This article explains how to write a simple web server application using C#. Though it can be developed in any .NET supported language, I chose C# for this example. The code is compiled using Beta 2. Microsoft (R) Visual C# Compiler Version 7.00.9254 [CLR version v1.0.2914]. It can be used with Beta 1 with some minor modification. This application can co-exists with IIS or any web server, the key is to choose any free port. I assume that the user has some basic understanding of .NET and C# or Visual Basic .Net.
This Web server returns HTML formatted files and also supports images. It does not loads the embedded image or supports any kind of scripting. I have developed a console-based application for simplicity.
First...
First we will define the root folder for the Web server. Eg: C:\MyPersonalwebServer. Then create a data directory underneath the root directory Eg: C:\MyPersonalwebServer\Data. Create three files under data directory i.e.
Mimes.Dat
Vdirs.Dat
Default.Dat
Mime.Dat will have the mime type supported by our web server. The format will be <EXTENSION>; <MIME Type>e.g.
.html; text/html
.htm; text/html
.bmp; image/bmp
VDirs.Dat will have the virtual directory Information. The format will be </VIRTUALDIR />; <PHYSICAL>e.g.
<DRIVE:\PHYSICALDIR \>/; C:\myWebServerRoot/
test/; C:\myWebServerRoot\Imtiaz\
Default.Dat will have the virtual directory Information; e.g. default.html
default.htm
Index.html
Index.htm;
We will store all the information in plain text file for simplicity, we can use XML, registry or even hard code it. Before proceeding to the code first look at the header information which the browser will pass while requesting the web site
Let say we make a request for test.html. We type http://localhost:5050/test.html
(Remember to include port in the url), here is what the web server gets:
</DRIVE:\PHYSICALDIR>
GET /test.html
HTTP/1.1
Accept: image/gif, image/x-xbitmap,
image/jpeg, image/pjpeg, application/vnd.ms-powerpoint,
application/vnd.ms-excel, application/msword, */*
Accept-Language: en-usAccept-Encoding: gzip,
deflate User-Agent: Mozilla/4.0 (compatible; MSIE
5.5; Windows NT 4.0; .NET CLR 1.0.2914)
Host: localhost:5050Connection: Keep-Alive
Diving into the code...
// MyWebServer Written by Imtiaz Alamnamespace Imtiaz
{
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading ;
class MyWebServer
{
private TcpListener myListener ;
privateint port = 5050 ; // Select any free port you wish//The constructor which make the TcpListener start listening on th//given port. It also calls a Thread on the method StartListen().public MyWebServer()
{
try
{
//start listing on the given port
myListener = new TcpListener(port) ;
myListener.Start();
Console.WriteLine("Web Server Running... Press ^C to Stop...");
//start the thread which calls the method 'StartListen'
Thread th = new Thread(new ThreadStart(StartListen));
th.Start() ;
}
catch(Exception e)
{
Console.WriteLine("An Exception Occurred while Listening :" +e.ToString());
}
}
We defined namespace, included the references required in our application and initialized the port in the constructor, started the listener and created a new thread and called startlisten function.
Now let us assume that the user does not supplies the
file name, in that case we have to identify the default filename and send to the
browser, as in IIS we define the default document under documents tab.
We have already stored the default file name in the
default.dat and stored in the data directory. The GetTheDefaultFileName function takes the directory
path as input, open the default.dat file and looks for the file in the directory
provided and returns the file name or blank depends on the situation.
publicstring GetTheDefaultFileName(string sLocalDirectory)
{
StreamReader sr;
String sLine = "";
try
{
//Open the default.dat to find out the list// of default file
sr = new StreamReader("data\\Default.Dat");
while ((sLine = sr.ReadLine()) != null)
{
//Look for the default file in the web server root folderif (File.Exists( sLocalDirectory + sLine) == true)
break;
}
}
catch(Exception e)
{
Console.WriteLine("An Exception Occurred : " + e.ToString());
}
if (File.Exists( sLocalDirectory + sLine) == true)
return sLine;
elsereturn "";
}
We also
need to resolve the virtual directory to the actual physical directory like we
do in IIS. We have already stored the mapping between the Actual and Virtual
directory in Vdir.Dat. Remember in all the cases the file format is very
important.
publicstring GetLocalPath(string sMyWebServerRoot, string sDirName)
{
StreamReader sr;
String sLine = "";
String sVirtualDir = "";
String sRealDir = "";
int iStartPos = 0;
//Remove extra spaces
sDirName.Trim();
// Convert to lowercase
sMyWebServerRoot = sMyWebServerRoot.ToLower();
// Convert to lowercase
sDirName = sDirName.ToLower();
try
{
//Open the Vdirs.dat to find out the list virtual directories
sr = new StreamReader("data\\VDirs.Dat");
while ((sLine = sr.ReadLine()) != null)
{
//Remove extra Spaces
sLine.Trim();
if (sLine.Length > 0)
{
//find the separator
iStartPos = sLine.IndexOf(";");
// Convert to lowercase
sLine = sLine.ToLower();
sVirtualDir = sLine.Substring(0,iStartPos);
sRealDir = sLine.Substring(iStartPos + 1);
if (sVirtualDir == sDirName)
{
break;
}
}
}
}
catch(Exception e)
{
Console.WriteLine("An Exception Occurred : " + e.ToString());
}
if (sVirtualDir == sDirName)
return sRealDir;
elsereturn "";
}
We also
need to identify the Mime type, using the file extension supplied by the
user
publicstring GetMimeType(string sRequestedFile)
{
StreamReader sr;
String sLine = "";
String sMimeType = "";
String sFileExt = "";
String sMimeExt = "";
// Convert to lowercase
sRequestedFile = sRequestedFile.ToLower();
int iStartPos = sRequestedFile.IndexOf(".");
sFileExt = sRequestedFile.Substring(iStartPos);
try
{
//Open the Vdirs.dat to find out the list virtual directories
sr = new StreamReader("data\\Mime.Dat");
while ((sLine = sr.ReadLine()) != null)
{
sLine.Trim();
if (sLine.Length > 0)
{
//find the separator
iStartPos = sLine.IndexOf(";");
// Convert to lower case
sLine = sLine.ToLower();
sMimeExt = sLine.Substring(0,iStartPos);
sMimeType = sLine.Substring(iStartPos + 1);
if (sMimeExt == sFileExt)
break;
}
}
}
catch (Exception e)
{
Console.WriteLine("An Exception Occurred : " + e.ToString());
}
if (sMimeExt == sFileExt)
return sMimeType;
elsereturn "";
}
Now write the function, to build and sends header information to the browser (client):
We now have all the building blocks ready, now we will delve into the key function of our application.
publicvoid StartListen()
{
int iStartPos = 0;
String sRequest;
String sDirName;
String sRequestedFile;
String sErrorMessage;
String sLocalDir;
String sMyWebServerRoot = "C:\\MyWebServerRoot\\";
String sPhysicalFilePath = "";
String sFormattedMessage = "";
String sResponse = "";
while(true)
{
//Accept a new connection
Socket mySocket = myListener.AcceptSocket() ;
Console.WriteLine ("Socket Type " + mySocket.SocketType );
if(mySocket.Connected)
{
Console.WriteLine("\nClient Connected!!\n==================\n
CLient IP {0}\n", mySocket.RemoteEndPoint) ;
//make a byte array and receive data from the client
Byte[] bReceive = new Byte[1024] ;
int i = mySocket.Receive(bReceive,bReceive.Length,0) ;
//Convert Byte to Stringstring sBuffer = Encoding.ASCII.GetString(bReceive);
//At present we will only deal with GET typeif (sBuffer.Substring(0,3) != "GET" )
{
Console.WriteLine("Only Get Method is supported..");
mySocket.Close();
return;
}
// Look for HTTP request
iStartPos = sBuffer.IndexOf("HTTP",1);
// Get the HTTP text and version e.g. it will return "HTTP/1.1"string sHttpVersion = sBuffer.Substring(iStartPos,8);
// Extract the Requested Type and Requested file/directory
sRequest = sBuffer.Substring(0,iStartPos - 1);
//Replace backslash with Forward Slash, if Any
sRequest.Replace("\\","/");
//If file name is not supplied add forward slash to indicate//that it is a directory and then we will look for the//default file name..if ((sRequest.IndexOf(".") <1) && (!sRequest.EndsWith("/")))
{
sRequest = sRequest + "/";
}
//Extract the requested file name
iStartPos = sRequest.LastIndexOf("/") + 1;
sRequestedFile = sRequest.Substring(iStartPos);
//Extract The directory Name
sDirName = sRequest.Substring(sRequest.IndexOf("/"), sRequest.LastIndexOf("/")-3);
The code is self-explanatory. It receives the request, converts it into string from bytes then look for the request type, extracts the HTTP Version, file and directory information.
/////////////////////////////////////////////////////////////////////// Identify the Physical Directory/////////////////////////////////////////////////////////////////////if ( sDirName == "/")
sLocalDir = sMyWebServerRoot;
else
{
//Get the Virtual Directory
sLocalDir = GetLocalPath(sMyWebServerRoot, sDirName);
}
Console.WriteLine("Directory Requested : " + sLocalDir);
//If the physical directory does not exists then// dispaly the error messageif (sLocalDir.Length == 0 )
{
sErrorMessage = "<H2>Error!! Requested Directory does not exists</H2><Br>";
//sErrorMessage = sErrorMessage + "Please check data\\Vdirs.Dat";//Format The Message
SendHeader(sHttpVersion, "", sErrorMessage.Length, " 404 Not Found", ref mySocket);
//Send to the browser
SendToBrowser(sErrorMessage, ref mySocket);
mySocket.Close();
continue;
}
Note: Microsoft Internet Explorer usually displays a 'friendy' HTTP Error Page if you want to display our error message then you need to disable the 'Show friendly HTTP error messages' option under the 'Advanced' tab in Tools->Internet Options. Next we look if the directory name is supplied, we call GetLocalPath function to get the physical directory information, if the directory not found (or does not mapped with entry in Vdir.Dat) error message is sent to the browser.. Next we will identify the file name, if the filename is not supplied by the user we will call the GetTheDefaultFileName function to retrieve the filename, if error occurred it is thrown to browser.
/////////////////////////////////////////////////////////////////////// Identify the File Name///////////////////////////////////////////////////////////////////////If The file name is not supplied then look in the default file listif (sRequestedFile.Length == 0 )
{
// Get the default filename
sRequestedFile = GetTheDefaultFileName(sLocalDir);
if (sRequestedFile == "")
{
sErrorMessage = "<H2>Error!! No Default File Name Specified</H2>";
SendHeader(sHttpVersion, "", sErrorMessage.Length, " 404 Not Found",
ref mySocket);
SendToBrowser ( sErrorMessage, ref mySocket);
mySocket.Close();
return;
}
}
Now, let say user send the request, our web server will identify the default file name and sends to the browser.
User can also request the Image file..
Possible Improvements
There are many improvements can be made to the WebServer application. Currently it does not supports embedded images and no supports for scripting. You can write your own ISAPI filter for the same or you can use the IIS ISAPI filter for learning purpose. The code to write basic ISAPI filter is very well explained at
ISAPI Filters: Designing SiteSentry, an Anti-Scraping Filter for IIS
Conclusion
This article gives very basic idea of writing Web server application, lots of improvement can be done. I'll appreciate any comments on improving this. I am also looking forward to adding the capabilities of calling a Microsoft ISAPI filter from this application.
Imtiaz Alam is a Senior Developer, currently residing in Phoenix, Arizona.He has more than five years of development experience in developing Mirosoft based
Solution. He can be reached at alamimtiaz@hotmail.com.
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