C语言 如何使用setsockopt(SO_REUSEADDR)？

How do I use setsockopt(SO_REUSEADDR)?

提问by user3735849

I am running my own http server on a raspberry pi. The problem is when I stop the program and restart it, the port is no longer available. Sometimes I get the same issue when receiving lots of requests.
I want to use SO_REUSEADDR so that I can keep using the port even when the error occurs but have had no luck getting it set up. Below is my code.
The error I get is "ERROR on binding:Address already in use".

我在树莓派上运行我自己的 http 服务器。问题是当我停止程序并重新启动它时，端口不再可用。有时我在收到大量请求时会遇到同样的问题。
我想使用 SO_REUSEADDR，这样即使发生错误，我也可以继续使用该端口，但没有成功设置它。下面是我的代码。
我得到的错误是“绑定错误：地址已在使用中”。

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

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
    printf("Starting Listener\n");
     int sockfd, newsockfd, portno;
     socklen_t clilen;
     char buffer[256];
     struct sockaddr_in serv_addr, cli_addr;
     int n;
     if (argc < 2) {
         fprintf(stderr,"ERROR, no port provided\n");
         exit(1);
     }
     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     if (sockfd < 0) 
        error("ERROR opening socket");
     bzero((char *) &serv_addr, sizeof(serv_addr));
     portno = atoi(argv[1]);
     serv_addr.sin_family = AF_INET;
     serv_addr.sin_addr.s_addr = INADDR_ANY;
     serv_addr.sin_port = htons(portno);
     if (bind(sockfd, (struct sockaddr *) &serv_addr,
              sizeof(serv_addr)) < 0) 
              error("ERROR on binding");

     printf("about to listen\n");
     listen(sockfd,5);
     printf("finished listening\n");
     clilen = sizeof(cli_addr);
     printf("About to accept\n");

     int i;
     for(i=0; i<100; i++){
         newsockfd = accept(sockfd, 
                 (struct sockaddr *) &cli_addr, 
                 &clilen);

         if (newsockfd < 0) 
             error("ERROR on accept");
         bzero(buffer,256);
         n = read(newsockfd,buffer,255);
         if (n < 0) error("ERROR reading from socket");
         printf("Here is the message: %s\n",buffer);
         n = write(newsockfd,"I got your message",18);
         if (n < 0) error("ERROR writing to socket");
         close(newsockfd);
     }
     close(sockfd);
     return 0; 
}

回答by Chnossos

After :

后 ：

sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) 
    error("ERROR opening socket");

You can add (with standard C99 compound literalsupport) :

您可以添加（使用标准C99 复合文字支持）：

if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)
    error("setsockopt(SO_REUSEADDR) failed");

Or :

或者 ：

int enable = 1;
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(int)) < 0)
    error("setsockopt(SO_REUSEADDR) failed");

回答by mpromonet

Depending on the libc release it could be needed to set both SO_REUSEADDR and SO_REUSEPORT socket options as explained in socket(7)documentation :

根据 libc 版本，可能需要设置 SO_REUSEADDR 和 SO_REUSEPORT 套接字选项，如socket(7)文档中所述：

   SO_REUSEPORT (since Linux 3.9)
          Permits multiple AF_INET or AF_INET6 sockets to be bound to an
          identical socket address.  This option must be set on each
          socket (including the first socket) prior to calling bind(2)
          on the socket.  To prevent port hiHymaning, all of the
          processes binding to the same address must have the same
          effective UID.  This option can be employed with both TCP and
          UDP sockets.

   SO_REUSEPORT (since Linux 3.9)
          Permits multiple AF_INET or AF_INET6 sockets to be bound to an
          identical socket address.  This option must be set on each
          socket (including the first socket) prior to calling bind(2)
          on the socket.  To prevent port hiHymaning, all of the
          processes binding to the same address must have the same
          effective UID.  This option can be employed with both TCP and
          UDP sockets.

As this socket option appears with kernel 3.9 and raspberry use 3.12.x, it will be needed to set SO_REUSEPORT.

由于此套接字选项出现在内核 3.9 中，而 raspberry 使用 3.12.x，因此需要设置 SO_REUSEPORT。

You can set theses two options before calling bind like this :

您可以在调用 bind 之前设置这两个选项，如下所示：

    int reuse = 1;
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const char*)&reuse, sizeof(reuse)) < 0)
        perror("setsockopt(SO_REUSEADDR) failed");

#ifdef SO_REUSEPORT
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEPORT, (const char*)&reuse, sizeof(reuse)) < 0) 
        perror("setsockopt(SO_REUSEPORT) failed");
#endif

回答by Meir Gerenstadt

I think you should use SO_LINGER options (with timeout 0). In this case, you connection will close immediately after closing your program; and next restart will be able to bind again.

我认为您应该使用 SO_LINGER 选项（超时为 0）。在这种情况下，您的连接将在关闭程序后立即关闭；并且下次重新启动将能够再次绑定。

example:

例子：

linger lin;
lin.l_onoff = 0;
lin.l_linger = 0;
setsockopt(fd, SOL_SOCKET, SO_LINGER, (const char *)&lin, sizeof(int));

see definition: http://man7.org/linux/man-pages/man7/socket.7.html

见定义：http: //man7.org/linux/man-pages/man7/socket.7.html

SO_LINGER
          Sets or gets the SO_LINGER option.  The argument is a linger
          structure.

              struct linger {
                  int l_onoff;    /* linger active */
                  int l_linger;   /* how many seconds to linger for */
              };

          When enabled, a close(2) or shutdown(2) will not return until
          all queued messages for the socket have been successfully sent
          or the linger timeout has been reached.  Otherwise, the call
          returns immediately and the closing is done in the background.
          When the socket is closed as part of exit(2), it always
          lingers in the background.

More about SO_LINGER: TCP option SO_LINGER (zero) - when it's required

有关 SO_LINGER 的更多信息：TCP 选项 SO_LINGER（零）- 需要时