Thread: cannot establish two way communication

hello, i am trying to implement a client and server program. i have managed to establish one way communication btw client and server where server can continuously receive messages from client until i press Ctrl-C upon which connection closes.

now i want to establish continuous two way communication. i can paste my code if u want but i wanted to know if there are any specific methods that i should look up and understand how to establish two way communication?? all i did was have both send() and recv() functions inside infinite loops but that didnt do anything!!

wud appreciate some help!!!!

here is my code. this is the farthest i have reached. i just want to now figure out full duplex btw client and server like chatting

Client:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>


#define PORT 3490
#define MAXSIZE 1024


int main(int argc, char *argv[])
{
	struct sockaddr_in server_info;
	struct hostent *he;
	int socket_fd,num;
	char buffer[1024];
	
	char buff[1024];
	
	if (argc != 2) {
		fprintf(stderr, "Usage: client hostname\n");
		exit(1);
	}
	
	if ((he = gethostbyname(argv[1]))==NULL) {
		fprintf(stderr, "Cannot get host name\n");
		exit(1);
	}
	
	if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
		fprintf(stderr, "Socket Failure!!\n");
		exit(1);
	}
	
	memset(&server_info, 0, sizeof(server_info));
	server_info.sin_family = AF_INET;
	server_info.sin_port = htons(PORT);
	server_info.sin_addr = *((struct in_addr *)he->h_addr);
	if (connect(socket_fd, (struct sockaddr *)&server_info, sizeof(struct sockaddr))<0) {
		fprintf(stderr, "Connection Failure\n");
		exit(1);
	}
	while(1) {
		fgets(buffer,MAXSIZE-1,stdin);
		if ((send(socket_fd,buffer, strlen(buffer),0))== -1) {
			fprintf(stderr, "Failure Sending Message\n");
			close(socket_fd);
			exit(1);
		}
		else {
			printf("Client sent: %s\n",buffer);
		}		
		num = recv(socket_fd, buffer, 1023,0);
		if (num == -1) {
			fprintf(stderr, "Failure Sending Message\n");
			close(socket_fd);
			exit(1);
			}
		else if (num == 0) {
			printf("Connection closed\n");
			return 0;
		}
		buffer[num] = '\0';
		printf("Client received: %s\n",buffer);			
		//}
	}		
	close(socket_fd);		
}

Server:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>


#define PORT 3490
#define BACKLOG 10


int main()
{
	struct sockaddr_in server;
	struct sockaddr_in dest;
	int status,socket_fd, client_fd,num;
	socklen_t size;
	char buffer[10241];
	char *buff;
	
	if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
		fprintf(stderr, "Socket failure!!\n");
		exit(1);
	}	
	memset(&server, 0, sizeof(server));
	memset(&dest,0,sizeof(dest));
	server.sin_family = AF_INET;
	server.sin_port = htons(PORT);
	server.sin_addr.s_addr = INADDR_ANY; 
	if ((bind(socket_fd, (struct sockaddr *)&server, sizeof(struct sockaddr )))== -1)	 { //sizeof(struct sockaddr) 
		fprintf(stderr, "Binding Failure\n");
		exit(1);
	}	
	if ((listen(socket_fd, BACKLOG))== -1){
		fprintf(stderr, "Listening Failure\n");
		exit(1);
	}	
	while(1) {
		size = sizeof(struct sockaddr_in);	
		if ((client_fd = accept(socket_fd, (struct sockaddr *)&dest, &size))==-1) {
			//fprintf(stderr,"Accept Failure\n");
			perror("accept");
			exit(1);
		}
		printf("Server got connection from client %s\n", inet_ntoa(dest.sin_addr));
		while(1) {
			
			if ((num = recv(client_fd, buffer, 1024,0))== -1) {
				perror("recv");
				exit(1);
			}	
			else if (num == 0) {
				printf("Connection closed\n");
				return 0;
			}
		buffer[num] = '\0';
		printf("Server received: %s\n", buffer);
		fgets(buffer,1023,stdin);
		if (send(client_fd,buffer,strlen(buffer),0)==-1) {
			fprintf(stderr,"Failure sending message\n");
			close(client_fd);
			exit(1);
		}
		else {
		printf("Server sent: %s\n", buffer);
		
		}
	}
	close(client_fd);	
	close(socket_fd);	
	
	}


	return 0;
}

If you want an asynchronous chat, you need to have a look at the select or poll functions. From the looks of your code though, I think you will have a hard time integrating either function.

I fixed your code up a bit.

CLIENT:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
	struct sockaddr_in server_info;
	struct hostent *he;
	int socket_fd, num, portno, yes = 1;
	char buffer[1024];
	
	if (argc != 3) {
		printf("USAGE: %s + hostname + port\n", argv[0]);
		exit(1);
	}
	
	if ((he = gethostbyname(argv[1]))==NULL) {
		fprintf(stderr, "Cannot get host name\n");
		exit(1);
	}
	
	if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
		fprintf(stderr, "Socket Failure!!\n");
		exit(1);
	}

	setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));	

	memset(&server_info, 0, sizeof(server_info));
	portno = atoi(argv[2]);
	server_info.sin_family = AF_INET;
	server_info.sin_port = htons(portno);
	memcpy(&server_info.sin_addr.s_addr, he->h_addr, he->h_length);
	//or you could use -> server_info.sin_addr.s_addr = htonl(INADDR_ANY);
	if (connect(socket_fd, (struct sockaddr *)&server_info, sizeof(server_info)) < 0) {
		fprintf(stderr, "Connection Failure\n");
		exit(1);
	}
	while(1) {
		memset(buffer, 0, sizeof(buffer));
		printf("Message: ");
		fgets(buffer, sizeof(buffer), stdin);
		if ((send(socket_fd, buffer, strlen(buffer), 0)) < 0) {
			fprintf(stderr, "Failure Sending Message\n");
			close(socket_fd);
			exit(1);
		}
	
		num = recv(socket_fd, buffer, sizeof(buffer), 0);
		if (num == -1) {
			fprintf(stderr, "Failure Sending Message\n");
			close(socket_fd);
			exit(1);
			}
		else if (num == 0) {
			printf("Connection closed\n");
			return 0;
		}
		
		printf("Server: %s\n",buffer);			

	}		
	close(socket_fd);		
}

SERVER:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

int main(int argc, char *argv[])
{
	if(argc < 3) {
	printf("USAGE: %s + hostaddr + port.\n", argv[0]);
	exit(1);
	}

	struct sockaddr_in server;
	struct sockaddr_in dest;
	struct hostent *he;
	int socket_fd, client_fd, num, portno, yes = 1;
	socklen_t size;
	char buffer[1024];
	
	if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
		fprintf(stderr, "Socket failure!!\n");
		exit(1);
	}
	
	if(socket_fd) {
	  do {
	    {
	    printf("waiting for a connection.\n");
	    }
	  } while(!accept);
	}

	setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));

	he = gethostbyname(argv[1]);
	if(he == NULL) {
	//This error handling requires errno.h
	printf("GETHOSTBYNAME(NULL) error --> %s.\n", strerror(errno));
	exit(1);
	}

	memset(&server, 0, sizeof(server));
	memset(&dest,0,sizeof(dest));
	portno = atoi(argv[2]);
	server.sin_family = AF_INET;
	server.sin_port = htons(portno);
	memcpy(&server.sin_addr.s_addr, he->h_addr, he->h_length);
	if ((bind(socket_fd, (struct sockaddr *)&server, sizeof(server)))== -1)	 { 
		fprintf(stderr, "Binding Failure\n");
		close(socket_fd);
		exit(1);
	}	
	if ((listen(socket_fd, 10))== -1){
		fprintf(stderr, "Listening Failure\n");
		exit(1);
	}	
	
		size = sizeof(dest);	
		if ((client_fd = accept(socket_fd, (struct sockaddr *)&dest, &size))==-1) {
			//fprintf(stderr,"Accept Failure\n");
			perror("accept");
			exit(1);
		}

		printf("Server got connection from client %s\n", inet_ntoa(dest.sin_addr));
		while(1) {
			
			memset(buffer, '\0', sizeof(buffer));			
			if ((num = recv(client_fd, buffer, sizeof(buffer), 0)) < 0) {
				perror("recv");
				exit(1);
			}	

			else if (num == 0) {
				printf("Connection closed\n");
				return 0;
			}

		printf("Client: %s\n", buffer);

		printf("Message: ");
		fgets(buffer, sizeof(buffer), stdin);
		if (send(client_fd, buffer, strlen(buffer), 0) < 0) {
			fprintf(stderr,"Failure sending message\n");
			close(client_fd);
			exit(1);
		}

	}
	close(client_fd);	
	close(socket_fd);	
	

	return 0;
}

why will it be a hard time integrating select and poll??
also, i used fork() to enable full duplex communication....is that ok too?? or is the select/poll method a better solution??