Inside Macintosh: Networking With Open Transport / Part 1 - Open Transport Essentials

Chapter 6 - Mappers

About Mappers

A mapper is a communications path between your application and a mapper provider, which is a protocol that allows you to map a name to a network address, if the underlying protocol allows it, and to register that name-address pair so that it becomes visible to all other entities on a network. Which mapper functions you call depends on the name-registration protocol you select when you create a mapper. For example, if you select the AppleTalk Name-Binding Protocol (NBP), which supports dynamic name and address registration, you can use all the mapper functions described in this chapter: you can register a name, look up a name, and remove a registered name. If you select the TCP/IP domain name resolver (DNR), you can only look up a name that has been registered using other means.

When you create a mapper, you obtain a mapper reference. A mapper reference, like an endpoint reference, identifies the instance of the provider you have created. You must pass this reference as a parameter to all other mapper functions. You can open multiple mappers. For example, if you are writing a network administration application, you might want to create a mapper for each protocol used over the network. If you do open multiple mappers, the mapper reference tells Open Transport which mapper is invoked for any one function call.

Like endpoint providers, mapper providers also have a state attribute, which helps Open Transport manage these providers. Unlike endpoints, however, mappers do not provide functions that allow you to determine their state.
A mapper can be either in an uninitialized (T_UNINIT) state if it was closed by the system, or in the idle (T_IDLE) state after it has been opened.