#335 MD UDP notification sometimes dropped at listener side

[Kari Keinanen]

When receiving MD UDP notify message, looks like occasionally message is dropped at trdp_mdHandleRequest(), code snapshot below.

trdp_mdcom.c

trdp_mdHandleRequest()

    for ( iterMD = appHandle->pMDRcvQueue; iterMD != NULL; iterMD = iterMD->pNext )
    {
        numOfReceivers++; /* count the list items here */
        if ( 0 == memcmp(iterMD->pPacket->frameHead.sessionID, pH->sessionID, TRDP_SESS_ID_SIZE)) 
        /* KK-PROPOSAL: COULD THIS HAVE ANOTHER CONDITION, ONLY IF sessionID != 0 */
        {
            /* According IEC61375-2-3 A.7.7.1 */
            /* encountered a matching session */
            if ((pH->sequenceCounter == iterMD->pPacket->frameHead.sequenceCounter)
                ||
                (isTCP == TRUE) /* include TCP as topmost discard criterium */
                ||
                (iterMD->addr.mcGroup != 0))  /* discard multicasts anyway */
            {

Best regards, Kari

[Bernd Löhr]

MD notification have their sessionId set to zero, thus the if-clause will always evaluate to false. By additionally comparing to pH->sessionID[16] with all zeros we will not gain much, I assume. But I also don't understand where and why notifications are dropped? Do you have any logs? Are there possibly receivers with sessionID==0?

[Kari Keinanen]

In our use case multiple MD notifications (each with different content) are sometimes sent in sequence and this seems to cause the issue. I think the problem happens when old session with sessionId=0 exist, for example:

1. Receive notification 1, replier session 1 is created (sessionId=0)
2. Receive notification 2, replier session with sessionId=0 already exist -> message is dropped
3. Freeing replier session 1
4. Receive notification 3, OK

Snapshot from logs below.

[90158.893] Received UDP MD packet (type: 'Mn' UUID: 0000000000000000 Data len: 21) at trdp_mdcom.c, line 2019
[90158.893] Creating UDP MD replier session '0000000000000000' at trdp_mdcom.c, line 1745
[90158.893] vos_memAlloc() 0x7f44ef6c09e8, size 264 at vos_mem.c, line 479
[90158.893] vos_memAlloc() 0x7f44ef6c0bf8, size 1480 at vos_mem.c, line 479
[90158.893] Received UDP MD packet (type: 'Mn' UUID: 0000000000000000 Data len: 23) at trdp_mdcom.c, line 2019
[90158.893] trdp_mdRecv: Repeated request discarded! at trdp_mdcom.c, line 1577
[90158.894] Freeing MD UDP replier session '0000000000000000' at trdp_mdcom.c, line 765

[Bernd Löhr]

Couldn't replicate your error, but excluded the for-loop searching for existing sessions in case of notifications.

[Kari Keinanen]

Just tested trunk-code, I'm afraid the fix doesn't work, some notifications are still dropped.

trdp_mdcom.c: trdp_mdHandleRequest()
   ...
    /* Only if no Notification */
    if (state != TRDP_ST_TX_NOTIFY_ARM)
    /* In my application, state is TRDP_ST_RX_NOTIFY_RECEIVED
       which cause "trdp_mdRecv: Repeated request discarded!"
       TRDP_ST_TX_NOTIFY_ARM -> TRDP_ST_RX_NOTIFY_RECEIVED ?
    */

[Bernd Löhr]

Of course, you're right. TRDP_ST_RX_NOTIFY_RECEIVED is the state...

[Kari Keinanen]

Just tested current trunk, looks good.
This ticket can be closed.