source: azure_iot_hub/trunk/musl-1.1.18/src/network/resolvconf.c@ 389

#include "lookup.h"
#include "stdio_impl.h"
#include <ctype.h>
#include <errno.h>
#include <string.h>
#include <netinet/in.h>

int __get_resolv_conf(struct resolvconf *conf, char *search, size_t search_sz)
{
        char line[256];
        unsigned char _buf[256];
        FILE *f, _f;
        int nns = 0;

        conf->ndots = 1;
        conf->timeout = 5;
        conf->attempts = 2;
        if (search) *search = 0;

        f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
        if (!f) switch (errno) {
        case ENOENT:
        case ENOTDIR:
        case EACCES:
                goto no_resolv_conf;
        default:
                return -1;
        }

        while (fgets(line, sizeof line, f)) {
                char *p, *z;
                if (!strchr(line, '\n') && !feof(f)) {
                        /* Ignore lines that get truncated rather than
                         * potentially misinterpreting them. */
                        int c;
                        do c = getc(f);
                        while (c != '\n' && c != EOF);
                        continue;
                }
                if (!strncmp(line, "options", 7) && isspace(line[7])) {
                        p = strstr(line, "ndots:");
                        if (p && isdigit(p[6])) {
                                p += 6;
                                unsigned long x = strtoul(p, &z, 10);
                                if (z != p) conf->ndots = x > 15 ? 15 : x;
                        }
                        p = strstr(line, "attempts:");
                        if (p && isdigit(p[9])) {
                                p += 9;
                                unsigned long x = strtoul(p, &z, 10);
                                if (z != p) conf->attempts = x > 10 ? 10 : x;
                        }
                        p = strstr(line, "timeout:");
                        if (p && (isdigit(p[8]) || p[8]=='.')) {
                                p += 8;
                                unsigned long x = strtoul(p, &z, 10);
                                if (z != p) conf->timeout = x > 60 ? 60 : x;
                        }
                        continue;
                }
                if (!strncmp(line, "nameserver", 10) && isspace(line[10])) {
                        if (nns >= MAXNS) continue;
                        for (p=line+11; isspace(*p); p++);
                        for (z=p; *z && !isspace(*z); z++);
                        *z=0;
                        if (__lookup_ipliteral(conf->ns+nns, p, AF_UNSPEC) > 0)
                                nns++;
                        continue;
                }

                if (!search) continue;
                if ((strncmp(line, "domain", 6) && strncmp(line, "search", 6))
                    || !isspace(line[6]))
                        continue;
                for (p=line+7; isspace(*p); p++);
                size_t l = strlen(p);
                /* This can never happen anyway with chosen buffer sizes. */
                if (l >= search_sz) continue;
                memcpy(search, p, l+1);
        }

        __fclose_ca(f);

no_resolv_conf:
        if (!nns) {
                __lookup_ipliteral(conf->ns, "127.0.0.1", AF_UNSPEC);
                nns = 1;
        }

        conf->nns = nns;

        return 0;
}