Chapter 5: Type Information and Location Transparency

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Objectives:

• Understand the relationship between stubs, proxies, and marshaling.

• Learn to run legacy COM DLLs in a surrogate process.

• Understand the various marshaling options provided by COM.

• Assemble local (EXE) component housing to host your coclasses.

• Learn to securely access remote COM servers à la DCOM.

In Chapter 3, you learned about the nuts and bolts required to build COM-based DLLs using C++. In Chapter 4, you injected type information into an existing DLL, allowing your coclasses to be accessed from COM-aware languages such as Java and Visual Basic. In addition to language independence, location transparency is another virtue provided by the path of COM and IDL, the key to which are stubs and proxies.

Here, we dig into the inner workings of stubs and proxies and investigate COM's marshaling options. To illustrate location transparency, we will begin by loading an existing COM DLL into a surrogate process. Next, you will see how to configure class factories and coclasses to dwell within a COM-based EXE server. Finally, we learn how to use the DCOM protocol to securely access EXE servers located on a distant machine.

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