c++ multi client/server chat - c++

Question

I am hitting rock bottom, thinking about a solution for a problem I am having with my chat server and client.
What is supposed to do, client asks for a username, then for a connection request to the user with answer [Y/N].
When hitting yes, client has to connect to server, when it does it needs to go in a separate thread( for handling multiple clients (but my problem is, when more then one user joins( the username of the user current logged in is changed to the last one who joined the chat.
While that is happening (the server shows the username, while on the client screen it disappears and none or all weird signs appear).
What I need also help with is the distribution of the messages to the other clients connected (excluding the user himself)
Code Server:
#include "stdafx.h"
long antwoord;
char chatname[100];
char bericht[498];
char sbericht[498];
using namespace std;
DWORD WINAPI SocketHandler(void*);
//our main function
void main()
{
//here we set the Winsock-DLL to start
WSAData wsaData;
WORD DLLVERSION;
DLLVERSION = MAKEWORD(2,1);
//here the Winsock-DLL will be started with WSAStartup
//version of the DLL
antwoord = WSAStartup(DLLVERSION, &wsaData);
if(antwoord != 0)
{
WSACleanup();
exit(1);
}
else
{
cout << "WSA started successfully" <<endl;
cout << "The status: \n" << wsaData.szSystemStatus <<endl;
}
//the DLL is started
//structure of our socket is being created
SOCKADDR_IN addr;
//addr is our struct
int addrlen = sizeof(addr);
//socket sListen - will listen to incoming connections
SOCKET sListen;
//socket sConnect - will be operating if a connection is found.
SOCKET sConnect;
//setup of our sockets
//opgezocht op internet - AF_INET bekend dat het lid is van de internet familie
//Sock_STREAM betekenend dat onze socket een verbinding georiënteerde socket is.
sConnect = socket(AF_INET,SOCK_STREAM,NULL);
//now we have setup our struct
//inet_addr is our IP adres of our socket(it will be the localhost ip
//that will be 127.0.0.1
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
//retype of the family
addr.sin_family = AF_INET;
//now the server has the ip(127.0.0.1)
//and the port number (4444)
addr.sin_port = htons(4444);
//here we will define the setup for the sListen-socket
sListen = socket(AF_INET,SOCK_STREAM,NULL);
if (sConnect == INVALID_SOCKET)
{
cout << "Error at socket(): \n" << WSAGetLastError() <<endl;
WSACleanup();
}
else
{
cout << "Connect socket() is OK!" <<endl;
}
if(sListen == INVALID_SOCKET)
{
cout << "Error at socket(): \n" << WSAGetLastError() <<endl;
WSACleanup();
}
else
{
cout << "Listen socket() is OK!" <<endl;
}
//here the sListen-socket will be bind
//we say that the socket has the IP adress of (127.0.0.1) and is on port (4444)
//we let the socket become the struct "addr"
if(bind(sListen, (SOCKADDR*)&addr, sizeof(addr)) == SOCKET_ERROR)
{
cout << "bind() failed: \n" << WSAGetLastError() <<endl;
WSACleanup();
exit(1);
}
else{
cout << "bind() is OK!" <<endl;
}
if(listen( sListen, 10) == -1 ){
cout << "Error listening %d\n" << WSAGetLastError() <<endl;
}
//here we will tell what the server must do when a connection is found
//therefor we will create an endless loop
cout << "Waiting for a incoming connection..." <<endl;
//now we let the socket listen for incoming connections
//SOMAXCOMM heeft het nut dat het dan voordurend luisterd naar inkomende verbindingen zonder limiet
int* csock;
while(true)
{
csock = (int*)malloc(sizeof(int));
//if a connection is found: show the message!
if((*csock = accept(sListen, (SOCKADDR*)&addr, &addrlen))!= INVALID_SOCKET)
{
cout << "A Connection was found with :" << inet_ntoa(addr.sin_addr) <<endl;
antwoord = send(*csock, "Welcome to our chat:", 21,NULL);
CreateThread(0,0,&SocketHandler, (void*)csock , 0,0);
cout << *csock <<endl;
}
}
}
//sbericht is the message
DWORD WINAPI SocketHandler(void* lp)
{
int *csock = (int*)lp;
for(;;)
{
antwoord = recv(*csock, sbericht, sizeof(sbericht), NULL);
antwoord = recv(*csock, chatname, sizeof(chatname), NULL);
while(antwoord = recv(*csock, sbericht, sizeof(sbericht), NULL) && (antwoord = recv(*csock, sbericht, sizeof(sbericht), NULL)) )
{
printf("%s\: \"%s\"\n", chatname, sbericht);
antwoord = send(*csock, sbericht, sizeof(sbericht), NULL);
antwoord = send(*csock, chatname, sizeof(chatname), NULL);
}
return 0;
}
}
Client code:
#include "stdafx.h"
using namespace std;
//our main function
int main()
{
//here we set the Winsock-DLL to start
string bevestiging;
char chatname[100];
char bericht[250];
char sbericht[250];
string strbericht;
string strsbericht;
long antwoord;
//here the Winsock-DLL will be started with WSAStartup
//version of the DLL
WSAData wsaData;
WORD DLLVERSION;
DLLVERSION = MAKEWORD(2,1);
antwoord = WSAStartup(DLLVERSION, &wsaData);
if(antwoord != 0)
{
exit(1);
}
else
{
cout << "WSA started successfully" <<endl;
cout << "The status: \n" << wsaData.szSystemStatus <<endl;
}
SOCKADDR_IN addr;
int addrlen = sizeof(addr);
SOCKET sConnect;
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
if (sConnect == INVALID_SOCKET)
{
cout << "Error at socket(): \n" << WSAGetLastError() <<endl;
}
else
{
cout << "socket() is OK!\n" <<endl;
}
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_family = AF_INET;
addr.sin_port = htons(4444);
cout << "What is your chat name?" <<endl;
cin.getline(chatname, 100);
cout << "Do you want to connect to the server? [Y/N]" <<endl;
cin >> bevestiging;
if (bevestiging == "N")
{
exit(1);
}
else
{
if(bevestiging == "Y")
{
connect(sConnect, (SOCKADDR*)&addr, sizeof(addr));
antwoord = recv(sConnect, bericht, sizeof(bericht), NULL);
strbericht = bericht;
cout << strbericht << chatname <<endl;
while(true)
{
if(antwoord > 1)
{
cin.clear();
cin.sync();
cout << chatname << " :" <<endl;
cin.getline(sbericht, sizeof(sbericht));
antwoord = send(sConnect, sbericht, sizeof(sbericht), NULL);
antwoord = send(sConnect, chatname, sizeof(chatname), NULL);
while(antwoord = send(sConnect, sbericht, sizeof(sbericht), NULL) && (antwoord = send(sConnect, sbericht, sizeof(sbericht), NULL)))
{
antwoord = recv(sConnect, sbericht, sizeof(sbericht), NULL);
antwoord = recv(sConnect, chatname, sizeof(chatname), NULL);
cout << chatname << ":" <<endl;
cout << sbericht <<endl;
cin.getline(sbericht, 250);
}
}
else
{
cout << "The connection to the server has been lost... \n" << "please exit the client." <<endl;
}
}
Sorry if I didn't write it well (I'm just learning to program sockets) but I can't figure this one out. So don't be hard on me, I still need to learn but cant find the things I need. So I think if somebody can show me how to do it, I can see it how its done and why.
Always learn something(I'm currently also busy with beejee's network programming tutorial).

Answer 1

sbericht and chatname - global variables
Your 2 threads working with this global buffers at the same time
So one thread rewrites data of another thread

Answer 2

There are a few issues with this code but sockets are a sticky thing to wrap your head around when you start. It seems in your server code that multithreading is your real beast. Note that threads and sockets are very different concepts but they are often used together. A large issue (as Andrew said) is that you have race conditions. You need to use mutexes to ensure mutual exclusion if you are writing to your global variables across multiple threads. For instance, in SocketHandler you need to protect your variable antwoord. Furthermore, use new and delete in C++ rather than malloc() and free() (these are used in C). Also, notice that for every new connection you overwrite the value of your csock variable. You need separate variables to hold each client's open connection socket.
Server sockets basically work in this manner: socket(), bind(), listen(), accept(). Now, in order to keep the port you are bind()'ed to and are listen()'ing on open for more connections, accept() reroutes your client and puts them on another socket file descriptor (which is the return value of accept()) so that you can continue to communicate with this client. Therefore, for each client, you need to hold the value of accept() uniquely.
I am skeptical, however, that in your client code, you are receiving what you expect. Does your protocol somewhere guarantee it will send just the username and then the chatname? You may simply need a single recv() call to retrieve all your data. Also, what is the relevance of the following line?
while(antwoord = send(sConnect, sbericht, sizeof(sbericht), NULL) && (antwoord = send(sConnect, sbericht, sizeof(sbericht), NULL)))
You are simply doing the same work twice - one time should be sufficient (and perhaps the program may block at this point and overwrite data without you knowing). For a simple text protocol, it is very likely that you can create a variable ~512bytes and receive all the information from the server appropriately in a single call to recv().
I tried to pick out the large issues in your code, and these problems are, more or less, frequent in other areas of your code too. If you are not familiar with multithreading, attack that problem later. Learn how to do single-threaded sockets, then go and learn multithreading. Tackling them both at once is going to bite you. Good luck!