Retrieving and Specifying Client Cookies

A Windows Media server can recognize HTTP and RTSP cookies from a client, and a cache proxy plug-in can modify them. Cookie modification can be used to stop recursive redirection. That is, you can create plug-ins that read the cookie, recognize that the client has already been redirected, and then do not request the same redirection.

When specifying a cookie value, you must indicate whether it is a persistent or a session-based cookie. A client remembers a session-based cookie only as long as the client is running. Also, each instance of the client has a unique cookie. Persistent cookies, on the other hand, remain after the client shuts down and are shared among clients. You can create a persistent cookie by appending an expiration date to the end of a cookie value. The date has the following format:

    ; expires = DDD dd-MMM-yyyy hh:mm:ss GMT

The following table identifies the values in the expiration date string.

The following example code illustrates how to retrieve and specify a cookie. Because other plug-ins can specify cookie values, you must first retrieve the Set-Cookie value from the response context and concatenate it with your cookie before specifying the value. You must use semicolons to separate cookie values.

C++ Example

// Declarations.
HRESULT hr = S_OK;
IWMSHeaderLine *pHeaderLine = NULL;
IWMSContext *pRequestContext = NULL;
IWMSContext *pResponseContext = NULL;
CComBSTR bstrCookie;
CComBSTR bstrNewSetCookie;
CComBSTR bstrOrigSetCookie;

hr = pCommandCtx->GetCommandRequest( &pRequestContext );
if (FAILED(hr))
    return(hr);
hr = pCommandCtx->GetCommandResponse( &pResponseContext );
if (FAILED(hr))
    return(hr);

// Retrieve a pointer to the IWMSHeaderLine interface.
// Specify the cookie value of the request context.
hr = pRequestContext->GetAndQueryIUnknownValue( 
                        L"Cookie", 
                        WMS_CONTEXT_NO_NAME_HINT, 
                        IID_IWMSHeaderLine, 
                        (IUnknown**) &pHeaderLine, 
                        0);
if (FAILED(hr))
    return(hr);

// Retrieve the cookie.
hr = pHeaderLine->GetValue( &bstrCookie );
if (FAILED(hr))
    return(hr);

// If this is an authorization plug-in, you can add a Set-Cookie header
// to the response.  This cannot be done from an event plug-in, however,
// because the response may already have been sent by the time the code
// is executed.

// TODO: You can modify the cookie here.

// Retrieve the "Set-Cookie" value from the response context if it
// already exists. Do not overwrite the existing value.
hr = pResponseContext->GetStringValue( L"Set-Cookie",
                                       WMS_CONTEXT_NO_NAME_HINT,
                                       &bstrOrigSetCookie,
                                       0 );

if( SUCCEEDED( hr ) )
{
    // The response already contains a Set-Cookie header. Concatenate
    // your cookie to the existing value.
    bstrNewSetCookie.AssignBSTR( bstrOrigSetCookie );
    if( !bstrNewSetCookie )
    {
        return( E_OUTOFMEMORY );
    }

    bstrNewSetCookie.Append( L", " );
    if( !bstrNewSetCookie )
    {
        return( E_OUTOFMEMORY );
    }

     bstrNewSetCookie.AppendBSTR( bstrCookie );
    if( !bstrNewSetCookie )
    {
        return( E_OUTOFMEMORY );
    }
}
else
{
    // The response does not already contain a Set-Cookie header.
    hr = S_OK;

    bstrNewSetCookie.AssignBSTR( bstrCookie );
    if( !bstrNewSetCookie )
    {
        return( E_OUTOFMEMORY );
    }
}

// Specify the new cookie.
hr = pResponseContext->SetStringValue( L"Set-Cookie", 
                                       WMS_CONTEXT_NO_NAME_HINT,
                                       bstrNewSetCookie,
                                       0 );
if (FAILED(hr))
    return(hr);

// Release the pointers.

See Also

Concepts

Custom Plug-in Basics

IWMSHeaderLine Interface

IWMSHeaderLine Object (C#)

IWMSHeaderLine Object (Visual Basic .NET)