Chat program in C++ returning infinite messages - c++

Question

Here is a chat application code below which I'm having troubles with.
The chat system works by having a master server, where all clients connect to. So, here is the code for the master server.
#pragma comment(lib, "Ws2_32.lib")
#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
using namespace std;
SOCKADDR_IN addr;
SOCKET sListen;
SOCKET sConnect;
SOCKET* Connections;
int addrlen = sizeof(addr);
int ConCounter = 0;
struct Buffer
{
int ID;
char Message[256];
};
int ServerThread(int ID)
{
Buffer sbuffer;
char* Recv = new char[256];
ZeroMemory(Recv, 256);
char* Send = new char[sizeof(Buffer)];
ZeroMemory(Send, sizeof(Buffer));
for(;; Sleep(10))
{
if(recv(Connections[ID], Recv, 256, NULL))
{
sbuffer.ID = ID;
memcpy(sbuffer.Message, Recv, 256);
memcpy(Send, &sbuffer, sizeof(Buffer));
for(int a = 0; a != ConCounter; a++)
{
if(Connections[a] == Connections[ID])
{
}
else
{
send(Connections[a], Send, sizeof(Buffer), NULL);
}
}
ZeroMemory(Recv, 256);
}
}
return 0;
}
int InitWinSock()
{
int RetVal = 0;
WSAData wsaData;
WORD DllVersion = MAKEWORD(2,1);
RetVal = WSAStartup(DllVersion, &wsaData);
return RetVal;
}
int main()
{
int RetVal = 0;
RetVal = InitWinSock();
if(RetVal != 0)
{
MessageBoxA(NULL, "Winsock startup failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
Connections = (SOCKET*)calloc(64, sizeof(SOCKET));
sListen = socket(AF_INET, SOCK_STREAM, NULL);
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(1234);
addr.sin_family = AF_INET;
bind(sListen, (SOCKADDR*)&addr, sizeof(addr));
listen(sListen, 64);
for(;; Sleep(50))
{
if(sConnect = accept(sListen, (SOCKADDR*)&addr, &addrlen))
{
Connections[ConCounter] = sConnect;
char* ID = new char[64];
ZeroMemory(ID, sizeof(ID));
itoa(ConCounter, ID, 10);
send(Connections[ConCounter], ID, sizeof(ID), NULL);
ConCounter = ConCounter + 1;
CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE) ServerThread, (LPVOID)(ConCounter - 1), NULL, NULL);
}
}
return 0;
}
Here is the source for the client chat:
#pragma comment(lib, "Ws2_32.lib")
#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
using namespace std;
SOCKADDR_IN addr;
SOCKET sConnect;
// For this we need to send two information at one time:
// 1. The main message
// 2. The ID
// To send more than one information I will use a struct
struct Buffer
{
int ID;
char Message[256];
};
int ClientThread()
{
Buffer sbuffer;
char buffer[sizeof(sbuffer)] = {0};
for(;; Sleep(10))
{
// The server will send a struct to the client
// containing message and ID
// But send only accepts a char as buffer parameter
// so here we need to recv a char buffer and then
// we copy the content of this buffer to our struct
if(recv(sConnect, buffer, sizeof(sbuffer), NULL))
{
memcpy(&sbuffer, buffer, sizeof(sbuffer));
cout << "<Client " << sbuffer.ID << ":> " << sbuffer.Message <<endl;
}
}
return 0;
}
int main()
{
system("cls");
int RetVal = 0;
WSAData wsaData;
WORD DllVersion = MAKEWORD(2,1);
RetVal = WSAStartup(DllVersion, &wsaData);
if(RetVal != 0)
{
MessageBoxA(NULL, "Winsock startup failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(1234);
addr.sin_family = AF_INET;
cout << "Connect to Masterserver? [ENTER]" <<endl;
getchar();
RetVal = connect(sConnect, (SOCKADDR*)&addr, sizeof(addr));
if(RetVal != 0)
{
MessageBoxA(NULL, "Could not connect to server", "Error", MB_OK | MB_ICONERROR);
main();
}
else
{
int ID;
char* cID = new char[64];
ZeroMemory(cID, 64);
recv(sConnect, cID, 64, NULL);
ID = atoi(cID);
cout << "Connected" <<endl;
cout << "You are Client No: " << ID <<endl;
CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE) ClientThread, NULL, NULL, NULL);
for(;; Sleep(10))
{
char* buffer = new char[256];
ZeroMemory(buffer, 256);
cin >> buffer;
getchar();
send(sConnect, buffer, 256, NULL);
}
}
return 0;
}
Now, everything works fine except when you connect for example with two clients (run app twice) and close one of them the client that closed the application spam the chat with infinite messages which never stop! Any help fixing that?
I would like to ask someone if possible to help me comment the source code!
Updated code:
#pragma comment(lib, "Ws2_32.lib")
#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
#include <string>
using namespace std;
SOCKADDR_IN addr;
SOCKET sConnect;
struct Buffer
{
int ID;
char Message[256];
};
int ClientThread()
{
Buffer sbuffer;
string buffer;
//char buffer[sizeof(sbuffer)] = {0};
for(;; Sleep(10))
{
if(recv(sConnect, buffer.c_str(), sizeof(sbuffer), NULL)!=SOCKET_ERROR)
{
strncpy(sbuffer.Message, buffer.c_str(), sizeof(sbuffer.Message));
cout << "<Client " << sbuffer.ID << ":> " << sbuffer.Message <<endl;
}
}
return 0;
}
int main()
{
system("cls");
int RetVal = 0;
WSAData wsaData;
WORD DllVersion = MAKEWORD(2,1);
RetVal = WSAStartup(DllVersion, &wsaData);
if(RetVal != 0)
{
MessageBoxA(NULL, "Winsock startup failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(1234);
addr.sin_family = AF_INET;
cout << "Connect to Masterserver? [ENTER]" <<endl;
getchar();
RetVal = connect(sConnect, (SOCKADDR*)&addr, sizeof(addr));
if(RetVal != 0)
{
MessageBoxA(NULL, "Could not connect to server", "Error", MB_OK | MB_ICONERROR);
main();
}
else
{
int ID;
char* cID = new char[64];
ZeroMemory(cID, 64);
recv(sConnect, cID, 64, NULL);
ID = atoi(cID);
cout << "Connected" <<endl;
cout << "You are Client No: " << ID <<endl;
CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE) ClientThread, NULL, NULL, NULL);
for(;; Sleep(10))
{
char* buffer = new char[256];
ZeroMemory(buffer, 256);
getline(cin,buffer);
//cin >> buffer;
getchar();
send(sConnect, buffer, 256, NULL);
}
}
return 0;
}

Answer 1

When a client disconnects gracefully, recv() will return 0. When a client disconnects abnormally, or any other error occurs for that matter, recv() will return SOCKET_ERROR and you can then use WSAGetLastError() to find out why it errored. You need to handle both conditions and make the server "forget about the client" when recv() returns <= 0 (except in the specific case of SOCKET_ERROR/WSAEWOULDBLOCK, which is not a fatal error). Currently you are treating a socket error as if you had instead really received data from the client.
You are testing the return value of recv() against zero, but that is not what recv() returns on an error (SOCKET_ERROR is actually an alias for -1, and if (-1) evaluates as true, not false).

Answer 2

The reason your server gets stuck in a loop is because you are not using the return value of recv() correctly.
There are other problems with your code as well (abusing CreateThread(), for starters).
Try this instead:
#pragma comment(lib, "Ws2_32.lib")
#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
using namespace std;
SOCKADDR_IN addr;
int addrlen;
SOCKET sListen;
SOCKET sConnect;
SOCKET Connections[64];
struct Buffer
{
int ID;
char Message[256];
};
bool doSend(SOCKET s, void *data, int datalen)
{
char pdata = (char*) data;
while (datalen > 0)
{
int numSent = send(s, pdata, datalen, NULL);
if (numSent < 1)
return false;
pdata += numSent;
datalen -= numSent;
}
return true;
}
DWORD WINAPI ServerThread(LPVOID lpParam)
{
int ID = (int) lpParam;
SOCKET sThisClient = Connections[ConID];
char cID[64];
ZeroMemory(cID, sizeof(cID));
itoa(ID, cID, 10);
if (doSend(sThisClient, cID, sizeof(cID)))
{
Buffer sbuffer;
sbuffer.ID = ID;
ZeroMemory(sbuffer.Message, sizeof(sbuffer.Message));
for (;; Sleep(10))
{
int numRecv = recv(sThisClient, sbuffer.Message, sizeof(sbuffer.Message), NULL);
if (numRecv < 1)
break;
for (int a = 0; a < 64; a++)
{
SOCKET sOtherClient = Connections[a];
if ((sOtherClient != INVALID_SOCKET) && (sOtherClient != sClient))
doSend(sOtherClient, &sbuffer, sizeof(Buffer));
}
}
ZeroMemory(sbuffer.Message, sizeof(sbuffer.Message));
}
closesocket(Connections[ID]);
Connections[ID] = INVALID_SOCKET;
return 0;
}
int main()
{
for (int i = 0; i < 64; ++i)
Connections[i] = INVALID_SOCKET;
WSAData wsaData;
int RetVal = WSAStartup(MAKEWORD(2,1), &wsaData);
if (RetVal != 0)
{
MessageBoxA(NULL, "Winsock startup failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
sListen = socket(AF_INET, SOCK_STREAM, NULL);
if (sListen == INVALID_SOCKET)
{
MessageBoxA(NULL, "Socket create failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
if (sConnect == INVALID_SOCKET)
{
MessageBoxA(NULL, "Socket create failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(1234);
addr.sin_family = AF_INET;
if (bind(sListen, (SOCKADDR*)&addr, sizeof(addr)) != 0)
{
MessageBoxA(NULL, "bind failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
if (listen(sListen, 64) != 0)
{
MessageBoxA(NULL, "listen failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
for(;; Sleep(50))
{
addrlen = sizeof(addr);
sConnect = accept(sListen, (SOCKADDR*)&addr, &addrlen);
if (sConnect != INVALID_SOCKET)
{
int ConID = -1;
for (int i = 0; i < 64; ++i)
{
if (Connections[i] == INVALID_SOCKET);
{
ConID = i;
break;
}
}
if (ConID == -1)
{
closesocket(sConnect);
continue;
}
Connections[ConID] = sConnect;
HANDLE hThread = CreateThread(NULL, NULL, &ServerThread, (LPVOID)ConID, NULL, NULL);
if (!hThread)
{
closesocket(sConnect);
Connections[ConID] = INVALID_SOCKET;
continue;
}
CloseHandle(hThread);
}
}
return 0;
}
.
#pragma comment(lib, "Ws2_32.lib")
#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
using namespace std;
SOCKADDR_IN addr;
SOCKET sConnect;
struct Buffer
{
int ID;
char Message[256];
};
bool doRecv(SOCKET s, void *data, int datalen)
{
char pdata = (char*) data;
while (datalen > 0)
{
int numRecv = recv(s, pdata, datalen, NULL);
if (numRecv < 1)
return false;
pdata += numRecv;
datalen -= numRecv;
}
return true;
}
DWORD WINAPI ClientThread(LPVOID lpParam)
{
Buffer sbuffer;
for(;; Sleep(10))
{
if (!doRecv(sConnect, &sbuffer, sizeof(sbuffer)))
break;
cout << "<Client " << sbuffer.ID << ":> " << sbuffer.Message << endl;
}
return 0;
}
int main()
{
system("cls");
WSAData wsaData;
int RetVal = WSAStartup(MAKEWORD(2,1), &wsaData);
if (RetVal != 0)
{
MessageBoxA(NULL, "Winsock startup failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
if (sConnect == INVALID_SOCKET)
{
MessageBoxA(NULL, "Socket create failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(1234);
addr.sin_family = AF_INET;
do
{
cout << "Connect to Masterserver? [ENTER]" << endl;
getchar();
RetVal = connect(sConnect, (SOCKADDR*)&addr, sizeof(addr));
if (RetVal == 0)
break;
MessageBoxA(NULL, "Could not connect to server", "Error", MB_OK | MB_ICONERROR);
}
while (true);
char cID[64];
ZeroMemory(cID, 64);
if (!doRecv(sConnect, cID, 64))
exit(1);
int ID = atoi(cID);
cout << "Connected" << endl;
cout << "You are Client ID: " << ID << endl;
if (!CreateThread(NULL, NULL, &ClientThread, NULL, NULL, NULL))
exit(1);
for(;; Sleep(10))
{
string buffer;
getline(cin, buffer);
doSend(sConnect, buffer.c_str(), buffer.length());
}
return 0;
}
Update: Given your recent update, you still have problems with your client code. Did you even try the code I gave you above? Below is a fix for your recent code, though I still suggest you review the code above, which addresses a lot of other issues with your original code:
#pragma comment(lib, "Ws2_32.lib")
#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
#include <string>
using namespace std;
SOCKADDR_IN addr;
SOCKET sConnect;
struct Buffer
{
int ID;
char Message[256];
};
int ClientThread()
{
Buffer sbuffer;
char buffer[sizeof(sbuffer)];
for(;; Sleep(10))
{
int numRead = recv(sConnect, &buffer, sizeof(buffer), NULL);
if (numRead < 1) break;
memcpy(&sbuffer, buffer, numRead);
cout << "<Client " << sbuffer.ID << ":> " << sbuffer.Message << endl;
}
return 0;
}
int main()
{
system("cls");
int RetVal = 0;
WSAData wsaData;
WORD DllVersion = MAKEWORD(2,1);
RetVal = WSAStartup(DllVersion, &wsaData);
if (RetVal != 0)
{
MessageBoxA(NULL, "Winsock startup failed", "Error", MB_OK | MB_ICONERROR);
exit(1);
}
sConnect = socket(AF_INET, SOCK_STREAM, NULL);
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(1234);
addr.sin_family = AF_INET;
do
{
cout << "Connect to Masterserver? [ENTER]" <<endl;
getchar();
RetVal = connect(sConnect, (SOCKADDR*)&addr, sizeof(addr));
if (RetVal == 0) break;
MessageBoxA(NULL, "Could not connect to server", "Error", MB_OK | MB_ICONERROR);
}
while (true);
char cID[64];
ZeroMemory(cID, 64);
recv(sConnect, cID, 64, NULL);
int ID = atoi(cID);
cout << "Connected" << endl;
cout << "You are Client No: " << ID << endl;
CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE) ClientThread, NULL, NULL, NULL);
for(;; Sleep(10))
{
string buffer;
getline(cin, buffer);
if (send(sConnect, buffer.c_str(), buffer.length(), NULL) < 1)
exit(1);
}
return 0;
}