psgi application

gistfile1.pl

package Hoge::PSGIErrors;

use strict;
use IO::Handle;

sub new {
    my $class = shift;
    my $env = shift;
    my %self;
    $self{io} = IO::Handle->new;
    $self{io}->fdopen(fileno(STDERR), 'w');
    $self{env} = $env;
    my $o = bless \%self, $class;
    # ...
    $SIG{__WARN__} = sub { $o->print(@_) };
    return $o;
}

sub print {
    my $self = shift;
    my @msg = @_;
    $self->{io}->print(map {s/^/$self->{env}->{REMOTE_ADDR} /mg; $_} @msg);
}

1;

# app.psgi
use Hoge::PSGIErrors;

builder {
    # ...
    enable sub {
        my $app = shift;
        sub {
            my $env = shift;
            $env->{'psgi.errors'} = Hoge::PSGIErrors->new($env);
            $app->($env);
        }
    };
   # ...
}