I need to combine a read which produces chunks of (mostly) equal size (till EOF) of read data with an option to control where the read() starts and where it ends. This is what I came up with: 
    # chunked read() with optional ranges: the way read() is used here
+, we can't use the LENGTH, OFFSET feature of read()
    # so we need to use the initial seek() in combination with a limit
+ by position
    my $chunk_size = $cnf->{chunk_size} || 1024;
    my $bytes_in = $cnf->{bytes_in} || 0;
    my $bytes_out= $cnf->{bytes_out};

    my $pos = $bytes_in;
    seek($fh,$bytes_in,0);
    while ( read( $fh, my $buffer, $chunk_size ) ) {
        $pos += length($chunk_size);

        if( defined($bytes_out) && $pos >= $bytes_out){
            # return bytes::substr($buffer, 0, ($chunk_size - ($pos - 
+$bytes_out)) );       # make last chunk shorter
            print bytes::substr($buffer, 0, ($chunk_size - ($pos - $by
+tes_out)) );
            last;
        }else{
            # return $buffer;
            print $buffer;
        }
    }

[download]
As you can see, I avoided tell() to determine position. I blindly assumed it would be slower/produce a disk operation, hence the reliance on a calculated $pos.

Please suggest improvements, monks!

In reply to Advice needed on chunked read + byte-range logic by isync

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.