Why do I have header checksum erro in AutoIt UDP protocol?

Question

I am using standart UDP function of AutoIt. I tested and dumped UDP packets to loopback interface 127.0.0.1 (send udp packets to myself). I captured it with RawCap, then opened in Wireshark. It showed me that there is a problem with Header Check sum. Why? Can I somehow encapsulate HTTP inside UDP (using AutoIt)?

    #include <GUIConstantsEx.au3>
#include <WindowsConstants.au3>
#include <ButtonConstants.au3>
HotKeySet("{esc}", "Cleanup")
HotKeySet("{enter}", "sendData")
Global $ConnectedSocket = -1
Global $MainSocket
Local $g_IP, $RogueSocket, $GOOEY, $edit, $input, $butt, $msg
Local $ret, $recv
$g_IP = "127.0.0.1"
$_INCOMING_FLAG = "UDP DATA: "
OnAutoItExitRegister ("Cleanup")


; 1. UDP Listener ### Start The UDP Services ###
;==============================================
UDPStartup()
OnAutoItExitRegister ("Cleanup")

; 1. UDP Listener ### Create a Listening "SOCKET"
;==============================================
$socket = UDPBind($g_IP, 65432)
If @error <> 0 Then Exit

; 3. GUI ### Create a GUI for chatting
;==============================================
$GOOEY = GUICreate("P2P Chat", 300, 200)
$edit = GUICtrlCreateEdit("", 10, 40, 280, 150, $WS_DISABLED)
$input = GUICtrlCreateInput("", 10, 10, 200, 20)
$butt = GUICtrlCreateButton("Send", 210, 10, 80, 20, $BS_DEFPUSHBUTTON)
GUISetState()

; GUI Message Loop
;==============================================
While 1
    $msg = GUIGetMsg()
    If $msg = $GUI_EVENT_CLOSE Then ExitLoop

    If $msg = $butt Then sendData()

    $data = UDPRecv($socket, 200)
    If $data <> "" Then
        GUICtrlSetData($edit, GUICtrlRead($edit) & $_INCOMING_FLAG &$data & @CRLF)
    EndIf
;~  Sleep(50)

WEnd
GUIDelete($GOOEY)

Func sendData()
    If $socket <> 0 Then
        $status = UDPSend($socket, GUICtrlRead($input))
        If $status = 0 Then
            MsgBox(0, "ERROR", "Error while sending UDP message: " & @error)
            Exit
        EndIf

    ElseIf $ret > 0 Then
        ; UPDATE EDIT CONTROL WITH DATA WE SENT
        ;----------------------------------------------------------------
        GUICtrlSetData($edit, GUICtrlRead($edit) & GUICtrlRead($input) & @CRLF)
        GUICtrlSetData($input, "")
    EndIf
EndFunc   ;==>sendData


Func Lookup()
    ; If no connection look for one
    Return 0
EndFunc   ;==>Lookup

Func Cleanup()
    UDPCloseSocket($socket)
    UDPShutdown()
EndFunc   ;==>Cleanup

Answer 1

I'm guessing all of the errant checksums are 0x0000 ; in that case, you are probably running into TCP Checksum Offloading . This is the operating system trying to let the networking hardware calculate the checksum (which will reduce load on the CPU). These checksums are not an error in your application.