Web Server’s Role

Web Server can refer to either the hardware (the computer) or the software (the computer application) that helps to deliver content that can be accessed through the Internet.
The primary function of a web server is to deliver web pages on the request to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and scripts.

The most common use of web servers is to host web sites but there are other uses like data storage or for running enterprise applications.

The web server provides the content and the web browser displays it to the user. At the simplest,a web server sends static files, such as static HTML or image files, through an HTTP connection to a web browser.

Modern web servers do far more, however. When a web server receives a request, some of the actions it takes are to:
1. Verify that the request is structured legitimately.
Sometimes, malicious clients send malformed web requests to compromise web servers. Web servers must be able to detect this and respond appropriately—usually by ignoring the request.
2. Authenticate itself.
If the server has a Secure Sockets Layer (SSL) certificate and the request was made with HTTPS, the web browser uses the certificate to authenticate the server. The web server will also encrypt all content before returning it to the web browser.
3. Authenticate the user.
If the content requires authorization, the web server verifies that the user has submitted credentials. If the user has not been authenticated, the web server redirects the user to an authentication form.
4. Authorize the user.
  After the Web server authenticates the user, the web server verifies that the user is allowed to access the requested content.
5. Determine how to handle a request.
If the web browser requested static content or was simply determining whether cached content could still be used, the web server can directly respond. If the web browser requested an ASP.NET page, the web server must forward the request to ASP.NET.
6. Handle errors.
If a server cannot process the user’s request, it provides error information to the web browser.
7. Cache output.
Web servers can cache output to improve the response time of subsequent requests. Web servers also provide caching information to web browsers, so browsers know how long to keep content cached.
8. Compress output.
Before returning a page to a web browser, a web server can compress the content to reduce the bandwidth required.
9. Log access.
Web servers typically record usage information for security and performance-monitoring purposes.

For more information about web server see following links

http://en.wikipedia.org/wiki/Web_server
http://www.webdevelopersnotes.com/basics/what_is_web_server.php
http://create-website.org/concepts/webserver.html

Web Browser’s Role

client is an application that runs on a personal computer and relies on a server to perform operations.In our case web browser is the client to access web pages resides on the web server.
web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web.
Their role is relatively simple:

1. Send requests to the web server.
If the user enters http://www.dotnetcypher.com, the web browser resolves the www.dotnetcypher.com Domain Name System (DNS) address, uses HTTP to connect to the server, and requests a page.
2. Authenticate the server.
If the server has an SSL certificate and the request was made with HTTPS, the web browser uses the certificate to authenticate the server and then decrypt future communications.
3. Process the response.
If the server has provided HTML, the browser retrieves embedded objects, such as images, videos, or animations referenced in the HTML. If the server has provided an error, redirection, or other response, the browser responds appropriately.
4. Display HTML and embedded objects.
Web browsers use HTML standards to determine how to display a webpage to the user. Because HTML can contain embedded objects, a web browser might have to display dozens of objects to render a single webpage.
5. Run client scripts.
Client scripts, such as those written in JavaScript, enable interactive and responsive pages without reloading the page.

Here are the more links.

http://www.allaboutcookies.org/browsers/index.html
http://create-website.org/concepts/webbrowser.html

Understanding Web Communications

Like all client-server applications, web applications have two distinct components:
Client Also known as the front-end interface, the web browser presents the user interface, accepts user input, and sends data to the server for processing.
Server Also known as the back end, the web server responds to requests from clients for specific pages. It responds with an HTML page that includes instructions for how to generate the user interface.

The web browser (the client) and the web server communicate by using Hypertext Transfer Protocol (HTTP), a text-based network protocol assigned to TCP port 80. If the server has a certificate, the client and server can use HTTP Secure (HTTPS) to authenticate the server and encrypt communications. HTTPS is assigned to TCP port 443.

Communications typically follow these steps:
1. A user enters an address, such as http://www.dotnetcypher.com/, into the web browser.
2. The web browser connects by using HTTP and sends a GET request, such as GET / (to retrieve the root page), to the web server.
3. The web server processes the requested page. This action might cause the server to return static HTML or image files, or it might execute application code(ASP.NET code) that performs workflow tasks or connects to a database.
4. The web server uses HTTP to send a response back to the web browser. If the request was processed successfully, the web server returns the HTTP status code 200, along with an HTML document. If the server cannot find the page, it returns the code 404. If the user requests an outdated or relocated page, the server returns the code 302 and the new URL so that the browser can access the correct page. This is known as redirection. Several other responses are possible as well, depending on the particular situation.
5. The user’s web browser then processes the response by displaying the HTML page (if the code was 200), showing an error message (if the code was 404), or loading a different page (if the code was 302). Other server responses are similarly handled by the browser, depending upon the response.

This process is repeated each time the user clicks a button or link(any of post back behavior control).

Find out the open files in the specified directory path using c#

Every developer getting following errors frequently. i.e."The file could not be accessed."File "can not be deleted"
Recently i also faced the same problem in one of my project task where i worked with some of open pdf files.Generally we will get these type of errors ,due to the following reasons
1. File is opened already.
2. File is using by another process
Finally find out the following simple and great example in c#..
This example is using the try-catch blocks.

Check all files from the specified folder:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO; //Required for directory and file operations

namespace File_operations
{
class Program
{
static void Main(string[] args)
{
DirectoryInfo Dir = new DirectoryInfo("C:\\Applictions\\SampleFiles");\\ Folder Path
FileInfo[] filePaths = Dir.GetFiles("*.*");\\Get all the files
foreach (FileInfo file in filePaths)
{
if (IsFileOpen(file))
Console.WriteLine("File is opened");
else
Console.WriteLine("File is not opened");
}
Console.ReadLine();
}

public static bool IsFileOpen(FileInfo file)
{
FileStream stream = null;
try
{
stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
}
catch (IOException)
{
return true;//file is opened
}
finally
{
if (stream != null)
stream.Close();
}
return false;//file is not opened
}
}
}



Find out specified format of files:

Change the following lines of code in the above example to get specific format files from a folder.
FileInfo[] filePaths = Dir.GetFiles("*.pdf");//Get all the pdf files from the folder
FileInfo[] filePaths = Dir.GetFiles("*.doc");//Get all the word document files from the folder
FileInfo[] filePaths = Dir.GetFiles("*.jpg");//Get all the jpg image files from the folder

please feel free to leave comments...!