The information in this article applies to:
- Microsoft ActiveX SDK, version 1.0
- Internet Client SDK, versions 4.0, 4.01
- Microsoft Internet Explorer (Programming), versions 3.0, 3.01, 3.02,
4.0
SUMMARY
An automation controller such as Microsoft Visual Basic can automate
Internet Explorer (IE) to send data using the POST method to an HTTP server
such as Internet Information Server (IIS). This article demonstrates how to
automate IE to perform a POST of form data from Visual Basic and from a
simple Visual C++ application. While the examples illustrate automation of
the whole Internet Explorer application, the same techniques can be applied
to the Web Browser ActiveX control when it is hosted in an application.
MORE INFORMATION
Several methods are available for sending data to an HTTP server. GET and
POST are currently the most common. POST is typically used to submit form
data to an HTTP server when that data exceeds the maximum allowable
transfer using the GET method. This limit is typically 2K.
IE exposes the IWebBrowser(App) interface to automation controllers. The
IWebBrowser(App) interface exposes a Navigate method. In interface
definition language (IDL) syntax (a universal representation from which
both the Visual Basic and Visual C++ syntax is derived), the Navigate
method looks like the following:
HRESULT Navigate([in] BSTR URL, [in] VARIANT* Flags,
[in] VARIANT* TargetFrameName, [in] VARIANT* PostData,
[in] VARIANT* Headers);
For the purposes of performing a POST, only the URL, PostData, and Headers
parameters are relevant. See the Internet Client SDK documentation for
information on the other parameters.
To call Navigate and POST form data to an HTTP server, the URL parameter
must specify a valid address, the PostData parameter must contain a
SAFEARRAY of bytes, and the Headers parameter must contain a BSTR that
contains the following HTTP header:
Content-Type: application/x-www-form-urlencoded
This header indicates that the data being posted is encoded according to
the rules specified in the HTML specification.
Internet Explorer versions 3.0, 3.01, and 3.02 do not support posting data
to an HTTP server via the Navigate method. WinInet and URL Monikers are two
possible alternatives. For more information on WinInet and Monikers, see
the REFERENCES section of this article.
Note that the Internet Explorer Script Object Model object "window" has a
"navigate" method as well. This navigate method will only accept a URL and
cannot be used to POST data to a web server.
To test the examples below, the following Active Server Page (ASP) should
be saved to the file NAVPOST.ASP in a directory on an NT 4.0 server
running Internet Information Server (IIS) version 3.0. The directory
should be recognized by IIS as a virtual root with execute permission:
<HTML>
<%
cFlavor = Request("Flavor")
cName = Request("FName")
%>
<BODY>
Hello, <% =cName %>. <br>
One scoop of <% =cFlavor %> coming right up!
</BODY>
</HTML>
Visual Basic
To demonstrate a POST in Visual Basic, perform the following steps:
- Start a new Standard EXE project in Visual Basic. Form1 is created by
default. Add the following controls to Form1:
Object Name Caption
-------------------------------------------------------------------
Label lblName First Name
Label lblFlavor Flavor
CommandButton cmdSubmit Submit
ComboBox cboFlavor
TextBox txtName
TextBox edtPostData
(edtPostData should be multi-line and have scroll bars)
- Invoke "References" from the Project menu and add a reference to the
project for "Microsoft Internet Controls" (SHDOCVW.DLL). Make sure this
is done from the References dialog and not just from the Components
dialog.
- Insert the following code in the General Declarations section:
Dim g_oIE As InternetExplorer ' Global reference to an
' instance of IE
Private Sub cmdSubmit_Click()
edtPostData.Text = "" ' Initialize an edit box for testing
ReDim aByte(0) As Byte ' Array of bytes to hold data to post
' Extract the URL encoded data from the UI,
' and pack it into an array of bytes
cFlavor = cboFlavor.List(cboFlavor.ListIndex)
cParamName = "FName="
cParamFlavor = "Flavor="
cSeparator = "&"
cPostData = cParamName & txtName.Text _
& cSeparator & cParamFlavor & cFlavor
PackBytes aByte(), cPostData
' For testing, rebuild the POST data and stuff
' it into an edit box
For i = LBound(aByte) To UBound(aByte)
edtPostData = edtPostData + Chr(aByte(i))
Next
Dim vPost As Variant
vPost = aByte ' Assign the byte array to a VARIANT
Dim vFlags As Variant
Dim vTarget As Variant
Dim vHeaders As Variant
vHeaders = _
"Content-Type: application/x-www-form-urlencoded" _
+ Chr(10) + Chr(13)
' You're done. Now call Navigate
' Note: modify path to server as appropriate
g_oIE.Navigate "http://<server>/scripts/navpost.asp", _
vFlags, vTarget, vPost, vHeaders
End Sub
Private Sub Form_Load()
' Create an instance of IE
Set g_oIE = New InternetExplorer
g_oIE.Visible = True
' Populate a combobox with some flavor choices
cboFlavor.List(0) = "Vanilla"
cboFlavor.List(1) = "Chocolate"
cboFlavor.List(2) = "Strawberry"
cboFlavor.ListIndex = 0 ' The default choice
End Sub
' Utility function to pack the data to post into an array of bytes
Private Sub PackBytes(ByteArray() As Byte, ByVal PostData As String)
iNewBytes = Len(PostData)
If iNewBytes = 0 Then
Exit Sub
End If
iCursize = UBound(ByteArray) - LBound(ByteArray)
ReDim Preserve ByteArray(iNewBytes + iCursize)
For i = 1 To iNewBytes
ch = Mid(PostData, i, 1)
If ch = Space(1) Then
ch = "+"
End If
ByteArray(i + iCursize - 1) = Asc(ch)
Next
End Sub
- Modify the URL in the call to Navigate as appropriate, close all
running instance of IE, and choose Start from the Run menu.
- Enter your name in the first name textbox, choose a flavor, and click
the Submit command button. The data from the Visual Basic form will be
posted to the HTTP server and the response will appear in the visible
browser window.
Visual C++
To demonstrate a POST in Visual C++, perform the following steps:
- Ensure that the ActiveX or Internet Client SDK is installed.
- Launch Visual C++, and create a new Win32 console project.
- Create a new text document, and add the following code:
#include <windows.h>
#define INITGUID
#include <initguid.h>
#include <exdisp.h>
#include <memory.h>
HRESULT GetPostData(LPVARIANT pvPostData);
void main()
{
HRESULT hr;
IWebBrowserApp* pWBApp = NULL; // Derived from IWebBrowser
BSTR bstrURL = NULL, bstrHeaders = NULL;
VARIANT vFlags = {0},
vTargetFrameName = {0},
vPostData = {0},
vHeaders = {0};
if (FAILED(hr = CoInitialize(NULL)))
{
return;
}
if (FAILED(hr = CoCreateInstance(CLSID_InternetExplorer,
NULL,
CLSCTX_SERVER,
IID_IWebBrowserApp,
(LPVOID*)&pWBApp)))
{
goto Error;
}
bstrURL = SysAllocString(L"http://<server>/scripts/navpost.asp");
if (!bstrURL)
{
goto Error;
}
bstrHeaders = SysAllocString(
L"Content-Type: application/x-www-form-urlencoded\r\n");
if (!bstrHeaders)
{
goto Error;
}
V_VT(&vHeaders) = VT_BSTR;
V_BSTR(&vHeaders) = bstrHeaders;
hr = GetPostData(&vPostData);
hr = pWBApp->Navigate(bstrURL, &vFlags,
&vTargetFrameName, &vPostData, &vHeaders);
pWBApp->put_Visible(VARIANT_TRUE);
Error:
if (bstrURL) SysFreeString(bstrURL);
if (bstrHeaders) SysFreeString(bstrHeaders);
VariantClear(&vPostData);
if (pWBApp) pWBApp->Release();
CoUninitialize();
}
// Pack some data into a SAFEARRAY of BYTEs. Return in a VARIANT
HRESULT GetPostData(LPVARIANT pvPostData)
{
HRESULT hr;
LPSAFEARRAY psa;
LPCTSTR cszPostData = "FName=Matt&Flavor=Mocha+Chip";
UINT cElems = lstrlen(cszPostData);
LPSTR pPostData;
if (!pvPostData)
{
return E_POINTER;
}
VariantInit(pvPostData);
psa = SafeArrayCreateVector(VT_UI1, 0, cElems);
if (!psa)
{
return E_OUTOFMEMORY;
}
hr = SafeArrayAccessData(psa, (LPVOID*)&pPostData);
memcpy(pPostData, cszPostData, cElems);
hr = SafeArrayUnaccessData(psa);
V_VT(pvPostData) = VT_ARRAY | VT_UI1;
V_ARRAY(pvPostData) = psa;
return NOERROR;
}
- Modify the URL reference as appropriate, and save the code. Add it to
the project, and then build.
- Close all browser instances and run the application.
- Switch to the running instance of IE to see that the data was posted.
REFERENCES
Berners-Lee, T. RFC 1866. "Hypertext Markup Language - 2.0."
Internet Client SDK documentation
For more information on how to use WinInet to simulate a form POST request,
please refer to the following article in the Microsoft Knowledge Base:
ARTICLE-ID: Q165298
TITLE : HOWTO: Simulate a Form POST Request Using WinInet
For more information on how to use a URL Moniker to simulate a form POST
request, please refer to the following article in the Microsoft Knowledge
Base:
ARTICLE-ID: Q165800
TITLE : SAMPLE: Using a URL Moniker to POST Data
Keywords : kbinterop kbhowto
Technology : kbole
Version : Win:1.0,3.0,3.01,3.02,4.0,4.01
Platform : WINDOWS
Issue type : kbhowto