Linux setsockopt和getsockopt函数的用法分析

套接字机制提供两个套接字选项来控制套接字行为。一个接口用来控制选项，另一个接口允许查询一个选项的状态。

1 #include <sys/types.h>
2 #include <sys/socket.h>
3
4 int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen);
5 int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen);
6 返回值：若成功则返回0，若出错则返回-1

参数说明：

sockfd:必须指向一个打开的套接字描述符。

level:标识了选项应用的协议。

optname:要设置或获取套接字选项的名字。

optval:指向函数设置或获取值得地址，即保存选项值的缓存区。

optlen:指定了optval指向的对象的大小。

示例1：使用选项SO_RCVBUF和SO_SNDBUF获取缓冲区大小

server.c

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<sys/types.h>
 4 #include<sys/socket.h>
 5 #include<unistd.h>
 6 #include<arpa/inet.h>
 7 #include<netinet/in.h>
 8 #include<string.h>
 9 #include<errno.h>
10
11 #define N 64
12 #define err_log(log) do{ perror(log); exit(1);}while(0)
13
14 int main(int argc, const char *argv[])
15 {
16     int sockfd, connectfd;
17     char buf[N];
18     struct sockaddr_in serveraddr, clientaddr;
19     int optval;
20     socklen_t optlen = sizeof(optval);
21     socklen_t len = sizeof(clientaddr);
22
23     if(argc != 3)
24     {
25         fprintf(stderr, "Usage:%s serverip port", argv[0]);
26         return -1;
27     }
28     sockfd = socket(AF_INET, SOCK_STREAM, 0);
29     if(sockfd < 0)
30         err_log("fail to sockfd");
31
32     serveraddr.sin_family = AF_INET;
33     serveraddr.sin_addr.s_addr = inet_addr(argv[1]);
34     serveraddr.sin_port = htons(atoi(argv[2]));
35
36     if(getsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, &optval, &optlen) < 0)
37         err_log("fail to getsockopt");
38     printf("SO_SNDBUF:%d K\n", optval/1024);
39
40     if(getsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &optval, &optlen) < 0)
41         err_log("fail to getsockopt");
42     printf("SO_RCVBUF:%d K\n", optval/1024);
43
44     if(bind(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0)
45         err_log("fail to bind");
46     if(listen(sockfd, 5) < 0)
47         err_log("fail to listen");
48     if((connectfd = accept(sockfd, (struct sockaddr*)&clientaddr, &len)) < 0)
49         err_log("fail to connectfd");
50
51     printf("client:%s--->%d\n", inet_ntoa(clientaddr.sin_addr), ntohs(clientaddr.sin_port));
52
53     while(1)
54     {
55         if(recv(connectfd, buf, N, 0) < 0)
56             err_log("fail to recv");
57         if(strncmp(buf, "quit", 4) == 0)
58             break;
59         buf[strlen(buf) - 1] = ‘\0‘;
60         printf("buf:%s\n", buf);
61         strcat(buf, "+++***---");
62         if(send(connectfd, buf, N, 0) < 0)
63             err_log("fail to send");
64     }
65     close(connectfd);
66     close(sockfd);
67     return 0;
68 }

client.c

 1 #include<stdio.h>
 2 #include<sys/types.h>
 3 #include<sys/socket.h>
 4 #include<unistd.h>
 5 #include<arpa/inet.h>
 6 #include<netinet/in.h>
 7 #include<string.h>
 8 #include<stdlib.h>
 9 #include<errno.h>
10
11 #define N 64
12 #define err_log(log) do{perror(log); exit(1);}while(0)
13
14 int main(int argc, const char *argv[])
15 {
16     int sockfd;
17     struct sockaddr_in serveraddr;
18     char buf[N];
19
20     if(argc != 3)
21     {
22         fprintf(stderr, "Usage:%s serverip port.", argv[1]);
23         return -1;
24     }
25     sockfd = socket(AF_INET, SOCK_STREAM, 0);
26     if(sockfd < 0)
27         err_log("fail to sockfd");
28
29     serveraddr.sin_family = AF_INET;
30     serveraddr.sin_addr.s_addr = inet_addr(argv[1]);
31     serveraddr.sin_port = htons(atoi(argv[2]));
32     if(connect(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0)
33         err_log("fail to connect");
34
35     while(1)
36     {
37         printf("<client>");
38         fgets(buf, N, stdin);
39         if(send(sockfd, buf, N, 0) < 0)
40             err_log("fail to send");
41         if(strncmp(buf, "quit", 4) == 0)
42             break;
43         if(recv(sockfd, buf, N, 0) < 0)
44             err_log("fail to recv");
45         printf("buf:%s\n", buf);
46     }
47     close(sockfd);
48     return 0;
49 }

服务器运行结果：

客户端运行结果：

示例2：使用选项SO_RCVTIMEO超时接收

server.c

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<sys/types.h>
 4 #include<sys/socket.h>
 5 #include<unistd.h>
 6 #include<netinet/in.h>
 7 #include<arpa/inet.h>
 8 #include<string.h>
 9 #include<errno.h>
10
11 #define N 64
12 #define err_log(log) do{ perror(log); exit(1);}while(0)
13
14 int main(int argc, const char *argv[])
15 {
16     int sockfd, connectfd;
17     char buf[N];
18     struct sockaddr_in serveraddr, clientaddr;
19     socklen_t len = sizeof(clientaddr);
20     struct timeval tv;
21     socklen_t optlen = sizeof(tv);
22
23     if(argc != 3)
24     {
25         fprintf(stderr, "Usage:%s serverip port", argv[0]);
26         return -1;
27     }
28
29     sockfd = socket(AF_INET, SOCK_STREAM, 0);
30     if(sockfd < 0)
31         err_log("fail to sockfd");
32
33     serveraddr.sin_family = AF_INET;
34     serveraddr.sin_addr.s_addr = inet_addr(argv[1]);
35     serveraddr.sin_port = htons(atoi(argv[2]));
36
37     tv.tv_sec = 5;
38     tv.tv_usec = 0;
39     if(setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, optlen) < 0)
40         err_log("fail to setsockopt");
41
42     if(bind(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0)
43         err_log("fail to bind");
44
45     if(listen(sockfd, 5) < 0)
46         err_log("fail to listen");
47
48     if((connectfd = accept(sockfd, (struct sockaddr*)&clientaddr, &len)) < 0)
49     {
50         if(errno == 11)
51         {
52             printf("errno = %d--->%s\n", errno, strerror(errno));
53         }
54         else
55         {
56             err_log("fail to accept");
57         }
58     }
59     printf("client:%s--->%d\n", inet_ntoa(clientaddr.sin_addr), ntohs(clientaddr.sin_port));
60     while(1)
61         {
62             if(recv(connectfd, buf, N, 0) < 0)
63                 err_log("fail to recv");
64             if(strncmp(buf, "quit", 4) == 0)
65                 break;
66             buf[strlen(buf) - 1] = ‘\0‘;
67             printf("buf:%s\n", buf);
68         }
69     close(connectfd);
70     close(sockfd);
71     return 0;
72 }

client.c

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<sys/types.h>
 4 #include<sys/socket.h>
 5 #include<unistd.h>
 6 #include<arpa/inet.h>
 7 #include<netinet/in.h>
 8 #include<string.h>
 9 #include<errno.h>
10
11 #define N 64
12 #define err_log(log) do{perror(log); exit(1);}while(0)
13
14 int main(int argc, const char *argv[])
15 {
16     int sockfd;
17     char buf[N];
18     struct sockaddr_in serveraddr;
19
20     if(argc != 3)
21     {
22         fprintf(stderr, "Usage:%s serverip port.", argv[0]);
23         return -1;
24     }
25
26     sockfd = socket(AF_INET, SOCK_STREAM, 0);
27     if(sockfd < 0)
28         err_log("fail to sockfd");
29
30     serveraddr.sin_family = AF_INET;
31     serveraddr.sin_addr.s_addr = inet_addr(argv[1]);
32     serveraddr.sin_port = htons(atoi(argv[2]));
33
34     if(connect(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0)
35         err_log("fail to connect");
36
37     while(1)
38     {
39         printf("<client>");
40         fgets(buf, N, stdin);
41         if(send(sockfd, buf, N, 0) < 0)
42             err_log("fail to send");
43         if(strncmp(buf, "quit", 4) == 0)
44             break;
45     }
46     close(sockfd);
47     return 0;
48 }

运行程序如下：

（1）正常运行/退出

服务器端:

客服端：

（2）当正常发送/接收数据时，客户端停止发送，服务器端在设定5s后退出

服务器端：

客户端：

(3)客户端不连接服务器，那么服务器会在设置的5s后退出

服务器端：