socket programming: 'accept: Bad file descriptor' - c++

Question

I'm trying to write a game that will let multiple clients connect and play - below is the relevant code (it's very messy - cleaning up later):
Edit: I realized it's a lot of scrolling... the crash occurs towards the end of the game during:
std::cout << black_hits << " black hits & " << white_hits
<< " white hits.\n";
if (black_hits == 4) {
std::cout << "you won!\n";
std::cin.ignore().get();
close(client); //<<<< CRASH HERE
return 0;
}
Not really a crash I guess... but close enough :)
#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <string>
#include <sstream>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>
#define BACKLOG 10
#define MAXDATASIZE 100
typedef enum {RED,GREEN,BLUE,YELLOW,ORANGE} color;
int StartMasterMind(int client, sockaddr_storage addr_in);
struct msgstruct {
int length;
char* send_data;
};
void sigchld_handler(int s)
{
while(waitpid(-1, NULL, WNOHANG) > 0);
}
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int tcp_connect(const char *serv, const char *host = NULL)
{
int sockfd, new_fd; // listen on sock_fd, new connection on new_fd
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage their_addr; // connector's address information
socklen_t sin_size;
struct sigaction sa;
int yes=1;
char s[INET6_ADDRSTRLEN];
int rv;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // use my IP
if ((rv = getaddrinfo(host, serv, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("server: socket");
continue;
}
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("server: bind");
continue;
}
break;
}
if (p == NULL) {
fprintf(stderr, "server: failed to bind\n");
return 2;
}
freeaddrinfo(servinfo); // all done with this structure
if (listen(sockfd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
sa.sa_handler = sigchld_handler; // reap all dead processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1) {
perror("sigaction");
exit(1);
}
printf("server: waiting for connections...\n");
while(1) { // main accept() loop
sin_size = sizeof their_addr;
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
if (new_fd == -1) {
perror("accept");
continue;
}
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr),
s, sizeof s);
printf("server: got connection from %s\n", s);
if (!fork()) { // this is the child process
close(sockfd); // child doesn't need the listener
//if (send(new_fd, "Hello, world!", 13, 0) == -1)
// perror("send");
//close(new_fd);
StartMasterMind(new_fd,their_addr);
// exit(0);
}
close(new_fd); // parent doesn't need this
}
return 0;
}
void InitializeGame(const char* port)
{
tcp_connect(port);
}
std::vector<color> GetInputAsColorMap(char* input)
{
[...]//redacted for clarity
}
int StartMasterMind(int client, sockaddr_storage addr_in)
{
struct msgstruct message;
struct sockaddr_storage their_addr = addr_in;
socklen_t addr_len;
message.send_data = "Welcome to ... M A S T E R M I N D.\n";
message.length = strlen(message.send_data);
send(client, message.send_data, message.length, 0);
[...]//redacted for clarity
if (strcmp(theValue, "random") == 0 || strcmp(theValue, "Random") == 0)
{
[...]//redacted for clarity
}
else
{
[...]//redacted for clarity
}
char* buf;
for (int i = 0; i < 8; ++i) {
std::vector<color> current_try(4);
int black_hits = 0, white_hits = 0;
std::vector<int> correctColorIndex;
std::vector<int> correctColor;
bool exclude[4] = {false};
std::cout << "test\n";
message.send_data = "Please enter your guess: ";
message.length = strlen(message.send_data);
send(client, message.send_data, message.length, 0);
addr_len = sizeof their_addr;
std::cout << "addr_len: " << addr_len << std::endl;
recvfrom(client, buf, MAXDATASIZE-1, 0, (struct sockaddr *)&their_addr, &addr_len);
current_try = GetInputAsColorMap(buf);
std::cout << "the buffer: " << buf << std::endl;
std::cout << "current_try: " << current_try[0] << current_try[1] << current_try[2] << current_try[3] << std::endl;
[...]//redacted for clarity
std::cout << black_hits << " black hits & " << white_hits
<< " white hits.\n";
if (black_hits == 4) {
std::cout << "you won!\n";
std::cin.ignore().get();
close(client); //<<<< CRASH HERE
return 0;
}
}
[...]//redacted for clarity
}
int main(int argc, char** argv)
{
InitializeGame(argv[1]);
return 0;
}
Here is sample output:
server: waiting for connections...
server: got connection from 127.0.0.1
value or random:
1122
test
addr_len: 128
the buffer: 1123�
current_try: 1123
3 black hits & 0 white hits.
test
addr_len: 128
the buffer: 1223�
current_try: 1223
2 black hits & 1 white hits.
test
addr_len: 128
the buffer: 1122�
current_try: 1122
4 black hits & 0 white hits.
you won!
accept: Bad file descriptor
accept: Bad file descriptor
accept: Bad file descriptor
... // continuously, hundreds of times
I'm very new to socket programming; could someone give me a hand? This crashes with or without trying to close(client) at the end of the game.

Answer 1

I think when the child process is wrapping back to start of while(1) loop, it tries to accept a connection with server socket descriptor = "sockfd" which you already closed for the child:
if (!fork()) { // this is the child process
close(sockfd);
....
}
Try this link to read as how to terminate the child process after its work is complete.

Answer 2

That message means that you're calling accept() on an invalid file descriptor, i.e. probably one that you've closed.