Beefy Boxes and Bandwidth Generously Provided by pair Networks
Don't ask to ask, just ask

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

Yeah, I'm responding to my own post. This is because what follows is really a rather off-topic rant on my part, and not really related to the question asked above.

So I got vaguely interested in figuring out what exactly that useless-looking $flags variable was there for. I quickly learned that, unlike $datagram, it's not modified by send or recv, as I had anticipated. Rather, it's says "make me a packet with this set of flags" or "do this special thing when trolling for packets."

It just happens that one of the machines that I tested my UDP code on was a machine running Windows and ActivePerl. So I started poking around, looking at which constant values for the flags were defined. Under Windows, I found exactly four: MSG_OOB, MSG_PEEK, MSG_DONTROUTE, and MSG_MAXIOVLEN. These, of course, were nicely mysterious to me, so I set out to see what I could see about each:

  • MSG_OOB is supposed to be a flag which signals "urgent" or "priority" messages. It's what catches control-C in Telnet connections, for example. When used with recv, it serves as a filter, only recv'ing "priority" packets. It doesn't work with UDP, though.
  • MSG_PEEK allows you to recv the first packet without taking it off of the server's stack of waiting packets. This is of dubious usefulness, but actually works under windows.
  • MSG_DONTROUTE probably does what it implies. I didn't have much way to test this.

And this brings me to my main victim -- MSG_MAXIOVLEN. Not only does it have the most ugly-looking name, it's apparently only defined under Windows. A Google search for it shows up a decent number of hits -- but upon careful perusal, every one of them defines it as a constant with no comment after it. In fact, the Winsock specification does the exact same thing -- defined, with no comment, and never refenced again. In an example of huge-scale cargo-cultism, hundreds of header files, including every Windows-based Perl install out there, have copied an absolutly useless constant which is not implemented or described anywhere. A little further reasearch shows that it might be implemented on the UNICOS/mk cray operating system. And even if it is, it's misnamed, as it's not a flag on a message at all, but an arbitrary constant of the TCP stack!

So there's the sordid tale of a misnamed, unimplmented, useless, but omnipresent constant. Gah!

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^+*`^ ve^#$&V"+@( NO CARRIER'

In reply to OT: Random useless misnamed Windows constants and cargo-cultism by Chmrr
in thread Simple UDP example anyone? by Anonymous Monk

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, 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, 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.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others musing on the Monastery: (8)
    As of 2021-01-25 14:56 GMT
    Find Nodes?
      Voting Booth?