C语言返回网关

Nicole_F

今天作了个网络连接连通性的测试程序，需要PING下网关。ioctl好像能得到很多NET_INFO。不过不能返回网关。
想想/proc下虽然有ROUTE信息。。但是要写解析代码 懒了－ －。。。
另外想想route命令也能返回网关。。。看看代码也不多 于是就分析它了。。。。
route是属于net-tools下的一个工具 其下还有libnet-tools 简单分析了下route的代码 几乎没有可提取的内容。继续往LIB里分析，发现内容都在里面。。。测试程序也能跑通了。。但是LIB代码太多了  不少用不到。。。于是把需要的代码全部提取出来了。。。
其实。。。他源代码也是在分析proc。。。- -  也罢。。。
贴上留作备份
#include arpa/inet.h>
#include arpa/nameser.h>
#include netinet/in.h>
#include sys/types.h>
#include sys/socket.h>
#include ctype.h>
#include ctype.h>
#include errno.h>
#include netdb.h>
#include resolv.h>
#include stdarg.h>
#include stdio.h>
#include stdlib.h>
#include string.h>
#include unistd.h>
#define RTF_UP                        0x0001
#define RTF_GATEWAY                    0x0002
#define RTF_HOST                    0x0004
#define _PATH_PROCNET_ROUTE            "/proc/net/route"
struct addr {
    struct sockaddr_in addr;
    char *name;
    int host;
    struct addr *next;
};
static struct addr *INET_nn = NULL;    /* addr-to-name cache */
struct aftype {
    char *name;
    char *title;
    int af;
    int alen;
    char *(*print) (unsigned char *);
    char *(*sprint) (struct sockaddr *, int numeric);
    int (*input) (int type, char *bufp, struct sockaddr *);
    void (*herror) (char *text);
    int (*rprint) (int options);
    int (*rinput) (int typ, int ext, char **argv);
    /* may modify src */
    int (*getmask) (char *src, struct sockaddr * mask, char *name);
    int fd;
    char *flag_file;
};
struct aftype inet_aftype;
struct sockaddr snet_gateway;
char *proc_gen_fmt(char *name, int more, FILE * fh,...)
{
    char buf[512], format[512] = "";
    char *title, *head, *hdr;
    va_list ap;
    if (!fgets(buf, (sizeof buf) - 1, fh))
    return NULL;
    strcat(buf, " ");
    va_start(ap, fh);
    title = va_arg(ap, char *);
    for (hdr = buf; hdr;) {
    while (isspace(*hdr) || *hdr == '|')
     hdr++;
    head = hdr;
    hdr = strpbrk(hdr, "| \t\n");
    if (hdr)
     *hdr++ = 0;
    if (!strcmp(title, head)) {
     strcat(format, va_arg(ap, char *));
     title = va_arg(ap, char *);
     if (!title || !head)
        break;
    } else {
     strcat(format, "%*s");    /* XXX */
    }
    strcat(format, " ");
    }
    va_end(ap);
    if (!more && title) {
    fprintf(stderr, "warning: %s does not contain required field %s\n",
        name, title);
    return NULL;
    }
    return strdup(format);
}
static int INET_getsock(char *bufp, struct sockaddr *sap)
{
    char *sp = bufp, *bp;
    unsigned int i;
    unsigned val;
    struct sockaddr_in *sin;
    sin = (struct sockaddr_in *) sap;
    sin->sin_family = AF_INET;
    sin->sin_port = 0;
    val = 0;
    bp = (char *) &val;
    for (i = 0; i  sizeof(sin->sin_addr.s_addr); i++) {
    *sp = toupper(*sp);
    if ((*sp >= 'A') && (*sp = 'F'))
     bp |= (int) (*sp - 'A') + 10;
    else if ((*sp >= '0') && (*sp = '9'))
     bp |= (int) (*sp - '0');
    else
     return (-1);
    bp = 4;
    sp++;
    *sp = toupper(*sp);
    if ((*sp >= 'A') && (*sp = 'F'))
     bp |= (int) (*sp - 'A') + 10;
    else if ((*sp >= '0') && (*sp = '9'))
     bp |= (int) (*sp - '0');
    else
     return (-1);
    sp++;
    }
    sin->sin_addr.s_addr = htonl(val);
    return (sp - bufp);
}
static int INET_resolve(char *name, struct sockaddr_in *sin, int hostfirst)
{
    struct hostent *hp;
    struct netent *np;
    /* Grmpf. -FvK */
    sin->sin_family = AF_INET;
    sin->sin_port = 0;
    /* Default is special, meaning 0.0.0.0. */
    if (!strcmp(name, "default")) {
    sin->sin_addr.s_addr = INADDR_ANY;
    return (1);
    }
    /* Look to see if it's a dotted quad. */
    if (inet_aton(name, &sin->sin_addr)) {
    return 0;
    }
#ifdef EMBED
    return(-1);
#else
    /* If we expect this to be a hostname, try hostname database first */
#ifdef DEBUG
    if (hostfirst) fprintf (stderr, "gethostbyname (%s)\n", name);
#endif
    if (hostfirst &&
    (hp = gethostbyname(name)) != (struct hostent *) NULL) {
    memcpy((char *) &sin->sin_addr, (char *) hp->h_addr_list[0],
        sizeof(struct in_addr));
    return 0;
    }
    /* Try the NETWORKS database to see if this is a known network. */
#ifdef DEBUG
    fprintf (stderr, "getnetbyname (%s)\n", name);
#endif
    if ((np = getnetbyname(name)) != (struct netent *) NULL) {
    sin->sin_addr.s_addr = htonl(np->n_net);
    return 1;
    }
    if (hostfirst) {
    /* Don't try again */
    errno = h_errno;
    return -1;
    }
#ifdef DEBUG
    res_init();
    _res.options |= RES_DEBUG;
#endif
#ifdef DEBUG
    fprintf (stderr, "gethostbyname (%s)\n", name);
#endif
    if ((hp = gethostbyname(name)) == (struct hostent *) NULL) {
    errno = h_errno;
    return -1;
    }
    memcpy((char *) &sin->sin_addr, (char *) hp->h_addr_list[0],
     sizeof(struct in_addr));
    return 0;
#endif
}
static int INET_input(int type, char *bufp, struct sockaddr *sap)
{
    switch (type) {
    case 1:
    return (INET_getsock(bufp, sap));
    case 256:
    return (INET_resolve(bufp, (struct sockaddr_in *) sap, 1));
    default:
    return (INET_resolve(bufp, (struct sockaddr_in *) sap, 0));
    }
}
char *safe_strncpy(char *dst, const char *src, size_t size)
{
    dst[size-1] = '\0';
    return strncpy(dst,src,size-1);
}
static int INET_rresolve(char *name, size_t len, struct sockaddr_in *sin,
             int numeric, unsigned int netmask)
{
    struct hostent *ent;
    struct netent *np;
    struct addr *pn;
    unsigned long ad, host_ad;
    int host = 0;
    /* Grmpf. -FvK */
    if (sin->sin_family != AF_INET) {
        errno = EAFNOSUPPORT;
    return (-1);
    }
    ad = (unsigned long) sin->sin_addr.s_addr;
    if (ad == INADDR_ANY) {
    if ((numeric & 0x0FFF) == 0) {
     if (numeric & 0x8000)
        safe_strncpy(name, "default", len);
     else
     safe_strncpy(name, "*", len);
     return (0);
    }
    }
    if (numeric & 0x0FFF) {
        safe_strncpy(name, inet_ntoa(sin->sin_addr), len);
    return (0);
    }
    if ((ad & (~netmask)) != 0 || (numeric & 0x4000))
    host = 1;
    pn = INET_nn;
    while (pn != NULL) {
    if (pn->addr.sin_addr.s_addr == ad && pn->host == host) {
     safe_strncpy(name, pn->name, len);
     return (0);
    }
    pn = pn->next;
    }
    host_ad = ntohl(ad);
    np = NULL;
    ent = NULL;
#ifndef EMBED
    if (host) {
        ent = gethostbyaddr((char *) &ad, 4, AF_INET);
    if (ent != NULL)
     safe_strncpy(name, ent->h_name, len);
    }
#ifndef __UC_LIBC__
    else {
    np = getnetbyaddr(host_ad, AF_INET);
    if (np != NULL)
     safe_strncpy(name, np->n_name, len);
    }
#endif
#endif
    if ((ent == NULL) && (np == NULL))
    safe_strncpy(name, inet_ntoa(sin->sin_addr), len);
    pn = (struct addr *) malloc(sizeof(struct addr));
    pn->addr = *sin;
    pn->next = INET_nn;
    pn->host = host;
    pn->name = (char *) malloc(strlen(name) + 1);
    strcpy(pn->name, name);
    INET_nn = pn;
    return (0);
}
static char *INET_sprint(struct sockaddr *sap, int numeric)
{
    static char buff[128];
    if (sap->sa_family == 0xFFFF || sap->sa_family == 0)
    return safe_strncpy(buff, "[NONE SET]", sizeof(buff));
    if (INET_rresolve(buff, sizeof(buff), (struct sockaddr_in *) sap,
         numeric, 0xffffff00) != 0)
    return (NULL);
    return (buff);
}
int main()
{
    int ext=1,numeric=0;
    char buff[1024], iface[16], flags[64];
    char gate_addr[128], net_addr[128];
    char mask_addr[128];
    int num, iflags, metric, refcnt, use, mss, window, irtt;
    FILE *fp = fopen(_PATH_PROCNET_ROUTE, "r");
    char *fmt;
    if (!fp) {
        perror(_PATH_PROCNET_ROUTE);
        printf("INET (IPv4) not configured in this system.\n");
    return 1;
    }
    irtt = 0;
    window = 0;
    mss = 0;
    fmt = proc_gen_fmt(_PATH_PROCNET_ROUTE, 0, fp,
         "Iface", "%16s",
         "Destination", "%128s",
         "Gateway", "%128s",
         "Flags", "%X",
         "RefCnt", "%d",
         "Use", "%d",
         "Metric", "%d",
         "Mask", "%128s",
         "MTU", "%d",
         "Window", "%d",
         "IRTT", "%d",
         NULL);
    /* "%16s %128s %128s %X %d %d %d %128s %d %d %d\n" */
    if (!fmt)
    return 1;
    while (fgets(buff, 1023, fp)) {
    num = sscanf(buff, fmt,
         iface, net_addr, gate_addr,
         &iflags, &refcnt, &use, &metric, mask_addr,
         &mss, &window, &irtt);
    if (num  10 || !(iflags & RTF_UP))
     continue;
    INET_input(1, gate_addr, &snet_gateway);
     strcpy(gate_addr, INET_sprint(&snet_gateway, numeric | 0x4000));
     gate_addr[15] = '\0';
    if (iflags & RTF_GATEWAY)   
        printf("==gateway=======%s===%s=====\n",gate_addr,iface);
   
    }
    free(fmt);
    (void) fclose(fp);
    return (0);
}


本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u3/91787/showart_1807083.html