bad file descriptor: error on accept() (socket) - c

Question

I am trying to write a simple chat application using TCP protocol in Linux, in which server receives strings from the client and it sends strings size to the client. When I run client, the server throws a "Bad file descriptor" error and exits. Nevertheless if I send input strings by client it receives correct sizes of strings, but as I said before server goes down.
Here is the code :
SERVER
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#define MAX_LINE 1024
int main(int argc, char const *argv[]) {
int listen_fd, connect_fd, logging, str_lenght;
struct sockaddr_in serv_addr, client;
char buffer_str[MAX_LINE], buffer[MAX_LINE];
pid_t pid;
socklen_t len;
logging = 1;
if ((listen_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("socket");
exit(-1);
}
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(1024);
if (bind(listen_fd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
perror("bind");
exit(-1);
}
if (listen(listen_fd, 1024) < 0) {
perror("listen");
exit(-1);
}
for (;;) {
len = sizeof(client);
if ((connect_fd = accept(listen_fd, (struct sockaddr *)&client, &len)) < 0) {
perror("accept");
exit(-1);
}
if ((pid = fork()) < 0) {
perror("fork");
exit(-1);
}
if (pid == 0) {
close(listen_fd);
for (;;) {
bzero(buffer_str, MAX_LINE);
if (read(connect_fd, buffer_str, sizeof(buffer_str)) < 0) {
perror("read");
exit(-1);
}
if (strcmp(buffer_str, "exit") == 0) break;
str_lenght = (int)strlen(buffer_str) - 1;
bzero(buffer_str, MAX_LINE);
snprintf(buffer_str, sizeof(buffer_str), "%d\n", str_lenght);
if (write(connect_fd, buffer_str, sizeof(buffer_str)) < 0) {
perror("write");
exit(-1);
}
if (logging) {
inet_ntop(AF_INET, &client.sin_addr, buffer, sizeof(buffer));
printf("Request from host %s, port %d\n", buffer, ntohs(client.sin_port));
}
}
close(connect_fd);
exit(0);
} else close(listen_fd);
}
exit(0);
}
CLIENT
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#define MAX_LINE 1024
void clientEcho(int socket_fd) {
char recv_buffer[MAX_LINE], send_buffer[MAX_LINE];
for (;;) {
bzero(recv_buffer, MAX_LINE);
bzero(send_buffer, MAX_LINE);
printf("insert string: ");
if (fgets(send_buffer, sizeof(send_buffer), stdin) == NULL) {
perror("fgets");
return;
}
if (write(socket_fd, send_buffer, sizeof(send_buffer)) < 0) {
perror("write");
return;
}
if (strcmp(send_buffer, "exit") == 0) break;
if (read(socket_fd, recv_buffer, sizeof(recv_buffer)) < 0) {
perror("read");
return;
}
printf("string size: ");
if (fputs(recv_buffer, stdout) < 0) {
perror("fputs");
return;
}
}
}
int main(int argc, char const *argv[]) {
int socket_fd;
struct sockaddr_in serv_addr;
if (argc != 2) {
perror("usage: <IPaddress>");
exit(-1);
}
if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("socket");
exit(-1);
}
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(1024);
if (inet_pton(AF_INET, argv[1], &serv_addr.sin_addr) <= 0) {
perror("inet_pton");
exit(-1);
}
if (connect(socket_fd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
perror("connect");
exit(-1);
}
clientEcho(socket_fd);
close(socket_fd);
exit(0);
}

Answer 1

In addition to what the other answer says: you're never sending the "exit" string, but "exit\n" (i.e. followed by a newfile -- and 1019 zero bytes), and the strcmp(buffer_str, "exit") == 0 in the server will never be true.
BTW, this piece is code is broken:
bzero(buffer_str, MAX_LINE);
if (read(connect_fd, buffer_str, sizeof(buffer_str)) < 0) {
perror("read");
exit(-1);
}
if (strcmp(buffer_str, "exit") == 0) break;
str_lenght = (int)strlen(buffer_str) - 1;
If the read returns exactly sizeof(buffer_str) bytes, the buffer may not be zero-terminated, and you could not use strcmp on it. And I don't see the point of setting str_lenght (sic) to one less than the actual length of the string.

Answer 2

As per the comment. Your server code is essentially the following...
if (listen(listen_fd, 1024) < 0) {
perror("listen");
exit(-1);
}
for (;;) {
len = sizeof(client);
if ((connect_fd = accept(listen_fd, (struct sockaddr *)&client, &len)) < 0) {
perror("accept");
exit(-1);
}
if ((pid = fork()) < 0) {
perror("fork");
exit(-1);
}
if (pid == 0) {
...
exit(0);
} else {
close(listen_fd); /* #Here */
}
}
exit(0);
Ate the line marked #Here you close the listening file descriptor listen_fd meaning the next...
connect_fd = accept(listen_fd, (struct sockaddr *)&client, &len)
call in the for (;;) loop will fail due to listen_fd being invalid.
Your subsequent comments suggest that might not be the only issue but I'm pretty sure it's the one causing the bad file descriptor: error on accept() error message.

Answer 3

Thank you to every one. This code run:
SERVER
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#define MAX_LINE 1024
int main(int argc, char const *argv[]) {
int listen_fd, connect_fd, logging, str_lenght;
struct sockaddr_in serv_addr, client;
char buffer_str[MAX_LINE], buffer[MAX_LINE];
pid_t pid;
socklen_t len;
logging = 1;
if ((listen_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("socket");
exit(-1);
}
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(1024);
if (bind(listen_fd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
perror("bind");
exit(-1);
}
if (listen(listen_fd, 1024) < 0) {
perror("listen");
exit(-1);
}
for (;;) {
len = sizeof(client);
if ((connect_fd = accept(listen_fd, (struct sockaddr *)&client, &len)) < 0) {
perror("accept");
exit(-1);
}
if ((pid = fork()) < 0) {
perror("fork");
exit(-1);
}
if (pid == 0) {
for (;;) {
bzero(buffer_str, MAX_LINE);
if (read(connect_fd, buffer_str, sizeof(buffer_str)) < 0) {
perror("read");
exit(-1);
}
if (strcmp(buffer_str, "exit\n") == 0) break;
str_lenght = (int)strlen(buffer_str) - 1;
bzero(buffer_str, MAX_LINE);
snprintf(buffer_str, sizeof(buffer_str), "%d\n", str_lenght);
if (write(connect_fd, buffer_str, sizeof(buffer_str)) < 0) {
perror("write");
exit(-1);
}
if (logging) {
inet_ntop(AF_INET, &client.sin_addr, buffer, sizeof(buffer));
printf("Request from host %s, port %d\n", buffer, ntohs(client.sin_port));
}
}
close(connect_fd);
exit(0);
} else close(connect_fd);
}
exit(0);
}
CLIENT
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#define MAX_LINE 1024
void clientEcho(int socket_fd) {
char recv_buffer[MAX_LINE], send_buffer[MAX_LINE];
for (;;) {
bzero(recv_buffer, MAX_LINE);
bzero(send_buffer, MAX_LINE);
printf("insert string: ");
if (fgets(send_buffer, sizeof(send_buffer), stdin) == NULL) {
perror("fgets");
return;
}
if (write(socket_fd, send_buffer, sizeof(send_buffer)) < 0) {
perror("write");
return;
}
if (strcmp(send_buffer, "exit\n") == 0) break;
if (read(socket_fd, recv_buffer, sizeof(recv_buffer)) < 0) {
perror("read");
return;
}
printf("string size: ");
if (fputs(recv_buffer, stdout) < 0) {
perror("fputs");
return;
}
}
}
int main(int argc, char const *argv[]) {
int socket_fd;
struct sockaddr_in serv_addr;
if (argc != 2) {
perror("usage: <IPaddress>");
exit(-1);
}
if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("socket");
exit(-1);
}
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(1024);
if (inet_pton(AF_INET, argv[1], &serv_addr.sin_addr) <= 0) {
perror("inet_pton");
exit(-1);
}
if (connect(socket_fd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
perror("connect");
exit(-1);
}
clientEcho(socket_fd);
close(socket_fd);
exit(0);
}