This has been a minor sore point for decades in the socket interface - how to refer to a structure that could hold any of a number of different address types. Early on, it was decided just to refer to a sockaddr object - an object of a well-known type and size - too small these days, but at least useful for ipv4 addresses. This was done because void* was not actually added to the C standard till 1989 when the C89 standard came out. Prior to that, your only option was to typecast.
In short, this is exactly the sort of thing for which void * was originally introduced. You pass a generic pointer to the data structure, along with a type discriminator and a buffer length. In this case, the type discriminator is always at a well-known offset within the buffer referred to, and the size is a separate argument. Had void* been available when the sockets interface was being designed, I believe they would have used it instead of passing sockaddr pointers around, because in the C language, you can automatically cast to and from void (not so in C++, of course, but not relevant here), so you can simply use a void* as if it were any of the sockaddr family of structures. Is it type safe? Of course not. You can just as easily auto-cast it to the wrong type of thing. But given the fact that the original socket spec has you manually type-casting from one type of structure to another all over the place, it's at least as safe, but much more convenient. John -----Original Message----- From: Roel van de Kraats [mailto:rkra...@dds.nl] Sent: Wednesday, May 25, 2011 6:06 AM To: 'openslp-devel@lists.sourceforge.net' Subject: Re: [Openslp-devel] Bug in libslp_knownda.c On 05/25/2011 01:18 PM, Morrell Richard (external) wrote: > Hi Roel, > > The change in r1597 was only supposed to abstract the cache refresh > code into a separate function, not change anything else, so the change > to the address size in the second call was incorrect. Please go ahead > with the update. Done. See r1673. In my opinion it is a bit 'dangerous' to pass through void pointers like this. Wouldn't it be better to explicitly use 'struct sockaddr_storage' pointers? Or even use a union throughout the whole source tree to hold the different 'sockaddr' types, like http://svn.tartarus.org/sgt/putty/unix/uxnet.c?p2=%2Fputty%2Funix%2Fuxnet.c&; p1=putty%2Funix%2Fuxnet.c&r1=8612&r2=8611&view=diff&pathrev=8612 ? BR, Roel > Regards, > > Richard > > -----Original Message----- > From: Roel van de Kraats [mailto:rkra...@dds.nl] > Sent: 25 May 2011 11:34 > To: 'openslp-devel@lists.sourceforge.net' > Subject: [Openslp-devel] Bug in libslp_knownda.c > > > Dear all, > > It seems that libslp_knownda.c has a bug on line 716 (see > http://openslp.svn.sourceforge.net/viewvc/openslp/trunk/openslp/libslp/libsl > p_knownda.c?view=markup&pathrev=1672), > because sizeof(struct in_addr) is too small to copy the whole address. > This causes 'slptool findsrvtypes' to fail in case another host acts as > DA. This was introduced in r1597 (see > http://openslp.svn.sourceforge.net/viewvc/openslp?view=revision&revision=159 > 7). > > I guess it is safe to replace 'sizeof (struct in_addr)' with > 'sizeof(struct sockaddr_storage)', but I'm not sure. If anyone can > confirm this, I'll commit the fix. > > BR, > Roel > > > > ---------------------------------------------------------------------------- > -- > vRanger cuts backup time in half-while increasing security. > With the market-leading solution for virtual backup and recovery, > you get blazing-fast, flexible, and affordable data protection. > Download your free trial now. > http://p.sf.net/sfu/quest-d2dcopy1 > _______________________________________________ > Openslp-devel mailing list > Openslp-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/openslp-devel > > This email, including any attachment, is a confidential communication > intended solely for the use of the individual or entity to whom it is > addressed. It contains information which is private and may be proprietary > or covered by legal professional privilege. If you have received this email > in error, please notify the sender upon receipt, and immediately delete it > from your system. > > Anything contained in this email that is not connected with the businesses > of this company is neither endorsed by nor is the liability of this company. > > Whilst we have taken reasonable precautions to ensure that any attachment to > this email has been swept for viruses, we cannot accept liability for any > damage sustained as a result of software viruses, and would advise that you > carry out your own virus checks before opening any attachment. > > > ---------------------------------------------------------------------------- -- > vRanger cuts backup time in half-while increasing security. > With the market-leading solution for virtual backup and recovery, > you get blazing-fast, flexible, and affordable data protection. > Download your free trial now. > http://p.sf.net/sfu/quest-d2dcopy1 > _______________________________________________ > Openslp-devel mailing list > Openslp-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/openslp-devel ---------------------------------------------------------------------------- -- vRanger cuts backup time in half-while increasing security. With the market-leading solution for virtual backup and recovery, you get blazing-fast, flexible, and affordable data protection. Download your free trial now. http://p.sf.net/sfu/quest-d2dcopy1 _______________________________________________ Openslp-devel mailing list Openslp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openslp-devel ------------------------------------------------------------------------------ vRanger cuts backup time in half-while increasing security. With the market-leading solution for virtual backup and recovery, you get blazing-fast, flexible, and affordable data protection. Download your free trial now. http://p.sf.net/sfu/quest-d2dcopy1 _______________________________________________ Openslp-devel mailing list Openslp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openslp-devel
