resolv.h 用法解决方案 - C语言

来自 : www.myexceptions.net/c/3948... 发布时间：2021-03-25

int dns_query_t::mx_query(const char* domain, vector string mx_list, vector string default_mx) logtrace((COMMON, dns_query_t::mx_query begin with domain: %s ... , domain)); // make a clean start if(default_mx != mx_list) mx_list.clear(); mx_list.assign(default_mx.begin(), default_mx.end()); // initialize resolver if (res_init()) { logerror((COMMON, dns_query_t::mx_query = res_init() failed )); return -1; // do MX query union { HEADER hdr; u_char buf[NS_PACKETSZ]; } response; int response_len = res_query(domain, C_IN, T_MX, (u_char *) response, sizeof(response)); if (response_len 0) { logerror((COMMON, dns_query_t::mx_query = res_query() failed )); return -1; if ((size_t)response_len sizeof(response)) { response_len = sizeof(response); u_char * response_end = response.buf + response_len; u_char * response_pos = response.buf + sizeof(HEADER); // skip queries int response_count = ntohs(response.hdr.qdcount); while (response_count-- 0) { char query_name[MAXDNAME]; int bytes_read = dn_expand(response.buf, response_end, response_pos, query_name, MAXDNAME); if (bytes_read 0) { logerror((COMMON, dns_query_t::mx_query = dn_expand() failed:parse QUERY part in MX lookup 1. )); return -1; response_pos += bytes_read; if ((response_end - response_pos) QFIXEDSZ) { logerror((COMMON, dns_query_t::mx_query = dn_expand() failed:parse QUERY part in MX lookup 2. )); return -1; response_pos += QFIXEDSZ; // now process answers response_count = ntohs(response.hdr.ancount); while (response_count-- 0) { char mx_name[MAXDNAME]; int bytes_processed = dn_expand(response.buf, response_end, response_pos, mx_name, MAXDNAME); if (bytes_processed 0) { logerror((COMMON, dns_query_t::mx_query = dn_expand() failed:parse QUERY part in MX lookup 3. )); return -1; response_pos += bytes_processed; if ((response_end - response_pos) 10) { logerror((COMMON, dns_query_t::mx_query = dn_expand() failed:parse QUERY part in MX lookup 4. )); return -1; unsigned short rrtype = getshort(response_pos); unsigned short rrdlen = getshort(response_pos + 8); response_pos += 10; if (rrtype == T_MX) { //!unsigned short priority = (response_pos[0] 8) + response_pos[1]; memset(mx_name, 0, MAXDNAME); if (dn_expand(response.buf, response_end, response_pos+2, mx_name, MAXDNAME) 0) { logerror((COMMON, dns_query_t::mx_query = dn_expand() failed:parse QUERY part in MX lookup 5. )); return -1; //! VERBOSE( MTA::get_mx_list(): entry [ mx_name ] priority [ priority ] mx_list.push_back(std::string(mx_name)); response_pos += rrdlen; logtrace((COMMON, dns_query_t::mx_query domain: %s end ok. , domain)); return mx_list.empty();#endif /* DNS_QUERY_H */