Today, the topic in the field of information technology dedicated to the development and deployment of the client-server architecture remains very relevant. This is due to the fact that information systems of various scales are increasingly used in various fields. In addition, the structure of any database is created according to certain parameters, and in such a way that working with it in normal mode is possible only with the use of special applications. Therefore, the implementation of the client-server architecture is a very important task that arises before the departments of information technology at various facilities, the successful solution of which will allow the company to work optimally and smoothly.
Socket Server
A socket protocol server allows you to simultaneously process requests from a large number of users. At the same time, the administrator can make adjustments to the settings at any time in order to introduce a limit on the number of simultaneously served users. By default, this parameter contains no restrictions.
After the client connects to the server, a separate channel opens with a socket through which data is exchanged. However, the most optimal and safe is the deployment for each new connection of a special separate process.
The architecture of the client-server architecture
Let's consider in more detail the architecture implementation scheme, sequentially analyzing commonly used definitions:
1. Properties of ServerType and Port. In order for the user to be able to connect to the server, it is important to ensure that the port used by both the server and the client matches. The purpose of this parameter is made in the Port property. The type of connection is determined by the ServerType parameter.
2. The process of opening a socket. To start a client-server session, it is important to open the socket and port. The Listen property is used.
3. Next, data is exchanged with the user. When shutting down, the client disconnects. With the appropriate command from the system administrator, the server shuts down, interrupting all established connections and terminating the process of waiting for new connections.
Using TServerSocket in Delphi Client-Server Applications
To send and receive information from the user, the OnClientWrite and OnClientRead events are used. At the same time, you can interact with the user through a parameter such as ClientSocket. When working, the following methods and properties are often used:
- the number of currently connected users;
- the number of active processes;
- the number of free processes;
- port, host name and local IP address;
- Unlock and block the socket.
In conclusion, we pay attention to the often used special property - Data. This property is applied in the following situation. As a rule, the server is used to serve a large number of users, which means that there is a need to store information about each client, and this information needs to be bound to a specific socket. In such situations, the use of manual binding is very inconvenient, and therefore the Data property is widely used. However, it is important to remember that Data is a pointer, and therefore it is important to check if all the rules for working with pointers are fulfilled (type indication, memory allocation, etc.)
Documentation
To date, there is very little literature on Delphi client-server application development related to socket development and use. Therefore, for a detailed study of this aspect, you can refer to the documentation on Linux and Unix systems, because it discusses in sufficient detail the technology for deploying applications using sockets, however, as a rule, in Perl or C ++.