Tiny DNS Resolver异步DNS解析

众所周知，Unix/Linux系统下面gethostbyname()是不可重入的，就是说当多线程程序都要进行DNS解析时，必须保证同时只能有一个线程在执行gethostbyname()代码，其他线程在函数外等待。当多线程/进程进行大量DNS解析时，如果还调用gethostbyname()方法，显然会成为程序的一个瓶颈。所以我编写一个DNS解析程序，很简单就是基于UDP利用DNS协议发送和解析DNS包。由于代码工作在操作系统的用户态达到了并行异步的效果。

 

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TinyDNSResolver.h

/* * TinyDNSResolver.h * * Created on: Jun 2, 2009 * Author: luo */ #ifndef TINYDNSRESOLVER_H_ #define TINYDNSRESOLVER_H_ #include <iostream> typedef struct { unsigned short id; unsigned short flag; unsigned short questions; unsigned short answerRRs; unsigned short authorityRRs; unsigned short additionalRRs; } DNS_PKG_HEADER, *DNS_PKG_HEADER_PTR; typedef struct { unsigned char * dns_name; unsigned short dns_type; unsigned short dns_class; } DNS_PKG_QUERY, *DNS_PKG_QUERY_PTR; typedef struct{ unsigned short dns_name; unsigned short dns_type; unsigned short dns_class; unsigned short dns_ttl; unsigned char* data; }DNS_RESPONSE_ANSWER, *DNS_RESPONSE_ANSWER_PTR; class TinyDNSResolver { public: TinyDNSResolver(); ~TinyDNSResolver(); bool resolve(const char*, char* ip, unsigned short id); private: typedef struct { char _domain[256]; char _ip[16]; } DNSCACHE; int pkgDNS(const char*, DNS_PKG_HEADER_PTR&, DNS_PKG_QUERY_PTR&, unsigned char*,unsigned short); bool recvAnalyse(unsigned char*, size_t, size_t, char*); /* * recvfromTimeOut func is copied from : * http://blog.phamansinh.com/2008/08/10/recvfrom-with-time-out-checking/ * * I think its name is not very good, it just used select to realize time control * and I have to use recvfrom again after it returns not 0 or -1 * * I will follow GPL, though this is not required by the author */ int recvfromTimeOut(int socket, long sec, long usec); DNSCACHE dnscache; enum{DNS_SERVERS= 2 }; static const char* DNS_ADDR; static const int DNS_PORT; }; #endif /* TINYDNSRESOLVER_H_ */

 

TinyDNSResolver.cpp

注意这段代码里的const char* TinyDNSResolver::DNS_ADDR = "202.106.0.20";是dns解析服务器地址，你可以把ip改为一个离你更近，更加稳定的dns服务器地址，当然你也可以设置多个dns服务器地址，随机选取一个解析dns地址减轻服务器负载

/* * TinyDNSResolver.cpp * * Created on: Jun 2, 2009 * Author: luo */ #include "TinyDNSResolver.h" #include <iostream> #include <netinet/in.h> #include <sys/types.h> #include <sys/socket.h> #include <arpa/inet.h> #include <string.h> #include <errno.h> #include <time.h> #include <stdlib.h> const char* TinyDNSResolver::DNS_ADDR = "202.106.0.20"; const int TinyDNSResolver::DNS_PORT = 53; TinyDNSResolver::TinyDNSResolver() { bzero(dnscache._domain, sizeof(dnscache._domain)); bzero(dnscache._ip, sizeof(dnscache._ip)); } TinyDNSResolver::~TinyDNSResolver() { } bool TinyDNSResolver::resolve(const char* domain, char* ip, unsigned short id) { bool result = false; if (strcmp(domain, dnscache._domain) == 0) { //hit dns cache if (dnscache._ip[0] == '/0') return false; strncpy(ip, dnscache._ip, 16); return true; } else { DNS_PKG_HEADER_PTR nphp = new DNS_PKG_HEADER; DNS_PKG_QUERY_PTR dkqp = new DNS_PKG_QUERY; unsigned char dnsBuff[1024]; unsigned char dnsRecv[2048]; bzero(dnsBuff, 1024); bzero(dnsRecv, 2048); int send_size = pkgDNS(domain, nphp, dkqp, dnsBuff, id);//fulfil dns package if(send_size == -1) return false; int sockfd = socket(AF_INET, SOCK_DGRAM, 0); if (sockfd < 0) { std::cout << "tiny dns:ERROR opening socket" << std::endl; return false; } struct sockaddr_in server_addr; unsigned int pkg_len = 0; bzero(&server_addr, sizeof(struct sockaddr_in)); int server_id = id % DNS_SERVERS; server_addr.sin_family = AF_INET; //在寝室用［1］ inet_aton(DNS_ADDR, &server_addr.sin_addr); server_addr.sin_port = htons(DNS_PORT); pkg_len = sizeof(server_addr); int in_len = sendto(sockfd, dnsBuff, sizeof(dnsBuff), 0, (struct sockaddr*) &server_addr, pkg_len); if (in_len < 0) { std::cout << "tiny dns:ERROR sendto" << strerror(errno)<<std::endl; close(sockfd); return false; } int recv_len = 0; // if time is out , try again (3 times totally) // for (int i = 0; i < 3 && recv_len == 0; i++) recv_len = recvfromTimeOut(sockfd, 0, 10000000);//wait 10 seconds if (recv_len == 0 || recv_len < 0) { // if in_len == 0 stands for timeout, if -1 stands for error strncpy(dnscache._domain, domain, 256); dnscache._ip[0] = '/0'; close(sockfd); return false; } else { //select returns fd it must be sockfd, because only sockfd is selected; recv_len = recvfrom(sockfd, dnsRecv, sizeof(dnsRecv), 0, (struct sockaddr*) &server_addr, &pkg_len); if (recv_len < 0) { std::cout << "tiny dns:ERROR recvfrom" << std::endl; strncpy(dnscache._domain, domain, 256); dnscache._ip[0] = '/0'; close(sockfd); return false; } result = recvAnalyse(dnsRecv, recv_len, send_size, ip); if (result) { strncpy(dnscache._domain, domain, 256); if(strcmp(ip, "125.211.213.133") == 0){ result = false; dnscache._ip[0] = '/0'; } else{ strncpy(dnscache._ip, ip, 16); } } else { strncpy(dnscache._domain, domain, 256); dnscache._ip[0] = '/0'; } } close(sockfd); return result; } } int TinyDNSResolver::pkgDNS(const char* domain, DNS_PKG_HEADER_PTR& nphp, DNS_PKG_QUERY_PTR& dkqp, unsigned char* dnsBuff, unsigned short id) { char tmpBuf[256]; bzero(tmpBuf, 256); int domainLen = strlen( domain); if(domainLen <= 0) return -1; memcpy(tmpBuf, domain, domainLen); dkqp->dns_name = new unsigned char[domainLen + 2* sizeof (unsigned char)]; bzero(dkqp->dns_name, domainLen+2* sizeof (unsigned char)); char* tok = NULL; tok = strtok(tmpBuf, "."); unsigned char dot = '/0'; int offset = 0; while(tok != NULL) { dot = (unsigned char)strlen(tok); memcpy(dkqp->dns_name +offset, &dot, sizeof(unsigned char)); offset += sizeof(unsigned char); memcpy(dkqp->dns_name +offset, tok, strlen(tok)); offset += strlen(tok); tok = strtok(NULL, "."); } dkqp->dns_name[domainLen+ 2*sizeof(unsigned char) -1] = 0x00; nphp->id = htons(id);//dns transaction id, given randomly nphp->flag = htons(0x0100); //dns standard query; nphp->questions = htons(0x0001); //num of questions; nphp->answerRRs = htons(0x0000); nphp->authorityRRs = htons(0x0000); nphp->additionalRRs = htons(0x0000); dkqp->dns_type = htons(0x0001); //Type : A dkqp->dns_class = htons(0x0001); //Class : IN memcpy(dnsBuff, (unsigned char*)nphp, sizeof(DNS_PKG_HEADER)); memcpy(dnsBuff+sizeof(DNS_PKG_HEADER), (unsigned char*)dkqp->dns_name,domainLen+2*sizeof(unsigned char)); memcpy(dnsBuff+sizeof(DNS_PKG_HEADER)+(domainLen+2*sizeof(unsigned char)), (unsigned char*)&dkqp->dns_type, sizeof(unsigned short)); memcpy(dnsBuff+sizeof(DNS_PKG_HEADER)+(domainLen+2*sizeof(unsigned char))+sizeof(unsigned short), (unsigned char*)&dkqp->dns_class, sizeof(unsigned short)); delete[] dkqp->dns_name; return sizeof(DNS_PKG_HEADER)+(domainLen+2*sizeof(unsigned char))+sizeof(unsigned short)+sizeof(unsigned short); } bool TinyDNSResolver::recvAnalyse(unsigned char* buf, size_t buf_size, size_t send_size, char* ip) { bool result = false; unsigned char* p = buf; p += 2;//dns id unsigned short flag =ntohs(*((unsigned short*) p));// p[0] * 0x100 + p[1]; if (flag != 0x8180) { std::cout << "not a /"standard query response no error/"! " << std::endl; return false; } p += 2;//dns flag p += 2;//dns questions unsigned short answerRRs = ntohs(*((unsigned short*) p));//p[0] * 0x100 + p[1];//dns answer RRs p = buf + send_size;//p point to Answers unsigned short type; unsigned short dataLen; for (int i = 0; i < answerRRs; i++) { p += 2;//Name type = ntohs(*((unsigned short*) p));//p[0] * 0x100 + p[1]; p += 2;//Type; if (type == 0x0001) { p += 2;//Class p += 4;//TTL p += 2;//Data Length strncpy(ip, inet_ntoa(*(struct in_addr*) p), 16); result = true; break; } p += 2;//Class p += 4;//TTL dataLen = ntohs(*((unsigned short*) p));//p[0] * 0x100 + p[1]; p += 2;//Data Length p += dataLen;//data } return result; } int TinyDNSResolver::recvfromTimeOut(int socket, long sec, long usec) { // Setup timeval variable timeval timeout; timeout.tv_sec = sec; timeout.tv_usec = usec; // Setup fd_set structure fd_set fds; FD_ZERO(&fds); FD_SET(socket, &fds); // Return value: // -1: error occured // 0: timed out // >0: data ready to be read return select(FD_SETSIZE, &fds, 0, 0, &timeout); }

 

 

TinyDNSResolver.cpp

#include <iostream> #include <fstream> #include "./DNS_Resolver/TinyDNSResolver.h" using namespace std; int main() { char * domain = "www.chinarank.org.cn"; char ip[16] = { '/0' }; int nbytes = 0; TinyDNSResolver tr; if (!tr.resolve(domain, ip, 110)) { cout << " dns resolve failed domain : "<<domain << endl; }else{ cout<<"domain : "<<domain<<endl; cout<<"ip : "<<ip<<endl; } return 0; }