[ns] Creating a new header in NS2

[Eclipse612]

Hi everyone,

I'm trying to develop a p2p module for NS2, and I've included a new header
and packet type into it. These are the things I did:

1) I defined the new header in a couple of files ( a ".h" and a ".cc") using
the struct and the mapping class as explained in tutorials, like this:

struct FakePayload
{
	vector<string> payload_;
};

//C++ p2p Header Structure

struct hdr_p2p
{
	string headerType_;		// this is a p2p application packet
	static int offset_; 		//offset of the p2p header first bit in the packet
        string aduType_;         	// Could be: exploratory packet,
location_info, resource_confirmation,application_data
	string idFile_;         	//resource identifier, nonzero only if
aduType_="application_data"
	int idPart_;			//part identifier, nonzero only if
aduType_="application_data"
	FakePayload fakePayload_; 	//dummy payload, used to insert info that
shouldn't be in the header. We avoid using Appdata as recommended by
Teerawat.
	double timestamp_;		// time of the packet forwarding

	//header access methods

        string& headerType() { return headerType_; }
	inline static int& offset() { return offset_; }
        string& aduType() { return aduType_; }
	string& idFile() { return idFile_; }
        int& idPart() { return idPart_; }
	double& timestamp() { return timestamp_; }
	FakePayload& fakePayload() {return fakePayload_;}
	inline static hdr_p2p* access (const Packet* p)
		{return (hdr_p2p*) p->access(offset_); }
};

int hdr_p2p::offset_;

// C++ Header Mapping Class

static class p2pHeaderClass : public PacketHeaderClass
{
	public:
	p2pHeaderClass(): PacketHeaderClass ("PacketHeader/p2p", sizeof(hdr_p2p))
		{ bind_offset(&hdr_p2p::offset_); }
} class_p2phdr;

2) I edited packet.h and ns-packet.tcl that way:

Added 

p2p     #In use for p2p downloading time optimization experiments

to the "foreach prot" cycle in ns-packet.tcl;

Added

" static const packet_t PT_P2P = 62; "

just before the NTYPE, and

" name_[PT_P2P]="p2p"; "

to packet.h.



I verified - using some puts - that the p2p header is added to the packet
header when I allocate a packet, being the first header with offset_ = 0. 
The problem raises when, on a freshly allocated packet, I try to access the
p2p header. The call to hdr_p2p::access(p) seems to be succesful, but when I
try to get one  of the data members of the hdr_p2p struct (by cout or by
writing into them), I get a segmentation fault.
If I try to access one of the other protocol specific headers on the same
packet, everything is right and working.

What did I do wrong? It looks like the allocation procedure just reserves
space for the new header, but actually doesn't create any hdr_p2p object,
thus causing the segmentation fault. 

Thanks in advance for your help!

Stefano Vecchi 



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