Firstly, erroneousBollock == bollock. Sorry for any confusion.

Hmmmmm, well this is embarassing, it seems that my test case which was stalling (no errors in apache log, logfile showed progress up to ~2.5MB) is now not failing. :-/

Here is the test-case anyway.

  use strict;
  use warnings;
  use CGI qw(:all);
  use File::Slurp qw(write_file);
  sub hook {
    my ($file, $buffer, $bytes, $data) = @_;
    write_file('/tmp/uplog', {append => 1}, "[$file][$bytes][$data]");
  }
  my $q = CGI->new(\&hook, 'AppName');
  my $f = $q->param('upload_file');
  print header(), "Done.";
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