Multiplexing I/O client-server (message exchange)

See more:

C

sockets

client-server

I stated learning C language and now I'm trying to get deal with WinSockets. I have to write Server and Client application using Multiplexing and non-blocking sockets (in prespective it will be a chat but now I just want to make it finally work with simple message exchange).

What I have tried:

Let me show you my code of Server and Client and I'll explain what and how I want to do and what problems I've met.
Server code:

<pre>
#pragma comment(lib, "ws2_32.lib")
#define _WINSOCK_DEPRECATED_NO_WARNINGS
#define _CRT_SECURE_NO_WARNINGS
#include <winsock2.h>
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
//#include "list.h"

#define PRINTUSERS if (nclients)\
	printf("We have %d user online\n", nclients);\
	else printf("No users online\n***************\n");

#define PORT 3765
#define BACKLOG 10
#define MAXDATASIZE 1024
#define MAXUSERSONLINE 64

struct client
{
	int numClient;
	struct client* next;
};

void print(struct client* head);
int pushBack(struct client** head, int numClient);
int checkSockOpt(int socket);

int main(int argc, char* argv[])
{
	struct sockaddr_in serverAddr;
	struct sockaddr_in clientAddr;

	SOCKET socketDescriptor;
	fd_set readSocketDescriptor;
	fd_set writeSocketDescriptor;
	int newSocketDescriptor;

	WSADATA wsaData;
	WORD wsaStart;
	timeval tv;

	// LIST TEST #1
	struct client* head = 0;
	pushBack(&head, 111);
	pushBack(&head, 222);
	pushBack(&head, 999);
	print(head); //

	int retVal;
	int clientAddrSize = sizeof(clientAddr);
	char bufferData[MAXDATASIZE] = { 0 };
	int nclients = 0;
	int numBytes = 0;

	if (argc > 1)
	{
		printf("Uses: <chatserver>\n");
		return -1;
	}
	do
	{
		if ((wsaStart = WSAStartup(MAKEWORD(2, 2), &wsaData)) != 0)
		{
			printf("WSAStartup error ");
			break;
		}
		if ((socketDescriptor = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
		{
			printf("Socket error ");
			closesocket(socketDescriptor);
			break;
		}

		serverAddr.sin_family = AF_INET;
		serverAddr.sin_port = htons(PORT);
		serverAddr.sin_addr.s_addr = INADDR_ANY;

		if (bind(socketDescriptor, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR)
		{
			printf("Bind error ");
			closesocket(socketDescriptor);

			break;
		}
		if (listen(socketDescriptor, BACKLOG) == SOCKET_ERROR)
		{
			printf("Listening error ");
			closesocket(socketDescriptor);
			break;
		}

		while (1)
		{

			FD_ZERO(&readSocketDescriptor);
			FD_ZERO(&writeSocketDescriptor);
			FD_SET(socketDescriptor, &readSocketDescriptor);
			FD_SET(socketDescriptor, &writeSocketDescriptor);

			printf("Setup SERVER socket descriptor number: %d\n", socketDescriptor);
			tv.tv_sec = 5;

			// Do not forget to put after WHILE(1)
			if ((retVal = select(socketDescriptor + 1, &readSocketDescriptor, &writeSocketDescriptor, NULL, &tv)) == SOCKET_ERROR)
			{
				printf("Select error ");
				break;
			}
			if ((FD_ISSET(socketDescriptor, &readSocketDescriptor)) != 0)
			{
				printf("CHECK FD_ISSET value #1: %d\n", FD_ISSET(socketDescriptor, &readSocketDescriptor));
				//int clientList[MAXUSERSONLINE] = { 0 };
				//for (int i = 0; i <= MAXUSERSONLINE; i++)
				//{

				if ((newSocketDescriptor = accept(socketDescriptor, (struct sockaddr *)&clientAddr, &clientAddrSize)) == SOCKET_ERROR)
				{
					printf("Accept error ");
					break;
				}
				//	newSocketDescriptor = clientList[i];
				struct client* head = 0;
				pushBack(&head, newSocketDescriptor);
				print(head); //
				nclients++; PRINTUSERS

					printf("Server got connection from %s\n", inet_ntoa(clientAddr.sin_addr));
				FD_SET(newSocketDescriptor, &readSocketDescriptor);
				//FD_CLR(socketDescriptor, &readSocketDescriptor);

				printf("CHECK FD_ISSET value #2: %d\n", (FD_ISSET(socketDescriptor, &readSocketDescriptor)));
				printf("newSocketDescriptor = %d, READ_FD status #1 after accept = %d\n", newSocketDescriptor, FD_ISSET(socketDescriptor, &readSocketDescriptor));
				checkSockOpt(newSocketDescriptor);

				if (FD_ISSET(newSocketDescriptor, &readSocketDescriptor) != 0)
				{

					pushBack(&head, newSocketDescriptor);
					print(head);
					//RECV function
					if ((numBytes = recv(newSocketDescriptor, bufferData, MAXDATASIZE, 0)) == SOCKET_ERROR)
					{
						printf("Recv error ");
						break;
					}

					bufferData[numBytes] = '\0';
					printf("Recv: retVal = %d, bufferData = %s\n", retVal, bufferData);
					printf("newSocketDescriptor = %d, READ_FD status #2 after recv = %d\n", newSocketDescriptor, FD_ISSET(socketDescriptor, &readSocketDescriptor));
					if (numBytes == -1)
					{
						printf("One user has disconnected");
						nclients--;
						PRINTUSERS
					}
					else
					{
						// SEND message to CLIENT
						char *testmsg = "Hello, world!\n";
						if (send(newSocketDescriptor, testmsg, strlen(testmsg), 0) == SOCKET_ERROR)
						{
							printf("Send error ");
							break;
						}
						FD_CLR(newSocketDescriptor, &readSocketDescriptor);
					}
					printf("newSocketDescriptor = %d, READ_FD status #3 after send = %d\n", newSocketDescriptor, FD_ISSET(socketDescriptor, &readSocketDescriptor));
					FD_SET(newSocketDescriptor, &readSocketDescriptor);
					closesocket(newSocketDescriptor);
				}
				//closesocket(newSocketDescriptor);
				//}
			}
			else
			{
				printf("Sorry, time limit is expired, there is no active sockets\n");
			}
		}

	} while (FALSE);
	printf("- Error code: %d\n", WSAGetLastError());
	closesocket(socketDescriptor);
	WSACleanup();
	return 0;
}

// Check Socket Option
int checkSockOpt(int socket)
{
	int optVal = 0;
	int optLen = sizeof(int);
	if (getsockopt(socket, SOL_SOCKET, SO_ACCEPTCONN, (char*)&optVal, &optLen) != SOCKET_ERROR)
	{
		printf("SockOpt Value: %ld. Error code: %d\n", optVal, WSAGetLastError());
	}
	return 0;
}

// Print Client List
void print(struct client* head)
{
	struct client* list = head;
	while (list != 0)
	{
		printf("Client socket %d successfully added to the list\n", list->numClient);
		list = list->next;
	}
}

void printAllFD(struct client* head)
{
	struct client* list = head;
	while (list != 0)
	{
		printf("Client socket %d successfully added to the list\n", list->numClient);
		list = list->next;
	}
}

// pushBack for Client 
int pushBack(struct client** head, int numClient)
{
	//struct client* fd = 0;
	struct client* fd = (struct client*)malloc(sizeof(struct client));
	struct client* list = *head;
	fd->numClient = numClient;
	fd->next = 0;

	if (list == 0)
	{
		*head = fd;
		return 0;
	}
	while (list->next != 0)
	{
		list = list->next;
	}
	list->next = fd;
	return 0;
}

Client code:

<pre>
#pragma comment(lib, "ws2_32.lib")
#define _WINSOCK_DEPRECATED_NO_WARNINGS
#include <winsock2.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h> 
#include <sys/types.h>

#define SERVERADDR argv[1]
#define PORT 3765
#define MAXDATASIZE 1024

int main(int argc, char *argv[])
{
	struct sockaddr_in destAddr = { 0 };
	SOCKET socketDescriptor;
	WSADATA wsaData;
	fd_set readSet;
	fd_set writeSet;
	timeval tv;

	char bufferData[MAXDATASIZE];
	int numBytes;
	unsigned long int nb = 1;
	int retVal;

	if (argc != 2)
	{
		printf("Uses: <client> <hostname>\nExample: \"client 127.0.0.1\"\n");
		return -1;
	}
	do
	{
		if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
		{
			printf("WSAStartup error ");
			break;
		}
		if (gethostbyname(SERVERADDR) == NULL)
		{
			printf("Gethostbyname error ");
			break;
		}
		if ((socketDescriptor = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
		{
			printf("Socket error ");
			break;
		}
		if (ioctlsocket(socketDescriptor, FIONBIO, (unsigned long *)&nb) != 0)
		{
			printf("ioctlsocket error ");
			break;
		}

		destAddr.sin_family = AF_INET;
		destAddr.sin_port = htons(PORT);
		destAddr.sin_addr.s_addr = inet_addr(SERVERADDR);

		printf("Attempt to connect %s:%d\n", inet_ntoa(destAddr.sin_addr), htons(destAddr.sin_port));
		tv.tv_sec = 20;

		if (connect(socketDescriptor, (sockaddr *)&destAddr, sizeof(destAddr)))
		{
			printf("Connect error ");
			FD_ZERO(&writeSet);
			FD_SET(socketDescriptor, &writeSet);
			retVal = select(socketDescriptor + 1, NULL, &writeSet, NULL, &tv);
			if (retVal == SOCKET_ERROR)
			{
				printf("Send non-blocking error ");
				break;
			}
			else if (retVal == 0)
			{
				printf("Non-blocking connect time limit is expired");
				break;
				;
			}
		}
		printf("Connection with %s\n", SERVERADDR);

		while (1)
		{
			FD_ZERO(&readSet);
			FD_ZERO(&writeSet);
			FD_SET(socketDescriptor, &readSet);
			FD_SET(socketDescriptor, &writeSet);

			retVal = select(1, &readSet, &writeSet, NULL, &tv);

			if (retVal == SOCKET_ERROR)
			{
				printf("Select error ");
				break;
			}
			else if (retVal == 0)
			{
				printf("Time limit is expired ");
				continue;
			}
			char *testmsg = "Hello, Earth!\n";
			if (FD_ISSET(socketDescriptor, &writeSet) != 0)
			{
				if (send(socketDescriptor, testmsg, strlen(testmsg), 0) == SOCKET_ERROR)
				{
					printf("Send error ");
					break;
				}
				printf("Send function - OK\n");
			}
			if (FD_ISSET(socketDescriptor, &readSet) != 0)
			{
				if ((numBytes = recv(socketDescriptor, bufferData, MAXDATASIZE, 0)) == SOCKET_ERROR)
				{
					printf("Recv error ");
					break;
				}
				printf("Recv function - OK\n");
			}
			bufferData[numBytes] = '\0';
			printf("Received text: %s\n", bufferData);
		}
	} while (FALSE);

	printf("- Error code: %d\n", WSAGetLastError());
	closesocket(socketDescriptor);
	WSACleanup();
	return 0;
}

Client: not sure but it seems almost ok. I get my sockDescriptor, make my socket non-blocking using ioctlsocket function, then make connection with connect. As I need to send a message I set my writeSet with FD_ZERO and FD_SET and use select function. It seems fine (or not?)

After I have to wrtie my logic in while(1) cycle. I set up my read and write descriptors, user select function (is it used correct?) and check my write descriptor if it ready to send a message. Then send. And the same with recv. After I need to add the symbol of the end of string "\0" and print my text received from server.

Server: first of all I wanna talk about the list of connected clients. I wrote a structure (client) and a few function to work with them (In the end of this post I'll show my list function, how it should work). The function pushBack make a list, print, obviously, print the list. How to add my new client to this list? And I also have to clean the memory. As I didn't get how to add my client, I don't know how to clean that.

Then my server logic: socket -> bind -> listen and while(1) where I set up my readfds and writefds>. Then I use select for my socketDescriptor and if everything is ok I check if it's ready for work. Then accept for my new client user (newSocketDescriptor - is that what I whould add to my list?). Then I try to add to my list (not even sure if it works fine). nclients is my client counter. Then I make FD_SET for my newSocketDescriptor and AFTER here is my issue where I'm not even sure what started to happen. I use recv, check if the user is disconnected and if it's not - send message and FD_CLR my newSocketDescriptor.
Server output in cmd:

Setup SERVER socket descriptor number: 256
CHECK FD_ISSET value #1: 1
Client socket 264 successfully added to the list
We have 1 user online
Server got connection from 127.0.0.1
CHECK FD_ISSET value #2: 1
newSocketDescriptor = 264, READ_FD status #1 after accept = 1
SockOpt Value: 0. Error code: 0
Client socket 264 successfully added to the list
Client socket 264 successfully added to the list
Recv: retVal = 1, bufferData = Hello, Earth!
Hello, Earth!
Hello, Earth!

newSocketDescriptor = 264, READ_FD status #2 after recv = 1
newSocketDescriptor = 264, READ_FD status #3 after send = 1
Setup SERVER socket descriptor number: 256

Client output:

Attempt to connect 127.0.0.1:3765
Connect error Connection with 127.0.0.1
Send function - OK
Received text: ä
Send function - OK
Received text: ä
Send function - OK
Received text: ä
Send function - OK
Received text: ä
Send function - OK
Received text: ä
Send function - OK
eceived text: ä

Send error - Error code: 10054

As you cand see I have the error with 10054 code but couldn't get for 1.5 days where is the problem. Could you help me, please?

I also don't understand why I receive a few messages in server and client part (there is a random symbol everytime in client part, don't also understand why). Why?

Thank you for attention, the question is big, sorry for that.