How to decode MAP Invoke messages using asn1c generated code - c++

Question

I am using the c code generated by asn1c from the MAP protocol specification (i.e., the corresponding ASN1 files). Please consider the following sample code:
// A real byte stream of a MAP message:
unsigned char packet_bytes[] = {
0xa2, 0x60, 0x02, 0x01, 0x00, 0x30, 0x5b, 0x02,
0x01, 0x38, 0xa3, 0x56, 0xa1, 0x54, 0x30, 0x52,
0x04, 0x10, 0x7a, 0x0e, 0x1f, 0xef, 0x73, 0x77,
0xbe, 0xb0, 0x9d, 0x6f, 0x23, 0x13, 0xfb, 0xc2,
0x32, 0xa6, 0x04, 0x08, 0x65, 0xda, 0x19, 0x1e,
0x18, 0x4b, 0x04, 0x99, 0x04, 0x10, 0x47, 0xe1,
0x36, 0x82, 0xe9, 0xb3, 0xf3, 0x54, 0x76, 0x67,
0x1d, 0xe4, 0xed, 0x25, 0xc8, 0x76, 0x04, 0x10,
0x37, 0x1d, 0x80, 0x82, 0xde, 0xec, 0x70, 0x51,
0xc6, 0xcd, 0x08, 0xc9, 0x30, 0x64, 0xc6, 0x54,
0x04, 0x10, 0x82, 0xbc, 0x2d, 0xdb, 0x1d, 0x92,
0x82, 0x34, 0x55, 0xbc, 0xeb, 0x87, 0x72, 0xf3,
0x90, 0xce
};
// Initializing ...
MAP_Component_t _pdu, *pdu = &_pdu;
memset(pdu, 0, sizeof(*pdu));
// Decoding:
asn_dec_rval_t dec_ret = ber_decode(NULL, &asn_DEF_MAP_Component, (void **) &pdu, MAP_packet_bytes, sizeof(MAP_packet_bytes));
The invokeId and opCode parameters are truely detected, and the parser gives us a buffer named as invokeParameters which is of type ANY.
GSM Mobile Application
Component: invoke (1)
invoke
invokeID: -70
opCode: localValue (0)
invokeParameters: ....
The question is how to decode (parse) invokeParameters?
GSM Mobile Application
Component: returnResultLast (2)
returnResultLast
invokeID: 0
resultretres
opCode: localValue (0)
localValue: sendAuthenticationInfo (56)
authenticationSetList: quintupletList (1)
quintupletList: 1 item
AuthenticationQuintuplet
rand: 7a0e1fef7377beb09d6f2313fbc232a6
xres: 65da191e184b0499
ck: 47e13682e9b3f35476671de4ed25c876
ik: 371d8082deec7051c6cd08c93064c654
autn: 82bc2ddb1d92823455bceb8772f390ce

Answer 1

The invokeId and opCode parameters are truely detected, and the parser gives us a buffer named as invokeParameters which is of type ANY.
The question is how to decode (parse) invokeParameters?
You need to call ber_decode with the appropriate type (depending on the operation code) and the content of the ANY buffer. From ANY.h
typedef struct ANY {
uint8_t *buf; /* BER-encoded ANY contents */
int size; /* Size of the above buffer */
asn_struct_ctx_t _asn_ctx; /* Parsing across buffer boundaries */
} ANY_t;
In your case it should be something like
SendAuthenticationInfoArg_t _sai, *sai = &_sai;
memset(sai, 0, sizeof(*sai));
asn_dec_rval_t dec_ret = ber_decode(NULL,
&asn_DEF_SendAuthenticationInfoArg,
(void **) &sai,
_pdu.invoke.invokeparameter->buf,
_pdu.invoke.invokeparameter->size);