Socket Programming in C: When client exit server, the server is crashed - c

Question

I run a socket programming code for communication of multiple clients with one server. Everything happens properly but when I ctrl C to exit one of client, the server does not show as I expected. Below is the code:
Client.c
#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 clientSocket, ret;
struct sockaddr_in serverAddr;
char buffer[1024];
clientSocket = socket(AF_INET, SOCK_STREAM, 0);
if(clientSocket < 0){
printf("[-]Error in connection.\n");
exit(1);
}
printf("[+]Client 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 = connect(clientSocket, (struct sockaddr*)&serverAddr, sizeof(serverAddr));
if(ret < 0){
printf("[-]Error in connection.\n");
exit(1);
}
printf("[+]Connected to Server.\n");
while(1){
printf("Client: \t");
scanf("%s", &buffer[0]);
send(clientSocket, buffer, strlen(buffer), 0);
if(strcmp(buffer, ":exit") == 0){
close(clientSocket);
printf("[-]Disconnected from server.\n");
exit(1);
}
if(recv(clientSocket, buffer, 1024, 0) < 0){
printf("[-]Error in receiving data.\n");
}else{
printf("Server: \t%s\n", buffer);
}
}
return 0;
}
Server.c
#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){
close(sockfd);
while(1){
recv(newSocket, buffer, 1024, 0);
if(strcmp(buffer, ":exit") == 0){
printf("Disconnected from %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
break;
}else{
printf("Client: %s\n", buffer);
send(newSocket, buffer, strlen(buffer), 0);
bzero(buffer, sizeof(buffer));
}
}
}
}
close(newSocket);
return 0;
}
When I press ctrl C to exit the client. On the server side, it shows:
Client:
Client:
Client:
Client:
and it's seem to loop "Client:" forever instead of showing message of printf"Disconnected from..." and continue to work with other clients as I expected. I look at this code from on youtube, they can run it properly in the video but I do not know why when I download this code and run on my computer, it gets that problem. Can anyone help me to fix that problem so that the server can print the message "Disconnection...". Thank you.

Answer 1

When I press ctrl C to exit the client. On the server side, it shows:
Client:
Client:
Client:
Client:
and it's seem to loop "Client:" forever instead of showing message of
printf"Disconnected from..." and continue to work with other clients
as I expected.
Your code prints the disconnection message and exits the loop only if it receives an ":exit" message from the client. If you kill the client with a Ctrl-C, then it terminates without sending any such message.
Robust server code would check the return value of the recv() call, which would return -1 to signal an error. Your server ignores that and just tries to read again, and again, and again. Although you cannot rely on getting an error in every scenario where the client goes away, the fact that your server keeps printing "Client:" indicates that you are getting one in this case.
I look at this code from on youtube, they can run it properly in the
video but I do not know why when I download this code and run on my
computer, it gets that problem.
Either what they demonstrated in the video was different from the code you've presented (maybe the video was deceptive about that), or they exited the client by typing an ":exit" command, not just killing the client.

Answer 2

It sounds like your client isn't properly closing the connection. If you're using Ctrl C to stop the client, then you are killing the client program and not breaking the loop. If you want to stop the client that way, you should handle SIGINT and close the socket connection.