Programmer Diaries

A simple Chat application based on .NET Remoting

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It is good to be back writing again! This time on a simple chat application (windows console based). So here goes the C# code, just one single file named Server.cs, that is all you will need. Note that there are no validations done. Just take the exe and run from two client machines and enjoy chatting. Hope you will find it exciting. (Disclaimer: Tested over a LAN with host computers in the same domain. Not tested over the open Internet.)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Http;
using System.Net;

namespace KChat
{
public class Server : MarshalByRefObject
{
private static Server _objRecipientServer = null;
private static Server _objCallingServer = null;
private static string _strCallingClientChatName = string.Empty;
private static string _strCallingClientIPAddress = string.Empty;
private static string _strCommandText = string.Empty;
private static string _strRecipientIPAddress = string.Empty;
private static string _strSenderChatName = string.Empty;
private static string _strSenderIPAddress = string.Empty;

static void Main(string[] args)
{
Server _objServer = new Server();
_objServer.StartSelfAsServer();
_strCommandText = Console.ReadLine();
bool _bContinue = true;

while (_bContinue)
{
if (_strCommandText.ToUpper() == "QUIT")
{
_bContinue = false;
break;
}
else if (_strCommandText.ToUpper() == "CONNECT")
{
Console.WriteLine("--------------------");
Console.Write("Enter your chat name: ");
_strSenderChatName = Console.ReadLine();
Console.Write("Enter your IP Address: ");
_strSenderIPAddress = Console.ReadLine();
Console.Write("Enter recipient IP Address: ");
_strRecipientIPAddress = Console.ReadLine();
Console.WriteLine("Chat Agent>> Initializing connection...");
_objServer.InitializeRecipient(_strRecipientIPAddress, _strSenderChatName, _strSenderIPAddress);
Console.WriteLine("Chat Agent>> Connected to " + _strRecipientIPAddress + "...");
}
else
{
if (_strSenderChatName.Length == 0)
{
Console.Write("Enter your chat name: ");
_strSenderChatName = Console.ReadLine();
}
Console.WriteLine("Chat Agent>> Sending...");
_objServer.DispatchMessage(_strCommandText);
Console.WriteLine("Chat Agent>> Message sent...");
}
_strCommandText = Console.ReadLine();
}
}

public void StartSelfAsServer()
{
HttpChannel _objChannel = new HttpChannel(1095);
ChannelServices.RegisterChannel(_objChannel, false);
RemotingConfiguration.RegisterWellKnownServiceType(typeof(KChat.Server), "Server", WellKnownObjectMode.Singleton);
Console.WriteLine("Chat Agent>> Chat server started.");
}

public void Listener(string strMessage)
{
Console.WriteLine(strMessage);
}

public void InitializeRecipient(string strRecipientIPAddress, string strCallingClientChatName, string strCallingClientIPAddress)
{
if (_objRecipientServer == null)
{
_objRecipientServer = (Server)Activator.GetObject(typeof(KChat.Server), "http://" + strRecipientIPAddress + ":1095/Server");
_objRecipientServer.RegisterCallingClient(strCallingClientChatName, strCallingClientIPAddress);
}
}

public void RegisterCallingClient(string strCallingClientChatName, string strCallingClientIPAddress)
{
Console.WriteLine("Chat Agent>> Incoming connection from person named '" + strCallingClientChatName + "' on client IP=" + strCallingClientIPAddress + " waiting for your acceptance...");
Console.WriteLine("You can start replying below...");
_strCallingClientChatName = strCallingClientChatName;
_strCallingClientIPAddress = strCallingClientIPAddress;

if (_objCallingServer == null)
{
_objCallingServer = (Server)Activator.GetObject(typeof(KChat.Server), "http://" + strCallingClientIPAddress + ":1095/Server");
}
}

public void DispatchMessage(string strMessage)
{
_objRecipientServer.Listener(_strSenderChatName + ">>" + strMessage);
}
}
}

Authenticating Windows NT Credentials via Form Input

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This week has been a busy one with little time for research. But then this topic turned out to be an exciting one. There will be a standard windows form (the web/asp version might need adjustments) with three textboxes: (1) txtUserName, (2) txtPassword and (3) txtDomain. The end user will enter any windows credentials into this form; and the code logic will validate the entered information is true or false - and you shall have an enterprise class login interface that you will often find in off the shelf enterprise products.

The C#.NET code lising is provided below (it can be done in other languages and platforms also):
------------------------------
using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsAuthenticationDialog
{
public partial class Login : Form
{
[DllImport("ADVAPI32.dll", EntryPoint = "LogonUserW", SetLastError = true, CharSet = CharSet.Auto)]
public static extern bool LogonUser(string lpszUsername, string lpszDomain, string lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);

public Login()
{
InitializeComponent();
}

private void btnLogin_Click(object sender, EventArgs e)
{
IntPtr _ptr = IntPtr.Zero;
bool _result = LogonUser(txtUserName.Text, txtDomain.Text, txtPassword.Text, 2, 0, ref _ptr);

if (_result)
{
MessageBox.Show("Access granted!");
}
else
{
MessageBox.Show("Incorrect credentials!");
}
}
}
}

The above code is actually calling a windows API (which is unmanaged) by importing the API DLL and declaring the LogonUser() function and passing appropriate arguments.

For detailed literature on using windows APIs or interoperability with unmanaged libraries you might want to consider the following references:

(1) http://msdn.microsoft.com/en-us/library/aa984739(VS.71).aspx
(2) http://www.pinvoke.net

Design Precaution with .NET Connection Pooling and IIS Virtual Directories

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A few months earlier, I was setting up a web service library which would contain multiple versions of the same web service. The business behind hosting multiple versions of the same service was that if any changes were made to the web service to alter the input or output then a new version would have to be hosted which would be used as the active version of the service. This strategy took care of backward compatibility in systems that were already consuming the sevice and saved significant cost of quality and testing.

The web services would look something like below in the IIS (real application names have been masked).

IIS Root
|__AppName.ModuleName.WebServices
|__v1.0
|__ServiceName.asmx
|__v1.1
|__ServiceName.asmx
|__v1.2
|__ServiceName.asmx

-Each service version would contain 3 files:
(1) a DLL in the /bin folder
(2) an ASMX file and
(3) a WEB.CONFIG file.
-Each service version would be configured as an APPLICATION in IIS.
-All the services would connect to the same database (Oracle in this case).
-In the WEB.CONFIG file connection pooling would be true and pool size set to 25.
-The total number to allowed connections to the database was set to 300.

Now, there is a technical consideration to be made while this web hosting is done. Everytime a version of the service is hit for the first time, it will block 25 (pool size) connections. So if simultaneously two versions of the service hit the database then 50 connections will be blocked. Theoretically, 300 connections would be able to support only 300/25 = 12 versions of the service hitting simultaneously. This meant that if there is ever more than 12 versions of the same service hitting the database simultaneously, then the first 12 services will succeed. What happens to the 13th request - well I guess it will error - but I haven't tested it out. If you happen to read my article and test it please post the results.

In my case, a workaround was adopted - we simply decided to turn off connection pooling on the earlier versions and keep it active only in the most recent version.

Finding Oracle Tablespace Utilization (Free v/s Consumed space)

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Last week I was working on my project when we discovered that space monitoring was not active in our application's database. During the process of addressing this problem, I figured out how we can easily query the database to get a report on various tablespaces and their free space. The query I used is provided below (the results are in MBs), the Oracle version I used was 10g.

SELECT
tablespace_name,
SUM(space)/1024/1024 "Size MB",
SUM(free)/1024/1024 "Free MB",
(1-(sum(free)/1024/1024)/(sum(space)/1024/1024))*100 "% Used"
FROM
(
SELECT
tablespace_name,
sum(bytes) space,
0 free
FROM dba_data_files
GROUP BY tablespace_name
UNION
SELECT
tablespace_name,
0 space,
sum(bytes) free
FROM dba_free_space
GROUP BY tablespace_name
)
WHERE TABLESPACE_NAME like UPPER('%')
GROUP BY tablespace_name
order by (1-(sum(free)/1024/1024)/(sum(space)/1024/1024))*100;

Dynamically Parsing Fields/Columns From a DataReader

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Today I was faced with a situation where I had to write a data layer function using ADO.NET that would be able to read the resultset from a stored procedure irrespective of number of field/columns and their names. And eventually serialize the stored procedure output for consumption through a web service. Here is the code listing:
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public DataSet GetDataTableFromReader(string strDataSetName, string strDataTableName, OracleDataReader objReader)
{
DataSet _dsResult = new DataResult(strDataSetName);
DataTable _dtResult = new DataTable(strTableName);
DataRow _dtRow;

DataColumn _dc = new DataColumn();
for (int i = 0; i < objReader.FieldCount; i++)
{
_dc.ColumnName = objReader.GetName(i);
_dtResult.Columns.Add(_dc);
_dc = new DataColumn();
}
if (objReader.HasRows)
{
while (objReader.Read())
{
_dtRow = _dtResult.NewRow();
for (int i = 0; i < objReader.FieldCount; i++)
{
_dtRow[objReader.GetName(i)] = objReader[objReader.GetName(i)];
}
_dtResult.Rows.Add(_dtRow);
}
_dsResult.Tables.Add(_dtResult);
}
_dc.Dispose();
_dtRow = null;
_dtResult.Dispose();
return _dsResult.GetXML();
}

Sideways Sliding DIV (Animated Sideways Sliding Panel in Javascript)

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Last week I was in need of a DIV that could slide sideways. My search on the internet led me to an useful article on up and down sliding DIV by Harry Maugans. But I could not find a sideways sliding DIV that could be readily used. So I decided to write my own. The JS code is listed below.

Start out by placing a hyperlink and a DIV on your web page, as shown below.

Next, place the following javascript code within the head tag of your web page. Just remember to remove all the BR tags from the JS code below :)

And of course don't forget to initialize the the DIV on page onload event by calling the Init function.

Auto Incrementing Primary Key in ORACLE

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You will have to do the following in order to achieve an auto incrementing primary key in oracle. First, create a table with a primary key.

CREATE TABLE OwnerSchema.Users
(
UserId NUMBER NOT NULL,
UserName VARCHAR(30) NOT NULL
)
LOGGING
NOCOMPRESS
NOCACHE
NOPARALLEL
NOMONITORING;

COMMIT;

ALTER TABLE OwnerSchema.Users ADD (
CONSTRAINT Users_PK
PRIMARY KEY
(UserId));

COMMIT;

Then create a sequence, this will be used to read the primary key values from.

CREATE SEQUENCE Users_Seq
START WITH 1
INCREMENT BY 1
NOMAXVALUE;

COMMIT;

Finally, create a trigger to auto increment the primary key using the sequence.

CREATE TRIGGER OwnerSchema.Users_Trigger
BEFORE INSERT ON OwnerSchema.USERS FOR EACH ROW
BEGIN
SELECT Users_Seq.NEXTVAL INTO :NEW.UserId FROM Dual;
END;