error_t snmpProcessPdu(SnmpAgentContext *context)
{
error_t error;
//Parse PDU header
error = snmpParsePduHeader(&context->request);
//Any error to report?
if(error) return error;
//Check PDU type
switch(context->request.pduType)
{
case SNMP_PDU_GET_REQUEST:
case SNMP_PDU_GET_NEXT_REQUEST:
//Process GetRequest-PDU or GetNextRequest-PDU
error = snmpProcessGetRequestPdu(context);
break;
case SNMP_PDU_GET_BULK_REQUEST:
//Process GetBulkRequest-PDU
error = snmpProcessGetBulkRequestPdu(context);
break;
case SNMP_PDU_SET_REQUEST:
//Process SetRequest-PDU
error = snmpProcessSetRequestPdu(context);
break;
default:
//Invalid PDU type
error = ERROR_INVALID_TYPE;
break;
}
//Check status code
if(!error)
{
//Total number of SNMP Get-Response PDUs which have been generated
//by the SNMP protocol entity
MIB2_INC_COUNTER32(mib2Base.snmpGroup.snmpOutGetResponses, 1);
//Format PDU header
error = snmpWritePduHeader(&context->response);
}
//Return status code
return error;
}
error_t snmpParseMessage(SnmpAgentContext *context, const uint8_t *p, size_t length)
{
error_t error;
int32_t version;
Asn1Tag tag;
//Debug message
TRACE_INFO("SNMP message received from %s port %" PRIu16 " (%" PRIuSIZE " bytes)...\r\n",
ipAddrToString(&context->remoteIpAddr, NULL), context->remotePort, length);
//Display the contents of the SNMP message
TRACE_DEBUG_ARRAY(" ", p, length);
//Dump ASN.1 structure
error = asn1DumpObject(p, length, 0);
//Any error to report?
if(error) return error;
//The SNMP message is encapsulated within a sequence
error = asn1ReadTag(p, length, &tag);
//Failed to decode ASN.1 tag?
if(error) return error;
//Enforce encoding, class and type
error = asn1CheckTag(&tag, TRUE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_SEQUENCE);
//The tag does not match the criteria?
if(error) return error;
//Point to the first field of the sequence
p = tag.value;
length = tag.length;
//Read version identifier
error = asn1ReadInt32(p, length, &tag, &version);
//Failed to decode ASN.1 tag?
if(error) return error;
//The SNMP agent verifies the version number. If there is a mismatch,
//it discards the datagram and performs no further actions
if(version != context->version)
return ERROR_INVALID_VERSION;
//Point to the next field
p += tag.totalLength;
length -= tag.totalLength;
//Read SNMP community name
error = asn1ReadTag(p, length, &tag);
//Failed to decode ASN.1 tag?
if(error) return error;
//Enforce encoding, class and type
error = asn1CheckTag(&tag, FALSE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_OCTET_STRING);
//The tag does not match the criteria?
if(error) return error;
//Save community name
context->request.community = tag.value;
context->request.communityLen = tag.length;
//Point to the next field
p += tag.totalLength;
length -= tag.totalLength;
//Read PDU
error = asn1ReadTag(p, length, &tag);
//Failed to decode ASN.1 tag?
if(error) return error;
//Check encoding
if(tag.constructed != TRUE)
return ERROR_WRONG_ENCODING;
//Enforce class
if(tag.class != ASN1_CLASS_CONTEXT_SPECIFIC)
return ERROR_INVALID_CLASS;
//Save PDU type
context->request.pduType = (SnmpPduType) tag.type;
//Process the protocol data unit
switch(context->request.pduType)
{
case SNMP_PDU_GET_REQUEST:
case SNMP_PDU_GET_NEXT_REQUEST:
//Parse GetRequest-PDU or GetNextRequest-PDU
error = snmpParseGetRequestPdu(context, tag.value, tag.length);
break;
case SNMP_PDU_GET_BULK_REQUEST:
//Parse GetBulkRequest-PDU
error = snmpParseGetBulkRequestPdu(context, tag.value, tag.length);
break;
case SNMP_PDU_SET_REQUEST:
//Parse SetRequest-PDU
error = snmpParseSetRequestPdu(context, tag.value, tag.length);
break;
default:
//Invalid PDU type
error = ERROR_INVALID_TYPE;
break;
}
//Failed to parse PDU?
if(error)
return error;
//Format response PDU header
error = snmpWritePduHeader(context);
//Any error to report?
if(error) return error;
//Debug message
TRACE_INFO("SNMP message sent (%" PRIuSIZE " bytes)...\r\n", context->response.messageLen);
//Display the contents of the SNMP message
TRACE_DEBUG_ARRAY(" ", context->response.message, context->response.messageLen);
//Display ASN.1 structure
error = asn1DumpObject(context->response.message, context->response.messageLen, 0);
//Any error to report?
if(error) return error;
//Send SNMP response message
error = socketSendTo(context->socket, &context->remoteIpAddr, context->remotePort,
context->response.message, context->response.messageLen, NULL, 0);
//Return status code
return error;
}
