resolv.h 用法
resolv.h 怎么用啊？ 是不是查域名的mx、a记录的？ 哪位哥哥能写个c的例子
我的需求是 根据域名查出mx 记录，然后查其a记录
我用c写的，调用DIG 命令，也可以查到，但同事说这样不好
有同事写的是C++的，小弟不会C++, 真是罪过
C++ 代码如下：
- C/C++ code
#ifndef DNS_QUERY_H#define DNS_QUERY_H#include <netinet/in.h>#include <arpa/nameser.h>#include <resolv.h>#include "log.h"#include <string>#include <vector>using namespace std;class dns_query_t{public: static int mx_query(const char* domain, vector<string> & mx_list, vector<string>& default_mx);};unsigned short getshort(unsigned char *c) { return (c[0] << 8) + c[1]; }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 */
[解决办法]
- C/C++ code
NAME res_init, res_query, res_search, res_querydomain, res_mkquery, res_send, dn_comp, dn_expand - resolver routinesSYNOPSIS #include <netinet/in.h> #include <arpa/nameser.h> #include <resolv.h> extern struct state _res; int res_init(void); int res_query(const char *dname, int class, int type, unsigned char *answer, int anslen); int res_search(const char *dname, int class, int type, unsigned char *answer, int anslen); int res_querydomain(const char *name, const char *domain, int class, int type, unsigned char *answer, int anslen); int res_mkquery(int op, const char *dname, int class, int type, char *data, int datalen, struct rrec *newrr, char *buf, int buflen); int res_send(const char *msg, int msglen, char *answer, int anslen); int dn_comp(unsigned char *exp_dn, unsigned char *comp_dn, int length, unsigned char **dnptrs, unsigned char **lastdnptr); int dn_expand(unsigned char *msg, unsigned char *eomorig, unsigned char *comp_dn, char *exp_dn, int length); Link with -lresolv.