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Re^2: Does IO::Select work? Anywhere?

by BrowserUk (Pope)
on Oct 24, 2012 at 12:24 UTC ( #1000622=note: print w/ replies, xml ) Need Help??


in reply to Re: Does IO::Select work? Anywhere?
in thread Does IO::Select work? Anywhere?

Do you think those sorts of tests on a select socket would be able to detect your "eternal a" script, and dispose of it?

The solution is to not use readline, or anything that blocks waits for a terminator that may never arrive.

Instead, use recv or sysread and get whatever is available when can_read() tells you there is something there, and accumulate those somethings until a newline (or other terminator) is seen before taking action.

In the case of the client that never sends a terminator, it will eventually time out if it never transmits anything more.

The most effective DOS strategy against badly written multiplexing servers is to send one character every (say) 890 seconds (default timeouts are often 900), but to never send a terminator.

Another strategy is to send huge packets that overrun memory. For badly designed C code, that usually results in the classic buffer overrun. For a perl program, it can actually be worse. As Perl will just keep increasing the size of the scalar, it can put the server into swapping and bring everything to a crawl without actually blowing it out of the water.


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i


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