By the way, that code has a memory leak (cyclic reference ($fetch contains a reference to a closure which captures $fetch)).

Replace

my $fetch;
$fetch = sub {
   ...
   $fetch->();
   ...
};

...
$fetch->();
...
[download]

with

use feature qw( current_sub );

my $fetch = sub {
   ...
   __SUB__->();
   ...
};

...
$fetch->();
...
[download]