Writing an Inbound Hook Tutorial

How to write an Inbound Hook example

The following is an example code for how to write an inbound hook:

CHookExample::ApplyL(RMBufHookPacket &aPacket, RMBufRecvInfo &aInfo)
 {
   if (aInfo.iProtocol != iProtocol)
        // Normally, it should never get here in this example. But,
       // if the prototocol was just changed via SetOption...
   return KIp6Hook_PASS;
   TInet6Packet<TExtensionHeader> ext(aPacket, aInfo.iOffset);
   if (ext.iHdr == NULL)
   return KIp6Hook_PASS;   // Bad packet? But let someone else worry about it.
     if (ext.iHdr->Port() != iPort)
         return KIp6Hook_PASS;   // Not for me, let someone else handle it.

     const TInt hdrlen = aInfo.CheckL(ext.iHdr->HeaderLength());
     if (aInfo.iIcmp)
         {
         // Header is in returned packet of an ICMP Error
         const TInt offset = aInfo.iOffset - aInfo.iOffsetIp;// Relative offset within problem packet
         if (aInfo.iIcmp == KProtocolInet6Icmp && // only ICMP6 can be tested like this
             aInfo.iType == KInet6ICMP_ParameterProblem &&// A parameter problem...
             offset <= (TInt)aInfo.iParameter && // after start of this header?
             offset + hdrlen > (TInt)aInfo.iParameter)// and before end of this header?
             {
             // Someone didn't accept my strange header.
             // Could set some flag and stop sending it.
             aPacket.Free();
             return -1;
             }
         // Error is not about my header, fall to DONE
         }
     else
         {
         // Implement header semantics
         // (none in this example).
         }
     // Header processed (Done), skip over
     // - need to indicate the location of "my next header" field,
     aInfo.iPrevNextHdr = (TUint16)(aInfo.iOffset+1);
     // - need to make the protocol of the following header available
     aInfo.iProtocol = ext.iHdr->NextHeader();
     // - and finally, update the offset over my header.
     aInfo.iOffset += hdrlen;
     return KIp6Hook_DONE;
     }