[mel]

I want to change some bytes before they come to my browser.
Do i have to recalculate TCPchecksum?

also, i like to buy code for D5 for doing this if is availble.

Thanks.

program Pass;

{$APPTYPE CONSOLE}



uses

forms,

SysUtils,

Windows,

Winsock,

winpkf,

iphlp;



var

ExitProcessProc: procedure;

iIndex, counter : DWORD;

hFilt : THANDLE;

Adapts : TCP_AdapterList;

AdapterMode : ADAPTER_MODE;

Buffer, ParsedBuffer : INTERMEDIATE_BUFFER;

ReadRequest : ETH_REQUEST;

hEvent : THANDLE;

hAdapter : THANDLE;

pEtherHeader : TEtherHeaderPtr;

pIPHeader : TIPHeaderPtr;

pTcpHeader : TTCPHeaderPtr;

pUdpHeader : TUDPHeaderPtr;

SourceIP, DestIP : TInAddr;

thePacket : PChar;

SourceIpString, DestinationIpString : string;

SourceName, DestinationName : string;



function IPAddrToName(IPAddr : string) : string;

var

SockAddrIn : TSockAddrIn;

HostEnt : PHostEnt;

WSAData : TWSAData;

begin

WSAStartup($101, WSAData);

SockAddrIn.sin_addr.s_addr := inet_addr(PChar(IPAddr));

HostEnt := gethostbyaddr(@SockAddrIn.sin_addr.S_addr, 4, AF_INET);

if HostEnt <> nil then

begin

result := StrPas(Hostent^.h_name)

end

else

begin

result := '';

end;

end;

















procedure ReleaseInterface();

begin

AdapterMode.dwFlags := 0;

AdapterMode.hAdapterHandle := hAdapter;

SetAdapterMode(hFilt, @AdapterMode);

SetPacketEvent(hFilt, hAdapter, 0);

if hEvent <> 0 then

CloseHandle(hEvent);

CloseFilterDriver(hFilt);

FreeNDISAPI();

end;



begin

iIndex := 4;

InitNDISAPI();

hFilt := OpenFilterDriver('NDISRD');

if not IsDriverLoaded(hFilt) then exit;

ExitProcessProc:= ReleaseInterface;

GetTcpipBoundAdaptersInfo(hFilt, @Adapts);

hAdapter := Adapts.m_nAdapterHandle[iIndex];

AdapterMode.dwFlags :=  MSTCP_FLAG_RECV_TUNNEL or MSTCP_flag_sent_TUNNEL  ;

AdapterMode.hAdapterHandle := hAdapter;

hEvent := CreateEvent(nil, TRUE, FALSE, nil);



if hEvent <> 0 then

begin//1



if SetPacketEvent(hFilt, hAdapter, hEvent) <> 0 then

begin//2

ReadRequest.EthPacket.Buffer := @Buffer;

ReadRequest.hAdapterHandle := hAdapter;

SetAdapterMode(hFilt, @AdapterMode);

WaitForSingleObject(hEvent,INFINITE);



while ReadPacket(hFilt, @ReadRequest) <> 0 do

begin//3



pEtherHeader := TEtherHeaderPtr(@Buffer.m_IBuffer);

if ntohs(pEtherHeader.h_proto) = ETH_P_IP then

begin

pIPHeader := TIPHeaderPtr(Integer(pEtherHeader) +

SizeOf(TEtherHeader));

SourceIP.S_addr := pIPHeader.SourceIp;

DestIP.S_addr := pIPHeader.DestIp;

if pIPHeader.Protocol = IPPROTO_TCP then

begin

pTcpHeader := TTCPHeaderPtr(Integer(pIPHeader) + (pIPHeader.VerLen and $F) * 4);

if (pTcpHeader.SourcePort = htons(80)) or (pTcpHeader.DestPort = htons(80)) then begin thePacket := pchar(pEtherHeader)+ (sizeof(TEtherHeaderPtr) + pIpHeader.VerLen * 4  +  pTcpHeader.Offset * 4);writeln(thePacket);end;

end;

end;

case Buffer.m_dwDeviceFlags of



PACKET_FLAG_ON_SEND:

/////////***************************************

//lets say i want ReadRequest.EthPacket.Buffer.m_IBuffer[30]=100;

/// do i have to recalculate TCPChecksum ????

/////////***************************************

begin SendPacketToAdapter(hFilt, @ReadRequest);

end;

PACKET_FLAG_ON_RECEIVE: SendPacketToMstcp(hFilt, @ReadRequest);

end;

end;//3



ResetEvent(hEvent);

end;//2

end;//1



end.

[Vadim Smirnov]

Yes, you have to recalculate checksums if modify the packet content. What code do you need? Checksum recalculation?

[Author]

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