Using snmpgetnext on a table - snmp

Question

I am writing my own MIB Module containing a table with 2 columns. Using snmptable works just fine and retrieves all values of the table with all the rows.
But with snmpgetnext I can only retrieve the first row of the table.
snmpgetnext -v2c -c public localhost sensorTable
MY-PERSONAL-MIB::sensorVoltage."1" = STRING: "2.3V"
To retrieve the next value I must run:
snmpgetnext -v2c -c public localhost sensorVoltage."2"
MY-PERSONAL-MIB::sensorTemperature."1" = "3.2C"
Running snmpgetnext -v2c -c public localhost sensorVoltage."1" would result in sensorVoltage."1" again, the same for sensorTemperature."1".
snmpgetnext -v2c -c public localhost sensorTemperature."2"
SNMPv2-MIB::snmpSetSerialNo.0 = INTEGER: 1664041205
Also, I ran snmptable -CB so the manager only uses GETNEXT to retrieve the table values. This works fine as well.
So why can't I retrieve the single values with a simple snmpgetnext request?
As last, snmpget doesn't work at all. I get the following error:
snmpget -v2c -c publicl localhost sensorTemperature."1"
MY-PERSONAL-MIB::sensorTemperature.1 = No such Instance currently exists at this OID
At last, my code I use for my MIB-Module. I use the handler to read data from a file and create a table struct through it. I tried using snmpgetnext with a table created through the initialization routine resulting in the same problem, so the handler routine shouldn't be the issue here but I still appended it just for completion and well, who knows!
#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>
#include "sensorTable.h"
#define firstEntryRow 2
netsnmp_table_data_set *table_set;
void
initialize_table_sensorTable(void)
{
netsnmp_ds_set_string(NETSNMP_DS_APPLICATION_ID, NETSNMP_DS_AGENT_X_SOCKET, "tcp:localhost:705");
const oid sensorTable_oid[] = { 1 ,3 ,6 ,1 ,4 ,1 ,8072 ,1259 ,1 ,1 };
table_set = netsnmp_create_table_data_set("sensorTable");
netsnmp_table_row *row;
table_set->allow_creation = 1;
DEBUGMSGTL(("initialize_table_sensorTable",
"adding indexes to table sensorTable\n"));
netsnmp_table_dataset_add_index(table_set,
ASN_OCTET_STR);
DEBUGMSGTL(("initialize_table_sensorTable",
"adding column types to table sensorTable\n"));
netsnmp_table_set_multi_add_default_row(table_set,
COLUMN_SENSORVOLTAGE, ASN_OCTET_STR, 1,
NULL, 0,
COLUMN_SENSORTEMPERATURE, ASN_OCTET_STR, 1,
NULL, 0,
0);
netsnmp_register_table_data_set(netsnmp_create_handler_registration("sensorTable", sensorTable_handler,
sensorTable_oid,
OID_LENGTH(sensorTable_oid),
HANDLER_CAN_RWRITE),
table_set, NULL);
row = netsnmp_create_table_data_row();
netsnmp_table_row_add_index(row, ASN_OCTET_STR, "1",
strlen("1"));
netsnmp_set_row_column(row, 2, ASN_OCTET_STR,
"5.9V", strlen("5.9V"));
netsnmp_set_row_column(row, 3, ASN_OCTET_STR,
"21.5C", strlen("21.5C"));
netsnmp_table_dataset_add_row(table_set, row);
}
void
init_sensorTable(void)
{
initialize_table_sensorTable();
}
int
sensorTable_handler(
netsnmp_mib_handler *handler,
netsnmp_handler_registration *reginfo,
netsnmp_agent_request_info *reqinfo,
netsnmp_request_info *requests) {
netsnmp_table_row *row, *tempRow;
if( table_set != NULL )
{
for ( tempRow = table_set->table->first_row;
tempRow; tempRow = tempRow->next )
{
row = netsnmp_table_data_set_get_first_row(table_set);
netsnmp_table_dataset_remove_row(table_set, row);
}
}
/* Start reading "input.txt */
char sensorValues[32];
char *singleValue;
FILE *f = fopen("/home/supra/Desktop/input.txt", "r");
/* check if the file was found */
if( f == NULL ) {
printf("Error opening file!\n");
exit(EXIT_FAILURE);
}
/* check if the file is empty */
if ( fgets( sensorValues, sizeof(sensorValues), f) == NULL )
{
printf("Warning: File is empty!\n");
exit(EXIT_FAILURE);
}
/* if the file is not empty, create a row and start
* breaking the string into words. Fill the row with the words
* and add it to the table. */
do
{
int rowEntries = firstEntryRow;
singleValue = strtok( sensorValues, " ");
row = netsnmp_create_table_data_row();
netsnmp_table_row_add_index(row, ASN_OCTET_STR, singleValue, strlen(singleValue) );
singleValue = strtok( NULL, " ");
/* Fill the row with values */
while(singleValue != NULL)
{
netsnmp_set_row_column(row, rowEntries, ASN_OCTET_STR, singleValue, strlen(singleValue) );
rowEntries++;
singleValue = strtok(NULL, " ");
}
netsnmp_table_dataset_add_row(table_set, row);
} while( fgets( sensorValues, sizeof(sensorValues), f) != NULL);
fclose(f);
return SNMP_ERR_NOERROR;
}

Answer 1

Regarding :
So why can't I retrieve the single values with a simple snmpgetnext request?
Quoting man snmpgetnext
DESCRIPTION
snmpget is an SNMP application that uses the SNMP GETNEXT request to query for information on a network entity. One or more
object identifiers (OIDs) may
be given as arguments on the command line. Each variable name is given in the format specified in variables(5). For each one, the
variable that is lexicographically "next" in the remote entity's MIB will be returned. For example:
snmpgetnext -c public zeus interfaces.ifTable.ifEntry.ifType.1
will retrieve the variable
interfaces.ifTable.ifEntry.ifType.2
In other words its job is to get one thing back.
If you want to use it to get a full table, you need to invoke it multiple times. Quoting man page for snmptable :
snmptable is an SNMP application that repeatedly uses the SNMP GETNEXT or GETBULK requests to query for information on a network entity.