Services

The second core CANS component are services. Unlike drivers that represent rigidly constrained, mobile, soft-state adaptation functionality, services can export data using any standard internet protocol (e.g., TCP or HTTP), encapsulate more heavyweight functions, process concurrent requests, and maintain persistent state. The different interface requirements of drivers and services stem from the observation that most current services distributed in the internet are legacy in nature: their source code is general unavailable, and rewriting or modifying them is impractical. The price paid for not adhering to a standard interface is that unlike driver migration, CANS does not explicitly support service migration; a service individually determines how it manages its own state transfer. This design choice reflects the view that services are migrated infrequently and doing so requires protocols that are difficult to abstract cleanly. CANS provides applications with a general platform to create, compose, and control services across the network. A service is required to register itself identifying the data types it supports, optionally providing a delegate object that can control the service and act on its behalf in interactions with the rest of CANS. The delegate object implements a standard interface consisting of activating and suspending the service, and receiving CANS events. Service composition is similar to driver composition, using types supplied at registration time.