无法 printf 客户端 sun_path unix 域套接字

Question

这里是我使用的 UNIX 域服务器和客户端代码。 服务器和客户端通过相互接收消息来相互发送消息。

服务器代码通过填充 client_address 从 recvfrom 向客户端发送消息。 此外，正如您所看到的，这个 unix 域套接字代码使用抽象命名系统。 服务器名为 UnixServer，客户端名为 UnixClient。 如果服务器可以通过填充其 client_address 向客户端发送消息，我想看看该地址是什么。 这是一个有意义的地址，我可以将其打印为#UdsClient 等吗？

服务器代码：

#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h> 
#include <string.h>

#include <unistd.h>`

#define SERVER_SOCKET "#UdsServer" // The # is replaced by 0 for abstract namespace

int main(void)
{
int socket_fd;
struct sockaddr_un server_address, client_address; 
int bytes_received, bytes_sent, integer_buffer;


socklen_t address_length = sizeof(server_address.sun_family)+strlen(SERVER_SOCKET );

if ((socket_fd = socket(AF_UNIX, SOCK_DGRAM, 0)) < 0)
{
    perror("server: socket");
    return -1;
}

memset(&server_address, 0, sizeof(server_address));
server_address.sun_family = AF_UNIX;
memcpy(server_address.sun_path, SERVER_SOCKET,sizeof(SERVER_SOCKET)-1);// the path is not a C string, and is not NULL turminated
server_address.sun_path[0] = 0; 

if (bind(socket_fd,
         (const struct sockaddr *) &server_address,
         address_length) < 0)
{
    perror("server: bind");
    close(socket_fd);        
    return -1;
}

for (;;)
{
    bytes_received = recvfrom(socket_fd,
                              &integer_buffer,
                              sizeof(integer_buffer),
                              0, 
                              (struct sockaddr *) &client_address,
                              &address_length);

    

    struct sockaddr_storage ss;
    socklen_t sslen = sizeof(struct sockaddr_storage);
    if (getsockname(socket_fd, (struct sockaddr *)&ss, &sslen) == 0) {
           struct sockaddr_un *un = (struct sockaddr_un *)&ss;
           printf("socket name is: %s\n", un->sun_path);
    }

    if(bytes_received != sizeof(integer_buffer))
    {
        printf("Error: recvfrom - %d.\n", bytes_received);

    } else {
        printf("received: %d.\n", integer_buffer);



        integer_buffer += 10;

        bytes_sent = sendto(socket_fd,
                            &integer_buffer,
                            sizeof(integer_buffer),
                            0,
                            (struct sockaddr *) &client_address, 
                            address_length);

    //printf("clientaddress: %s", client_address.sa_data);
    }
}

close(socket_fd);

return 0;
}

客户代码：

#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define SERVER_SOCKET "#UdsServer" 
#define CLIENT_SOCKET "#UdsClient"
int main(void)
{
int socket_fd;
struct sockaddr_un server_address, client_address; 
int bytes_received, bytes_sent, integer_buffer;
socklen_t address_length = sizeof(server_address.sun_family) + strlen(CLIENT_SOCKET);

if((socket_fd = socket(AF_UNIX, SOCK_DGRAM, 0)) < 0)
{
    perror("client: socket");
    return -1;
}

memset(&client_address, 0, sizeof(client_address));
client_address.sun_family = AF_UNIX;
memcpy(client_address.sun_path, CLIENT_SOCKET,sizeof(CLIENT_SOCKET )-1 );
client_address.sun_path[0] = 0;

if(bind(socket_fd,
        (const struct sockaddr *) &client_address, 
        address_length) < 0)
{
    perror("client: bind");
    return -1;
}

memset(&server_address, 0, sizeof(server_address));
server_address.sun_family = AF_UNIX;
memcpy(server_address.sun_path, SERVER_SOCKET,sizeof(SERVER_SOCKET)-1);
server_address.sun_path[0] = 0;

integer_buffer = 1;

for (;;)
{
   bytes_sent = sendto(socket_fd, 
                       &integer_buffer,
                       sizeof(integer_buffer),
                       0,
                       (struct sockaddr *) &server_address, 
                       address_length);
      printf("clientaddress: %s", server_address.sun_path);

   bytes_received = recvfrom(socket_fd,
                             &integer_buffer,
                             sizeof(integer_buffer),
                             0, 
                             (struct sockaddr *) &server_address,
                             &address_length);
     printf("clientaddress: %s", server_address.sun_path);

   if (bytes_received != sizeof(integer_buffer))
   {
       printf("Error: recvfrom - %d.\n", bytes_received);
       return -1;
   }

   printf("received: %d\n", integer_buffer);

   integer_buffer += 1;

   sleep(10);
}

close(socket_fd);

return 0;
}

此外，我尝试使用这些代码行打印它，但它什么也没打印：

   struct sockaddr_storage ss;
    socklen_t sslen = sizeof(struct sockaddr_storage);
    if (getsockname(socket_fd, (struct sockaddr *)&ss, &sslen) == 0) {
           struct sockaddr_un *un = (struct sockaddr_un *)&ss;
           printf("socket name is: %s\n", un->sun_path);
    } 

我在如何打印#UdsClient 或任何其他含义完整的东西时做错了什么？

编辑，我的解决方案

我相信这是一个相对容易的问题。 而不是最后一段代码，我可以阅读如下：

printf("socket name is: #%s\n", client_address.sun_path + 1);

所以路径被填充但是它不能直接打印出来，因为第一个字母是空的。

您也可以将此方法用于非抽象文件路径系统。

Answer 1

当您使用%s作为printf的格式说明符时，它会将相关参数视为空终止字符数组。 但是，您正在通过设置来使用抽象套接字...

server_address.sun_path[0] = 0;

因此printf会将server_address.sun_path视为零长度字符串——它对紧跟在前导空字符之后的数据一无所知。