c - 接受函数不等待连接(不阻塞)

Question

我正在尝试用 C 语言制作一个简单的套接字服务器，并按照“The Art Of Exploitation”一书中的教程进行操作

每次我尝试运行服务器时，都会得到输出:

Could not accept new connection

我的C代码:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PORT 4444

int main(void) {
    // Declare initial values;
    int domain, sock_fd, type;
    struct sockaddr_in localAddr;
    socklen_t addr_length;
    ...
    sock_fd = socket(domain, type, 0);
    ...
    bind(sock_fd, (struct sockaddr *) &localAddr, sizeof(struct sockaddr))
    ...
    // Setup listening
    sock_fd = listen(sock_fd, 1);
    char buffer[1024];
    int sin_size, recv_len;
    while (1) {
        int client_fd;
        struct sockaddr_in clientAddr;
        sin_size = sizeof(clientAddr);
        client_fd = accept(sock_fd, (struct sockaddr *) (&clientAddr), &sin_size);
        if (client_fd == -1) { <----------- HERE
            printf("Could not accept new connection");
            exit(-1);
        }   
        close(client_fd);
    }
    close(sock_fd);
    return 0;
}

Answer 1

编译器针对您的代码给出了许多错误和警告。

但我猜破坏交易的是你正在做的事情，

 sock_fd = listen(sock_fd, 1);

应该是，

 listen(sock_fd, 1);

并且您正在使用带有未初始化变量的套接字命令。

// sock_fd = socket(domain, type, 0); // wrong
(sock_fd=socket(AF_INET,SOCK_STREAM,0); // correct

以下设置也丢失了，

// The following three lines were missing
localAddr.sin_family = AF_INET;
localAddr.sin_addr.s_addr = htonl(INADDR_ANY);
localAddr.sin_port = htons(PORT);

这是带有更多修复的完整代码，其中仍然有一些有关未使用变量等的警告，但至少它一直“准备好接受连接”。

您确实应该打开编译器上所有可能的警告并阅读 Beej's network programming book .

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PORT 4444

int main(void) {
    // Declare initial values;
    int domain, sock_fd, type;
    struct sockaddr_in localAddr;

    // The following three lines were missing
    localAddr.sin_family = AF_INET;
    localAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    localAddr.sin_port = htons(PORT);

    socklen_t addr_length;

    // sock_fd = socket(domain, type, 0);
    //////////////////////Creating a SOCKET/////////////////////////
    if((sock_fd=socket(AF_INET,SOCK_STREAM,0))==-1)
    {
        printf("ERROR:Socket failed\n");
        return -1;
    }

    if (bind(sock_fd, (struct sockaddr *) &localAddr, sizeof(struct sockaddr)) == -1)
    {
        printf("ERROR:Binding on server\n");
        close(sock_fd);
        return -1;
    }

    // Setup listening
    listen(sock_fd, 1);
    char buffer[1024];
    int sin_size, recv_len;
    while (1) {
        int client_fd;
        struct sockaddr_in clientAddr;
        sin_size = sizeof(clientAddr);
        client_fd = accept(sock_fd, NULL, NULL);
        if (client_fd == -1) {
            printf("Could not accept new connection");
            exit(-1);
        }
        close(client_fd);
    }
    close(sock_fd);
    return 0;
}