使用setsockopt来控制connect超时

我不是女神ヾ 2022-08-04 14:52 243阅读 0赞

原来我们实现connect()超时基本上都使用unix网络编程一书的非阻塞方式（connect\_nonb），今天在网上看到一篇文章，觉得很有意思，**转载**如下：

读Linux内核源码的时候偶然发现其connect的超时参数竟然和用SO\_SNDTIMO操作的参数一致:  
File: net/ipv4/af\_inet.c

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   <td>&nbsp;&nbsp;&nbsp; 559&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; timeo = sock_sndtimeo(sk, flags &amp; O_NONBLOCK);<br>&nbsp;&nbsp;&nbsp; 560<br>&nbsp;&nbsp;&nbsp; 561&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if ((1 &lt;&lt; sk-&gt;sk_state) &amp; (TCPF_SYN_SENT | TCPF_SYN_RECV)) { <br>&nbsp;&nbsp;&nbsp; 562&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /* Error code is set above */<br>&nbsp;&nbsp;&nbsp; 563&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (!timeo || !inet_wait_for_connect(sk, timeo))<br>&nbsp;&nbsp;&nbsp; 564&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto out;<br>&nbsp;&nbsp;&nbsp; 565<br>&nbsp;&nbsp;&nbsp; 566&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; err = sock_intr_errno(timeo);<br>&nbsp;&nbsp;&nbsp; 567&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (signal_pending(current))<br>&nbsp;&nbsp;&nbsp; 568&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto out;<br>&nbsp;&nbsp;&nbsp; 569&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }</td> 
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这意味着： **在Linux平台下，可以通过在connect之前设置SO\_SNDTIMO来达到控制连接超时的目的**。简单的写了份测试代码:

\#include <stdlib.h> \#include <stdio.h> \#include <sys/types.h> \#include <sys/socket.h> \#include <netinet/in.h> \#include <errno.h> \#include <sys/socket.h> \#include <netinet/in.h> \#include <arpa/inet.h> int main(int argc, char \*argv\[\]) \{ int fd; struct sockaddr\_in addr; struct timeval timeo = \{3, 0\}; socklen\_t len = sizeof(timeo); fd = socket(AF\_INET, SOCK\_STREAM, 0); if (argc == 4) timeo.tv\_sec = atoi(argv\[3\]); setsockopt(fd, SOL\_SOCKET, SO\_SNDTIMEO, &timeo, len); addr.sin\_family = AF\_INET; addr.sin\_addr.s\_addr = inet\_addr(argv\[1\]); addr.sin\_port = htons(atoi(argv\[2\])); if (connect(fd, (struct sockaddr\*)&addr, sizeof(addr)) == -1) \{ if (errno == EINPROGRESS) \{ fprintf(stderr, "timeout/n"); return -1; \} perror("connect"); return 0; \} printf("connected/n"); return 0; \}

使用 ./cmd  ip地址  端口  超时秒数

(测试的ip和端口必须是不存在的，或者是ip的机器是死掉的，才会出现，否则机器存在而端口不存在会立即返回的)