19.1 Introduction

The int library handles four distinct Internet protocols: FTP, HTTP, POP3, and SMTP. Each protocol is represented by agent and client classes. The client class provides a "nuts-and-bolts" access layer that allows low-level access to the protocol. Object orientation encapsulates details of the underlying protocol inside the client class. An agent class makes use of the respective client class to provide a layer that performs common protocol requests.

Figure 17 -- The protocol agent concept

This two-tiered architecture makes the int library flexible and easy to use, without losing functionality. Once you understand the basics of the class library design, you can plug in easily at the level you need, or add your own modules to the architecture.

The int library is multithread hot, which means it creates threads to complete its tasks. With the int library, you can create multithread hot C++ Internet applications without knowing multithread programming. This is because the int library does thread creation, management, and synchronization for you, using Threads.h++.

The int library also uses Threads.h++ IOUs to allow asynchronous communication. Each protocol command request immediately returns an IOUResult that can be redeemed at a later time.

The overall architecture of the int library is described in this chapter. For protocol-specific architectural information, please refer to the individual chapters that follow on FTP, HTTP, POP3, and SMTP.