Microsoft KB Archive/175474

= INFO: Header Required Posting HTML Form Encoded Data to ASP Page =

Article ID: 175474

Article Last Modified on 8/18/2005

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APPLIES TO


 * Microsoft Internet Explorer 4.0 128-Bit Edition
 * Microsoft Internet Explorer 4.01 Service Pack 2
 * Microsoft ActiveX SDK
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition

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This article was previously published under Q175474



SUMMARY
When writing an Internet client application that posts HTML form data to an ASP page using Wininet API or Visual Basic Internet Transfer Control, it is necessary to add the following HTTP header in the POST request: Content-Type: application/x-www-form-urlencoded This header indicates that the data being posted is encoded according to the rules in the HTML specification (RFC 1866). ASP will not retrieve your HTML form variables if this header is not present in the POST request.

The following Visual Basic example demonstrates adding a custom HTTP header to a POST request using either Wininet API or the Internet Transfer Control (SP2). Please note that you need the Internet Transfer Control from at least Visual Basic 5.0 Service Pack 2 or Visual Studio Service Pack 2 to implement POST. The original control cannot post correctly due to a bug. The code fragment in the CommandButton1 Click event in the following example uses Wininet API. The code fragment in the CommandButton2 Click event uses Internet Transfer Control (SP2).

Step-by-Step Example
 Start a new Standard EXE project. Form1 is added by default. From the Project menu, choose Components, and select the Internet Transfer Control(SP2) into the project. Place an Internet Transfer Control 5.0(SP2), Inet1, on Form1. Place two CommandButtons, Command1 and Command2, on Form1.  Add the following code to the project code window: Private Declare Function InternetOpen Lib "wininet.dll" _ Alias "InternetOpenA" _ (ByVal lpszCallerName As String, _            ByVal dwAccessType As Long, _             ByVal lpszProxyName As String, _             ByVal lpszProxyBypass As String, _             ByVal dwFlags As Long) As Long

Private Declare Function InternetConnect Lib "wininet.dll" _ Alias "InternetConnectA" _ (ByVal hInternetSession As Long, _            ByVal lpszServerName As String, _             ByVal nProxyPort As Integer, _             ByVal lpszUsername As String, _             ByVal lpszPassword As String, _             ByVal dwService As Long, _             ByVal dwFlags As Long, _             ByVal dwContext As Long) As Long

Private Declare Function InternetReadFile Lib "wininet.dll" _ (ByVal hFile As Long, _            ByVal sBuffer As String, _             ByVal lNumBytesToRead As Long, _             lNumberOfBytesRead As Long) As Integer

Private Declare Function HttpOpenRequest Lib "wininet.dll" _ Alias "HttpOpenRequestA" _ (ByVal hInternetSession As Long, _            ByVal lpszVerb As String, _             ByVal lpszObjectName As String, _             ByVal lpszVersion As String, _             ByVal lpszReferer As String, _             ByVal lpszAcceptTypes As Long, _             ByVal dwFlags As Long, _             ByVal dwContext As Long) As Long

Private Declare Function HttpSendRequest Lib "wininet.dll" _ Alias "HttpSendRequestA" _ (ByVal hHttpRequest As Long, _            ByVal sHeaders As String, _             ByVal lHeadersLength As Long, _             ByVal sOptional As String, _             ByVal lOptionalLength As Long) As Boolean

Private Declare Function InternetCloseHandle Lib "wininet.dll" _ (ByVal hInternetHandle As Long) As Boolean

Private Declare Function HttpAddRequestHeaders Lib "wininet.dll" _ Alias "HttpAddRequestHeadersA" _ (ByVal hHttpRequest As Long, _            ByVal sHeaders As String, _             ByVal lHeadersLength As Long, _             ByVal lModifiers As Long) As Integer

Private Sub Command1_Click Dim hInternetOpen As Long Dim hInternetConnect As Long Dim hHttpOpenRequest As Long Dim bRet As Boolean

hInternetOpen = 0 hInternetConnect = 0 hHttpOpenRequest = 0

'Use registry access settings. Const INTERNET_OPEN_TYPE_PRECONFIG = 0 hInternetOpen = InternetOpen("http generic", _                           INTERNET_OPEN_TYPE_PRECONFIG, _                            vbNullString, _                            vbNullString, _                            0)

If hInternetOpen <> 0 Then 'Type of service to access. Const INTERNET_SERVICE_HTTP = 3 Const INTERNET_DEFAULT_HTTP_PORT = 80 'Change the server to your server name hInternetConnect = InternetConnect(hInternetOpen, _                                 "yourserver", _                                  INTERNET_DEFAULT_HTTP_PORT, _                                  vbNullString, _                                  "HTTP/1.0", _                                  INTERNET_SERVICE_HTTP, _                                  0, _                                  0)

If hInternetConnect <> 0 Then 'Brings the data across the wire even if it locally cached. Const INTERNET_FLAG_RELOAD = &H80000000 hHttpOpenRequest = HttpOpenRequest(hInternetConnect, _                                    "POST", _                                     "/scripts/testpost.asp", _                                     "HTTP/1.0", _                                     vbNullString, _                                     0, _                                     INTERNET_FLAG_RELOAD, _                                     0)

If hHttpOpenRequest <> 0 Then Dim sHeader As String Const HTTP_ADDREQ_FLAG_ADD = &H20000000 Const HTTP_ADDREQ_FLAG_REPLACE = &H80000000 sHeader = "Content-Type: application/x-www-form-urlencoded" _ & vbCrLf bRet = HttpAddRequestHeaders(hHttpOpenRequest, _                      sHeader, Len(sHeader), HTTP_ADDREQ_FLAG_REPLACE _                       Or HTTP_ADDREQ_FLAG_ADD)

Dim lpszPostData As String Dim lPostDataLen As Long

lpszPostData = "lname=Doe&fname=John" lPostDataLen = Len(lpszPostData) bRet = HttpSendRequest(hHttpOpenRequest, _                           vbNullString, _                            0, _                            lpszPostData, _                            lPostDataLen)

Dim bDoLoop            As Boolean Dim sReadBuffer        As String * 2048 Dim lNumberOfBytesRead As Long Dim sBuffer            As String bDoLoop = True While bDoLoop sReadBuffer = vbNullString bDoLoop = InternetReadFile(hHttpOpenRequest, _                        sReadBuffer, Len(sReadBuffer), lNumberOfBytesRead) sBuffer = sBuffer & _ Left(sReadBuffer, lNumberOfBytesRead) If Not CBool(lNumberOfBytesRead) Then bDoLoop = False Wend MsgBox sBuffer bRet = InternetCloseHandle(hHttpOpenRequest) End If                 bRet = InternetCloseHandle(hInternetConnect) End If              bRet = InternetCloseHandle(hInternetOpen) End If

End Sub

Private Sub Command2_Click Dim strURL As String, strFormData As String 'Change the server to your server name strURL = "http://yourserver/scripts/testpost.asp" strFormData = "lname=Doe&fname=John" Inet1.Execute strURL, "Post", strFormData, _ "Content-Type: application/x-www-form-urlencoded" End Sub

Private Sub Inet1_StateChanged(ByVal State As Integer) Dim vtData As Variant ' Data variable.

Select Case State ' ... Other cases not shown. Case icError ' 11 ' In case of error, return ResponseCode and ' ResponseInfo. vtData = Inet1.ResponseCode & ":" & _ Inet1.ResponseInfo

Case icResponseCompleted ' 12 Dim strData As String: strData = "" Dim bDone As Boolean: bDone = False

' Get first chunk. vtData = Inet1.GetChunk(1024, icString) DoEvents

Do While Not bDone

strData = strData & vtData ' Get next chunk. vtData = Inet1.GetChunk(1024, icString) DoEvents

If Len(vtData) = 0 Then bDone = True End If          Loop

MsgBox strData End Select End Sub

Private Sub Form_Load Inet1.Cancel End Sub  From the File menu, choose Make Project1.exe to compile the project.

Note that tracing the Inet1_StateChanged event callback function in the VB debugger may not work properly because this callback function needs to be repeated called and can't be stopped in debugger before a complete HTTP response is received. If you need to trace the Inet1_StateChanged event callback function in the debugger, use Debug.Print.  Create a testpost.asp file and place it in your Web server scripts directory: <HTML> <HEAD> <TITLE>test asp</TITLE> </HEAD> <BODY BGCOLOR=#FFFFFF> <H3>test asp</H3> fname is     <% =Request("fname") %> <BR> lname is     <% =Request("lname") %> </BODY> </HTML> </li></ol>

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