正确使用getsockopt和setsockopt用于SO_RCVTIMEO和SO_SNDTIMEO

Question

由于各种原因,我想在读取和写入服务器中的套接字时实现超时但无法使其运行,因此请求了解问题可能存在的地方.

为了设置读取和写入套接字的超时,我正在尝试使用函数setsocketopt()和getsocketopt().但是我必须做错了,因为返回值表明发生了问题并且perror输出"Invalid argument".奇怪的是错误并不总是发生在第一次使用setsocketopt()和getsocketopt(),这令我费解位.

以下服务器和客户端代码重现我的问题(使用gcc编译)

服务器代码:

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

int main() {
   struct sockaddr_in saddr,caddr; 
   socklen_t clen;
   int sock, csock, reuse = 1, ret=0;
   socklen_t ntrcv, ntsnd;
   struct timeval tout, tsnd, trcv;

   // create a new stream socket
   if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) perror("failed to create socket");
   else {          
      // enable the socket to reuse the address
      if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0) perror("failed allowing server socket to reuse address");
      else {
         // set up the server address
         memset((char *) &saddr, 0, sizeof(saddr));
         saddr.sin_family = AF_INET;
         saddr.sin_addr.s_addr = inet_addr("127.0.0.1");
         saddr.sin_port = htons(45454);

         // bind socket to address
         if (bind(sock, (struct sockaddr *) &saddr, sizeof(saddr)) < 0) perror("failed to bind");
         else {
            // listen to the socket for connections 
            if (listen(sock,5) < 0) perror("failed to listen");
            else {
               clen = sizeof(caddr);
               if ((csock = accept(sock, (struct sockaddr *) &caddr, &clen)) < 0) perror("failed to accept");
               else {
                  tout.tv_sec=0;
                  tout.tv_usec=10000;

                  // check value of errno prior to setting timeout
                  perror("errno prior to timeout");

                  if (getsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &trcv, &ntrcv) < 0) perror("2");
                  else if (getsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, &tsnd, &ntsnd) < 0) perror("3");
                  else if (setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tout, sizeof(tout)) < 0) perror("4");
                  else if (setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, &tout, sizeof(tout)) < 0) perror("5");
                  else {
                     printf ("all ok so far in server\n");
                 sleep(1);
                     if (setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &trcv, ntrcv) < 0) perror("6");
                     else if (setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, &tsnd, ntsnd) < 0) perror("7");
                  }
                  if (close(csock) < 0) perror("failed to close csock");
               }
            }
         }
      }
   }
   if (close(sock) < 0) perror("failed to close sock");
   return ret;
}

客户代码:

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

int main() {
   struct sockaddr_in addr;     
   struct hostent *server; 
   int sock = 0;

   // resolve server name
   if (!(server = gethostbyname("127.0.0.1"))) perror("failed to resolve host");
   else {
      // prepare the server address
      memset((char *) &addr, 0, sizeof(addr));
      addr.sin_family = AF_INET;
      bcopy((char *)server->h_addr, (char *)&addr.sin_addr.s_addr, server->h_length);
      addr.sin_port = htons(45454);

      // create a socket and connect to the server
      if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) perror("failed to create client socket");
      else {
         if (connect(sock,(struct sockaddr *) &addr,sizeof(addr)) < 0) perror("failed to connect to server");
         else {
            printf("Connection is established will sleep now\n");
            sleep(3);
            printf("done sleeping\n");
            close(sock);
            printf("socket is closed\n");
         }
      }
   }
   return 0;
}

在本示例getsockopts()中,服务器中的第二次调用失败,导致perror("3")被调用.但是,如果我将此行注释掉,以及对setsockopts()第一次调用getsockopts()失败的最后一次调用(之前似乎有效).

我对出错的任何见解表示赞赏

Answer 1

您没有初始化ntsnd和ntrcv可用的缓冲区大小getsockopt.因此,如果随机值大于或等于所需的大小,则调用将成功.否则它会失败EINVAL.从手册页:

参数optval和optlen用于访问选项值setsockopt().因为getsockopt()它们标识了一个缓冲区,在该缓冲区中将返回所请求选项的值.For getsockopt(),optlen是一个value-result参数,最初包含指向的缓冲区的大小optval,并在返回时修改,以指示返回值的实际大小.如果没有提供或返回选项值,optval可能是NULL.

要解决这个问题,请将它们初始化为sizeof(struct timeval).