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<task id="GUID-6998404B-CC51-5337-B04F-8444C32B99C9" xml:lang="en"><title> Writing

an Inbound Hook Tutorial</title><shortdesc>This topic describes how to write an inbound hook. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>

<steps id="GUID-538FFCBC-31FB-5B6A-B997-E38B68C54123">

<step id="GUID-6170D075-3962-59EA-BD58-28933D6214B9"><cmd>The <xref href="GUID-1A52EC87-DAD1-32C8-B530-295A65EB7292.dita"><apiname>CIp6Hook()</apiname></xref> is

a base class for all hook protocols. For more information, see the <xref href="GUID-3490B79F-7D03-3071-864E-D9C7107608DE.dita"><apiname>MIp6Hook()</apiname></xref> and <xref href="GUID-9A313A0F-FCEE-3C3E-808F-DE46FB577BD7.dita"><apiname>CProtocolBaseUnbind()</apiname></xref> classes. </cmd>

</step>

<step id="GUID-EACF710B-9FAB-511E-B3B9-45A33E553267"><cmd/>

<info>The <xref href="GUID-10F2F06B-003E-3F29-AE09-6A85D3682729.dita"><apiname>ApplyL()</apiname></xref> function is derived from the <codeph>CIp6Hook()</codeph> class

to create an inbound hook. The following are the parameters of an <codeph>ApplyL()</codeph> function: </info>

<choicetable id="GUID-37EC06D0-A557-4B55-B09E-33BD4B59DD7D" keycol="1">

<chrow>

<choption><p>aPacket</p></choption>

<chdesc><p>Packet to process</p></chdesc>

</chrow>

<chrow>

<choption><p>aInfo</p></choption>

<chdesc><p>Packet information </p></chdesc>

</chrow>

</choicetable>

<info>  Note: The <codeph>ApplyL()</codeph> function is not used for post

or pre-processing hooks. </info>

</step>

</steps>

<example><title>How to write an Inbound Hook example </title> <p>The following

is an example code for how to write an inbound hook: </p> <codeblock id="GUID-9EB3E680-7CAE-5EE3-8B15-8FF06E3294CA" xml:space="preserve">

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;

     }

</codeblock> </example>

</taskbody><related-links>

<link href="GUID-340C57A4-B799-502D-8B86-39955E2F4268.dita"><linktext>Creating

an ESK File</linktext></link>

<link href="GUID-88AB6957-6D2B-5668-8CC3-4E426E68C9B7.dita"><linktext>Writing an

Outflow  Hook</linktext></link>

</related-links></task>