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Brew Interview Questions


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46.When reading from a socket the phone reads whatever it can in one go, while the emulator reads large packets in chunks. Why?

This is a limitation of the phone.

Program should call ISOCKET_Readable() to be informed when more data can be read from the stream. The callback routine registered by ISOCKET_Readable() will be invoked whenever data becomes available---you can usually call ISOCKET_Read() at this point. Continue calling ISOCKET_Readable() for as long as your program expects more data.


 rv = ISOCKET_Read(piSock, (byte *)szBuf, sizeof(szBuf));

if (rv == AEE_NET_WOULDBLOCK) {
// WOULDBLOCK => no more data available at the moment
      // Register the callback to read the data later.
      ISOCKET_Readable(piSock, CommonReadCB, (void*)pMe);
return;
}
else if (rv == AEE_NET_ERROR) {
// error reading from socket
ReleaseNetAndSocket (pMe);
}
else if (rv > 0)  { 
// rv bytes of data has been read from the socket into
// szBuf

// Read remaining data
ISOCKET_Readable(piSock, CommonReadCB, (void*)pMe); 
}
else  {  // rv == 0
// There is no more data to be received.
// The peer has shut down the connection.
ReleaseNetAndSocket (pMe);
}


47.How can we check the status of my sockets and PPP connection?

We can check on the status of the PPP connection (active, inactive, opening or closing) using INETMGR_NetStatus().


 NetState netState = NET_INVALID_STATE;
AEENetStats netStats;
netState = INETMGR_NetStatus (pINetMgr, &netStats);


We can use INETMGR_OnEvent() to monitor both the status of the PPP connection and socket connections. Refer to NetMgrEvent enum in AEENet.h for a list of all network and socket events.


 // Register to receive Network and Socket events
INETMGR_OnEvent(piNet, (PFNNETMGREVENT)CheckNetStatus,
(void*)pMe, TRUE);

//Callback invoked when Network/Socket event is received
static void CheckNetStatus(void* cxt,
NetMgrEvent evt, uint32 dwData) {
SampleApp *pMe = (SampleApp*)cxt;

if(evt == NE_PPP) { 
// network event.  dwData  = NetState enum value
// refer NetState data structure in BREW API Reference doc
}
if(evt == NE_SO_CLOSING || evt == NE_SO_CLOSED) {
// socket event - closing or closed. 
// DwData is pointer to socket
}
 

return;
}


48.Is it possible to transfer data between two phones?

Peer to peer connections between two phones have been found to be unreliable, failing when the phones are on the same subnet. It is best therefore to use a proxy server, transferring data between the phones using the server as a go between.


49.Can a BREW-enabled device be used as a server?

In addition to the obvious memory and performance limitations, it is not possible to listen on a socket connection when a BREW application is running on a phone. These factors make implementing a server on BREW difficult at best.


50.Is there any way to tell if a socket is already connected?

There are two ways to determine if a socket is connected. The easiest is to check the return value of ISOCKET_Connect(). When a socket is already connected, ISOCKET_Connect() will return EISCONN.


It is also possible to monitor the state of a socket connection by registering for the socket status change events NE_SO_CLOSING, and NE_SO_CLOSED with INETMGR_OnEvent(). Using this method, your application can avoid trying to connect an already connected socket.


For more information about network and socket events, including NE_SO_CLOSING and NE_SO_CLOSED, please refer to the following include file: AEENet.h.

For Example:

 // Register to receive Network and Socket events
INETMGR_OnEvent(piNet, (PFNNETMGREVENT)CheckNetStatus,
(void*)pMe, TRUE);

//Callback invoked when Network/Socket event is received
static void CheckNetStatus(void* cxt, NetMgrEvent evt,
uint32 dwData)
 {
SampleApp *pMe = (SampleApp*)cxt;

if(evt == NE_SO_CLOSING || evt == NE_SO_CLOSED) {
// flag set to false to indicate socket is disconnected
pMe->m_SocketConnected = FALSE;
ReleaseNetAndSocket(pMe);
}
if(evt == NE_SO_CONNECTED) {
// flag set to true to indicate socket is connected
pMe->m_SocketConnected = TRUE;
}
return;
}



51.Why does ISOCKET_Release() return one when we are expecting a return value of zero?

When an application calls ISOCKET_Release(), the internal state of the ISocket object changes to "closing," and BREW begins waiting for the asynchronous "closed" event. Since the closed event is received in a callback, the reference count of the ISocket object is incremented to prevent it from being released before its internal state changes to closed.


52.Why does ISHELL_CreateInstance return ECLASSNOTSUPPORT when I try and create an instance of the net manager (AEECLSID_Net)?

This is because of the permissions on the MIF file for your applet. Please open your MIF file in the MIF editor and check the checkbox for Network privileges, then save


53.Can we have a listening TCP socket?

No. You use UDP, specifically, ISOCKET_Bind and ISOCKET_RecvFrom


54.Does BREW support blocking sockets?

No. BREW uses asynchronous sockets. You can use ISOCKET_Readable or ISOCKET_Writeable to be notified when it is safe to read/write.


55.How can we handle the case when we lose cellular coverage?

When the phone goes out of a coverage area, the data call will drop. When this happens, BREW cleans up the underlying OEM sockets that are in use. The ISocket(s) used by an app continue to exist, and the app will get appropriate error responses when it tries to use them.


For synchronous (TCP/IP) data communication, there are two ways to handle the potentially bad sockets:



  1. Check the return value from all Socket operations

    Writing or reading from the socket will cause AEE_NET_ERROR to be returned. In your code, you should check the return value from the Socket connect, read, write and take appropriate action.

     // Connect callback
    static void SampleApp_ConnectCB(void *cxt, int err)  {
    SampleApp *pMe = (SampleAppApp*)cxt;
    
    if (err) {
    // connect failed
    SampleApp_CleanUp(pMe);
    //Clean up net manager and
    // sockets 
    ShowMainMenu(pMe);
    return;
    }
    
    }
    
    // Writing
    iRet = ISOCKET_Write(pMe->m_piSock, (byte*)Request,
    (uint16)STRLEN(Request));
    if (iRet == AEE_NET_ERROR) {
    // Write error
    SampleApp_CleanUp(pMe);
    // Clean up net manager and sockets
    ShowMainMenu(pMe);
    return;
    }
    
    
    // Reading
    iRet = ISOCKET_Read(pMe->m_piSock, (byte*)buf,
    sizeof(buf));
    if (iRet == AEE_NET_ERROR) {
    // Read error
    SampleApp_CleanUp(pMe);
    // Clean up net manager and sockets
    ShowMainMenu(pMe);
    return;
    }
    


  2. Register for change in network/socket state

    Another way to handle the phone going out of coverage while a data call is in progress is to register for Network and Socket events using INETMGR_OnEvent() and take appropriate action when notified of change in network/socket status. In the example below, a flag is set to indicate that the socket is bad. The socket state is checked before it is used.

    For more information on Network and Socket events, please refer to NetMgrEvent and NetState enums in aeenet.h include file.

    For example:

     // Register to receive Network and Socket events
    INETMGR_OnEvent(piNet, (PFNNETMGREVENT)CheckNetStatus,
    (void*)pMe, TRUE);
    
    //Callback invoked when Network/Socket event is received
    static void CheckNetStatus(void* cxt, NetMgrEvent evt,
    uint32, dwData) {
    SampleApp *pMe = (SampleApp*)cxt;
    
    if(evt == NE_PPP) {
    if(dwData == NET_PPP_CLOSING || dwData ==
    NET_PPP_CLOSED) {
    // flag set to false to indicate socket is bad
    pMe->m_SocketState = FALSE;
    
    // clean up network and socket
    ReleaseNetAndSocket(pMe);
    }
    }
    
    if(evt == NE_SO_CLOSING || evt == NE_SO_CLOSED) {
    pMe->m_SocketState = FALSE;
    ReleaseNetAndSocket(pMe);
    }
    
    if(evt == NE_SO_CONNECTED) {
    pMe->m_SocketState = TRUE;
    }
    
    return;
    }
    
    // Check socket state before using it
    static void RoadWarriorApp_ReadCB(void *cxt)  {
    int rc;
    SampleApp *pMe = (SampleApp *)cxt;
    
    if(pMe->m_SocketState == FALSE) {  //socket is bad
    ReleaseNetAndSocket(pMe);
    ShowMainMenu(pMe);
    return;
    }
    
    rc = ISOCKET_Read(piSock, (byte*)buf, sizeof(buf));
    
    }
    


When registering for network and socket events using INETMGR_InEvent(), you must de- register before terminating the application by using INETMGR_OnEvent() with bRegister = FALSE.

Note:  After the phone goes out of coverage, the sockets are unusable. You must release your ISocket(s) and reinstantiate them when next required. The INetMgr does not need to be released and re-instantiated before using it for the next network operation, however there is no harm in doing so.


To handle potentially bad sockets for asynchronous(UDP) data communication, register for change in network/socket state (described in number 2 above).


56.When we terminate a data call by closing an open socket, why does the phone still indicate that a data call is in progress?

After the last connected socket is closed, BREW waits for a certain linger time before terminating the PPP connection. Hence the lingering call-in-progress indication.

The default linger time is 30 seconds. To change the linger time, use INETMGR_SetLinger().


57.Why does connect callback not timeout when service is lost (while attempting to connect) or the server does not respond?

This is due to a bug in the BREW version 1.0.1 SDK - connect callback is not invoked under the following circumstances:

  1. Service is lost while connect is being attempted
  2. Server does not respond

As a workaround, you should implement a timer in association with the callback. If the connect callback does not occur in 30 seconds, you should timeout the connection.

For example:

 // initialize pMe->connectCBInvoked = FALSE;

// Set timer for 30 seconds before invoking ISOCKET_Connect()
ISHELL_SetTimer(pMe->a.m_pIShell, 30000, ConnectTimeout_CB, (void *)pMe);
ISOCKET_Connect(pMe->m_pISocket, nodeINAddr, AEE_htons(USAGE_TEST_PORT),
SampleApp_ConnectCB, pMe);

// Set flag indicating connect CB was called
void SampleApp_ConnectCB(void *cxt, int err)  {
SampleApp *pMe = (SampleApp*)cxt;

// Set flag indicating connect CB was called
pMe->connectCbInvoked = TRUE;

if (err) {
DisplayOutput((IApplet*)pMe, 3, "Connect failed!");
return;
}
DisplayOutput((IApplet*)pMe, 3, "Connected!");

}

// When timer expires, check if connect CB was invoked
static void ConnectTimeout_CB(void* cxt) {
SampleApp *pMe = (SampleApp *)cxt;

if(pMe->connectCbInvoked == FALSE) {
// Callback was not invoked within 30seconds - cancel connect callback
ISOCKET_Cancel(pMe->m_pISocket, 0, 0);
DisplayOutput((IApplet*) pMe, 3, "Connection timed out");

}
else {
// Callback invoked.  Set flag to default value FALSE
pMe->connectCbInvoked = FALSE;
}
}

Note:  Multiple TCP sockets are not supported on the Kyocera 3035. It allows one TCP socket and one UDP socket at a given time.


58.Why is my INetMgr object NULL upon initialization using ISHELL_CreateInstance? Other objects such as IDisplay or IGraphics are initialized properly.

Refer to FAQ-52


59.57.What precautions should we take when I invoke INETMGR_GetHostByName() to perform DNS lookup?

You must ensure that your app cancels its pending DNS callback, if any, using CALLBACK_Cancel() in all exit routes. This includes when the app is suspended and when the app is stopped (both via the End key and the Clear key).

For example, if you used the following code to lookup a DNS address:


 CALLBACK_Init(&pMe->cbkLookup, GetHostByNameCB, pMe);
INETMGR_GetHostByName(pINetMgr,&pMe->dnsresult, hostName,
&pMe->cbkLookup);


You should use the following code to cancel the callback in all exit routes:


 
// Check if the callback can be cancelled. If NULL it has
// already happened and cannot be cancelled.
if(pMe->cbkLookup.pfnCancel != NULL) {
CALLBACK_Cancel(&pMe->cbkLookup);
}

The callback cancel code should be incorporated in the Suspend event handler code ( EVT_APP_SUSPEND), the app's FreeAppData function (which is called when the app is stopped, i.e. receives EVT_APP_STOP event), and in the Clear key event handler code (EVT_KEY and keycode AVK_CLR).


Note:  Please note that your app will not pass TRUE BREW Testing if it does not properly cancel its pending DNS callback. Some symptoms that might indicate that your app is not canceling its p ending DNS callback are:,/p>

  1. Phone crashes upon starting up app
  2. Phone displays "Please Re-insert Battery" error upon starting up app

Both might imply that the previously running app did not cancel its pending DNS callback.


60.Are there any restrictions on what value we can set my application's network linger time to?

The INETMGR_SetLinger() function is provided to give developers flexibility in designing their application. However, it is not recommended that you alter the OEM's chosen default linger time (usually 30 seconds), unless your application has a compelling reason to do so. Altering the default linger time in either direction may cause your application to fail TRUE BREW Testing, or carrier rejection of your application.



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