multiclientserver.c

/*

fork() in C

Fork system call use for creates a new process, which is called child process, which runs concurrently with process (which process called system call fork) and this process is called parent process. After a new child process created, both processes will execute the next instruction following the fork() system call. A child process uses the same pc(program counter), same CPU registers, same open files which use in the parent process.

It takes no parameters and returns an integer value. Below are different values returned by fork().

Negative Value: creation of a child process was unsuccessful.
Zero: Returned to the newly created child process.
Positive value: Returned to parent or caller. The value contains process ID of newly created child process.

*/

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

#define PORT 4444

int main(){

	int sockfd, ret;
	 struct sockaddr_in serverAddr;

	int newSocket;
	struct sockaddr_in newAddr;

	socklen_t addr_size;

	char buffer[1024];
	pid_t childpid;

	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	if(sockfd < 0){
		printf("[-]Error in connection.\n");
		exit(1);
	}
	printf("[+]Server Socket is created.\n");

	memset(&serverAddr, '\0', sizeof(serverAddr));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_port = htons(PORT);
	serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");

	ret = bind(sockfd, (struct sockaddr*)&serverAddr, sizeof(serverAddr));
	if(ret < 0){
		printf("[-]Error in binding.\n");
		exit(1);
	}
	printf("[+]Bind to port %d\n", 4444);

	if(listen(sockfd, 10) == 0){
		printf("[+]Listening....\n");
	}else{
		printf("[-]Error in binding.\n");
	}


	while(1){
		newSocket = accept(sockfd, (struct sockaddr*)&newAddr, &addr_size);
		if(newSocket < 0){
			exit(1);
		}
		printf("Connection accepted from %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));

		if((childpid = fork()) == 0){//This is the child process so it shouldn't use the main listening socket
			//Also only the child should talk to newly accepted client via newSocket and main parent process shouldn't
			close(sockfd);

			while(1){
				int l = recv(newSocket, buffer, 1024, 0);
				buffer[l] = '\0';
				if(strcmp(buffer, ":exit") == 0){
					printf("Disconnected from %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
					break;
				}else{
					printf("%s:%d: %s\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port), buffer);
					send(newSocket, buffer, strlen(buffer), 0);
					bzero(buffer, sizeof(buffer));
				}
			}
		}

	}

	close(newSocket);


	return 0;
}