套接字编程：'接受：错误的文件描述符'

Posted 2023-02-17

【中文标题】套接字编程：\'接受：错误的文件描述符\'

【英文标题】：socket programming: 'accept: Bad file descriptor'套接字编程：'接受：错误的文件描述符'

【发布时间】：2014-02-06 06:51:56

【问题描述】：

我正在尝试编写一个可以让多个客户端连接和玩的游戏 - 下面是相关代码（非常混乱 - 稍后清理）：

编辑：我意识到这是很多滚动...崩溃发生在游戏结束时：

    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;
    

我猜这不是真正的崩溃......但足够接近:)

---

#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;

---

这是示例输出：

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

---

我对套接字编程很陌生；有人可以帮帮我吗？无论是否在游戏结束时尝试close(client)，这都会崩溃。

【问题讨论】：

如果显示accept: Bad file descriptor，“崩溃”怎么会出现在close(client)。这肯定意味着accept 的问题。

你说得对，对不起——我对此很陌生，还没有弄清楚如何在 gdb 下有效地调试——但是，我想accept: 应该已经放弃了.. :)

【参考方案1】：

我认为当子进程返回到while(1) 循环的开始时，它会尝试accept 与您已经为子进程关闭的服务器套接字描述符 = "sockfd" 的连接：

if (!fork())  // this is the child process
            close(sockfd);
....

尝试this link 来解读如何在子进程的工作完成后终止子进程。

【讨论】：

我认为与上述答案相同，可能您可能会打开服务器套接字。在这种情况下，您所有的孩子都会尝试接受连接。或者您可能希望在子进程完成后退出它。

我刚刚测试了注释掉close(sockfd)，它似乎已经奏效了！但是，这似乎很糟糕......我想在什么时候关闭 sockfd？

因为服务器套接字正在接受连接，您应该在代码的最后部分关闭套接字。就像从函数返回之前一样。

好的，那么假设对于这么小的应用程序我不需要担心关闭套接字是否安全（因为那时我的程序很可能会退出）？

据我所知，如果您不关闭文件描述符套接字，内核将在程序退出时关闭所有这些。但关闭它们总是好的。

【参考方案2】：

该消息意味着您在一个无效的文件描述符上调用 accept()，即可能您已关闭的文件描述符。

【讨论】：

[edited] -- Sike，我撒谎了。看起来我完全按照@MadHatter 的建议关闭了 sockfd。