我编写了一个简单的客户端和服务器来处理带外数据。客户端只向服务器发送一个带外数据,服务器使用 SIGURG 来处理这个单个字节。服务器还应该在无限循环中处理正常流量。该代码具有无法按预期工作的竞争条件。有时,我从 SIGURG 处理程序中对 recv() 的调用中得到“无效参数”。我的另一个问题是,我应该在调用接受时阻止 SIGURG 信号吗?此外,哪一种是首选方案:
- 在调用 accept之前安装 SIGURG 处理程序并设置侦听套接字的套接字所有者。
- 安装 SIGURG 处理程序并在调用 accept后为连接的套接字设置套接字所有者。
- 如果以上都不是,请写下您的建议。
我的最后一个问题是,由于客户端立即发送带外数据,服务器是否有机会在完成三次握手之后但在从接受返回之前接收到 SIGURG?如果是这样,我认为“clifd”变量在 SIGURG 处理程序中使用时可能具有无效值。
客户端的代码:
#include "myheader.h"
int main(int argc, char *argv[])
{
struct sockaddr_in saddr;
int sockfd;
const char c = 'a';
if (2 != argc)
{
fprintf(stderr, "Usage: %s ipaddr\n", argv[0]);
exit(EXIT_FAILURE);
}
if (-1 == (sockfd = socket(AF_INET, SOCK_STREAM, 0)))
die("sockfd()");
(void)memset(&saddr, 0, sizeof(saddr));
saddr.sin_family = AF_INET;
saddr.sin_port = htons(PORT);
if (-1 == inet_pton(AF_INET, argv[1], &saddr.sin_addr))
die("inet_pton()");
if (-1 == connect(sockfd, (struct sockaddr*)&saddr, sizeof(saddr)))
die("connect()");
// if (-1 == send(sockfd, "HELLO\n", 6, 0))
// die("send()");
if (-1 == send(sockfd, &c, 1, MSG_OOB))
die("send()");
close(sockfd);
return 0;
}
和服务器的代码:
#include "myheader.h"
void sigurg_handler(int);
char oob;
int sockfd, clifd;
int main(void)
{
struct sockaddr_in myaddr;
char buf[BUFSIZ];
ssize_t nbytes;
sigset_t sset, oset;
sigemptyset(&sset);
sigaddset(&sset, SIGURG);
if (-1 == (sockfd = socket(AF_INET, SOCK_STREAM, 0)))
die("socket()");
(void)memset(&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_port = htons(PORT);
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
if (-1 == bind(sockfd, (struct sockaddr*)&myaddr, sizeof(myaddr)))
die("bind()");
if (-1 == listen(sockfd, BACKLOG))
die("listen()");
if (-1 == fcntl(sockfd, F_SETOWN, getpid()))
die("fcntl()");
if (SIG_ERR == signal(SIGURG, sigurg_handler))
die("signal()");
for (;;)
{
/* block SIGURG when accepting the connection */
// sigprocmask(SIG_SETMASK, &sset, &oset);
printf("bloking in accept()\n");
if (-1 == (clifd = accept(sockfd, NULL, NULL)))
die("accept()");
/* unblock SIGURG */
// sigprocmask(SIG_SETMASK, &oset, NULL);
printf("recv()ing normal data\n");
nbytes = recv(clifd, buf, sizeof(buf), 0);
buf[nbytes] = 0; /* null-terminate */
printf("%s", buf);
}
close(sockfd);
}
void
sigurg_handler(int signo)
{
char buff[100];
ssize_t nbytes;
printf("SIGURG received\n");
if (clifd != 0)
{
if (-1 == (nbytes = recv(clifd, buff, sizeof(buff) - 1, MSG_OOB)))
die("recv() in sigurg_handler()");
buff[nbytes] = 0;
printf("from sigurg_handler: received \"%s\"\n", buff);
}
else
{
printf("clifd = %d\n", clifd);
exit(1);
}
}
例子:
> ./serv
bloking in accept() /* first client */
SIGURG received
from sigurg_handler: received "a"
recv()ing normal data
bloking in accept() /* second client */
SIGURG received
recv() in sigurg_handler(): Invalid argument
> ./serv /* third client */
bloking in accept()
SIGURG received
clifd = 0
>