作为一个学校项目，我正在实施一个IRC服务器，我一直坚持这个问题。 我的服务器使用select来选择发送数据的客户端，然后从该用户读取一个命令（命令是\ r \ n分开），解析并执行它然后传递给下一个用户。 用户可以像这样一次发送多个命令：
"command1\r\ncommand2\r\n"
如果发生这种情况，我希望第一个命令被执行，第二个命令保留在流中，以便在下一个select（）调用时读取它。 （这样，每个用户每次“转”只执行一次comamnd）。 为此，我为每个客户端提供了一个FILE *流，只要它已连接就保持打开状态。
这项工作非常完美（如果我发送上面指定的双comamnd，这两个命令会一个接一个地执行）。
之后问题就是在那之后，select（）继续告诉我套接字中有东西要读（fd返回1的FD_ISSET），所以我的接收函数被调用为fd和getline（）在它失败（没有设置errno）并且它永远像这样循环。
我不明白为什么选择仍然认为套接字中有东西要读取以及为什么getline失败而不是阻塞。
有什么想法吗？
编辑：我不允许对此项目使用非阻塞套接字或fork（）
“主要”循环：
while (g_run_server)
{
fd_max = g_socket_fd;
FD_ZERO(fds);
FD_SET(g_socket_fd, fds);
tmp = users;
while (tmp)
{
FD_SET(tmp->fd, fds);
fd_max = (tmp->fd > fd_max ? tmp->fd : fd_max);
tmp = tmp->next;
}
if (select(fd_max + 1, &fds, NULL, NULL, NULL) < 0)
break;
if (FD_ISSET(g_socket_fd, &fds))
accept_new_user(&hdl, &users);
handle_clients(&hdl, &fds);
}
处理和读取客户端输入的函数：
static bool recv_and_execute(t_handle *hdl)
{
char *raw;
size_t len;
len = 0;
raw = NULL;
if (!hdl->sender->stream &&
(hdl->sender->stream = fdopen(dup(hdl->sender->fd), "r")) == NULL)
return (false);
if (getline(&raw, &len, hdl->sender->stream) != -1)
{
printf("Received \"%s\"\n", raw);
parse_cmd(hdl, raw);
exec_cmd(hdl);
}
else
printf("Getline failed %s\n", strerror(errno));
free(raw);
return (true);
}
int handle_clients(t_handle *hdl, fd_set *fds)
{
t_user *tmp;
tmp = *hdl->users;
while (tmp)
{
if (FD_ISSET(tmp->fd, fds))
{
printf("fd %d is ready to be read\n", tmp->fd);
hdl->sender = tmp;
recv_and_execute(hdl);
FD_CLR(tmp->fd, fds);
tmp = tmp->next;
if (hdl->sender->status == DEAD)
del_user(hdl->users, hdl->sender);
}
else
tmp = tmp->next;
}
return (0);
}
当我连接一个客户端并发送“USER foo \ r \ nUSER no bo dy：wa \ r \ n”时，这是输出：
fd 4 is ready to be read
Received "NICK foo
"
[DEBUG] Executing "NICK" with params "foo" "(null)" "(null)" "(null)"
[INFO] Nickname successfully changed.
fd 4 is ready to be read
Received "USER no bo dy :wa
"
[DEBUG] Executing "USER" with params "no" "bo" "dy" ":wa"
[INFO] User registered.
fd 4 is ready to be read
Getline failed Success
fd 4 is ready to be read
Getline failed Success
fd 4 is ready to be read
Getline failed Success
fd 4 is ready to be read
Getline failed Success
fd 4 is ready to be read
Getline failed Success
continue like this....
编辑：我根据alk的评论编辑了我的接收功能：
static bool recv_and_execute(t_handle *hdl)
{
char *raw;
size_t len;
ssize_t nread;
len = 0;
raw = NULL;
if (!hdl->sender->stream &&
(hdl->sender->stream = fdopen(dup(hdl->sender->fd), "r")) == NULL)
return (false);
errno = 0;
if ((nread = getline(&raw, &len, hdl->sender->stream)) > 0)
{
printf("Received \"%s\"\n", raw);
parse_cmd(hdl, raw);
exec_cmd(hdl);
}
else if (errno != 0)
printf("getline failed %s\n", strerror(errno));
else {
printf("EOF reached\n");
fclose(hdl->sender->stream);
hdl->sender->stream = NULL;
}
printf("nread = %zd\n", nread);
free(raw);
return (true);
}
所以这次，当EOF到达时（getline返回-1），我关闭流并将其设置为NULL，以便下次在套接字fd上选择查找数据时重新打开。但即使我关闭流，选择仍然检测到有可用数据并且无限循环继续：/
fd 4 is ready to be read
Received "NICK foo^M
"
nread = 10
fd 4 is ready to be read
Received "USER no bo dy :wa^M
"
nread = 19
fd 4 is ready to be read
EOF reached
nread = -1
fd 4 is ready to be read
EOF reached
nread = -1
fd 4 is ready to be read
EOF reached
nread = -1
and so on...
答案 0 :(得分：0)
我很确定您使用的是select错误。我向您展示了一个关于如何使用它的简单代码示例（我没有处理很多错误），您可以根据需要进行编辑。
/*
* If you read at man select bugs you can see
* that select could return that someone is
* ready but it isn't true
*/
int fd_c;
fd_set rdset;
fd_set set; /*That's the mask you'll use when new requests arrive*/
FD_ZERO(&set); /*Clears the mask*/
FD_SET(g_socket_fd,&set); /*Set the listening socket as ready*/
while(g_run_server){
/*
* YOU MUST INITIALIZATE IT EVERY LOOP
* read @ man select
*/
rdset = set;
if(select((fd_num_max+1),(&rdset),NULL,NULL,NULL) < 0){
perror("Failed on select\n");
exit(EXIT_FAILURE);
}
/*You go through the ready clients in the rdset*/
for(fd=0;fd<=fd_num_max;fd++) {
if(FD_ISSET(fd,&rdset)) { /*If the bit is set*/
if(fd == fd_skt) { /*If it's a new client*/
/*You can handle the new client here or delegete it to someone*/
fd_c=accept(fd_skt,NULL,0); /*File descriptor of new client*/
FD_SET(fd_c,&set);
if(fd_c > fd_num_max) fd_num_max = fd_c;
}else { /*If it's a request from an existing client*/
/*You can handle the new request here or delegete it to someone*/
FD_SET(fd,&set);
}
}
}
}
您还应该以这种方式修改static bool recv_and_execute(t_handle *hdl)：
errno = 0;
if ((nread = getline(&raw, &len, hdl->sender->stream)) != -1){
printf("Received \"%s\"\n", raw);
parse_cmd(hdl, raw);
exec_cmd(hdl);
}else{
if( errno == 0){
printf("EOF reached\n");
fclose(hdl->sender->stream);
hdl->sender->stream = NULL;
}else{
printf("getline failed %s\n", strerror(errno));
exit(EXIT_FAILURE); /*You must handle it in some way, exiting or doing something*/
}
}