Task: Chat server

C: #include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <netinet/ip.h>

int tsocket;
struct sockaddr_in tsockinfo;
fd_set status, current;
void ClientText(int handle, char *buf, int buf_len);

struct client
{
    char buffer[4096];
    int pos;
    char name[32];
} *connections[FD_SETSIZE];

void AddConnection(int handle)
{
    connections[handle] = malloc(sizeof(struct client));
    connections[handle]->buffer[0] = '\0';
    connections[handle]->pos = 0;
    connections[handle]->name[0] = '\0';
}

void CloseConnection(int handle)
{
    char buf[512];
    int j;

    FD_CLR(handle, &status);
    
    if (connections[handle]->name[0])
    {
        sprintf(buf, "* Disconnected: %s\r\n", connections[handle]->name);

        for (j = 0; j < FD_SETSIZE; j++)
        {
            if (handle != j && j != tsocket && FD_ISSET(j, &status))
            {
                if (write(j, buf, strlen(buf)) < 0)
                {
                    CloseConnection(j);
                }
            }
        }
    } else
    {
        printf ("-- Connection %d disconnected\n", handle);
    }
    if (connections[handle])
    {
        free(connections[handle]);
    }
    close(handle);
}

void strip(char *buf)
{
    char *x;
    
    x = strchr(buf, '\n');
    if (x) { *x='\0'; }
    x = strchr(buf, '\r');
    if (x) { *x='\0'; }
}

int RelayText(int handle)
{
    char *begin, *end;
    int ret = 0;
    begin = connections[handle]->buffer;
    if (connections[handle]->pos == 4000)
    {
        if (begin[3999] != '\n')
            begin[4000] = '\0';
        else {
            begin[4000] = '\n';
            begin[4001] = '\0';
        }
    } else {
        begin[connections[handle]->pos] = '\0';
    }
    
    end = strchr(begin, '\n');
    while (end != NULL)
    {
        char output[8000];
        output[0] = '\0';
        if (!connections[handle]->name[0])
        {
            strncpy(connections[handle]->name, begin, 31);
            connections[handle]->name[31] = '\0';
            
            strip(connections[handle]->name);
            sprintf(output, "* Connected: %s\r\n", connections[handle]->name);
            ret = 1;
        } else 
        {
            sprintf(output, "%s: %.*s\r\n", connections[handle]->name, 
                    end-begin, begin);
            ret = 1;
        }
        
        if (output[0])
        {
            int j;
            for (j = 0; j < FD_SETSIZE; j++)
            {
                if (handle != j && j != tsocket && FD_ISSET(j, &status))
                {
                    if (write(j, output, strlen(output)) < 0)
                    {
                        CloseConnection(j);
                    }
                }
            }
        }
        begin = end+1;
        end = strchr(begin, '\n');
    }
    
    strcpy(connections[handle]->buffer, begin);
    connections[handle]->pos -= begin - connections[handle]->buffer;
    return ret;
}

void ClientText(int handle, char *buf, int buf_len)
{
    int i, j;
    if (!connections[handle])
        return;
    j = connections[handle]->pos; 
    
    for (i = 0; i < buf_len; ++i, ++j)
    {
        connections[handle]->buffer[j] = buf[i];
        
        if (j == 4000)
        {
            while (RelayText(handle));
            j = connections[handle]->pos;
        }
    }
    connections[handle]->pos = j;
    
    while (RelayText(handle));
}


int ChatLoop()
{
    int i, j;
    FD_ZERO(&status);

    FD_SET(tsocket, &status);
    FD_SET(0, &status);

    while(1)
    {
        current = status;
        if (select(FD_SETSIZE, &current, NULL, NULL, NULL)==-1)
        {
            perror("Select");
            return 0;
        }
        for (i = 0; i < FD_SETSIZE; ++i)
        {
            if (FD_ISSET(i, &current))
            {
                if (i == tsocket)
                {
                    struct sockaddr_in cliinfo;
                    socklen_t addrlen = sizeof(cliinfo);
                    int handle;
                    handle = accept(tsocket, &cliinfo, &addrlen);
                    if (handle == -1)
                    {
                        perror ("Couldn't accept connection");
                    } else if (handle > FD_SETSIZE)
                    {
                        printf ("Unable to accept new connection.\n");
                        close(handle);
                    }
                    else
                    {
                        if (write(handle, "Enter name: ", 12) >= 0)
                        {
                            printf("-- New connection %d from %s:%hu\n",
                                handle, 
                                inet_ntoa (cliinfo.sin_addr),
                                ntohs(cliinfo.sin_port));
                            FD_SET(handle, &status);

                            AddConnection(handle);
                        }
                    }
                } 
                else
                {
                    char buf[512];
                    int b;

                    b = read(i, buf, 500);
                    if (b <= 0)
                    {
                        CloseConnection(i);
                    }
                    else
                    {
                        ClientText(i, buf, b);
                    }
                }
            }
        }
    } 
}

int main (int argc, char*argv[])
{
    tsocket = socket(PF_INET, SOCK_STREAM, 0);

    tsockinfo.sin_family = AF_INET;
    tsockinfo.sin_port = htons(7070);
    if (argc > 1)
    {
        tsockinfo.sin_port = htons(atoi(argv[1]));
    }
    tsockinfo.sin_addr.s_addr = htonl(INADDR_ANY);
    printf ("Socket %d on port %hu\n", tsocket, ntohs(tsockinfo.sin_port));

    if (bind(tsocket, &tsockinfo, sizeof(tsockinfo)) == -1)
    {
        perror("Couldn't bind socket");
        return -1;
    }

    if (listen(tsocket, 10) == -1)
    {
        perror("Couldn't listen to port");
    }

    ChatLoop();

    return 0;
}





Java: import java.io.*;
import java.net.*;
import java.util.*;

public class ChatServer implements Runnable
{
  private int port = 0;
  private List<Client> clients = new ArrayList<Client>();
  
  public ChatServer(int port)
  {  this.port = port;  }
  
  public void run()
  {
    try
    {
      ServerSocket ss = new ServerSocket(port);
      while (true)
      {
        Socket s = ss.accept();
        new Thread(new Client(s)).start();
      }
    }
    catch (Exception e)
    {  e.printStackTrace();  }
  }

  private synchronized boolean registerClient(Client client)
  {
    for (Client otherClient : clients)
      if (otherClient.clientName.equalsIgnoreCase(client.clientName))
        return false;
    clients.add(client);
    return true;
  }

  private void deregisterClient(Client client)
  {
    boolean wasRegistered = false;
    synchronized (this)
    {  wasRegistered = clients.remove(client);  }
    if (wasRegistered)
      broadcast(client, "--- " + client.clientName + " left ---");
  }
  
  private synchronized String getOnlineListCSV()
  {
    StringBuilder sb = new StringBuilder();
    sb.append(clients.size()).append(" user(s) online: ");
    for (int i = 0; i < clients.size(); i++)
      sb.append((i > 0) ? ", " : "").append(clients.get(i).clientName);
    return sb.toString();
  }
  
  private void broadcast(Client fromClient, String msg)
  {
    
    List<Client> clients = null;
    synchronized (this)
    {  clients = new ArrayList<Client>(this.clients);  }
    for (Client client : clients)
    {
      if (client.equals(fromClient))
        continue;
      try
      {  client.write(msg + "\r\n");  }
      catch (Exception e)
      {  }
    }
  }

  public class Client implements Runnable
  {
    private Socket socket = null;
    private Writer output = null;
    private String clientName = null;
    
    public Client(Socket socket)
    {
      this.socket = socket;
    }
    
    public void run()
    {
      try
      {
        socket.setSendBufferSize(16384);
        socket.setTcpNoDelay(true);
        BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        output = new OutputStreamWriter(socket.getOutputStream());
        write("Please enter your name: ");
        String line = null;
        while ((line = input.readLine()) != null)
        {
          if (clientName == null)
          {
            line = line.trim();
            if (line.isEmpty())
            {
              write("A name is required. Please enter your name: ");
              continue;
            }
            clientName = line;
            if (!registerClient(this))
            {
              clientName = null;
              write("Name already registered. Please enter your name: ");
              continue;
            }
            write(getOnlineListCSV() + "\r\n");
            broadcast(this, "+++ " + clientName + " arrived +++");
            continue;
          }
          if (line.equalsIgnoreCase("/quit"))
            return;
          broadcast(this, clientName + "> " + line);
        }
      }
      catch (Exception e)
      {  }
      finally
      {
        deregisterClient(this);
        output = null;
        try
        {  socket.close();  }
        catch (Exception e)
        {  }
        socket = null;
      }
    }
    
    public void write(String msg) throws IOException
    {
      output.write(msg);
      output.flush();
    }
    
    public boolean equals(Client client)
    {
      return (client != null) && (client instanceof Client) && (clientName != null) && (client.clientName != null) && clientName.equals(client.clientName);
    }
  }
  
  public static void main(String[] args)
  {
    int port = 4004;
    if (args.length > 0)
      port = Integer.parseInt(args[0]);
    new ChatServer(port).run();
  }
}