I might do something like:

  while ( <FILE> ) {
    if ( /--- start foo ---/ ) {
      # we're about to start processing
      while ( <FILE> ) {
        last if /--- end foo ---/;
        # here's a line of stuff to process
      }
      # we're done with this block
    }
  }
[download]

This approach eliminates the conditional, at the risk of not noticing that a file has ended mid block. If that's liable to be a problem, it's a straighforward mod to catch it.