Hello all, I'm trying to communicate via TCP to a legacy system. This infernal legacy system knows nothing of delimiting data and changing it isn't something "they" want to hear. This system processes barcode data which is transmitted to it from various barcode scanners. The data is, on average, between 6 and 18 A-Z0-9 characters plus a CR, or CRLF. If a single TCP packet has more than one "read" from the barcode scanner in it due to buffering (Nagle's Algorithm, or PerlIO buffering), the legacy system craps itself, and bad things happen from a process automation standpoint.

I have used setsockopt/TCP_NODELAY, and $socket->autoflush(1) for the sockets in question on my end, and there are still times when Perl (or something) buffers the data and sends out a TCP packet that contains more than one barcode read... I can see it on a packet sniffer.

FWIW, this Perl script is running on Debian R4.0.

Does anyone have any idea where this additional buffering is coming from? ... And more importantly, how to make it go away? :-)

Thanks!

In reply to Sockets, autoflush, and TCP_NODELAY by packetwhacker

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.