C NET-SNMP Get and Set specifically via MIB Name, Not OID - c

Question

I have written and am testing software for a generic SNMP client module in C as well as an implementation using this generic module. I am having trouble getting a get request to work by passing in a MIB name(e.g. sysDescr) instead of an OID(e.g. 1.3.6.1.2.1.1.1).
I am successful when I pass in a character array containing the OID to _snmp_parse_oid()_ but not the name.
I have checked the MIB file to make sure I am using the correct name. When I run the command line SNMP translate on the name it gives me the OID listed above:
$ snmptranslate -m +<MIB File> -IR -On <MIB Name>
.#.#.#.#.#.#.#####.#.#.#.#.#.#
(In the above command I replaced my actual mib file with <MIB File>, mib name with <MIB Name>, and OID numbers returned from the command with # characters)
The following is my code for my generic SNMP get function, assume returned values are #define numbers and I have removed some error handling for brevity:
/// #Synopsis Function to send out get request since the
/// SNMPOidData object has been setup
///
/// #Param oid_name String containing the OID to set
/// #Param value Value to set
///
/// #Returns Error
int snmpGet(SNMPAgent *this, char const * const oid_name, SNMPOidData * value)
{
netsnmp_pdu *pdu;
netsnmp_pdu *response;
netsnmp_variable_list *vars;
oid *retrieved_oid;
oidStruct oid_to_get;
int status = 0;
int result = ERROR_SUCCESS;
// Create the PDU for the data for our request
pdu = snmp_pdu_create(SNMP_MSG_GET);
oid_to_get.OidLen = MAX_OID_LEN; // Set max length
// Send out the request(s)
retrieved_oid = snmp_parse_oid(oid_name, oid_to_get.Oid, &oid_to_get.OidLen);
// Set the data
snmp_add_null_var(pdu, oid_to_get.Oid, oid_to_get.OidLen))
// Send the request out
status = snmp_synch_response(this->port.snmp_session_handle, pdu, &response);
if (STAT_SUCCESS == status)
{
if (SNMP_ERR_NOERROR == response->errstat)
{
vars = response->variables;
value->type = vars->type;
if (vars->next_variable != NULL)
{
// There are more values, set return type to null
value->type = ASN_NULL;
}
else if (!(CHECK_END(vars->type))) // Exception
{
result = ERROR_NOT_PRESENT;
fprintf(stderr, "Warning: OID=%s gets snmp exception %d \n",
oid_name, vars->type);
}
else if ((vars->type == ASN_INTEGER)
|| (vars->type == ASN_COUNTER)
|| (vars->type == ASN_UNSIGNED))
{
value->integer = *(vars->val.integer);
value->str_len = sizeof(value->integer);
}
else
{
value->str_len = vars->val_len;
if (value->str_len >= MAX_ASN_STR_LEN)
value->str_len = MAX_ASN_STR_LEN;
if (value->str_len > 0)
memcpy(value->string, vars->val.string, value->str_len);
// guarantee NULL terminated string
value->string[value->str_len] = '\0';
}
}
}
this->freePDU(response); // Clean up: free the response
return result;
}
The error I am getting:
oid_name: Unknown Object Identifier (Sub-id not found: (top) -> <MIB Name>)
Which comes from the following call:
retrieved_oid = snmp_parse_oid(oid_name, oid_to_get.Oid, &oid_to_get.OidLen);
I have made sure that the MIB files are on the machine in the configured place (snmptranslate wouldn't work if this weren't the case).
I have spent a good amount of time on Google results as well as directly searching here on Stack Overflow.
The following is a good tutorial but does not address my issue (they directly reference the OID they want to get the value of):
http://www.net-snmp.org/wiki/index.php/TUT:Simple_Application
Any help or insight would be much appreciated.
Some other info I can think of is that this is being compiled to run on an armv5tejl target running Linux communicating with an external device via ethernet.
Thanks,

Answer 1

When I call MIB variables by their string name I use the following net-snmp functions.
read_objid(OID, anOID, &anOID_len);
snmp_add_null_var(pdu, anOID, anOID_len);
Where:
oid anOID[MAX_OID_LEN];
size_t anOID_len = MAX_OID_LEN;
In my program I pack this all into a single function call.
void packSingleGetOID(const char *OID, struct snmp_pdu *pdu){
// OID in / PDU out
oid anOID[MAX_OID_LEN];
size_t anOID_len = MAX_OID_LEN;
read_objid(OID, anOID, &anOID_len);
snmp_add_null_var(pdu, anOID, anOID_len);
}
I pass in the MIB OID string and the pointer to session pdu. Remember the OID string is MIB_Name::variable.