UDP 'bytes=' option with comm.exchange()

[Brandon Enright <bmenrigh () ucsd edu>]

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In testing a script I'm working on fixing/updating I noticed that the
the comm.exchange() call in dns-test-open-recursion.nse doesn't behave
properly.

Right now the line is:

local status, result = comm.exchange(host, port, request, {proto="udp"})

When this script is run it appears to hang.  A packet capture shows
that the DNS server does, indeed, respond.

If I add the bytes=1 option to the call the script behaves properly.  I
propose changing the comm call to:

local status, result = comm.exchange(host, port, request, {proto="udp", bytes=1, timeout=10000})

So my question is, can comm.exchange be used with UDP without
specifying a byte count?  If so, how and under what circumstances?  Is
this by design?

Brandon

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