Winsock Problem: Unable to receive data

Do you know which records you missed? As in - are the missed records randomly distributed, or is it that you are always missing the last/first ones to be sent?

Might they have updated to IE7? They messed with the timeout setting.

I presume what happens is that your TCP packet containing 25 lines are somewhare along the route repackaged into multiple packets. The first packet contains the first 13 lines, the rest goes into a second packet. This repackaging is allowed by the standard - TCP does not preserve boundaries - this means that data sent in one single call to "send" may well require four separate calls to "recv" before you have all the data.

On your local network there may not be a router present that repackages the data - so if you send all in one single packet you will be likely to receive all in one single packet.

If you only do a single recv on the socket then chances are you only get the first packet and miss the second one. You may find that doing another recv (maybe a few ms later) will give you the rest of the packet. The best thing is to somehow include the total datasize in your first packet so that the receiving application can easily find out if all the data has been received or that it needs to do another call to "recv".

In my experience i have used communication protocol that
checking how many bytes was sent and how many bytes was received.
If sent byte != received byte then attempting to resend.

Thank you for your comment.

To Edders, MikeAThon:

If there is a TCP packet concern here, why does a cloned computer work for the other branches.

I say cloned computer because I cloned my development machine.

The project was written in VB6, and our Host is AS/400.

Please help.

Thank you

If the streaming nature of TCP is the cause, then the application might work perfectly well some of the time, and not work at other times. THis is because the way that TCP groups bytes into a packet is non-deterministic, and depends on many factors such as network load, complexity, number of routers between source and destination, etc. Usually, for example, a novice to TCP will find that his incorrect application works perfectly fine when using the loopback address (127.0.0.1), or when tested inside a simple LAN. In this case, TCP tends to group data almost precisely the same way as the calls to send() and recv(). The entire application then fails when deployed over a actual network or over the Internet, since in this deployment, TCP almost always groups the data in ways that are completely different from the corresponding calls to send() and recv().

Mike

What are send() and recv() functions ? Are these VB6 functions? How will I test the bytes sent and receive, what are the commands ?

Thank you.

I have nothing to add to MikeAThon's replies and unfortunately my knowledge of vb is very limited. Still, the underlying networking stack is of course the same for vb and c; the same kind of problem will have the same kind of solution regardless of the programming language used.

What are the names of the functions you use to send and receive data in vb?

What is the size of the buffer for incoming data which you used in recv() function? May be that is little less than the size of all the records( or data ) which you receive from host. Try incresing it to maximum value and let me know the results.

1024 Bytes only

Could you maybe post a short piece of code that shows how you have implemented the receiving side of your application?

Here is the code below.
NOTE !!
The AxGlobal.gMSMesg "Transaction Timed Out. Perform Last Transaction Inquiry." will be activated if the variable sDATA receives no data, please also check the condition...

If Trim(sData) <> "" Then
Call MSGetReturnCode(sData, sResend)
Else
g_bTimeOut = True
GoTo ReTry
End If

Here is my complete code entitled gMSSendHost()

Public Sub gMSSendHost(Optional sReturnMsg As String, _
Optional bIsStoreNForward As Boolean = False, _
Optional sJrnlSeqNo As String = "", _
Optional sTrancode As String = "", _
Optional sDetailData As String = "")
Dim sSendData As String * 4096
Dim lRC As Long
Dim sData As String
Dim sResend As String
Dim delay_Cnt As Integer
Dim delay_sDATA As Integer
Dim Retry_Count As Integer
Dim Try As Integer
Dim Msg_Switch As Integer

On Error GoTo err_handler

Screen.MousePointer = vbHourglass

g_sTrxStatus = "Accepted"
bDisplayMsg = False
g_bTimeOut = False


m_bIsStoreNForward = bIsStoreNForward

MSInitHostVar

bPassbook = False ' Passbook Printing

Set m_objPrnPrint = New AxOliPrt.CPBPrinter

m_objPrnPrint.DeviceName = AxGlobal.gMFGetLocalHostName
m_objPrnPrint.InitPrinter

g_szSendBuffer = ""


Do
DoEvents
'Normal Transaction
If bIsStoreNForward = False Then
sSendData = MFConstructData(sJrnlSeqNo, sTrancode)
g_szSendBuffer = sSendData
'store and forward
Else
sSendData = sDetailData
End If

'sResend update in host response header
sResend = ""

'Online
AxGlobal.gMSRetRef_gbBranchMode g_bBranchOnlineMode
If Not g_bBranchOnlineMode Then
GoTo Err_HostCommFail
End If


If objSli.Online Then
objSli.Write Trim(sSendData), Len(Trim(sSendData))
'Write Fail
If objSli.LastErrorCode <> 0 Then
GoTo Err_HostCommFail
End If


'Offline
Else
GoTo Err_HostCommFail
End If

Do
DoEvents
Screen.MousePointer = vbDefault
sData = Space(1024)

lRC = objSli.Read(sData)
'Read Fail
If objSli.LastErrorCode <> 0 Then
GoTo err_handler
Else
If Trim(sData) <> "" Then
Call MSGetReturnCode(sData, sResend)
Else
g_bTimeOut = True
GoTo ReTry
End If
End If
Loop Until objSli.EOM = 1

Loop While sResend <> ""

If (bPassbook = True) Then
m_objPrnPrint.AxPrint "99|" ' Eject
End If
Set m_objPrnPrint = Nothing

Screen.MousePointer = vbDefault

Exit Sub

Err_HostCommFail:
If (bPassbook = True) Then
m_objPrnPrint.AxPrint "99|" ' Eject
End If
Set m_objPrnPrint = Nothing

sReturnMsg = sSendData
If g_bBranchOnlineMode Then
AxGlobal.gMSMesg "Host is offline"
End If
g_sTrxStatus = "Offline"
Screen.MousePointer = vbDefault
MSGetSOForOffTrx
Exit Sub

err_handler:
If (bPassbook = True) Then
m_objPrnPrint.AxPrint "99|" ' Eject
End If
Set m_objPrnPrint = Nothing

If g_bTimeOut = True Then
AxGlobal.gMSMesg "Transaction Timed Out. Perform Last Transaction Inquiry."
gMSClose
End If

If Err <> 0 Then
AxGlobal.gMSMesgErr "gMFSendHost"
End If

g_sTrxStatus = "Pending"

Screen.MousePointer = vbDefault

End Sub