The HTTP service and web applications


Nowadays, the most used method of interacting with a Web server is that of the client/server architecture based on Web technology. The process of exchanging information used in Web technology does not differ from the process implemented by the standard client/server architecture, in which the server program manages the processing of the queries received from the client programs.

In the process of information exchange used by web technologies, client programs are executed in web browsing programs, which are usually found on workstations as auxiliary applications, as clients.

Web browsers are used for immediate viewing and interpretation of web documents stored on the server, as well as for access to other special services, such as:
1. Copy files from FTP servers.
2. Providing virtual sessions on the server.
3. Access through menus to the resources of the remote computers.

Access to these special features is possible considering that, from the beginning, web browsing programs were created for multi-protocol access, to provide a unique interface for access to multiple network resources.

Within the interaction scheme with web technologies, the web server acts as the main server program. It is launched on the server and implements the processing of the queries that are transmitted by the clients, the interaction between the web clients and the web server being fulfilled based on the rules established by the HTTP protocol (HyperText Transfer Protocol). When starting the webserver, it begins to “listen” or control a logical port on the network, which, as a standard for them, is the number 80, and assumes that all messages transmitted to this port are intended for the webserver.

When receiving a query from the web client, the webserver establishes a connection by using TCP/IP and begins exchanging information with the client through the HTTP protocol. If the client wants access to protected information from the web server, the server may request that an identifier and password be entered for the user, these protected web documents being thus accessible only to users with the appropriate access rights.

The web documents received by the browser from the web server are represented by text files written in a special language, called HTML (HyperText Markup Language), a language that consists of a set of “understandings” that define the formatting of the text and what it will look like in Web browser window. Bookmarks, which define formatting, also control how links to other objects or graphics will be displayed. In addition to the markup language, programs written in JavaScript and VBScript can be inserted into the HTML document, programs that will only be interpreted by the web browser when the web document will be loaded and displayed.

It is hard to imagine if a server administrator would want to make the Web server’s file system available to everyone. So web servers assign a root folder as the starting point for all GET requests. This term is also used in the form of the home directory, home folder, root directory, HTTP root, document root, or home root.

The way to view the data as part of the root folder in the webserver is very useful. Even if, in fact, the data resides on a different disk, for space management, or even on a different machine. Virtual folders represent solving the above dilemma by logically appearing from a folder outside the root directory of the web server as part of it.
One reason for creating virtual folders is security. Many web servers use virtual folders to implement folder-level access permissions.

Modern web servers can be used to solve a wider class of problems, including:
– support for a database of hierarchical documents, processing of queries and control of access to information for client-side programs
– pre-processing the data before answering the queries;
– interaction with other external programs and other servers (search engines, for example).

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