Continuously sending data from server to receiver using c++ - c++

Question

I am coding in C++ using winsock api. I am making a multi- client server chat. The problem that I am encountering in my code is that my server is able to send the message to the client only once. But I want this to happen multiple times. I cannot put accept() function out of infinite loop in server code. I have used select() for multi client. I am doing it without threading.
Server:
#include <iostream>
#include <WS2tcpip.h>
#include <string>
#include <sstream>
#pragma comment (lib, "ws2_32.lib")
using namespace std;
void main()
{
// Initialze winsock
WSADATA wsData;
WORD ver = MAKEWORD(2, 2);
int wsOk = WSAStartup(ver, &wsData);
if (wsOk != 0)
{
cerr << "Can't Initialize winsock! Quitting" << endl;
return;
}
// Create a socket
SOCKET listening = socket(AF_INET, SOCK_STREAM, 0);
if (listening == INVALID_SOCKET)
{
cerr << "Can't create a socket! Quitting" << endl;
return;
}
// Bind the ip address and port to a socket
sockaddr_in hint;
hint.sin_family = AF_INET;
hint.sin_port = htons(54000);
hint.sin_addr.S_un.S_addr = INADDR_ANY; // Could also use inet_pton ....
bind(listening, (sockaddr*)&hint, sizeof(hint));
// Tell Winsock the socket is for listening
listen(listening, SOMAXCONN);
// Create the master file descriptor set and zero it
fd_set master;
FD_ZERO(&master);
// Add our first socket that we're interested in interacting with; the listening socket!
// It's important that this socket is added for our server or else we won't 'hear' incoming
// connections
FD_SET(listening, &master);
// this will be changed by the \quit command (see below, bonus not in video!)
bool running = true;
while (running)
{
// Make a copy of the master file descriptor set, this is SUPER important because
// the call to select() is _DESTRUCTIVE_. The copy only contains the sockets that
// are accepting inbound connection requests OR messages.
// E.g. You have a server and it's master file descriptor set contains 5 items;
// the listening socket and four clients. When you pass this set into select(),
// only the sockets that are interacting with the server are returned. Let's say
// only one client is sending a message at that time. The contents of 'copy' will
// be one socket. You will have LOST all the other sockets.
// SO MAKE A COPY OF THE MASTER LIST TO PASS INTO select() !!!
fd_set copy = master;
// See who's talking to us
int socketCount = select(0, &copy, nullptr, nullptr, nullptr);
for (int i = 0; i < socketCount; i++) {
//Accept a new connection
SOCKET sock = copy.fd_array[i];
if (sock == listening) {
//Accept a new connection
SOCKET client = accept(listening, nullptr, nullptr);
//Add a new connection
FD_SET(client, &master);
string mssg = "Welcome to the awesome chat server\n";
//Send a welcome message to the connected client
send(client, mssg.c_str(), mssg.size() + 1, 0);
}
//Send a new message
string mssg;
getline(cin, mssg);
int bytes = send(sock, mssg.c_str(), mssg.size() + 1, 0);
for (int i = 0; i < master.fd_count; i++) {
SOCKET outsock = master.fd_array[i];
if (outsock != listening && outsock != sock) {
send(outsock, mssg.c_str(), mssg.size() + 1, 0);
}
}
}
}
// Remove the listening socket from the master file descriptor set and close it
// to prevent anyone else trying to connect.
FD_CLR(listening, &master);
closesocket(listening);
// Message to let users know what's happening.
string msg = "Server is shutting down. Goodbye\r\n";
while (master.fd_count > 0)
{
// Get the socket number
SOCKET sock = master.fd_array[0];
// Send the goodbye message
send(sock, msg.c_str(), msg.size() + 1, 0);
// Remove it from the master file list and close the socket
FD_CLR(sock, &master);
closesocket(sock);
}
// Cleanup winsock
WSACleanup();
system("pause");
}
Client code:
#include<iostream>
#include<ws2tcpip.h>
#include<string>
using namespace std;
#pragma comment(lib,"ws2_32.lib")
void main() {
string ipAddress = "127.0.0.1"; //IP Address of the server
int port = 54000; //Listening port on the sever
//Initialize Winsock
WSADATA data;
WORD ver = MAKEWORD(2, 2);
int wsResult = WSAStartup(ver, &data);
if (wsResult != 0) {
cerr << " Can't initialize winsock " << endl;
return;
}
//Create socket
SOCKET sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET) {
cerr << "Can't create a socket " << WSAGetLastError() << endl;
closesocket(sock);
WSACleanup();
return;
}
//Fill in a hint structure
sockaddr_in hint;
hint.sin_family = AF_INET;
hint.sin_port = htons(port);
inet_pton(AF_INET, ipAddress.c_str(), &hint.sin_addr);
//Connect to the server
int connResult = connect(sock, (sockaddr*)&hint, sizeof(hint));
if (connResult == SOCKET_ERROR) {
cerr << " Can't connect to the server " << WSAGetLastError() << endl;
closesocket(sock);
WSACleanup();
return;
}
//Do-While loop to send and receive data
//char b[4096];
//int bytes = recv(sock,b,4096, 0);
//cout << string(b, 0, bytes) << endl;
char buff[4096];
string userInput;
do {
//Prompt the user
//cout << ">";
//getline(cin, userInput);
//Send the result
//int sendResult = send(sock, userInput.c_str(), userInput.size() + 1, 0);
//if (sendResult != SOCKET_ERROR) {
//ZeroMemory(buff, 0);
int bytesrecieved = recv(sock, buff, 4096, 0);
if (bytesrecieved > 0) {
//Echo response to console
cout << "SERVER> " << string(buff, 0, bytesrecieved) << endl;
}
//}
} while (true);
//Shut down everything
closesocket(sock);
WSACleanup();
}

Answer 1

EDIT:
You should do some modifications :
Use timeval for select to avoid the blocking select (wait until a
new connection was made or there is something to read).
Move the read/send message section out of the for loop.
Separate key input processing in an other thread.
Use a safe queue to share the input between the input thread and the communciation one(main thread).
Here is an example:
#include <iostream>
#include <WS2tcpip.h>
#include <string>
#include <sstream>
#include <thread>
#include <mutex>
#include <list>
#pragma comment (lib, "ws2_32.lib")
using namespace std;
class safe_queue {
mutex m;
list<string> str_queue;
public:
safe_queue() {};
void add(const string &s) {
const lock_guard<mutex> lock(m);
str_queue.push_back(s);
}
bool pop( string &s ) {
const lock_guard<mutex> lock(m);
if (!str_queue.empty()) {
s = str_queue.front();
str_queue.pop_front();
return true;
}
return false;
}
};
int main()
{
// Initialze winsock
WSADATA wsData;
WORD ver = MAKEWORD(2, 2);
int wsOk = WSAStartup(ver, &wsData);
if (wsOk != 0)
{
cerr << "Can't Initialize winsock! Quitting" << endl;
return 0;
}
// Create a socket
SOCKET listening = socket(AF_INET, SOCK_STREAM, 0);
if (listening == INVALID_SOCKET)
{
cerr << "Can't create a socket! Quitting" << endl;
return 0;
}
// Bind the ip address and port to a socket
sockaddr_in hint;
hint.sin_family = AF_INET;
hint.sin_port = htons(54000);
hint.sin_addr.S_un.S_addr = INADDR_ANY; // Could also use inet_pton ....
bind(listening, (sockaddr*)&hint, sizeof(hint));
// Tell Winsock the socket is for listening
listen(listening, SOMAXCONN);
// Create the master file descriptor set and zero it
fd_set master;
FD_ZERO(&master);
// Add our first socket that we're interested in interacting with; the listening socket!
// It's important that this socket is added for our server or else we won't 'hear' incoming
// connections
FD_SET(listening, &master);
// this will be changed by the \quit command (see below, bonus not in video!)
bool running = true;
safe_queue sq;
auto io_thread = thread([&] {
string s;
while (running && getline(std::cin, s, '\n')){
sq.add(s);
}
});//thread.
while (running)
{
// Make a copy of the master file descriptor set, this is SUPER important because
// the call to select() is _DESTRUCTIVE_. The copy only contains the sockets that
// are accepting inbound connection requests OR messages.
// E.g. You have a server and it's master file descriptor set contains 5 items;
// the listening socket and four clients. When you pass this set into select(),
// only the sockets that are interacting with the server are returned. Let's say
// only one client is sending a message at that time. The contents of 'copy' will
// be one socket. You will have LOST all the other sockets.
// SO MAKE A COPY OF THE MASTER LIST TO PASS INTO select() !!!
fd_set copy = master;
timeval tv = {0,0};
// See who's talking to us
int socketCount = select(0, &copy, nullptr, nullptr, &tv);
for (int i = 0; i < socketCount; i++) {
//Accept a new connection
SOCKET sock = copy.fd_array[i];
if (sock == listening) {
//Accept a new connection
SOCKET client = accept(listening, nullptr, nullptr);
//Add a new connection
FD_SET(client, &master);
string mssg = "Welcome to the awesome chat server\n";
//Send a welcome message to the connected client
send(client, mssg.c_str(), mssg.size() + 1, 0);
}
}//for.
string mssg;
if (sq.pop(mssg) ) {
std::cout << "Send :" << mssg << endl;
for (u_int i = 0; i < master.fd_count; i++) {
SOCKET outsock = master.fd_array[i];
if (outsock != listening) {
send(outsock, mssg.c_str(), mssg.size() + 1, 0);
}
}
}
}//while
// Remove the listening socket from the master file descriptor set and close it
// to prevent anyone else trying to connect.
FD_CLR(listening, &master);
closesocket(listening);
// Message to let users know what's happening.
string msg = "Server is shutting down. Goodbye\r\n";
while (master.fd_count > 0)
{
// Get the socket number
SOCKET sock = master.fd_array[0];
// Send the goodbye message
send(sock, msg.c_str(), msg.size() + 1, 0);
// Remove it from the master file list and close the socket
FD_CLR(sock, &master);
closesocket(sock);
}
// Cleanup winsock
WSACleanup();
system("pause");
return 0;
}