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<DIV dir=ltr align=left><SPAN class=838003315-25062008><FONT face=Arial
color=#0000ff size=2>I suppose this change would have made things a little
easier, but I am writing against the Feb 2007 Spec, and I am not sure if my
bosses will ever ask me to get up to date with the newest
Spec.</FONT></SPAN></DIV>
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<P><FONT size=2>Patrick Donahue<BR>(256) 544-5943 office<BR>(256) 721-0726
home<BR>(256) 682-9753 cell</FONT> </P>
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<FONT face=Tahoma size=2><B>From:</B> sis-ams-bounces@mailman.ccsds.org
[mailto:sis-ams-bounces@mailman.ccsds.org] <B>On Behalf Of </B>Scott
Burleigh<BR><B>Sent:</B> Wednesday, June 25, 2008 10:32 AM<BR><B>To:</B> Ray,
Timothy J. (GSFC-583.0)<BR><B>Cc:</B>
sis-ams@mailman.ccsds.org<BR><B>Subject:</B> Re: [Sis-ams] validation of
Meta-AMS PDUs<BR></FONT><BR></DIV>
<DIV></DIV>Ray, Timothy J. (GSFC-583.0) wrote:
<BLOCKQUOTE
cite=mid:C3B9C435D7725E4EABE2B62200A42C127CD508@NDMSEVS36A.ndc.nasa.gov
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<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Dear WG
Members,</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">In my implementation, I am
trying to thoroughly validate each incoming Meta-AMS protocol message
(MPDU). The primary goal is to avoid program crashes that can occur
when an attempt is made to access an array element beyond the end of the
array’s allocated memory. For example, if the supplementary data
includes a field that is supposed to be a null-terminated character string,
but the null-terminator is missing, avoid any attempts to access past the
end of the entire array allocated to hold the raw MPDU
bytes.</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">I’m finding it quite complex to
validate MPDUs whose supplementary data includes null-terminated strings
(especially if the strings are buried within arrays of structures containing
sub-structures). Validation would be much simpler if, instead of
adding a one-byte null terminator at the end of each string, we added a
one-byte length field at the beginning of each string. (It would also
be possible to add the one-byte length field and keep the null terminator,
although that seems redundant).</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Any
thoughts/comments?</SPAN></FONT></P></DIV></BLOCKQUOTE>I kind of like this
idea, though I know it would have an impact on everybody's implementation
work. It would be not much harder to write up in the spec, it would
consume no additional bandwidth (assuming the string length byte was instead
of, rather than in addition to, the NULL string terminator), and it could very
well make validation simpler and therefore make implementations
safer.<BR><BR>But that's easy for me to say, as I'm way behind in retrofitting
my implementation to the Red-2 spec anyway and it would be fairly easy for me
to include this change when I finally get to work. Stuart, Pat, David,
what do you guys think?<BR><BR>Scott<BR></BLOCKQUOTE></BODY></HTML>