Reply To: Modify packet [DELPHI]

[heilong]

I not absolutely understand a question, therefore I shall answer how I have understood it.

...

var

ReadRequest: ETH_REQUEST;

Buffer: INTERMEDIATE_BUFFER;

pEthernetHeader: PETHERNET_HDR;

pIpHeader: PIP_HDR;

pTCPHeader: PTCP_HDR;

pData: Pbyte;

DataSize: Integer;

...



const

HSIZE = sizeof(ETHERNET_HDR) + sizeof(IP_HDR)+ sizeof(ICMP_HDR);



...



ReadRequest.EthPacket.Buffer := @Buffer;

ReadRequest.hAdapterHandle := hAdapter;



...



if ReadPacket (hFilt, @ReadRequest) <> 0 then

begin

...

pEthernetHeader := @ReadRequest.EthPacket.Buffer.m_IBuffer;

pIPHeader := Pointer(integer(pEthernetHeader)+sizeof(ETHERNET_HDR));

pTCPHeader := Pointer(integer(pIPHeader)+sizeof(IP_HDR));

DataSize := ReadRequest.EthPacket.Buffer.m_Length - HSIZE;



PData := Pointer(integer(pEthernetHeader)+HSIZE);

// or so

//PData := Pointer(integer(pTCPHeader)+sizeof(TCP_HDR));

...



// Change Port Destination to 4032



pTCPHeader.Destination := htons(4032);



// Tne IPHeader checksum it is not recalculated therefore as the size of a package has not changed



pTCPHeader.CheckSum := 00;

pTCPHeader.Checksum := htons(Checksum(Pword(pTCPHeader), (sizeof(TCP_HDR) + DataSize) div 2));



//If the size of a packet has changed, it is necessary to align a packet to word and recalc IP Header and accordingly TCP Header

...



SendPacketToAdapter(hFilt, @ReadRequest);

end;

...

In a code there can be mistakes, for what beforehand apologize.