Chapter 4. YAZ C++ API
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## Chapter 4. YAZ C++ API

The YAZ C++ API is an client - and server API that exposes all YAZ features. The API doesn't hide YAZ C data structures, but provides a set of useful high-level objects for creating clients - and servers.

All definitions from YAZ++ are part of namespace `yazpp_1`.

The following sections include a short description of the interfaces and implementations (concrete classes).

In order to understand the structure, you should look at the example client `yaz-my-client.cpp` and the example server `yaz-my-server.cpp`. If that is too easy, you can always turn to the implementation of the proxy itself and send us a patch if you implement a new useful feature.

### Note

The documentation here is very limited. We plan to enhance it - provided there is interest for it.

## 1. Interfaces

### 1.1. ISocketObservable

This interface is capable of observing sockets. When a socket even occurs it invokes an object implementing the ISocketObserver interface.

         #include <yazpp/socket-observer.h>

         class my_socketobservable : public ISocketObservable {
            // Add an observer interested in socket fd
            virtual void addObserver(int fd, ISocketObserver *observer) = 0;
            // Delete an observer
            virtual void deleteObserver(ISocketObserver *observer) = 0;
            // Delete all observers
            virtual void deleteObservers() = 0;
            // Specify the events that the observer is interested in.
            virtual void maskObserver(ISocketObserver *observer,
                                      int mask) = 0;
            // Specify timeout
            virtual void timeoutObserver(ISocketObserver *observer,
                                         int timeout)=0;
         };

### 1.2. ISocketObserver

This interface is interested in socket events supporting the ISocketObservable interface.

         #include <yazpp/socket-observer.h>

         class my_socketobserver : public ISocketObserver {
             public:
              // Notify the observer that something happened to socket
              virtual void socketNotify(int event) = 0;
         }

### 1.3. IPDU_Observable

This interface is is responsible for sending - and receiving PDUs over the network (YAZ COMSTACK). When events occur, an instance implementing IPDU_Observer is notified.

         #include <yazpp/pdu-observer.h>

         class my_pduobservable : public IPDU_Observable {
           public:
             // Send encoded PDU buffer of specified length
             virtual int send_PDU(const char *buf, int len) = 0;
             // Connect with server specified by addr.
             virtual void connect(IPDU_Observer *observer,
                         const char *addr) = 0;
             // Listen on address addr.
             virtual void listen(IPDU_Observer *observer, const char *addr)=0;
             // Close connection
             virtual void close() = 0;
             // Make clone of this object using this interface
             virtual IPDU_Observable *clone() = 0;
             // Destroy completely
             virtual void destroy() = 0;
             // Set Idle Time
             virtual void idleTime (int timeout) = 0;
             // Get peername
             virtual const char *getpeername() = 0;

             virtual ~IPDU_Observable();
         };

### 1.4. IPDU_Observer

This interface is interested in PDUs and using an object implementing IPDU_Observable.

         #include <yazpp/pdu-observer.h>

         class my_pduobserver : public IPDU_Observer {
           public:
             // A PDU has been received
             virtual void recv_PDU(const char *buf, int len) = 0;
             // Called when Iyaz_PDU_Observable::connect was successful.
             virtual void connectNotify() = 0;
             // Called whenever the connection was closed
             virtual void failNotify() = 0;
             // Called whenever there is a timeout
             virtual void timeoutNotify() = 0;
             // Make clone of observer using IPDU_Observable interface
             virtual IPDU_Observer *sessionNotify(
             IPDU_Observable *the_PDU_Observable, int fd) = 0;
         };

### 1.5. Yaz_Query

Abstract query.

         #include <yazpp/query.h>
         class my_query : public Yaz_Query {
           public:
             // Print query in buffer described by str and len
             virtual void print (char *str, int len) = 0;
         };

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