[asterisk-ss7] A fix to libss7 bug in SAM construction!

[sky earth]

> which libss7 version are you looked into

 

I am in fact looking in to your version checked out using the following:

 

svn co https://observer.router.hu/repos_pub/libss7/trunk libss7

 

 

> I'm using mine and have tons
> of incomming calls with SAM.

 

I know that you have tons of INCOMMING calls with SAM but I am reporting a bug in sending SAMs NOT receiving SAMs :-)

 

libss7 is currently not programmed to initiate OUTGOING calls with SAM, but I think the code should be correct any way.

 


> regards,
> Attila

 

Thank you Attila! You're so kind to share your code and provide help!

 

regards, 

Tian


> 
> On Tue, 2009-10-20 at 20:32 +0800, Tian wrote:
> > Hi guys,
> > 
> > I am reading libss7 source code and I think I've found a bug in it, 
> > following is my description of the bug and my tentative fix to the bug, as I 
> > don't have a running Asterisk box, I hope you will kindly help me check it, 
> > thanks!
> > 
> > According to ITU-T Recommendation Q.763, section 1.6 'Mandatory variable 
> > part':
> > 
> > "A pointer is also included to indicate the beginning of the optional part. 
> > If the message type indicates that no optional part is allowed, then this 
> > pointer will not be present. If the message type indicates that an optional 
> > part is possible, but there is no optional part included in this particular 
> > message, then a pointer field containing all zeros will be used."
> > 
> > Thus, ISUP messages that don't carry any optionals fall into two categories: 
> > 1) those include a 'Pointer to start of optional part' containing all zeros 
> > (e.g., SAM falls into this category) and 2) those don't include a 'Pointer 
> > to start of optional part'.
> > 
> > libss7 can only correctly construct ISUP messages carrying zero optional 
> > parameters that fall into category 2) if messages that fall into category 1) 
> > are to be constructed, libss7 will fail.
> > 
> > The bug shows up in the file isup.c (Libss7 trunk revison 272, lines 
> > 2425-2432), my fix to this bug specifically for SAM is as follows (you may 
> > adopt the fix by replacing everyting between the fisrt and the last two 
> > comment lines):
> > 
> > /* Make sure we grab our opional parameters */
> > if (optparams || (messagetype == ISUP_SAM)) {
> > if (optparams)
> > opt_ptr = &mh->data[offset + varparams];
> > /* a SAM message doesn't have any optionals,
> > * but the 'Pointer to start of optional part' is still present
> > */
> > offset += varparams + 1; /* add one for the optionals */
> > len -= varparams + 1;
> > } else {
> > offset += varparams;
> > len -= varparams;
> > }
> > 
> > /* Whew, some complicated math for all of these offsets and different 
> > sections */
> > 
> > 
> > 
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