Segfault in client disconnection - c

Question

I have a simple client-server program implemented in C where a client can send integers to a server and the server replies with their sums. However, there is a troubling Segmentation fault (core dumped) shown on the server side whenever the client disconnects suddenly. The Client:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define PORT 5010
int main(int argc, char **argv) {
char buf[BUFSIZ], buf2[BUFSIZ], message[BUFSIZ], serverReply[BUFSIZ];
int SOCKET;
struct sockaddr_in server;
SOCKET = socket(AF_INET, SOCK_STREAM, 0);
if (SOCKET < 0) {
perror("Could not create socket");
return -1;
}
printf("Socket created\n");
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_family = AF_INET;
server.sin_port = htons(PORT);
if (connect(SOCKET, (struct sockaddr *) &server, sizeof(struct sockaddr_in)) < 0) {
perror("Could not connect");
return -1;
}
memset(&serverReply, 0, sizeof(serverReply));
printf("Connected to server.\nEnter first number: ");
scanf("%s", buf);
fflush(stdin);
printf("Enter second number: ");
scanf("%s", buf2);
strcat(buf, " ");
strcat(buf, buf2);
strcpy(message, buf);
if (send(SOCKET, message, strlen(message), 0) < 0) {
perror("Failed to send message");
return -1;
}
if (recv(SOCKET, serverReply, sizeof(serverReply), 0) < 0) {
perror("Could not receive message");
return -1;
}
printf("Server: %s", serverReply);
close(SOCKET);
}
The Server:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#define PORT 5010
int main(int argc, char *argv[]) {
char msg[BUFSIZ], reply[BUFSIZ];
struct sockaddr_in server, client;
int SOCKET, ACCEPT, READ, sockSize, num1, num2, option = 1, maxClients = 30,
h, clientSocket[maxClients], maxsd, sd, SELECT;
fd_set readfds;
for (h = 0; h < maxClients; h++) {
clientSocket[h] = 0;
}
SOCKET = socket(AF_INET, SOCK_STREAM, 0);
if (SOCKET == -1) {
perror("Could not create socket");
return -1;
}
if (setsockopt(SOCKET, SOL_SOCKET, SO_REUSEADDR, &option, sizeof(option)) == -1) {
perror("Could not set OPTNAME");
return -1;
}
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(PORT);
printf("Created socket.\n");
if (bind(SOCKET, (struct sockaddr *) &server, sizeof(server)) < 0) {
perror("Could not bind");
return -1;
}
if (listen(SOCKET, 1) < 0) {
perror("Listen failed");
return -1;
}
printf("Server is listening.\n");
sockSize = sizeof(struct sockaddr_in);
while (1) {
FD_ZERO(&readfds);
FD_SET(SOCKET, &readfds);
maxsd = SOCKET;
for (h = 0; h < maxClients; h++) {
sd = clientSocket[h];
if (sd > 0) { FD_SET(sd, &readfds); }
if (sd > maxsd) { maxsd = sd; }
}
SELECT = select(maxsd + 1, &readfds, NULL, NULL, NULL);
if ((SELECT < 0) && (errno != EINTR)) {
perror("select error");
}
if (FD_ISSET(SOCKET, &readfds)) {
ACCEPT = accept(SOCKET, (struct sockaddr *) &server, (socklen_t *) &sockSize);
if (ACCEPT < 0) {
perror("Could not accept client");
return -1;
}
for (h = 0; h < maxClients; h++) {
if (clientSocket[h] == 0) {
clientSocket[h] = ACCEPT;
break;
}
}
printf("Client has joined the server.\n");
}
for (h = 0; h < maxClients; h++) {
sd = clientSocket[h];
if (FD_ISSET(sd, &readfds)) {
READ = read(sd, msg, sizeof(msg));
if (READ == -1) {
perror("Could not receive message");
return -1;
}
if (READ == 0) {
printf("Client disconnected\n");
fflush(stdout);
clientSocket[h]=0;
}
int e = 0;
char *p = strtok(msg, " ");
char *arr[2];
while (p != NULL) {
arr[e++] = p;
p = strtok(NULL, " ");
}
num1 = atoi(arr[0]);
num2 = atoi(arr[1]);
if ((strcmp(arr[0], "0") != 0 && num1 != 0) && (strcmp(arr[1], "0") != 0 && num2 != 0)) {
printf("Client: %d, %d\n", num1, num2);
sprintf(reply, "%d\n", num1 + num2);
if (write(sd, reply, strlen(reply)) < 0) {
perror("Could not send message");
return -1;
}
memset(&reply, 0, sizeof(reply));
} else {
printf("Conversion error");
strcpy(reply, "Conversion error.");
if (write(sd, reply, strlen(reply)) < 0) {
perror("Could not send message");
return -1;
}
}
}
}
}
}
How can the segfault be solved? How else can the codes be improved?

Answer 1

The segfault comes from the atoi function since NULL is received. Checking for NULL seems to do the trick...