Problem with http/https multipart form post using VB.Net

[shlim]

Currently I'm using VB.Net to perform a http/https multipart form post to a servlet. I'm able to perform the post using HttpWebrequest via GetRequestStream(). However, the servlet returned me with "The remote server returned an error: (500) Internal Server Error". Obviously, this means that I have not posted all the parameters as the servlet requested. But I just can't seem to find out what went wrong with my code. Hope someone can enlighten me, below is the code and sample form post for your reference:

VB.Net code:

Public Shared Function Send(ByVal URL As String, _
        Optional ByVal Port As String = "", _
        Optional ByVal Servlet As String = "", _
        Optional ByVal PostString As String = "", _
        Optional ByVal SSL As Boolean = Nothing, _
        Optional ByVal faxfile As String = "", _
        Optional ByVal faxlist As String = "")
 
        'https handling
        Dim oCertOverride As New CertificateOverride
        ServicePointManager.ServerCertificateValidationCallback = AddressOf oCertOverride.RemoteCertificateValidationCallback
 
        'set Port number
        If Port = "" Then
            If SSL = False Then
                Port = 80
            ElseIf SSL = True Then
                Port = 443
            End If
        End If
 
        'set the URL according to SSL
        If SSL = True Then
            URL = "https://" & URL & ":" & Port & Servlet
        ElseIf SSL = False Then
            URL = "http://" & URL & ":" & Port & Servlet
        Else
            Return ""
            Exit Function
        End If
 
        'fax file
        Dim boundary As String = "----------------------------------------AaB03x"
        Dim contentLength
        Dim postData2 = boundary & vbCrLf & "Content-Disposition: form data; name = ""faxfile""; " & _
                        "filename= """ & faxfile & """" & vbCrLf & _
                        "Content-Type: image/tiff" & vbCrLf & vbCrLf
        Dim faxStream As New FileStream(faxfile, FileMode.Open, FileAccess.Read)
        Dim faxBuffer() As Byte
        ReDim faxBuffer(Math.Min(4095, faxStream.Length))
 
        'fax list
        Dim postData3 = ""
        Dim listStream As FileStream = Nothing
        Dim listBuffer() As Byte = Nothing
        If faxlist <> "" Then
            postData3 = boundary & vbCrLf & "Content-Disposition: form-data; name = ""faxlist""; " & _
                            "filename=""" & faxlist & """" & vbCrLf & _
                            "Content-Type: text/plain" & vbCrLf & vbCrLf
            listStream = New FileStream(faxlist, FileMode.Open, FileAccess.Read)
            ReDim listBuffer(Math.Min(4095, listStream.Length))
        End If
        'end boundary
        Dim postData4 = vbCrLf & boundary & "--"
 
        MsgBox(PostString & postData2 & postData3 & postData4) 'debug
 
        'convert to bytes
        Dim byte1() As Byte
        Dim byte2() As Byte
        Dim byte3() As Byte = Nothing
        Dim byte4() As Byte
 
        byte1 = System.Text.Encoding.ASCII.GetBytes(PostString)
        byte2 = System.Text.Encoding.ASCII.GetBytes(postData2)
        byte4 = System.Text.Encoding.ASCII.GetBytes(postData4)
 
        'populate content length
        contentLength = byte1.Length + byte2.Length + faxStream.Length + byte4.Length
 
        If faxlist <> "" Then
            byte3 = System.Text.Encoding.Default.GetBytes(postData3)
            contentLength = contentLength + byte3.Length + listStream.Length
        End If
 
        Dim Request As HttpWebRequest = WebRequest.Create(URL)
       Dim Response As HttpWebResponse
        Dim ResponseData As String = ""
 
        ' Prepare Request Object
        Request.Method = "POST"
        Request.AllowWriteStreamBuffering = False
        Request.ContentType = "multipart/form-data; boundary=" & boundary
        Request.Accept = "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/tiff, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-shockwave-flash, */*"
        Request.Headers.Add("Cache-Control", "no-cache")
        Request.UserAgent = "http generic"
        System.Net.ServicePointManager.Expect100Continue = False
        Request.ContentLength = contentLength
        MsgBox(Request.ContentLength.ToString()) 'debug
 
        Dim SW As Stream = Nothing
        Dim SR As StreamReader = Nothing
 
        ' Send Request, If Request
        Try
            SW = Request.GetRequestStream()
            If SW.CanWrite Then
                MsgBox("Writing header") 'debug
                SW.Write(byte1, 0, byte1.Length)
                MsgBox("Writing fax file") 'debug
                SW.Write(byte2, 0, byte2.Length)
                Dim bytesRead = 1
                While bytesRead <> 0
                    bytesRead = faxStream.Read(faxBuffer, 0, faxBuffer.Length)
                    If bytesRead <> 0 Then
                        SW.Write(faxBuffer, 0, bytesRead)
                    End If
                End While
                If faxlist <> "" Then
                    MsgBox("Writing fax list")
                    SW.Write(byte3, 0, byte3.Length)
                    bytesRead = 1
                    While bytesRead <> 0
                        bytesRead = listStream.Read(listBuffer, 0, listBuffer.Length)
                        If bytesRead <> 0 Then
                            SW.Write(listBuffer, 0, bytesRead)
                        End If
                    End While
                End If
                MsgBox("Writing end boundary")
                SW.Write(byte4, 0, byte4.Length)
            End If
        Catch Ex As WebException
            MsgBox(" Writing Exception: " & Ex.Message)
        Catch Ex As Exception
            MsgBox("Writing Exception: " & Ex.Message)
            Return Nothing
            Exit Function
        Finally
            SW.Close()
        End Try
 
        ' Receive Response
        Try
            MsgBox("Receiving data") 'debug
            Response = Request.GetResponse()
            'MsgBox("retrieving from site") 'debug
            SR = New StreamReader(Response.GetResponseStream())
            ResponseData = SR.ReadToEnd()
            MsgBox(ResponseData) 'debug
            SR.Close()
        Catch Ex As WebException
            MsgBox("Servlet Exception: " & Ex.Message)
        Catch Ex As Exception
            MsgBox("Servlet Exception: " & Ex.Message)
            Return ""
            Exit Function
        End Try
 
        Return ResponseData
    End Function

Sample multipart form post:

----------------------------------------AaB03x
Content-Disposition: form data; name="destnum"

12345678;
----------------------------------------AaB03x
Content-Disposition: form data; name="loginname"

test
----------------------------------------AaB03x
Content-Disposition: form data; name="password"

test
----------------------------------------AaB03x
Content-Disposition: form data; name="line"

1
----------------------------------------AaB03x
Content-Disposition: form data; name="faxpri"

0
----------------------------------------AaB03x
Content-Disposition: form data; name="scheduletype"

1
----------------------------------------AaB03x
Content-Disposition: form-data; name = "faxfile"; filename="C:\Users\test\Appdata\Roaming\WindowsApp lication1\Application1\1.0.0.0\Microsoft Word - Document1.TIF"
Content-Type: image/tiff

follow by file content
----------------------------------------AaB03x--


Thanks for your kind advise.