Using Web Connections
Go Up to Choosing a Connection Protocol
HTTP lets you create clients that can communicate with an application server that is protected by a firewall. HTTP messages provide controlled access to internal applications so that you can distribute your client applications safely and widely. Like socket connections, HTTP messages provide a lowest common denominator that you know will be available for the connection to the application server. For more information about HTTP messages, see Creating Internet Server Applications
Instead of instantiating the remote data module directly from the client (as happens with DCOM), HTTP-based connections use a Web server application on the server (httpsrvr.dll) that accepts client requests and instantiates the remote data module using COM. Because of this, they are also called Web connections. The connection component on the client and httpsrvr.dll on the server are responsible for marshaling IAppServer calls.
Web connections can take advantage of the SSL security provided by wininet.dll (a library of Internet utilities that runs on the client system). Once you have configured the Web server on the server system to require authentication, you can specify the user name and password using the properties of the Web connection component.
As an additional security measure, the application server must register its availability to clients using a Web connection. By default, all new remote data modules automatically register themselves by adding a call to EnableWebTransport in the UpdateRegistry method. You can remove this call to prevent Web connections to your application server.
Web connections can take advantage of object pooling. This allows your server to create a limited pool of remote data module instances that are available for client requests. By pooling the remote data modules, your server does not consume the resources for the data module and its database connection except when they are needed.
Unlike most other connection components, you cannot use callbacks when the connection is formed via HTTP.