Applications can gain access to an Ice object representing an established connection.

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The `Connection` Interface

The Slice definition of the Connection interface is shown below:

Slice

module Ice {
    local class ConnectionInfo {
        bool incoming;
        string adapterName;
        string connectionId;
    };

    local interface ConnectionCallback {
        void heartbeat(Connection con);
        void closed(Connection con);
    };

    local enum ACMClose {
        CloseOff,
        CloseOnIdle,
        CloseOnInvocation,
        CloseOnInvocationAndIdle,
        CloseOnIdleForceful
    };

    local enum ACMHeartbeat {
        HeartbeatOff,
        HeartbeatOnInvocation,
        HeartbeatOnIdle,
        HeartbeatAlways
    };

    local struct ACM {
        int timeout;
        ACMClose close;
        ACMHeartbeat heartbeat;
    };

    local interface Connection {
        void close(bool force);
        Object* createProxy(Identity id);
        void setAdapter(ObjectAdapter adapter);
        ObjectAdapter getAdapter();
        Endpoint getEndpoint();
        void flushBatchRequests();
        void setCallback(ConnectionCallback callback);
        void setACM(optional(1) int timeout, optional(2) ACMClose close, optional(3) ACMHeartbeat heartbeat);
        ACM getACM();
        string type();
        int timeout();
        string toString();
        ConnectionInfo getInfo();
    };

    local class IPConnectionInfo extends ConnectionInfo {
        string localAddress;
        int localPort;
        string remoteAddress;
        int remotePort;
    };

    local class TCPConnectionInfo extends IPConnectionInfo {};

    local class UDPConnectionInfo extends IPConnectionInfo {
        string mcastAddress;
        int mcastPort;
    };
 
    local class WSConnectionInfo extends IPConnectionInfo {};
};

module IceSSL {
    local class ConnectionInfo extends Ice::IPConnectionInfo {
        string cipher;
        Ice::StringSeq certs;
    };
};

As indicated in the Slice definition, a connection is a local interface, similar to a communicator or an object adapter. A connection therefore is only usable within the process and cannot be accessed remotely.

The Connection interface supports the following operations:

void close(bool force)
Explicitly closes the connection. The connection is closed gracefully if force is false, otherwise the connection is closed forcefully.

Object* createProxy(Identity id)
Creates a special proxy that only uses this connection. This operation is primarily used for bidirectional connections.

void setAdapter(ObjectAdapter adapter)
Associates this connection with an object adapter to enable a bidirectional connection.

ObjectAdapter getAdapter()
Returns the object adapter associated with this connection, or nil if no association has been made.

Endpoint getEndpoint()
Returns an Endpoint object.

void flushBatchRequests()
Flushes any pending batch requests for this connection.

void setCallback(ConnectionCallback callback)
Associates a callback with this connection that is invoked whenever the connection receives a heartbeat message or is closed. Passing a nil value clears the current callback.

void setACM(optional(1) int timeout, optional(2) ACMClose close, optional(3) ACMHeartbeat heartbeat)
Configures Active Connection Management settings for this connection. All arguments are optional, therefore you can change some of the settings while leaving the others unaffected. Refer to your language mapping for more details on optional parameters.

ACM getACM()
Returns the connection's current settings for Active Connection Management.

string type()
Returns the connection type as a string, such as "tcp".

int timeout()
Returns the timeout value used when the connection was established.

string toString()
Returns a readable description of the connection.

ConnectionInfo getInfo()
This operation returns a ConnectionInfo class defined as follows:
Slice
```
local class ConnectionInfo {
    bool incoming;
    string adapterName;
};
```
The incoming member is true if the connection is an incoming connection and false, otherwise. If incoming is true, adapterName provides the name of the object adapter that accepted the connection. Note that the object returned by getInfo implements a more derived interface, depending on the connection type. You can down-cast the returned class instance and access the connection-specific information according to the type of the connection.

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Flushing Batch Requests for a Connection

The flushBatchRequests operation blocks the calling thread until any batch requests that are queued for a connection have been successfully written to the local transport. To avoid the risk of blocking, you can also invoke this operation asynchronously using the begin_flushBatchRequests method (in those language mappings that support it).

Since batch requests are inherently oneway invocations, the begin_flushBatchRequests method does not support a request callback. However, you can use the exception callback to handle any errors that might occur while flushing, and the sent callback to receive notification that the batch request has been flushed successfully.

For example, the code below demonstrates how to flush batch requests asynchronously in C++:

C++

class FlushCallback : public IceUtil::Shared
{
public:

    void exception(const Ice::Exception& ex)
    {
        cout << "Flush failed: " << ex << endl;
    }

    void sent(bool sentSynchronously)
    {
        cout << "Batch sent!" << endl;
    }
};
typedef IceUtil::Handle<FlushCallback> FlushCallbackPtr;

void flushConnection(const Ice::ConnectionPtr& conn)
{
    FlushCallbackPtr f = new FlushCallback;
    Ice::Callback_Connection_flushBatchRequestsPtr cb =
        Ice::newCallback_Connection_flushBatchRequests(
            f, &FlushCallback::exception, &FlushCallback::sent);
    conn->begin_flushBatchRequests(cb);
}

For more information on asynchronous invocations, please see the relevant language mapping chapter.

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The `Endpoint` Interface

The Connection::getEndpoint operation returns an interface of type Endpoint:

Slice

module Ice {
    const short TCPEndpointType = 1;
    const short UDPEndpointType = 3;

    local class EndpointInfo {
        int timeout;
        bool compress;
        short type();
        bool datagram();
        bool secure();
    };

    local interface Endpoint {
        EndpointInfo getInfo();
        string toString();
    };

    local class IPEndpointInfo extends EndpointInfo {
        string host;
        int port;
        string sourceAddress;
    };

    local class TCPEndpointInfo extends IPEndpointInfo {};

    local class UDPEndpointInfo extends IPEndpointInfo {
        byte protocolMajor;
        byte protocolMinor;
        byte encodingMajor;
        byte encodingMinor;
        string mcastInterface;
        int mcastTtl;
    };

    local class WSEndpointInfo extends IPEndpointInfo {
        string resource;
    };
 
    local class OpaqueEndpointInfo extends EndpointInfo {
        Ice::EncodingVersion rawEncoding;
        Ice::ByteSeq rawBytes;
    };
};

module IceSSL {
    const short EndpointType = 2;

    local class EndpointInfo extends Ice::IPEndpointInfo {};
};

The getInfo operation returns an EndpointInfo instance. Note that the object returned by getInfo implements a more derived interface, depending on the endpoint type. You can down-cast the returned class instance and access the endpoint-specific information according to the type of the endpoint, as returned by the type operation.

The timeout member provides the timeout in milliseconds. The compress member is true if the endpoint uses compression (if available). The datagram operation returns true if the endpoint is for a datagram transport, and the secure operation returns true if the endpoint uses SSL.

The derived classes provide further detail about the endpoint according to its type.

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Opaque Endpoints

An application may receive a proxy that contains an endpoint whose type is unrecognized by the Ice run time. In this situation, Ice preserves the endpoint in its encoded (opaque) form so that the proxy remains intact, but Ice ignores the endpoint for all connection-related activities. Preserving the endpoint allows an application to later forward that proxy with all of its original endpoints to a different program that might support the endpoint type in question.

Although a connection will never return an opaque endpoint, it is possible for a program to encounter an opaque endpoint when iterating over the endpoints returned by the proxy method ice_getEndpoints.

As a practical example, consider a program for which the IceSSL plug-in is not configured. If this program receives a proxy containing an SSL endpoint, Ice treats it as an opaque endpoint such that calling getInfo on the endpoint object returns an instance of OpaqueEndpointInfo.

Note that the type operation of the OpaqueEndpointInfo object returns the actual type of the endpoint. For example, the operation returns the value 2 if the object encodes an SSL endpoint. As a result, your program cannot assume that an EndpointInfo object whose type is 2 can be safely down-cast to IceSSL::EndpointInfo; if the IceSSL plug-in is not configured, such a down-cast will fail because the object is actually an instance of OpaqueEndpointInfo.

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Client-Side Connection Usage

Clients obtain a connection by using one of the proxy methods ice_getConnection or ice_getCachedConnection. If the proxy does not yet have a connection, the ice_getConnection method immediately attempts to establish one. As a result, the caller must be prepared for this method to block and raise connection failure exceptions. (Use the asynchronous version of this method to avoid blocking.) If the proxy denotes a collocated object and collocation optimization is enabled, calling ice_getConnection returns null.

If you wish to obtain the proxy's connection without the potential for triggering connection establishment, call ice_getCachedConnection; this method returns null if the proxy is not currently associated with a connection or if connection caching is disabled for the proxy.

As an example, the C++ code below illustrates how to obtain a connection from a proxy and print its type:

C++

Ice::ObjectPrx proxy = ...
try
{
    Ice::ConnectionPtr conn = proxy->ice_getConnection();
    if(conn)
    {
        cout << conn->type() << endl;
    }
    else
    {
        cout << "collocated" << endl;
    }
}
catch(const Ice::LocalException& ex)
{
    cout << ex << endl;
}

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Server-Side Connection Usage

Servers can access a connection via the con member of the Ice::Current parameter passed to every operation. For collocated invocations, con has a nil value.

For example, this Java code shows how to invoke toString on the connection:

Java

public int add(int a, int b, Ice.Current curr)
{
    if (curr.con != null)
    {
        System.out.println("Request received on connection:\n" + curr.con.toString());
    }
    else
    {
        System.out.println("collocated invocation");
    }
    return a + b;
}

Although the mapping for the Slice operation toString results in a Java method named _toString, the Ice run time implements toString to return the same value.

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Closing a Connection

Applications should rarely need to close a connection explicitly, but those that do must be aware of its implications. Since there are two ways to close a connection, we discuss them separately.

Graceful Closure

Passing an argument of false to the close operation initiates graceful connection closure, as discussed in Connection Closure. The operation blocks until all pending outgoing requests on the connection have completed.

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Forceful Closure

A forceful closure is initiated by passing an argument of true to the close operation, causing the peer to receive a ConnectionLostException.

A client must use caution when forcefully closing a connection. Any outgoing requests that are pending on the connection when close is invoked will fail with a ForcedCloseConnectionException. Furthermore, requests that fail with this exception are not automatically retried.

In a server context, forceful closure can be useful as a defense against hostile clients.

The Ice run time interprets a CloseConnectionException to mean that it is safe to retry the request without violating at-most-once semantics. If automatic retries are enabled, a client must only initiate a graceful close when it knows that there are no outgoing requests in progress on that connection, or that any pending requests can be safely retried.

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Using Connections

The `Connection` Interface

Flushing Batch Requests for a Connection

The `Endpoint` Interface

Opaque Endpoints

Client-Side Connection Usage

Server-Side Connection Usage

Closing a Connection

Graceful Closure

Forceful Closure

See Also

The Connection Interface

Flushing Batch Requests for a Connection

The Endpoint Interface

Opaque Endpoints

Client-Side Connection Usage

Server-Side Connection Usage

Closing a Connection

Graceful Closure

Forceful Closure

See Also

The `Connection` Interface

The `Endpoint` Interface