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17.  Pdu Class

Object Modeling Technique (OMT) view of the SNMP++ Snmp Class

 

The SNMP++ Pdu class is a C++ encapsulation of the SMI Protocol Data Unit (PDU). PDUs are the basic means of  SNMP communication between a manager and an agent. SNMP++ makes working with PDUs easy and safe through use of the Pdu class. The Pdu class allows easy construction, destruction, Vb object loading and unloading of Pdu objects. Since SNMP++ is a bilingual API, the Pdu class is abstract and does not contain SNMP version 1 or version 2 specific information. A single Pdu object can be used for all Snmp class request member functions. The Pdu class is used to interface with the Snmp class for SNMP requests and is also used as a callback parameter for asynchronous requests and notification reception. Note, Pdu objects are zero based in regard to storage of Vbs ( the first vb in the Pdu is Vb #0 ).

 

For the most part, all Pdu objects are the same in SNMP++. That is, all Pdu objects have identical attributes. The only exception is when using the Pdu objects for sending notifications , traps and informs. For notifications, three additional Pdu Class member functions may be used to set the identity, timestamp and enterprise of a Pdu object.

17.1.  Pdu Class Member Functions Overview

Pdu Class Member Functions

Description

Constructors

 

     Pdu::Pdu( void);

Construct an empty Pdu.

     Pdu::Pdu( Vb* pvbs, const int pvb_count);

Construct a Pdu with an array of Vbs and size.

     Pdu::Pdu( const Pdu &pdu);

Construct a Pdu with another Pdu.

Member Functions

 

     int get_vblist( Vb* pvbs, const int pvb_count);

Copies Vbs into caller parameters.

     int set_vblist( Vb* pvbs, const int pvb_count);

Sets callers Vbs into the Pdu.

     int get_vb( Vb &vb, const int index);

Get a particular Vb out of a Pdu.

     int set_vb( Vb &vb, const int index);

Set a particular Vb into a Vb.

     int get_vb_count();

Get the Vb count from a Pdu.

     int get_error_status();

Get the error status from a Pdu.

     int get_error_index();

Get the error index from a Pdu.

     unsigned long get_request_id();

Get the request id from a Pdu.

     unsigned short get_type();

Get the Pdu type.

     int valid();

Is the Pdu valid?

     Int delete_vb( const int position);

Removes Vb at specified position from Pdu.

     int trim(const int i=1);

Trim off the last Vb in the Pdu,.default 1.

Member Functions For Inform and Trap Usage

 

     void set_notify_timestamp( const TimeTicks

                                                 & timestamp);

Set timestamp on a trap or inform Pdu.

     void get_notify_timestamp( TimeTicks

                                                  & timestamp);

Get the timestamp from a trap or inform Pdu object.

     void set_notify_id( const Oid id);

Set the ID on a trap or inform Pdu.

     void get_notify_id( Oid &id);

Get the ID from a trap or inform Pdu.

     void set_notify_enterprise( const Oid

                                                &enterprise);

Set the enterprise ID on a trap or inform Pdu.

     void get_notify_enterprise( Oid & enterprise);

Get the enterprise ID on a trap or inform Pdu.

Overloaded Operators

 

     Pdu& operator=( const Pdu &pdu);

Assign one Pdu to another.

     Pdu& operator+=( Vb &vb);

Append a Vb to a Pdu;

 

 

 

17.2. Pdu Class Constructors and Destructors

There are a variety of ways to construct Pdu objects including with and without construction parameters.

// constructor, no args

Pdu::Pdu( void);

 

// constructor with Vbs and count

Pdu::Pdu( Vb *vbs, const int vb_count);

 

// constructor with another Pdu instance

Pdu::Pdu( const Pdu &pdu);

 

// destructor

Pdu::~Pdu();

 

 

17.3. Pdu Access Member Functions

The Pdu class supports a variety of member functions for getting and setting Pdu member variables. Included are ways to get and set the variable bindings, error information , request identification, and type information.

 

// extract all the Vbs from a Pdu

int Pdu::get_vblist( Vb* vbs, const int  vb_count);

 

// deposit Vbs to a Pdu

int Pdu::set_vblist( Vb* vbs, const int vb_count);

 

// get a particular vb

// where index 0 is the 1st vb

int Pdu::get_vb( Vb &vb, const int index);

 

// set a particular Vb

// where index 0 is the 1st Vb

int Pdu::set_vb( Vb &vb, const int index);

 

// return the number of Vbs

int Pdu::get_vb_count();

 

// return the error index

int Pdu::get_error_index();

 

// get the error status

int Pdu::get_error_status();

 

// return the request id

unsigned long Pdu::get_request_id();

 

// get the Pdu type

unsigned short Pdu::get_type();

 

// return the validity of a Pdu

int Pdu::valid();

 

17.4. Pdu Class Overloaded Operators

The Pdu class supports overloaded operators for assignment and concatenation of Vb objects to the Pdu.

// assignment operator for assigning one Pdu to another

Pdu& operator=( const Pdu &pdu);

 

// append a Vb object to the Pdu’s var bind list

Pdy& operator+=( Vb vb);

 

 

 

 

 

17.5. Pdu Class Member Functions for Traps and Informs

// set notify timestamp

void Pdu::set_notify_timestamp( const TimeTicks & timestamp);

 

// get notify timestamp

void Pdu::get_notify_timestamp( TimeTicks & timestamp);

 

// set the notify id

void Pdu::set_notify_id( const Oid id);

 

// get the notify id

void Pdu::get_notify_id( Oid &id);

 

// set the notify enterprise

void Pdu::set_notify_enterprise( const Oid &enterprise);

 

// get the notify enterprise

void Pdu::get_notify_enterprise( Oid & enterprise);

 

 

When working with notifications, traps and informs, SNMP++ provides member functions for getting and setting notification specific values. For usage on these member functions, please refer to the section on sending traps and informs.

 

 

17.6. Loading Pdu Objects

In order to use a Pdu object in a management application, the variable binding list must be loaded into the Pdu instance. This can be done in a variety of manners depending on your needs. Loading a Pdu is typically done before making a SNMP request.

// example of how to load a Pdu object

void load_pdu_examples()

{

   Pdu pdu;                                       // create a Pdu object

   Vb vb;                                         // create a Vb object

   vb.set_oid(  SYSDECR);          // set the oid portion of the Vb to System Descriptor

   pdu += vb;                                // loads the Vb to the Pdu

 

   Pdu my_pdu;                               // create another Pdu object

   Vb vbs[5];                                 // create 5 vbs

   pdu.set_vblist( vbs,5);                  // load all 5 to the pdu

}

 

 

 

17.7. Unloading Pdu Objects

After picking up a response Pdu either from a blocked or asynchronous request, it is necessary to unload the Vbs so that the SMI values may then be extracted.

 

// example of how to unload a Pdu

void unload_pdu_example( Pdu &pdu)

{

   ins staus;

   Pdu pdu;                                       // create a Pdu object

   Vb vb;                                         // create a Vb object

   vb.set_oid(  SYSDECR);          // set the oid portion of the Vb to System Descriptor

   pdu += vb;                                // loads the Vb to the Pdu

   char message[100];                      // for the system descriptor printable octet

 

   Snmp snmp( status);

   if ( status != SNMP_CLASS_SUCCESS) {

      cout < “SNMP++ error = “ << snmp.error_msg( status) ;

      return;

   }

 

   pdu.get_vb( vb,0);                   // unload the vb

   vb.get_value( message);            // pull the message out of the vb

   cout << message;                       // print it out

 

};