Receiving Data from the Remote Device

Context

When a remote device sends the first data packet, the MLlcpConnLessListener::FrameReceived() callback is called. The remote connection is stored and COwnLlcpConnection::Receive() is called. Once the first data packet is completed immediately, and COwnLlcpConnection::Receive() is repeated.

Steps

Call the CMyOwnLlcpApplication::FrameReceived() method and store the remote connection, as shown in the following code snippet:

// CMyOwnLlcpApplication::FrameReceived()
// From MLlcpConnLessListener
// -----------------------------------------------------------------------------
//
void CMyOwnLlcpApplication::FrameReceived( MLlcpConnLessTransporter* aConnection )
    {
    TInt error = KErrNone;
    
    // Only accepting one incoming remote connection
    if ( !iRemoteConnection )
        {
        // Creating a wrapper for the connection. 
        TRAP( error, iRemoteConnection = COwnLlcpConnection::NewL( aConnection ) );
        if ( error == KErrNone )
            {
            // Start receiving the data
            iRemoteConnection->Receive( *this );
            }
        else
            {
            delete aConnection;
            }
        }
    else
        {
        delete aConnection;
        }
    }
// -----------------------------------------------------------------------------
// End of CMyOwnLlcpApplication::FrameReceived()

Implement the COwnLlcpConnection::Receive() method as shown in the following code snippet:

// COwnLlcpConnection::Receive()
// -----------------------------------------------------------------------------
//
TInt COwnLlcpConnection::Receive( MLlcpTransmitCb& aLlcpTransmitCb )
    {
    TInt error = KErrNone;
    
    if ( iActionState == EIdle )
        {
        TInt length = 0;
        length = iConnection->SupportedDataLength();
        
        if ( length > 0 )
            {
            iReceiveBuf.Zero();
            error = iReceiveBuf.ReAlloc( length );
            
            if ( error == KErrNone )
                {
                iConnection->Receive( iStatus, iReceiveBuf );
                SetActive();
                iActionState = EReceiving;
                
                iLlcpTransmitCb = &aLlcpTransmitCb
                }
            }
        else
            {
            // If the length is 0 or negative, the LLCP link is destroyed.
            error = KErrNotReady;
            }
        }
    else
        {
        // The connection is already connecting or transferring data, 
        // Cannot start receiving.
        error = KErrInUse;
        }
    
    return error;
    }
// -----------------------------------------------------------------------------
// End of COwnLlcpConnection::Receive()

Note:

The COwnLlcpConnection::Receive() method cannot start receiving data if there are any pending transfer or receive requests. In such a scenario, KErrInUse is returned.
An LLCP link between the local and remote devices can be removed anytime and hence the MLlcpConnLessTransporter::SupportedDataLength() method can return negative values and must be handled correctly.

The following diagram illustrates the sequence diagram of data receiving: