008 查看套接字选项是否受支持(获取当前环境下套接字选项默认值)

代码来源：《UNIX网络编程 卷1：套接字联网API》

说明：为以后查看套接字默认值使用

代码：

/* include checkopts1 */
/* *INDENT-OFF* */

#include <netinet/tcp.h>        /* for TCP_xxx defines */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>
#include <time.h>
#include <sys/epoll.h>

union val {
  int                i_val;
  long                l_val;
  struct linger        linger_val;
  struct timeval    timeval_val;
} val;

static char    *sock_str_flag(union val *, int);
static char    *sock_str_int(union val *, int);
static char    *sock_str_linger(union val *, int);
static char    *sock_str_timeval(union val *, int);

struct sock_opts {
  const char       *opt_str;
  int        opt_level;
  int        opt_name;
  char   *(*opt_val_str)(union val *, int);
} sock_opts[] = {
    { "SO_BROADCAST",        SOL_SOCKET,    SO_BROADCAST,    sock_str_flag },
    { "SO_DEBUG",            SOL_SOCKET,    SO_DEBUG,        sock_str_flag },
    { "SO_DONTROUTE",        SOL_SOCKET,    SO_DONTROUTE,    sock_str_flag },
    { "SO_ERROR",            SOL_SOCKET,    SO_ERROR,        sock_str_int },
    { "SO_KEEPALIVE",        SOL_SOCKET,    SO_KEEPALIVE,    sock_str_flag },
    { "SO_LINGER",            SOL_SOCKET,    SO_LINGER,        sock_str_linger },
    { "SO_OOBINLINE",        SOL_SOCKET,    SO_OOBINLINE,    sock_str_flag },
    { "SO_RCVBUF",            SOL_SOCKET,    SO_RCVBUF,        sock_str_int },
    { "SO_SNDBUF",            SOL_SOCKET,    SO_SNDBUF,        sock_str_int },
    { "SO_RCVLOWAT",        SOL_SOCKET,    SO_RCVLOWAT,    sock_str_int },
    { "SO_SNDLOWAT",        SOL_SOCKET,    SO_SNDLOWAT,    sock_str_int },
    { "SO_RCVTIMEO",        SOL_SOCKET,    SO_RCVTIMEO,    sock_str_timeval },
    { "SO_SNDTIMEO",        SOL_SOCKET,    SO_SNDTIMEO,    sock_str_timeval },
    { "SO_REUSEADDR",        SOL_SOCKET,    SO_REUSEADDR,    sock_str_flag },
#ifdef    SO_REUSEPORT
    { "SO_REUSEPORT",        SOL_SOCKET,    SO_REUSEPORT,    sock_str_flag },
#else
    { "SO_REUSEPORT",        0,            0,                NULL },
#endif
    { "SO_TYPE",            SOL_SOCKET,    SO_TYPE,        sock_str_int },
    //{ "SO_USELOOPBACK",        SOL_SOCKET,    SO_USELOOPBACK,    sock_str_flag },
    { "IP_TOS",                IPPROTO_IP,    IP_TOS,            sock_str_int },
    { "IP_TTL",                IPPROTO_IP,    IP_TTL,            sock_str_int },
#ifdef    IPV6_DONTFRAG
    { "IPV6_DONTFRAG",        IPPROTO_IPV6,IPV6_DONTFRAG,    sock_str_flag },
#else
    { "IPV6_DONTFRAG",        0,            0,                NULL },
#endif
#ifdef    IPV6_UNICAST_HOPS
    { "IPV6_UNICAST_HOPS",    IPPROTO_IPV6,IPV6_UNICAST_HOPS,sock_str_int },
#else
    { "IPV6_UNICAST_HOPS",    0,            0,                NULL },
#endif
#ifdef    IPV6_V6ONLY
    { "IPV6_V6ONLY",        IPPROTO_IPV6,IPV6_V6ONLY,    sock_str_flag },
#else
    { "IPV6_V6ONLY",        0,            0,                NULL },
#endif
    { "TCP_MAXSEG",            IPPROTO_TCP,TCP_MAXSEG,        sock_str_int },
    { "TCP_NODELAY",        IPPROTO_TCP,TCP_NODELAY,    sock_str_flag },
#ifdef    SCTP_AUTOCLOSE
    { "SCTP_AUTOCLOSE",        IPPROTO_SCTP,SCTP_AUTOCLOSE,sock_str_int },
#else
    { "SCTP_AUTOCLOSE",        0,            0,                NULL },
#endif
#ifdef    SCTP_MAXBURST
    { "SCTP_MAXBURST",        IPPROTO_SCTP,SCTP_MAXBURST,    sock_str_int },
#else
    { "SCTP_MAXBURST",        0,            0,                NULL },
#endif
#ifdef    SCTP_MAXSEG
    { "SCTP_MAXSEG",        IPPROTO_SCTP,SCTP_MAXSEG,    sock_str_int },
#else
    { "SCTP_MAXSEG",        0,            0,                NULL },
#endif
#ifdef    SCTP_NODELAY
    { "SCTP_NODELAY",        IPPROTO_SCTP,SCTP_NODELAY,    sock_str_flag },
#else
    { "SCTP_NODELAY",        0,            0,                NULL },
#endif
    { NULL,                    0,            0,                NULL }
};
/* *INDENT-ON* */
/* end checkopts1 */

/* include checkopts2 */
int
main(int argc, char **argv)
{
    int                    fd;
    socklen_t            len;
    struct sock_opts    *ptr;

    for (ptr = sock_opts; ptr->opt_str != NULL; ptr++) {
        printf("%s: ", ptr->opt_str);
        if (ptr->opt_val_str == NULL)
            printf("(undefined)\n");
        else {
            switch(ptr->opt_level) {
            case SOL_SOCKET:
            case IPPROTO_IP:
            case IPPROTO_TCP:
                fd = socket(AF_INET, SOCK_STREAM, 0);
                break;
#ifdef    IPV6
            case IPPROTO_IPV6:
                fd = Socket(AF_INET6, SOCK_STREAM, 0);
                break;
#endif
#ifdef    IPPROTO_SCTP
            case IPPROTO_SCTP:
                fd = socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
                break;
#endif
            default:
                printf("Can't create fd for level %d\n", ptr->opt_level);
            }

            len = sizeof(val);
            if (getsockopt(fd, ptr->opt_level, ptr->opt_name, &val, &len) == -1) {
                printf("getsockopt error\n");
            } else {
                printf("default = %s\n", (*ptr->opt_val_str)(&val, len));
            }
            close(fd);
        }
    }
    exit(0);
}
/* end checkopts2 */

/* include checkopts3 */
static char    strres[128];

static char    *sock_str_flag(union val *ptr, int len)
{
/* *INDENT-OFF* */
    if (len != sizeof(int))
        snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
    else
        snprintf(strres, sizeof(strres),
                 "%s", (ptr->i_val == 0) ? "off" : "on");
    return(strres);
/* *INDENT-ON* */
}
/* end checkopts3 */

static char    *sock_str_int(union val *ptr, int len)
{
    if (len != sizeof(int))
        snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
    else
        snprintf(strres, sizeof(strres), "%d", ptr->i_val);
    return(strres);
}

static char    *sock_str_linger(union val *ptr, int len)
{
    struct linger    *lptr = &ptr->linger_val;

    if (len != sizeof(struct linger))
        snprintf(strres, sizeof(strres),
                 "size (%d) not sizeof(struct linger)", len);
    else
        snprintf(strres, sizeof(strres), "l_onoff = %d, l_linger = %d",
                 lptr->l_onoff, lptr->l_linger);
    return(strres);
}

static char    *sock_str_timeval(union val *ptr, int len)
{
    struct timeval    *tvptr = &ptr->timeval_val;

    if (len != sizeof(struct timeval))
        snprintf(strres, sizeof(strres),
                 "size (%d) not sizeof(struct timeval)", len);
    else
        snprintf(strres, sizeof(strres), "%d sec, %d usec", (int )tvptr->tv_sec, (int )tvptr->tv_usec);
    return(strres);
}

运行结果

 

SO_BROADCAST: default = off
SO_DEBUG: default = off
SO_DONTROUTE: default = off
SO_ERROR: default = 0
SO_KEEPALIVE: default = off
SO_LINGER: default = l_onoff = 0, l_linger = 0
SO_OOBINLINE: default = off
SO_RCVBUF: default = 87380       //接受缓冲区大小
SO_SNDBUF: default = 16384       //发送缓冲区大小
SO_RCVLOWAT: default = 1
SO_SNDLOWAT: default = 1
SO_RCVTIMEO: default = 0 sec, 0 usec
SO_SNDTIMEO: default = 0 sec, 0 usec
SO_REUSEADDR: default = off
SO_REUSEPORT: default = off
SO_TYPE: default = 1          //套接字类型
IP_TOS: default = 0
IP_TTL: default = 64          //存活时间
IPV6_DONTFRAG: (undefined)
IPV6_UNICAST_HOPS: Can't create fd for level 41
getsockopt error
IPV6_V6ONLY: Can't create fd for level 41
getsockopt error
TCP_MAXSEG: default = 536
TCP_NODELAY: default = off
SCTP_AUTOCLOSE: (undefined)
SCTP_MAXBURST: (undefined)
SCTP_MAXSEG: (undefined)
SCTP_NODELAY: (undefined)