(SOLVED - THANKS FOR HELP)connecting a server socket with several
client sockets
lazarus / 38-Networking and Web Programming

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Nukualofa · 2015-11-24 07:59

Hey,

I want to write a simple Chat using the Sockets unit. I have four
files: Server, ServerThread, Client & ClientThread.
The server creates a socket and waits for clients to connect to it. As
soon as a client connects, a new serverThread is started that manages
the communication with the client.
The client also creates a socket, connects to the server and starts a
clientThread that waits for incoming messages from the corresponding
serverThread.
Everything works fine if I use a different port for each client. But
Google says, the normal way is to have only one port (on the server
side) which can handle several clients. If a second client tries to
connect to the port, there is no SocketError, but it doesn't work
anyway. Apparently the fpaccept-function that waits for a client to
connect isn't reacting to the client's fpconnect-function.

I spent a few days reading everything I found about the topic and
tried almost everything but failed miserably. I would be really glad
if someone could tell me what's wrong with my code. Here it is (sorry,
the "insert code" button seems not to work):



unit Server;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
StdCtrls, Sockets, ServerThread;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  public
    procedure handle(ID, message: String);
  end;

var
  Form1: TForm1;
  threads: Array[1..4] of TServerThread;
  serverSocket: Longint;
  clientSocket: Longint;
  serverAddr: TInetSockAddr;
  opt: Integer = 1;
  addrSize: Longint;
  clientCount: Integer = 0;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
begin
  repeat
    serverSocket:= fpSocket(AF_INET, SOCK_STREAM, 0);
    if fpSetSockOpt(serverSocket, SOL_SOCKET, SO_REUSEADDR, @opt,
sizeOf(opt)) = SOCKET_ERROR then showMessage('Server : Multi : ' +
intToStr(socketError));
    if serverSocket = SOCKET_ERROR then showMessage('Server : Socket :
' + intToStr(socketError));
    serverAddr.sin_family:= AF_INET;
    serverAddr.sin_port:= htons(50000);
    serverAddr.sin_addr.s_addr:= htonl($7F000001);
    if fpBind(serverSocket, @serverAddr, sizeOf(serverAddr)) =
SOCKET_ERROR then showMessage('Server : Bind : ' +
intToStr(socketError));
    if fpListen(serverSocket, 4) = SOCKET_ERROR then
showMessage('Server : Listen : ' + intToStr(socketError));
    showMessage('Waiting for connect from Client...');
    addrSize:= sizeOf(serverAddr);
    clientSocket:= fpaccept(serverSocket, @serverAddr, @addrSize);
    if clientSocket = SOCKET_ERROR then showMessage('Server : Accept :
' + intToStr(socketError)) else clientCount:= clientCount + 1;
    threads[clientCount]:= TServerThread.create(true, clientSocket);
    threads[clientCount].start;
  until clientCount = 4;
end;

procedure TForm1.handle(ID, message: String);
var
  i, toTerminate: Integer;
  MyCriticalSection: TRTLCriticalSection;
begin
  InitCriticalSection(MyCriticalSection);
  EnterCriticalSection(MyCriticalSection);
  try
    for i:= 1 to clientCount do
    begin
      threads.send(ID + ': ' + message);
      if threads.getID = ID then toTerminate:= i;
    end;
    if message = 'ciao' then
    begin
      threads[toTerminate].send('ciao');
      threads[toTerminate].close;
      clientCount:= clientCount - 1;
      for i:= toTerminate to clientCount do threads:= threads[i + 1];
    end;
  finally
    LeaveCriticalSection(MyCriticalSection);
  end;
end;

end.



unit ServerThread;

{$mode objfpc}{$H+}

interface

uses Classes, Dialogs, Sockets, SysUtils;

type
  TServerThread = class(TThread)
  private
    ID: String;
    clientSocket: Longint;
  protected
    procedure execute; override;
  public
    constructor create(createSuspended: Boolean; client: Longint);
    procedure send(msg: String);
    function getID: String;
    procedure close;
  end;

var
  buffer: String[255];
  count: Longint;

implementation

uses Server;

constructor TServerThread.create(createSuspended: Boolean; client:
Longint);
begin
  freeOnTerminate:= true;
  inherited create(createSuspended);
  clientSocket:= client;
end;

procedure TServerThread.execute;
begin
  count:= fprecv(clientSocket, @buffer[1], 255, 0);
  if (count <> SOCKET_ERROR) and (count > 0) then
  begin
    setLength(buffer, count);
    ID:= buffer;
  end;
  buffer:= 'Herzlich willkommen im Chat, ' + ID;
  count:= length(buffer);
  if fpsend(clientSocket, @buffer[1], count, 0) = count then
  begin
    repeat
      count:= fprecv(clientSocket, @buffer[1], 255, 0);
      if (count <> SOCKET_ERROR) and (count > 0) then
      begin
        setLength(buffer, count);
        Form1.handle(ID, buffer);
      end;
    until (count = SOCKET_ERROR) or (count = 0);
  end;
end;

procedure TServerThread.send(msg: String);
begin
  fpsend(clientSocket, @msg[1], length(msg), 0);
end;

function TServerThread.getID: String;
begin
  result:= ID;
end;

procedure TServerThread.close;
begin
  closeSocket(clientSocket);
end;

end.



unit Client;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
StdCtrls, Sockets, ClientThread;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Edit1: TEdit;
    Edit2: TEdit;
    Memo1: TMemo;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Edit1Change(Sender: TObject);
    procedure handle(msg: String);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;
  thread: TClientThread;
  serverAddr: TInetSockAddr;
  serverSocket: Longint;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
begin
  serverSocket:= fpSocket(AF_INET, SOCK_STREAM, 0);
  if serverSocket = SOCKET_ERROR then showMessage('Client : Socket : '
+ intToStr(socketError));
  serverAddr.sin_family:= AF_INET;
  serverAddr.sin_port:= htons(50000);
  serverAddr.sin_addr.s_addr:= htonl($7F000001);
  //funktioniert beim zweiten Client nicht, da kein Error, obwohl die
Verbindung nicht zustande kommt (fpaccept reagiert nicht)
  if fpconnect(serverSocket, @serverAddr, sizeOf(serverAddr)) =
SOCKET_ERROR then showMessage('Client : Connect : ' +
intToStr(socketError));
  thread:= TClientThread.create(true, serverSocket);
  thread.start;
  buffer:= Edit1.Text;
  fpsend(serverSocket, @buffer[1], length(buffer), 0);
  Button2.Enabled:= true;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  buffer: String;
begin
  buffer:= Edit2.Text;
  fpsend(serverSocket, @buffer[1], length(buffer), 0);
end;

procedure TForm1.Edit1Change(Sender: TObject);
begin
  if length(Edit1.Text) > 0 then Button1.Enabled:= true else
Button1.Enabled:= false;
end;

procedure TForm1.handle(msg: String);
begin
  if msg = 'ciao' then closeSocket(serverSocket)
  else Memo1.Lines.Add(msg);
end;

end.



unit ClientThread;

{$mode objfpc}{$H+}

interface

uses Classes, Dialogs, Sockets, SysUtils;

type
  TClientThread = class(TThread)
  private
    serverSocket: Longint;
  protected
    procedure execute; override;
  public
    constructor create(createSuspended: Boolean; server: Longint);
  end;

var
  buffer: String[255];
  count, i: Longint;

implementation

uses Client;

constructor TClientThread.create(createSuspended: Boolean; server:
Longint);
begin
  freeOnTerminate:= true;
  inherited create(createSuspended);
  serverSocket:= server;
end;

procedure TClientThread.execute;
begin
  repeat
    count:= fprecv(serverSocket, @buffer[1], 255, 0);
    if count <> SOCKET_ERROR then
    begin
      setLength(buffer, count);
      Form1.handle(buffer);
    end;
  until buffer = 'ciao';
  closeSocket(serverSocket);
end;

end.

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SymbolicFrank · 2015-11-24 08:09

If you want multiple connections, you need multiple ports.

I think the issue is, that there has to be a single port on the server
that accepts incoming requests. But the server will then spawn a new
thread and assign it a new port, exclusively for that session.

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Nukualofa · 2015-11-24 09:32

Ok, but if Client A has "used" the single port on the server that
accepts incoming requests, this won't work for Client B, except there
is a way to "reset" the socket or the port after Client A has been
assigned a new port. Is there a simpler solution than closing and
reopening the socket?

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JD · 2015-11-24 10:01

Pardon me but why don't you use Indy or Synapse to do this? They
already have this multithreaded functionality built-in.

JD

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rvk · 2015-11-24 10:05

Quote from: Nukualofa on November 24, 2015, 10:32:42 amOk, but if
Client A has "used" the single port on the server that accepts
incoming requests, this won't work for Client B, except there is a way
to "reset" the socket or the port after Client A has been assigned a
new port. Is there a simpler solution than closing and reopening the
socket?
??
A server can receive multiple connection to one port. It's not the
receiving port that makes it unique but the incoming and outgoing port
(and incoming and outgoing IP). So a connection is made up of 4
numbers. All these numbers make a unique connection. So you can have
this (every line with 4 numbers must be unique):

192.168.1.77:80 -> 192.168.1.1:80
192.168.1.77:81 -> 192.168.1.1:80
192.168.1.66:80 -> 192.168.1.1:80
192.168.1.66:81 -> 192.168.1.1:80

So when I (192.168.1.55) try to make a connection to 192.168.1.1:80 I
give a local unique port at my end (for instance 1234) and connect to
port 80 of the server, you get
192.168.1.55:1234 -> 192.168.1.1:80

See the question and answers here:
http://stackoverflow.com/questions/3329641/how-do-multiple-clients-
connect-simultaneously-to-one-port-say-80-on-a-server

If this doesn't work for you there must be something else wrong in the
code.


(you can put [ code ] [/ code ] (without the spaces) around your
code.)

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rvk · 2015-11-24 10:32

The problem you're having is that your trying to bind multiple
listening-sockets to the same port in Button1Click.

You should only create ONE listening-socket. When a client connects
you get a unique Clientsocket from fpaccept and that one you put in
your server thread. The listening server-socket keeps checking for new
incoming connections.

So you should put the initialization of the listening-socket outside
the repeat loop.
Something like this: (not tested)
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);begin   serverSocket:=
fpSocket(AF_INET, SOCK_STREAM, 0);  if fpSetSockOpt(serverSocket,
SOL_SOCKET, SO_REUSEADDR, @opt, sizeOf(opt)) = SOCKET_ERROR then
showMessage('Server : Multi : ' + intToStr(socketError));  if
serverSocket = SOCKET_ERROR then showMessage('Server : Socket : ' +
intToStr(socketError));  serverAddr.sin_family:= AF_INET; 
serverAddr.sin_port:= htons(50000);  serverAddr.sin_addr.s_addr:=
htonl($7F000001);  if fpBind(serverSocket, @serverAddr,
sizeOf(serverAddr)) = SOCKET_ERROR then showMessage('Server : Bind : '
+ intToStr(socketError));  if fpListen(serverSocket, 4) = SOCKET_ERROR
then showMessage('Server : Listen : ' + intToStr(socketError)); 
showMessage('Waiting for connect from Client...');   repeat   
addrSize:= sizeOf(serverAddr);    clientSocket:=
fpaccept(serverSocket, @serverAddr, @addrSize);    if clientSocket =
SOCKET_ERROR then showMessage('Server : Accept : ' +
intToStr(socketError)) else clientCount:= clientCount + 1;   
threads[clientCount]:= TServerThread.create(true, clientSocket);   
threads[clientCount].start;  until clientCount = 4; end;
(B.T.W. I would put a TMemo on the form and instead of showing
ShowMessage put the messages in that TMemo.)

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Nukualofa · 2015-11-24 10:50

@rvk: that's it! I moved the "repeat" behind the "bind" and it works
perfectly! Thank you so much!

@everyone else: Thanks for your advice, too!