[RESOLVED] Poor man's web server with Winsock?

[fredtheman]

Hello

I need to write a front-end to a server-less database engine. To simplify things, and because the HTTP protocol is good enough for this (send a SQL query, get an answer), I was thinking of using the MS Inet control on the client side, the MS Winsock control on the server side, and have the server send a basic HTTP header followed by the payload (either OK/NOK for queries that don't return data, or CSV-formatted text for a SELECT).

This code works... but only for small payloads, eg. for a 19,000-line text file, only about 2,900 lines are displayed on the client. Same behavior when using a regular web browser, so the problem is on the server side.

Apparently, I need to pace the server down, so that it doesn't flood the client with more data than it can handle. Someone also mentionned that I should be using two Winsock controls instead of one, but I have no idea why, what the code would look like, and whether it's actually needed for a simple query-reply-close-listen setup.

Here's the code:

Private Sub Form_Load()
	Winsock1.Protocol = sckTCPProtocol
	Winsock1.LocalPort = 5555
	Winsock1.Listen
End Sub

Private Sub Winsock1_ConnectionRequest(ByVal requestID As Long)
    If Winsock1.State <> sckClosed Then
        'tell Winsock to stop listening for connections
        Winsock1.Close
    End If
    Winsock1.Accept requestID
End Sub

Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)
    On Error GoTo ErrHandler
    
    Dim sInput As String
    Dim sResult As String
    
    Winsock1.GetData sInput, vbString, bytesTotal
    'Here, we'll send SQL request to DBMS, and get reply
    'For now, just send data from file
		    
    '19,000-line, CSV-formatted text file
    sResult = ReadFileContents(App.Path & "\data.txt")

    sOutput = "HTTP/1.1 200 OK" + vbCrLf
    sOutput = sOutput + "Connection: Close" + vbCrLf
    sOutput = sOutput + "Content-Length: " + Str$(Len(sResult)) + vbCrLf
    sOutput = sOutput + "Content-Type: text/html" + vbCrLf + vbCrLf
    sOutput = sOutput + sResult
    
    'Only sending 2,900 lines instead of 19,000!
    If Winsock1.State = sckConnected Then
        Winsock1.SendData sOutput
        DoEvents
        Winsock1.Close
        DoEvents
        Winsock1.Listen
    End If
    
    Exit Sub
    
ErrHandler:
    MsgBox Err.Description, vbCritical, "Err #" & Err.Number
    End

End Sub

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
    Winsock1.Close
End Sub

Private Sub Winsock1_Close()
    If Winsock1.State <> sckClosed Then
        Winsock1.Close
        DoEvents
        Winsock1.Listen
    End If
End Sub

Private Sub Winsock1_Error(ByVal Number As Integer, Description As String, ByVal Scode As Long, ByVal Source As String, ByVal HelpFile As String, ByVal HelpContext As Long, CancelDisplay As Boolean)
    Debug.Print "Err : " & Description
		
    Winsock1.Close ' close the erraneous connection
    Winsock1.Listen ' listen again
End Sub

Thanks for any hint

[ccoder]

Well, for one thing, you are closing the connection after doing the send and the data most likely (in fact I would bet on it) has not finished being sent.

Move the Winsock1.Close & Winsock1.Listen lines to a Winsock1_SendComplete sub. And you can get rid of the DoEvents.

[CVMichael]

ccoder is right, you have to wait until all data is sent, and then close the connection (in the SendComplete event)... or just let the client close the connection...

Anyways... if you are interested to see how a regular web-server works, see this thread:
http://www.vbforums.com/showthread.php?t=283785

[fredtheman]

ccoder is right, you have to wait until all data is sent, and then close the connection (in the SendComplete event)... or just let the client close the connection...

Stupid me I should have suspected SendData was asynchronous, and move the Close/Listen bits in the SendComplete event. I can send a 1MB text file with no problem.

Thanks.