Task: Chat server




Go: package main

import (
	"bufio"
	"flag"
	"fmt"
	"log"
	"net"
	"strings"
	"time"
)

func main() {
	log.SetPrefix("chat: ")
	addr := flag.String("addr", "localhost:4000", "listen address")
	flag.Parse()
	log.Fatal(ListenAndServe(*addr))
}


type Server struct {
	add  chan *conn  
	rem  chan string 
	msg  chan string 
	stop chan bool   
}



func ListenAndServe(addr string) error {
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		return err
	}
	log.Println("Listening for connections on", addr)
	defer ln.Close()
	s := &Server{
		add:  make(chan *conn),
		rem:  make(chan string),
		msg:  make(chan string),
		stop: make(chan bool),
	}
	go s.handleConns()
	for {
		
		
		rwc, err := ln.Accept()
		if err != nil {
			
			
			close(s.stop)
			return err
		}
		log.Println("New connection from", rwc.RemoteAddr())
		go newConn(s, rwc).welcome()
	}
}



func (s *Server) handleConns() {
	
	
	
	
	
	conns := make(map[string]*conn)

	var dropConn func(string)
	writeAll := func(str string) {
		log.Printf("Broadcast: %q", str)
		
		for name, c := range conns {
			c.SetWriteDeadline(time.Now().Add(500 * time.Millisecond))
			_, err := c.Write([]byte(str))
			if err != nil {
				log.Printf("Error writing to %q: %v", name, err)
				c.Close()
				delete(conns, name)
				
				
				defer dropConn(name)
			}
		}
	}

	dropConn = func(name string) {
		if c, ok := conns[name]; ok {
			log.Printf("Closing connection with %q from %v",
				name, c.RemoteAddr())
			c.Close()
			delete(conns, name)
		} else {
			log.Printf("Dropped connection with %q", name)
		}
		str := fmt.Sprintf("--- %q disconnected ---\n", name)
		writeAll(str)
	}

	defer func() {
		writeAll("Server stopping!\n")
		for _, c := range conns {
			c.Close()
		}
	}()

	for {
		select {
		case c := <-s.add:
			if _, exists := conns[c.name]; exists {
				fmt.Fprintf(c, "Name %q is not available\n", c.name)
				go c.welcome()
				continue
			}
			str := fmt.Sprintf("+++ %q connected +++\n", c.name)
			writeAll(str)
			conns[c.name] = c
			go c.readloop()
		case str := <-s.msg:
			writeAll(str)
		case name := <-s.rem:
			dropConn(name)
		case <-s.stop:
			return
		}
	}
}





type conn struct {
	*bufio.Reader         
	net.Conn              
	server        *Server 
	name          string
}

func newConn(s *Server, rwc net.Conn) *conn {
	return &conn{
		Reader: bufio.NewReader(rwc),
		Conn:   rwc,
		server: s,
	}
}



func (c *conn) welcome() {
	var err error
	for c.name = ""; c.name == ""; {
		fmt.Fprint(c, "Enter your name: ")
		c.name, err = c.ReadString('\n')
		if err != nil {
			log.Printf("Reading name from %v: %v", c.RemoteAddr(), err)
			c.Close()
			return
		}
		c.name = strings.TrimSpace(c.name)
	}
	
	
	c.server.add <- c
}






func (c *conn) readloop() {
	for {
		msg, err := c.ReadString('\n')
		if err != nil {
			break
		}
		
		c.server.msg <- c.name + "> " + msg
	}
	c.server.rem <- c.name
}








Ada: with Ada.Containers.Vectors;
with Ada.Command_Line; use Ada.Command_Line;
with Ada.Exceptions;   use Ada.Exceptions;
with Ada.Text_IO;      use Ada.Text_IO;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Sockets;          use Sockets;

procedure Chat_Server is

   package Client_Vectors is new Ada.Containers.Vectors
     (Element_Type => Socket_FD, Index_Type => Positive);
   All_Clients : Client_Vectors.Vector;

   procedure Write (S : String) is
      procedure Output (Position : Client_Vectors.Cursor) is
         Sock : Socket_FD := Client_Vectors.Element (Position);
      begin
         Put_Line (Sock, S);
      end Output;
   begin
      All_Clients.Iterate (Output'Access);
   end Write;

   task type Client_Task is
      entry Start (FD : Socket_FD);
   end Client_Task;

   task body Client_Task is
      Sock    : Socket_FD;
      Sock_ID : Positive;
      Name    : Unbounded_String;
   begin
      select
         accept Start (FD : Socket_FD) do
            Sock := FD;
         end Start;
      or
         terminate;
      end select;

      while Name = Null_Unbounded_String loop
         Put (Sock, "Enter Name:");
         Name := To_Unbounded_String (Get_Line (Sock));
      end loop;
      Write (To_String (Name) & " joined.");
      All_Clients.Append (Sock);
      Sock_ID := All_Clients.Find_Index (Sock);
      loop
         declare
            Input : String := Get_Line (Sock);
         begin
            Write (To_String (Name) & ": " & Input);
         end;
      end loop;
   exception
      when Connection_Closed =>
         Put_Line ("Connection closed");
         Shutdown (Sock, Both);
         All_Clients.Delete (Sock_ID);
         Write (To_String (Name) & " left.");
   end Client_Task;

   Accepting_Socket : Socket_FD;
   Incoming_Socket  : Socket_FD;

   type Client_Access is access Client_Task;
   Dummy : Client_Access;
begin
   if Argument_Count /= 1 then
      Raise_Exception (Constraint_Error'Identity,
                       "Usage: " & Command_Name & " port");
   end if;
   Socket (Accepting_Socket, PF_INET, SOCK_STREAM);
   Setsockopt (Accepting_Socket, SOL_SOCKET, SO_REUSEADDR, 1);
   Bind (Accepting_Socket, Positive'Value (Argument (1)));
   Listen (Accepting_Socket);
   loop
      Put_Line ("Waiting for new connection");
      Accept_Socket (Accepting_Socket, Incoming_Socket);
      Put_Line ("New connection acknowledged");

      Dummy := new Client_Task;
      Dummy.Start (Incoming_Socket);
   end loop;
end Chat_Server;