OptionManagement call to set an endpoint option, I
receive one of two error messages, Error -3155 (bad option) or
Error -3160 (buffer overflow). What should I be looking at to resolve
these errors?
OTOptionManagement. For more information on call to
OTOptionManagement, please refer to "Inside Macintosh: Networking With
Open Transport", chapter 7, Option Management. You can download an
electronic copy of this documentation from the Open Transport Web Page.
The common reasons for Error -3151 are: 1. The option length for the option is incorrect. Most Open Transport Option Management option values are 4 bytes long. Some options take string and structure values. You must set both the
TOptMgmt opt.len
field, and the TOptionHeader len field to the exact length of the option
buffer request. You can also use the same buffer and TOptMgmt structure
for the Option Management response, which is discussed in the next
section regarding Error -3160.
Error -3151 occurs most often when the option value is 1 byte long, but a 4-byte length is specified. Again, there are two places where the length argument is set - in the
TOptMgmt structure and in the
TOptionHeader structure.
2. A return
TOptMgmt pointer was passed in the call to OTOptionManagement
and the maxlen field is not set correctly. Not setting this parameter
can also result in Error -3160, depending on its input value. The
OTMultiCastPitch code sample in the OpenTransport SDK demonstrates this
problem when trying to set the IP_ADD_MEMBERSHIP option. The corrected
call is shown as follows:
optReq.flags = T_NEGOTIATE;
optReq.opt.len = sizeof(optBuffer); // specify the size of the buffer
optReq.opt.maxlen = sizeof(optBuffer); // <--- add this line of code
optReq.opt.buf = (UInt8*) optBuffer;
OTMemzero(optBuffer, sizeof(optBuffer));
opt->level = INET_IP;
opt->name = IP_ADD_MEMBERSHIP;
opt->len = sizeof(optBuffer); // specify the size of the option
A similar correction is required in the same code sample when trying to IP_MULTICAST_TTL option. The modified code sample is shown below.The previous corrections applies to the Open Transport SDK v1.3 and earlier.
3. There is a known problem when using Open Transport v1.3 and earlier. You will encounter this error when using the
OTOptionManagement T_ALLOPT
value to obtain all of the current IP option settings in one call. This
problem is demonstrated with the OTMulticastPitchSample code running
under Open Transport v 1.3 and earlier. The workaround is to ask
individually for the status of each option where the current setting is
desired.
The common reasons for Error -3160 are:
1. The
TOptMgmt opt.maxlen field was not initialized, or incorrectly set.
This error can be returned even if the option was successfully
negotiated. The solution is to set the maxlen field correctly.
2. There is a known problem when using Open Transport v1.3 and earlier. If you try to negotiate a TCP/IP option whose length is 1 or 2 bytes, Open Transport will return this error if the return buffer is set for a buffer for less than a 4-byte response. Interestingly, the option may be successfully negotiated. The workaround for this problem is to define the size of the buffer as
kOTFourByteOptionSize and to continue to set
the two len fields as kOTOneByteOptionSize or kOTTwoByteOptionSize (as of
this writing, there are no 2-byte option settings).
Error -3160 will not be returned if there is no return parameter specified. On the other hand, without checking the return value, you cannot know whether the return status of the option call was T_SUCCESS or not. This problem applies when trying to set the following options
| Option Level | Option Name |
| INET_UDP | UDP_RX_ICMP |
| INET_IP | IP_RECVOPTS |
| INET_IP | IP_TOS |
| INET_IP | IP_TTL |
| INET_IP | IP_MULTICAST_LOOP |
| INET_IP | IP_MULTICAST_TTL |
| INET_IP | IP_RECVDSTADDR |
| INET_IP | IP_RECVIFADDR |
The following modifications and corrections apply to the
OTMultiCastPitchSample.cp file.
Correction 1: Change to the sample code for setting the IP_MULTICAST_TTL option.
//
// Setup time-to-live for multicast sends (defaults to 1)
// Can reuse the TOptMgmt, but not Option itself is different.
// While we could reuse the buffer above, I'll do it right to
// demonstrate correctness.
//
UInt8 ttlOptBuffer[ kOTFourByteOptionSize ]; // <-- 4 byte option length buffer
TOption*
ttlOpt = (TOption*)ttlOptBuffer;
optReq.flags = T_NEGOTIATE;
optReq.opt.len = kOTOneByteOptionSize; // <-- leave as 1 byte option size
optReq.opt.maxlen = sizeof(ttlOptBuffer); // <-- set return buffer maxlen
optReq.opt.buf = (UInt8*) ttlOptBuffer;
OTMemzero(optBuffer, sizeof(ttlOptBuffer));
ttlOpt->level = INET_IP;
ttlOpt->name = IP_MULTICAST_TTL;
ttlOpt->len = kOTOneByteOptionSize; // <-- leave as 1 byte option size
*(char*)(ttlOpt->value) = kDefaultTTL;
err = gEndpt->OptionManagement(&optReq, &optReq);
Correction 2:
Change to the sample code for setting the IP_MULTICAST_LOOP
option.
//
// Turn off loopback - unless you want to receive your own packets back.
//
TOptMgmt optReq;
UInt8 optBuffer[ kOTFourByteOptionSize ]; // <-- 4 byte option length buffer
TOption* opt = (TOption*)optBuffer;
OTMemzero(optBuffer, sizeof(optBuffer));
optReq.flags = T_NEGOTIATE;
optReq.opt.len = kOTOneByteOptionSize; // <-- leave as 1 byte option size
optReq.opt.maxlen = sizeof(optBuffer); // <-- set return buffer maxlen
optReq.opt.buf = (UInt8*) optBuffer;
opt->level = INET_IP;
opt->name = IP_MULTICAST_LOOP;
opt->len = kOTOneByteOptionSize; // <-- leave as 1 byte option size
*(char *)(opt->value) = gLoopbackState;
err = gEndpt->OptionManagement(&optReq, &optReq);