如何检查表单是否为输入文件字段？ ASP经典

Question

我有一些代码在将输入值插入数据库之前会检查输入值。它可以正常工作，它检查所有表单输入，但是我希望它排除所有文件上载输入，因此在上载图像时它不会检查文件输入的值。但是我不知道如何使它起作用，因此任何输入都非常感激。谢谢。

这就是我现在拥有的。

    Dim BlackList, ErrorPage
    BlackList = Array("#","$","%","^","&","|",_
                      "<",">","'","""","(",")",_
                      "--", "/*", "*/", "@@",_
                      "cursor","exec","execute",_
                      "nchar", "varchar", "nvarchar", "iframe", "char", "alter", "begin", "cast", "create", "insert","delete", "drop", "table"_
                      )

        Function CheckStringForSQL(str,varType) 
          On Error Resume Next 
          Dim lstr 
          ' If the string is empty, return false that means pass
          If ( IsEmpty(str) ) Then
            CheckStringForSQL = false
            Exit Function
          ElseIf ( StrComp(str, "") = 0 ) Then
            CheckStringForSQL = false
            Exit Function
          End If

          lstr = LCase(str)
          ' Check if the string contains any patterns in our black list
          For Each s in BlackList
            If(IsExceptionList(s,varType)=False) then
                If ( InStr (lstr, s) <> 0 ) Then
                  CheckStringForSQL = true
                  Exit Function
                End If
            End If
          Next
          CheckStringForSQL = false
        End Function 

        CookieExceptionList = Array("""","(",")","!")
        Function IsExceptionList(str,varType)
            If(varType="cookie") then
                For Each item in CookieExceptionList
                    If(item=str) then
                        IsExceptionList=True
                        Exit Function
                    End If
                Next
            End If
            IsExceptionList=False
        End Function

--SO HERE I NEED TO CHECK IF IT IS A FILE INPUT, AND IF SO, NOT RUN THE BELOW--
        For Each s in Request.form
          If ( CheckStringForSQL(Request.form(s),"form") ) Then

            feltext="Fel"
          End If
        Next