How an Ember+ client knows that the GetDirectory information received is complete

[sgruenfelder]

I wonder if other Ember+ developers have the same opinion on how an Ember+ client knows that it has received all the requested information after issuing a GetDirectory command.

In the last months all Ember+ servers I played with have send a single packet as reply to a GetDirectory command. The packet containes all the items found in the directory of interest.

Now I have seen an Ember+ server implementation that sends several replies after the receipt of a single GetDirectory command. Each reply contains one item of the directory the client wants to explore. The author claims that this is in line with Ember+. (1) I have my doubts, is that true? If that is truly in line: (2) how can the client ever know that the information received is complete? This is something needed when implementing clients that automatically change a large number of parameters. The clients would traverse the directories. (3) Does anyone know how this is handled by VSM?

Best regards
sgruenfelder

[mywave82]

It might be split up into multiple packets, since you might have more nodes than can fit into a single packet.

In libember_slim, when a new packet is allocated, we tell the glowOutput generator if is the last packet (and keeps a track in the buffer space if it the first package or not)

void glowOutput_beginPackage(GlowOutput *pThis, bool isLastPackage)
{
   bool isFirstPackage = pThis->packageCount == 0;

   writeFramingHeader(pThis, isFirstPackage, isLastPackage);

   if(isFirstPackage)
      ember_writeContainerBegin(&pThis->base.base.base, &glowTags.root, GlowType_RootElementCollection);

   pThis->packageCount++;
}

static void writeFramingHeader(GlowOutput *pThis, bool isFirstPackage, bool isLastPackage)
{
   byte flags = 0;

   if(isFirstPackage)
      flags |= EmberFramingFlag_FirstPackage;
   if(isLastPackage)
      flags |= EmberFramingFlag_LastPackage;

   berFramingOutput_writeHeader(&pThis->base, (EmberFramingFlags)flags);
   pThis->hasLastPackage = isLastPackage;
}

void berFramingOutput_writeHeader(BerFramingOutput *pThis, EmberFramingFlags flags)
{
   BerOutput *pBase = &pThis->base.base;
   unsigned short index;

   ASSERT(pThis != NULL);
   ASSERT(pThis->base.position == 0);

   if (pThis->useNonEscapingFrames)
   {
       berMemoryOutput_writeByte(pBase, S101_Invalid);
       berMemoryOutput_writeByte(pBase, 0x04);                  // Length Length
       berMemoryOutput_writeByte(pBase, 0x00);                  // Payload Length 0
       berMemoryOutput_writeByte(pBase, 0x00);                  // Payload Length 1
       berMemoryOutput_writeByte(pBase, 0x00);                  // Payload Length 2
       berMemoryOutput_writeByte(pBase, 0x00);                  // Payload Length 3
       berMemoryOutput_writeByte(pBase, 0x00);                  // slotid
       berMemoryOutput_writeByte(pBase, EMBER_MESSAGE_ID);      // message
       berMemoryOutput_writeByte(pBase, EMBER_COMMAND_PAYLOAD); // command
       berMemoryOutput_writeByte(pBase, 0x01);                  // framing version
       berMemoryOutput_writeByte(pBase, (byte)(flags & 0xFF));  // flags: first_package | last_package;
       berMemoryOutput_writeByte(pBase, pThis->dtd);

       if (pThis->pAppBytes != NULL)
       {
           berMemoryOutput_writeByte(pBase, pThis->appBytesCount);

           for (index = 0; index < pThis->appBytesCount; index++)
               berMemoryOutput_writeByte(pBase, pThis->pAppBytes[index]);
       }
       else
       {
           berMemoryOutput_writeByte(pBase, 0x00);
       }
   }
   else
   {
       pThis->crc = 0xFFFF;

       berMemoryOutput_writeByte(pBase, S101_BOF);
       writeEscapedByteWithCrc(pThis, 0x00);                  // slotid
       writeEscapedByteWithCrc(pThis, EMBER_MESSAGE_ID);      // message
       writeEscapedByteWithCrc(pThis, EMBER_COMMAND_PAYLOAD); // command
       writeEscapedByteWithCrc(pThis, 0x01);                  // framing version
       writeEscapedByteWithCrc(pThis, (byte)(flags & 0xFF));  // flags: first_package | last_package
       writeEscapedByteWithCrc(pThis, pThis->dtd);            // dtd

       if (pThis->pAppBytes != NULL)
       {
           writeEscapedByteWithCrc(pThis, pThis->appBytesCount);

           for (index = 0; index < pThis->appBytesCount; index++)
               writeEscapedByteWithCrc(pThis, pThis->pAppBytes[index]);
       }
       else
       {
           writeEscapedByteWithCrc(pThis, 0x00);            // appbytes count
       }
   }
}

[MrJones4u]

Actually, the correct way for a getDirectory response is to return a node with all parameters. While all sub nodes might be contained within the node all parameters [descriptions] must be contained. The actual parameter value can be part of the node, yet may also be sent separately.