Most chat programs are text based, and do not support multi languages. In this article, I would like to share with the reader, the techniques I used to implement multilingual support and picture/media transfer in a chat program.
A stream is a continuous flow of bytes. For a chat server and a chat client to communicate over the network, each would read and write to the network stream. The network stream is duplex, and bytes transmitted and read are always in FIFO order.
When a chat client is connected to a chat server, they would have established a common network stream to use.
However, for any meaningful communication, there must be some rules and order. These rules and order would be known as the communication protocols. There are at least a few layers of protocols.
At the lowest level, the communicating parties would need to know how to break a continuous flow of bytes into packets/frames. These rules would be referred to as the Network Protocol.
At the next level, the parties would need to interpret the packets/frames. These rules would be known as the Application Protocol(s).
I would like to make a distinction between a text stream and a binary stream. In a text stream, only text characters are allowed. In a binary stream, all byte values (0x00 - 0xFF) are allowed.
One way to set markers in a text stream is to use a non-text byte as a marker. For example, the traditional C string is terminated by 0x00, which serves as an end marker.
For a binary stream, there is no way to set a marker because all byte values are legal. Thus, one way to break a binary stream to packets is for the parties to communicate to one another about the size of the binary bytes to follow, before actually sending the bytes.
In ChatStream.cs, the ChatStream class is implemented with methods for reading and writing text data (Read() and Write()), and also methods for reading and writing binary data (ReadBinary() and WriteBinary()).
Note that in the Write() method, we set a 0x03 as the marker, and Read() will read until the marker is encountered. For the WriteBinary() method, no marker is set, and ReadBinary() requires an input parameter to indicate the number of bytes to read.
public class ChatStream:IChatStream
{
//..
public string Read(NetworkStream n)
{
//maximum buffer size is 256 double byte character
byte[] bytes=new byte[512];
//total number of bytes read
int totalbytes=0;
while(true){
//reading 2 byte at a time
int i=n.Read(bytes,totalbytes,2);
//small endian first byte is lsb
if(i==2)
{
//the special end byte if found
if(bytes[totalbytes]==(byte)0x03)
if(bytes[totalbytes+1]==(byte)0x00)
break;
}
else
{
//end of stream
return "";
}
//advance to the next position to store read byte(s)
totalbytes +=i;
}
//convert the bytes to a unicode string and return
UnicodeEncoding Unicode = new UnicodeEncoding();
int charCount = Unicode.GetCharCount(bytes, 0, totalbytes);
char[] chars = new Char[charCount];
Unicode.GetChars(bytes, 0, totalbytes, chars, 0);
string s=new string(chars);
return s;
}
public void Write(NetworkStream n,string s)
{
//Append char 0x03 to end of text string
s=s+new string((char)0x03,1);
//byte[] bytes=System.Text.Encoding.ASCII.GetBytes(s);
UnicodeEncoding Unicode = new UnicodeEncoding();
byte[] bytes=Unicode.GetBytes(s);
n.Write(bytes,0,bytes.Length );
n.Flush();
}
public byte[] ReadBinary(NetworkStream n,int numbytes)
{
//total bytes read
int totalbytes=0;
byte[] readbytes=new byte[numbytes];
while(totalbytes<numbytes)
{
//read as much as possible
int i=n.Read(readbytes,totalbytes,numbytes-totalbytes);
//End of stream
if(i==0)
return null;
//advence to the next position to store read byte(s)
totalbytes +=i;
}
return readbytes;
}
public void WriteBinary(NetworkStream n,byte[] b)
{
n.Write(b,0,b.Length);
n.Flush();
}
}
The traditional C string is a single-byte character string. It is adequate for representing all ASCII characters. However, for languages where the character set has more than 256 characters, a single-byte character representation is no longer adequate.
In .NET as in VB, strings are all internally double-byte.
To manipulate the double-byte characters in the String class, we can make use of the UnicodeEncoding class.
This code fragment shows how to extract out all the double-byte bytes from a string:
UnicodeEncoding Unicode = new UnicodeEncoding();
byte[] bytes=Unicode.GetBytes(s);
Similarly, to construct a Unicode string from a byte array:
UnicodeEncoding Unicode = new UnicodeEncoding();
int charCount = Unicode.GetCharCount(bytes, 0, totalbytes);
char[] chars = new Char[charCount];
Unicode.GetChars(bytes, 0, totalbytes, chars, 0);
string s=new string(chars);
Although the TextBox and RichTextBox controls in .NET support Unicode, a Unicode supported font is needed for display of Unicode characters, and an appropriate IME (Input Method Editor) is needed for Unicode input.
For this program, I make use of Arial Unicode MS which comes with Windows XP.
If you ever use a binary editor to view a picture file (JPG or BMP), you will know that all byte values are possible in a picture file. To transfer picture binary data from a file or memory stream, we would not be able to set a marker to break the stream as what we can do for text data.
For this program:
The protocol for sending a picture is as follows:
ChatStream ReadBinay method to get the binary data, and then saves the data to a file marked with the sender and target names. The protocol for getting a picture is as follows:
ChatStream ReadBinary method to get the binary data and display the image in the RichTextBox. The server code for acting on the send_pic and get_pic commands from the client:
//SEND PIC
private void action_send_pic()
{
string[] s=readdata.Split(':');
string name="";
//format is
//:send pic:<target>
if (s.Length==3)name=s[2];
//Locate the target
TcpClient t=null;
if (chatserver.FindUserRoom(name)!=0)
t=(TcpClient)chatserver.ClientConnections[name.ToUpper()];
//If target is found
if((t!=null))
{
//Inform the sender(client) to send the picture
chatserver.Write(client.GetStream(),
ChatProtocolValues.SEND_PIC_MSG);
//Find out the number of byte to read from sender
string snumbytes=chatserver.Read(client.GetStream());
int numbytes=int.Parse(snumbytes);
//read the bytes
byte[] b=chatserver.ReadBinary(client.GetStream(),numbytes);
if (b==null)
{
chatserver.Write(client.GetStream(),
"server> Transmission Error");
return;
}
//To store the data in a jpg file
//name convention is <sender>_<target>.jpg
FileStream f=new FileStream(nickname+"_"+name+".jpg",FileMode.Create);
f.Write(b,0,b.Length);
f.Close();
//Inform the target that there is a picture from sender
chatserver.Write (t.GetStream(),
ChatProtocolValues.PIC_FROM_MSG(nickname,name));
//Inform the sender that server had received the picture
chatserver.Write(client.GetStream(),
ChatProtocolValues.PIC_SEND_MSG(nickname));
}
else
{
//If target is not found inform sender
chatserver.Write(client.GetStream(),
ChatProtocolValues.USER_NOT_FOUND_MSG(name));
}
}
//GET PIC
private void action_get_pic()
{
string[] s=readdata.Split(':');
string sender="";
string picname="";
//format is
//:get pic:<sender>
if(s.Length==3)sender=s[2];
//format of saved jpg file is
//<sender>_<target>.jpg
//In this case the current user is the target
picname=sender + "_" + nickname + ".jpg";
//Check for existence of file
if(!File.Exists(picname))
chatserver.Write(client.GetStream(),
ChatProtocolValues.PIC_NOT_FOUND_MSG(picname));
else
{
//Create a file stream
FileStream f=new FileStream(picname,FileMode.Open);
//To get the size of the file for purpose of memory allocation
FileInfo fi=new FileInfo(picname);
byte[] b=new byte[fi.Length];
//Read the content of the file and close
f.Read(b,0,b.Length);
f.Close();
//Inform the client to get the pic
chatserver.Write (client.GetStream(),
ChatProtocolValues.GET_PIC_MSG);
//Inform the client of number of bytes
chatserver.Write(client.GetStream(),""+b.Length);
//Send the binary data
chatserver.WriteBinary(client.GetStream(),b);
//Inform the client that all binary data has been send
chatserver.Write(client.GetStream(),
ChatProtocolValues.PIC_SEND_ACK_MSG);
//Locate the sender of the picture
TcpClient t=null;
if (chatserver.FindUserRoom(sender)!=0)
t=(TcpClient)chatserver.ClientConnections[sender.ToUpper()];
//Inform the sender that the target has gotten the picture
if(t!=null)
chatserver.Write(t.GetStream(),
ChatProtocolValues.GOTTEN_PIC_MSG(nickname));
}
}
The client responses to the server's messages:
//SEND PIC
//Sending picture to the server
private void action_server_send_pic()
{
//Console.WriteLine("server> send pic");
//Save the picture box image to the memory
MemoryStream ms=new MemoryStream();
pic.Image.Save(ms,ImageFormat.Jpeg);
//Get the memory buffer
byte[] buf=ms.GetBuffer();
ms.Close();
Write("" + buf.Length);
//Thread.Sleep(500);
WriteBinary(buf);
Console.WriteLine("Send: {0} bytes", buf.Length);
}
//GET PIC
//Geting picture from server
private void action_server_get_pic()
{
string snumbytes=Read();
int numbytes=int.Parse(snumbytes);
//int numbytes=0;
byte[] readbytes=ReadBinary(numbytes);
if(readbytes==null)
{
Console.WriteLine("Error getting picture");
responseData="server> Error getting picture";
action_message();
return;
}
//Create the image from memory
MemoryStream ms=new MemoryStream(readbytes);
Image img=Image.FromStream(ms);
ms.Close();
//Paste picture to the rich text box
PastePictureToRTB(img);
}
The protocol for transferring media clips is very similar to that for picture transfer. The main difference is that unlike a picture which is basically copied from a picture box in the UI and saved to a file with a fixed jpg extension, the media clips are just files that are tagged and stored by the program, and can have various different extensions. The extension for these files has to be maintained as the media player relies on the extension to play the files.
When sending the binary data of a media clip to the server, the extension of the clip must be conveyed. And when the receiver retrieves the binary data from the server, the extension must also be made known so that the media clip file can be recreated with the correct extension.
To resolve this problem, there is a slight change in the protocol. When sending media clip data to the server, the sender first sends a three-character extension, followed by the number of bytes of binary data, and then finally, the binary data. The server first reads the extension, saves the extension to a file named <sender>_<target> (without the extension), and then saves the binary data to a file named <sender>_<target>.<ext>.
private void action_server_send_media()
{
//To store the data in a media file
//name convention is <sender>_<target>.ext
if(shp1.Text.Equals("Empty")){
Write(""+0);
return;
}
String ext=shp1.Text.Substring(shp1.Text.Length-3);
Write(ext);
FileInfo fi=new FileInfo(_currentpath +"\\"+nickname+"."+ext);
FileStream f=new FileStream(_currentpath +"\\"+nickname+"."+ext,
FileMode.Open);
byte[] b=new byte[fi.Length];
f.Read(b,0,b.Length);
f.Close();
Write("" + b.Length);
//Thread.Sleep(500);
WriteBinary(b);
//Console.WriteLine("Send: {0} bytes", b.Length);
}
Similarly, when the receiver retrieves the media clip, the server first locates the file that stores the extension, retrieves the extension, and the retrieves the file <sender>_<target>.<ext>, and then sends the extension followed by the media clip binary data to the receiver.
private void action_server_get_media()
{
string ext=Read();
string snumbytes=Read();
int numbytes=int.Parse(snumbytes);
//int numbytes=0;
byte[] readbytes=ReadBinary(numbytes);
if(readbytes==null)
{
//Console.WriteLine("Error getting picture");
responseData="server> Error getting picture";
action_message();
return;
}
FileStream f=new FileStream(_currentpath +
"\\"+nickname+"_received."+ext,
FileMode.Create);
f.Write(readbytes,0,numbytes);
f.Close();
// shpR.Text=""+(numbytes/1000)+"KB";
rtb.SelectionStart=rtb.Text.Length;
_media_id++;
string c_currentpath=_currentpath.Replace(" ","@");
rtb.SelectedText="\nfile:///" + c_currentpath +
"\\"+nickname+"_received" +
_media_id+"."+ext;
File.Copy(_currentpath +"\\"+nickname+"_received."+ext,
_currentpath +"\\"+nickname+"_received" +
_media_id+"."+ext,true);
}
To play the media clip, the system must have the media player installed. The chat client locates the media player from the Windows registry and sends the clip to be played by the media player.
public class WinMediaPlayer
{
public static string GetMediaPlayerDirectory()
{
try
{
Microsoft.Win32.RegistryKey localmachineregkey=
Microsoft.Win32.Registry.LocalMachine;
Microsoft.Win32.RegistryKey mediaplayerkey=
localmachineregkey.OpenSubKey(@"SOFTWARE\Microsoft\MediaPlayer");
return (string)mediaplayerkey.GetValue("Installation Directory");
}
catch
{
return "";
}
}
public static void Play(IntPtr hwnd,string strFileName)
{
if(!ChatClient.MediaPlayerDirectory.Equals(""))
Helpers.ShellExecute(hwnd,"open","wmplayer",
"\""+strFileName+"\"",ChatClient.MediaPlayerDirectory ,
Helpers.SW_NORMAL);
}
}
The server program starts by creating the requested number of chat rooms, and reads out the users by deserializing the users.bin file. Then, it continues to listen for connections. Once a connection is established, it sprouts a new SocketHelper object to manage the communication with the connected client.
public class ChatServer:ChatStream,IChatServer
{
//...
//2 parameters Constructor
public ChatServer(int port_no,int num_room)
{
this.port_no =port_no;
this.num_room=num_room;
//init num per room used for room assignment
num_per_room=DEFAULT_NUM_PER_ROOM;
//instantiate the connection listener
listener=new TcpListener(IPAddress.Any,this.port_no);
//get all the registered users from file
DeserializeChatUsers("users.bin");
//init all the rooms
roomusers=new Hashtable[num_room];
for(int i=0;i<num_room;i++)
roomusers[i]=new Hashtable();
//init connections
connections=new Hashtable();
//start listening for connection
Listener.Start();
//Loop forever
//The only way to break is to use clt break key
while(true)
{
Console.WriteLine("Waiting for connection...");
//get the connected client
TcpClient client=Listener.AcceptTcpClient();
//create a new socket helper to manage the connection
SocketHelper sh=new SocketHelper(this,client);
Console.WriteLine("Connected");
}
}
}
To run the server:
chatserver <port_number> <num_room>
E.g.: chatserver 1300 10 uses port 1300, and creates 10 chat rooms.
The client program starts by connecting to the server. It then attempts to perform authentication. If successful, a thread is started to listen for the server's messages. A form is then loaded to show the UI and handle user's interaction.
public ChatClient(string _host,int _port)
{
_currentpath=Path.GetDirectoryName(
Assembly.GetExecutingAssembly().GetModules()[0].FullyQualifiedName);
//store the host string
host =_host;
//store the port number
port=_port;
//Get the connection
try
{
tcpc=Connect(host,port);
stream=tcpc.GetStream();
Stream=stream;
}
catch//(Exception e)
{
//Console.WriteLine(e);
Environment.Exit(0);
}
//Initialize the GUI
init_components();
//Start Listening
tl=new Thread(new ThreadStart(Listen));
tl.Start();
}
To run the client program:
chatclient <server_name> <port_no>
E.g.: chatserver localhost 1300.
The user can either key in commands at the textbox, or use the menu system. The code below shows the implementation of the menu system:
private void init_components()
{
//shpE1=new ShapeControl.ShapeControl();
//font
cfont=new Font("Arial",14);
//form
//form=new Form();
this.Text="Client ISS Chat";
this.ClientSize = new System.Drawing.Size(400,570);
//this.FormBorderStyle=FormBorderStyle.FixedSingle;
this.WindowState=FormWindowState.Minimized;
this.TopMost=true;
//shp1 holds the reference to the media file that is loaded
shp1=new ShapeControl.ShapeControl();
this.Controls.Add(shp1);
shp1.BackColor = System.Drawing.Color.FromArgb(((System.Byte)(124)),
((System.Byte)(92)), ((System.Byte)(159)),
((System.Byte)(83)));
shp1.BorderColor = System.Drawing.Color.FromArgb(((System.Byte)(177)),
((System.Byte)(131)), ((System.Byte)(255)),
((System.Byte)(4)));
shp1.BorderStyle = System.Drawing.Drawing2D.DashStyle.Solid;
shp1.BorderWidth = 3;
shp1.CenterColor = System.Drawing.Color.FromArgb(((System.Byte)(255)),
((System.Byte)(0)), ((System.Byte)(0)));
shp1.Font = new System.Drawing.Font("Arial", 8F,
System.Drawing.FontStyle.Bold);
shp1.Location = new Point(5,495);
shp1.Shape = ShapeControl.ShapeType.RoundedRectangle;
shp1.Size = new System.Drawing.Size(150, 35);
shp1.SurroundColor = System.Drawing.Color.FromArgb(((System.Byte)(0)),
((System.Byte)(0)), ((System.Byte)(255)));
shp1.Text = "Empty";
shp1.UseGradient = false;
//context menu for shp1
contextmenu_shp1=new ContextMenu();
contextmenu_shp1.MenuItems.Add(new
MenuItem("Load Media File",new EventHandler(LoadMedia)));
contextmenu_shp1.MenuItems.Add(new MenuItem("Play Media File",
new EventHandler(PlayMediaFile)));
shp1.ContextMenu=contextmenu_shp1;
//rtb
rtb=new RichTextBox();
//rtb.Controls.Add(shpE1);
this.Controls.Add(rtb);
rtb.DetectUrls=true;
rtb.LinkClicked+=new LinkClickedEventHandler(rtb_LinkClicked);
rtb.Top=0;
rtb.Left=0;
rtb.Width=400;
rtb.Height=400;
rtb.BackColor=Color.LightBlue;
rtb.Font=new Font("Arial Unicode MS",10,FontStyle.Bold);
rtb.ReadOnly=true;
rtb.TabStop=false;
//checkbox
checkbox=new CheckBox();
this.Controls.Add(checkbox);
checkbox.Text="Auto Retrieve Picture/Media";
checkbox.Size=new Size(200,15);
checkbox.Checked=true;
checkbox.Location=new Point(5,405);
checkbox.TabStop=false;
//button
button=new Button();
this.Controls.Add(button);
button.Text="Clear Messages";
button.Size= new Size(120,20);
button.Location=new Point(275,400);
button.TabStop=false;
//contextMenu for picture box
contextmenu=new ContextMenu();
MenuItem menuItem1 =
new MenuItem("Clear Picture Box",
new EventHandler(ClearPicture));
MenuItem menuItem2 =
new MenuItem("Load Picture(s)",
new EventHandler(LoadPictureFile));
contextmenu.MenuItems.Add(menuItem1);
contextmenu.MenuItems.Add(menuItem2);
//pic
pic=new PictureBox();
this.Controls.Add(pic);
pic.BackColor = Color.White;
pic.Location = new Point(5, 425);
pic.Size = new Size(390, 60);
pic.BorderStyle=BorderStyle.FixedSingle;
pic.Image=new Bitmap(390,60,PixelFormat.Format32bppArgb);
pic.ContextMenu=contextmenu;
pic.TabStop=false;
//textbox
textbox=new TextBox();
this.Controls.Add(textbox);
textbox.Location=new System.Drawing.Point(5, 540);
textbox.Size=new Size(390,18);
textbox.MaxLength=240;
textbox.TabIndex=0;
textbox.TabStop=true;
textbox.Font=new Font("Arial Unicode MS",12);
// Create an empty MainMenu.
MainMenu mainMenu1 = new MainMenu();
MenuItem mItem1 = new MenuItem("&Command");
mItem1.Popup +=new EventHandler(CommandPopUp);
p_smItem5=new MenuItem(":send pic:");
p_smItem6=new MenuItem(":get pic:");
p_smItem7=new MenuItem(":private:");
p_smItemS1=new MenuItem(":send media:");
p_smItemS2=new MenuItem(":get media:");
mItem1.MenuItems.Add(new MenuItem(":help",
new EventHandler(Commands)));
mItem1.MenuItems.Add(new MenuItem(":list all",
new EventHandler(Commands)));
mItem1.MenuItems.Add(new MenuItem(":change room",
new EventHandler(Commands)));
mItem1.MenuItems.Add(new MenuItem(":which room",
new EventHandler(Commands)));
mItem1.MenuItems.Add(p_smItemS1);
mItem1.MenuItems.Add(p_smItemS2);
mItem1.MenuItems.Add(p_smItem5);
mItem1.MenuItems.Add(p_smItem6);
mItem1.MenuItems.Add(p_smItem7);
mItem1.MenuItems.Add(new MenuItem(":quit",
new EventHandler(Commands)));
MenuItem mItem2 = new MenuItem("&Picture");
mItem2.MenuItems.Add(new MenuItem("Clear Picture",
new EventHandler(ClearPicture)));
mItem2.MenuItems.Add(new MenuItem("Load Picture(s)",
new EventHandler(LoadPictureFile)));
MenuItem mItem3=new MenuItem("&Media");
mItem3.MenuItems.Add(new MenuItem("Load Media File",
new EventHandler(LoadMedia)));
mItem3.MenuItems.Add(new MenuItem("Play Media File",
new EventHandler(PlayMediaFile)));
// Add two MenuItem objects to the MainMenu.
mainMenu1.MenuItems.Add(mItem1);
mainMenu1.MenuItems.Add(mItem2);
mainMenu1.MenuItems.Add(mItem3);
// Bind the MainMenu to Form1.
this.Menu = mainMenu1;
//events
this.SizeChanged +=new EventHandler(textbox_SizeChanged);
textbox.KeyPress += new KeyPressEventHandler(textbox_KeyPressed);
pic.MouseMove += new MouseEventHandler(this.pic_MouseMove);
pic.MouseDown += new MouseEventHandler(this.pic_MouseDown);
this.Activated +=new EventHandler(form_Activated);
this.Closing +=new CancelEventHandler(form_Closing);
rtb.TextChanged +=new EventHandler(rtb_TextChanged);
button.Click +=new EventHandler(button_Click);
memberColor=new Hashtable();
}
private void CommandPopUp(object sender,System.EventArgs e)
{
pause_listening=true;
Thread.Sleep(0);
responseData="";
Write(":list all");
//if no data had been read after the write
//attempt to read
if(responseData==""){
responseData=Read();
}
string[] s=responseData.Split('\n');
ArrayList arrlist=new ArrayList();
foreach(string s1 in s)
if(s1.Trim()!="")
{
string[] s2=s1.Trim().Split(':');
if ((s2.Length==2)&& (s2[0].IndexOf("server>")<0))
arrlist.Add(s2[0].Trim());
}
p_smItemS1.MenuItems.Clear();
p_smItemS2.MenuItems.Clear();
p_smItem5.MenuItems.Clear();
p_smItem6.MenuItems.Clear();
p_smItem7.MenuItems.Clear();
foreach(string name in arrlist)
{
p_smItemS2.MenuItems.Add(new MenuItem(name,
new EventHandler(Param1Command)));
if(!shp1.Text.Equals("Empty"))
p_smItemS1.MenuItems.Add(new MenuItem(name,
new EventHandler(Param1Command)));
p_smItem5.MenuItems.Add(new MenuItem(name,
new EventHandler(Param1Command)));
p_smItem6.MenuItems.Add(new MenuItem(name,
new EventHandler(Param1Command)));
p_smItem7.MenuItems.Add(new MenuItem(name+":",
new EventHandler(Param1Command)));
}
responseData="";
pause_listening=false;
Thread.Sleep(0);
}
private void Param1Command(object sender,System.EventArgs e)
{
string p=((MenuItem)((MenuItem)sender).Parent).Text.Trim();
string s=((MenuItem)sender).Text.Trim();
if (p.ToUpper()==":PRIVATE:")
{
textbox.Text=p+s+"<Key in Message>";
textbox.SelectionStart=textbox.Text.Length-16;
textbox.SelectionLength=16;
}
else
Write(p+s);
}
I hope that the readers will benefit from this article and its associated code. I would welcome any comments and contributions.
Happy picture chatting.
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