Creating your own Web Server using C#

public void SendHeader(string sHttpVersion, string sMIMEHeader, int iTotBytes, string sStatusCode, ref Socket mySocket)
{
    string sBuffer = "";
    // if Mime type is not provided set default to text/html
    if (sMIMEHeader.Length == 0)
    {
        sMIMEHeader = "text/html"; // Default Mime Type is text/html
    }
    sBuffer += sHttpVersion + sStatusCode + "\r\n";
    sBuffer += "Server: cx1193719-b\r\n";
    sBuffer += "Content-Type: " + sMIMEHeader + "\r\n";
    sBuffer += "Accept-Ranges: bytes\r\n";
    sBuffer += "Content-Length: " + iTotBytes + "\r\n\r\n";
    byte[] bSendData = Encoding.ASCII.GetBytes(sBuffer);
    SendToBrowser(bSendData, ref mySocket);
    Console.WriteLine("Total Bytes: " + iTotBytes.ToString());
}

The SendToBrowser function sends information to the browser. This is an overloaded function.

public void SendToBrowser(string sData, ref Socket mySocket)
{
    SendToBrowser(Encoding.ASCII.GetBytes(sData), ref mySocket);
}
public void SendToBrowser(byte[] bSendData, ref Socket mySocket)
{
    int numBytes = 0;
    try
    {
        if (mySocket.Connected)
        {
            numBytes = mySocket.Send(bSendData, bSendData.Length, 0);
            if (numBytes == -1)
                Console.WriteLine("Socket Error: Cannot Send Packet");
            else
                Console.WriteLine("No. of bytes sent: {0}", numBytes);
        }
        else
        {
            Console.WriteLine("Connection Dropped....");
        }
    }
    catch (Exception e)
    {
        Console.WriteLine("Error Occurred: {0}", e);
    }
}

We now have all the building blocks ready, now we will delve into the key function of our application.

public void 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==================\nClient 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 String
            string sBuffer = Encoding.ASCII.GetString(bReceive);
            // At present we will only deal with GET type
            if (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 = 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 a string from bytes then looks for the request type, and 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 exist then
// display the error message
if (sLocalDir.Length == 0)
{
    string sErrorMessage = "<H2>Error!! Requested Directory does not exist</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 the GetLocalPath function to get the physical directory information, if the directory is not found (or is not mapped with an 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 an error occurs it is thrown to the browser.

/////////////////////////////////////////////////////////////////////
// Identify the File Name
/////////////////////////////////////////////////////////////////////
// If The file name is not supplied then look in the default file list
if (sRequestedFile.Length == 0)
{
    // Get the default filename
    sRequestedFile = GetTheDefaultFileName(sLocalDir);
    if (sRequestedFile == "")
    {
        string 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;
    }
}

Then we need to identify the Mime type

/////////////////////////////////////////////////////////////////////
// Get The Mime Type
/////////////////////////////////////////////////////////////////////
String sMimeType = GetMimeType(sRequestedFile);
// Build the physical path
sPhysicalFilePath = sLocalDir + sRequestedFile;
Console.WriteLine("File Requested : " + sPhysicalFilePath);

Now the final steps of opening the requested file and sending it to the browser.

if (File.Exists(sPhysicalFilePath) == false)
{
    sErrorMessage = "<H2>404 Error! File Does Not Exist...</H2>";
    SendHeader(sHttpVersion, "", sErrorMessage.Length, " 404 Not Found", ref mySocket);
    SendToBrowser(sErrorMessage, ref mySocket);
    Console.WriteLine(sFormattedMessage);
}
else
{
    int iTotBytes = 0;
    sResponse = "";
    FileStream fs = new FileStream(sPhysicalFilePath, FileMode.Open, FileAccess.Read, FileShare.Read);
    // Create a reader that can read bytes from the FileStream.
    BinaryReader reader = new BinaryReader(fs);
    byte[] bytes = new byte[fs.Length];
    int read;
    while ((read = reader.Read(bytes, 0, bytes.Length)) != 0)
    {
        // Read from the file and write the data to the network.
        sResponse = sResponse + Encoding.ASCII.GetString(bytes, 0, read);
        iTotBytes = iTotBytes + read;
    }
    reader.Close();
    fs.Close();
    SendHeader(sHttpVersion, sMimeType, iTotBytes, " 200 OK", ref mySocket);
    SendToBrowser(bytes, ref mySocket);
    //mySocket.Send(bytes, bytes.Length, 0);
}
mySocket.Close();

Compilation and Execution

To compile the program from the command line.

In my version.net I don't need to specify any library name maybe for the old version we were required to add the reference to dll, using the/r parameter.

To run the application simply type the application name and press Enter.

Now, let's say the user sends the request, our web server will identify the default file name and send it to the browser.

Users can also request the Image file.

Possible Improvements

Many improvements can be made to the WebServer application. Currently, it does not support embedded images and no support for scripting. We can write our own Isapi filter for the same or we can also use the IIS isapi filter for our learning purpose.

Conclusion

This article gives a very basic idea of writing Web server applications, lots of improvement can be done. I'd appreciate it if I could get any comments on improving the same. I am also looking forward to adding the capabilities of calling Microsoft Isapi Filter from this application.