sub read_bytes {
   my ($fh, $to_read) = @_;
   my $buf = '';
   while ($to_read) {
      my $bytes_read = read($fh, $buf, $to_read, length($buf));
      die("$!\n") if !defined($bytes_read);
      die("Unexpected end of file\n") if !$bytes_read;
      $to_read -= $bytes_read;
   }
   return $buf;
}

sub read_uint32 {
   my ($fh) = @_;
   return (unpack('N', read_bytes($fh, 4)));
}

sub read_str {
   my ($fh) = @_;
   my $length = read_uint32($fh);
   return read_bytes($fh, $length);
}

sub write_uint32 {
   my ($fh, $n) = @_;
   print $fh (pack('N', $n));
}

sub write_str {
   my ($fh, $str) = @_;
   print $fh (pack('N', length($str)), $str);
}