錯誤的檔案描述符：accept()上的錯誤（套接字）-有解無憂

我正在嘗試在 Linux 中使用 TCP 協議撰寫一個簡單的聊天應用程式，其中服務器從客戶端接收字串并將字串大小發送到客戶端。當我運行客戶端時，服務器拋出“錯誤的檔案描述符”錯誤并退出。盡管如此，如果我通過客戶端發送輸入字串，它會收到正確大小的字串，但正如我在服務器關閉之前所說的那樣。這是代碼：

服務器

#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);
}

客戶

#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);
}

uj5u.com熱心網友回復：

除了其他答案所說的：您永遠不會發送"exit"字串，但是"exit\n"（即后跟一個新檔案 -和1019 個零位元組），并且strcmp(buffer_str, "exit") == 0服務器中的永遠不會為真。

順便說一句，這段代碼被破壞了：

                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;

如果read回傳的正好是sizeof(buffer_str)位元組，則緩沖區可能不是以零結尾的，并且您不能使用strcmp它。而且我沒有看到將str_lenght(sic)設定為比字串的實際長度少 1 的意義。

uj5u.com熱心網友回復：

根據評論。您的服務器代碼基本上如下...

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);

吃了標記@Here您關閉偵聽檔案描述符的行，listen_fd這意味著下一個...

connect_fd = accept(listen_fd, (struct sockaddr *)&client, &len)

for (;;)由于listen_fd無效，回圈中的呼叫將失敗。

您隨后的評論表明這可能不是唯一的問題，但我很確定它是導致bad file descriptor: error on accept()錯誤訊息的原因。

uj5u.com熱心網友回復：

謝謝每一位。此代碼運行：

服務器

#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);
}

客戶

#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);
}

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標籤：C linux 插座

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