Connector A Design Pattern for Actively Initializing Network Services

This article is part of a continuingseries that describes objectoriented techniques for developing reusable, extensible, and efficient communication software. The topic of this article is the Connector pattern. This design pattern enables the tasks performed by network services to evolve independently of the mechanisms that actively initialize the services. The Connector pattern is a companion to the Acceptor pattern [1], which enables network services to evolve independently of the mechanisms that passively establish connections used by the services. The Connector and Acceptor patterns are commonly used in conjunction with connection-oriented protocols (such as TCP or SPX). These protocols reliably deliver data between two communication endpoints. Establishing connections between two endpoints involves both a passive role and an active role. The passive role initializes an endpoint of communication at a particular address (such as an Internet IP address and port number) and waits passively for other endpoints to connect with it. The active role initiates a connection to the address of an endpoint playing the passive role. The intent of the Connector and Acceptor patterns is to decouple the active and passive connection roles, respectively, from the network services performed once connections are established. Common connection-oriented network services include remote login, file transfer, and access to World-Wide Web resources. This article describes how separating the connection-related processing from the service processing yields more reusable, extensible, and efficient communication software. This article is organized as follows: Section 2 motivates the Connector pattern by illustrating how it can be used to actively establish connections with a large number of peers in a connection-oriented, multi-service, applicationlevel Gateway; Section 3 describes the Connector pattern in detail and illustrates one way to implement it in C++; and Section 4 presents concluding remarks. WIDE AREA