Event Notification Authorization Contexts

A context is an object that inherits and implements the IPropertyMap interface that manipulates the encapsulated member data. When the encapsulated data define a server, a user, or some content, the object is known as a server context, a user context, or a presentation context, respectively. The NetShow server uses contexts to pass client, server, and presentation data to the notification and authorization components. The IPropertyMap interface supports methods for adding, removing, evaluating, and modifying the properties of name/value pairs of data. The NetShow server maintains several different contexts to describe different aspects of each server task. Contexts supported by the server include the following:

Server Context Properties

Following is a list of predefined server context properties that are maintained by the server:

User Context Properties

Following is a list of predefined user context properties that are maintained by the server:

Presentation Context Properties

Following is a list of predefined presentation context properties that are maintained by the server:

Context Properties Set by the Server

The server sets different context properties for different types of events. The following table lists the property values that are set by the server for initialization or when authorization or notification of an event occurs:

Note   The NSS_USER_AUTHENTICATOR and NSS_USER_NAME properties are NOT set by the server unless authentication is enabled and the user has successfully been authenticated.

Context Properties set by a Component

The notification and authorization component can add new properties to the server, user, or presentation contexts, and set or retrieve the existing properties at any time during the life of the context. For example, the fee charged for viewing the title can be added to the presentation context when the title is opened. Then the billing cost can easily be retrieved from the context when the server sends notification that the title has been closed.

Context Lifetimes

Each context holds the value of its properties for a predetermined duration or lifetime. The values contained in the context can be set and retrieved until the end of that context’s lifetime. The following table details the lifespans of the contexts:

Note: The pointer to the context may be lost immediately after the method returns. To maintain access to the properties during asynchronous calls, call AddRef to increment the interface’s reference counter. Alternately, the data needed by the component could be stored in temporary variables. If AddRef is used, the component should call Release to free the pointer when the context is no longer needed.

Property Map Example

The following code demonstrates how you can retrieve the user name from the user context:

HRESULT hres;
VARIANT userName;
  hres = pUser->QueryInterface(IID_IPropertyMap,
           (void**) &pIUserPropMap);
  hres = pIUserPropMap->Read(_T("NSS_USER_NAME"),
              &userName);