c - 如何从接受调用中获取套接字端口号 (C UNIX)

Question

我已经完成了一个简单的客户端/服务器程序，其中服务器等待外部连接，如果客户端的端口号在 [1025-2048] 范围内，则返回连接套接字，否则返回 -1。问题是，当我通过客户端地址(应该存储在 sockaddr 结构中)获取端口号时，它告诉我客户端端口号为零，但在客户端程序中我已经将客户端端口号设置为 1999。

服务器

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/signal.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <errno.h>


int function(int fd_socket) {

    int fd_socket_acc;
    int len;
    int port;
    struct sockaddr_in client_addr;

    puts("WAITING FOR CLIENT...");

    fd_socket_acc = accept(fd_socket, (struct sockaddr*)&client_addr, &len);

    puts("CONNECTION DONE.");

    port = ntohs (client_addr.sin_port);
    printf("client port number: %d \n", port);


    if (port >= 1024 && port <= 2048) {

        close (fd_socket_acc);
        return fd_socket_acc;
    }   
    else {
        close(fd_socket_acc);
        return -1;
    }
}

int main(int argc, char *argv[]) {


    int fd_socket;
    struct sockaddr_in local_addr;

    fd_socket = socket(AF_INET, SOCK_STREAM, 0);

    local_addr.sin_family = AF_INET;
    local_addr.sin_port = htons(1887);
    local_addr.sin_addr.s_addr = INADDR_ANY;

    bind(fd_socket, (struct sockaddr*)&local_addr, sizeof(local_addr));

    listen(fd_socket, 3);

    function(fd_socket);

    //close(fd_socket);

}

客户

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/signal.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <errno.h>

int main(int argc, char *argv[]) {

    int fd_socket;
    struct sockaddr_in local_addr;
    struct sockaddr_in server_addr;
    struct hostent *hp;

    fd_socket = socket(AF_INET, SOCK_STREAM, 0);

    local_addr.sin_family = AF_INET;
    local_addr.sin_port = htons(1999);
    local_addr.sin_addr.s_addr = INADDR_ANY;

    bind(fd_socket, (struct sockaddr*)&local_addr, sizeof(local_addr));

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(1887);
    //hostname is "ubuntu"
    hp = gethostbyname("ubuntu");
    bcopy(hp->h_addr, &server_addr.sin_addr, 4);

    printf("%d \n", ntohs(local_addr.sin_port));

    connect(fd_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

    wait(2);

    close(fd_socket);

}

如果我使用 printf("%d", ntohs(local_addr.sin_port)) 在客户端中获取端口号，它会正确标记 1999，但如果我得到服务器中客户端的端口号 printf("%d", ntohs(client_addr.sin_port)) 标记为 0。为什么？

提前致谢!

Answer 1

为了获取client_addr中的客户端端口号通过accept你必须告诉accept通过设置该缓冲区有多大

socklen_t len = sizeof(client_addr);

您也可以通过事后调用来检索它

len = sizeof(client_addr);
getpeername(fd_socket_acc, (struct sockaddr*)&client_addr, &len);