GET / HTTP/1.0Host: linux.org.ua
Щодо отримання сторінки — то це вже не DNS, а HTTP починається.
... спочатку спробувати прибіндитися до айпішки комп'ютера, бо є вірогідність що з його вимкненням у вас пропаде системний резолвер dns.
//**************************************************************//// SERVER END UDP/IP APPLICATION //// DNS by Parfeniuk B.O. ////***************************************************************************//#include <stdio.h> // Standard input and output#include <sys/socket.h> // For socket(), connect(), send(), and recv()#include <arpa/inet.h> // For sockaddr_in and inet_addr()#include <stdlib.h> // For atoi() and exit()#include <string.h> // For memset()#include <unistd.h> // For close()#include <netdb.h> // For gethostbyname()#include <time.h> // For time_t//List of DNS Servers registered on the systemchar dns_servers[10][100];int dns_server_count = 0;//Types of DNS resource records#define T_A 1 //Ipv4 address#define T_NS 2 //Nameserver#define T_CNAME 5 // canonical name#define T_SOA 6 /* start of authority zone */#define T_PTR 12 /* domain name pointer */#define T_MX 15 //Mail server//Function Prototypesvoid ngethostbyname (unsigned char* , int);void ChangetoDnsNameFormat (unsigned char*,unsigned char*);unsigned char* ReadName (unsigned char*,unsigned char*,int*);void get_dns_servers();/*** The structure for DNS header ***/typedef struct{unsigned short id; // identification numberunsigned char rd :1; // recursion desiredunsigned char tc :1; // truncated messageunsigned char aa :1; // authoritive answerunsigned char opcode :4; // purpose of messageunsigned char qr :1; // query/response flagunsigned char rcode :4; // response codeunsigned char cd :1; // checking disabledunsigned char ad :1; // authenticated dataunsigned char z :1; // its z! reservedunsigned char ra :1; // recursion availableunsigned short q_count; // number of question entriesunsigned short ans_count; // number of answer entriesunsigned short auth_count; // number of authority entriesunsigned short add_count; // number of resource entries} DNS_HEADER;/*** The structure for the query ***/typedef struct{unsigned short qtype;unsigned short qclass;} QUESTION;/*** The structure for Resource Record ***/#pragma pack(push, 1)typedef struct{unsigned short type;unsigned short _class;unsigned int ttl;unsigned short data_len;} R_DATA;#pragma pack(pop)/*** Pointers to resource record contents***/typedef struct{unsigned char *name;R_DATA *resource;unsigned char *rdata;} RES_RECORD;/*** Structure of a Query***/typedef struct{unsigned char *name;QUESTION *ques;} QUERY;//-------------------------------------------------------------////***************** MAIN FUNCTION ********************////-------------------------------------------------------------//int main(int argc, char *argv[]) {unsigned char hostname[100]; int serverSock; // Socket descriptor for server // Socket descriptor for client struct sockaddr_in serverAddr; // Structure variable for Local address if (argc != 4) // Test for correct number of arguments { printf("\n\t\tNumber of command line parametes aren't proper. Terminating DNS service!"); } /* Create socket for incoming connections */ if ((serverSock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) //UDP packet for DNS queries { printf("\n\t\tERROR opening socket. Terminating DNS service!"); // exit(1); } // Zero out structure serverAddr.sin_family = AF_INET; // Internet address family serverAddr.sin_addr.s_addr = htonl(INADDR_ANY); // Any incoming interface serverAddr.sin_port = htons(atoi(argv[1])); // Local port 53 /* Bind to the local address */ if (bind(serverSock, (struct sockaddr *) &serverAddr, sizeof(serverAddr)) < 0){ printf("bind() failed"); } printf("\n\n\t\tWelcome to the DNS Doisser System \t\t\n"); printf("\n\t\tDNS Doisser listening on Port Number is: %s\n",argv[1]); /* Mark the socket so it will listen for incoming connections */ if (listen(serverSock, 5) < 0) printf("\n"); while(1){} //Now get the ip of this hostname , A record ngethostbyname(hostname , T_A);}//-------------------------------------------------------------////***************** MAIN FUNCTION ENDS ********************////-------------------------------------------------------------///* * Perform a DNS query by sending a packet * */void ngethostbyname(unsigned char *host , int query_type){ unsigned char buf[65536],*qname,*reader; int i , j , stop , s; struct sockaddr_in a; RES_RECORD answers[20],auth[20],addit[20]; //the replies from the DNS server struct sockaddr_in dest; DNS_HEADER *dns = NULL; QUESTION *qinfo = NULL; printf("Resolving %s" , host); s = socket(AF_INET , SOCK_DGRAM , IPPROTO_UDP); //UDP packet for DNS queries dest.sin_family = AF_INET; dest.sin_port = htons(53); dest.sin_addr.s_addr = inet_addr(dns_servers[0]); //dns servers //Set the DNS structure to standard queries dns = (DNS_HEADER *)&buf; dns->id = (unsigned short) htons(getpid()); dns->qr = 0; //This is a query dns->opcode = 0; //This is a standard query dns->aa = 0; //Not Authoritative dns->tc = 0; //This message is not truncated dns->rd = 1; //Recursion Desired dns->ra = 0; //Recursion not available! hey we dont have it (lol) dns->z = 0; dns->ad = 0; dns->cd = 0; dns->rcode = 0; dns->q_count = htons(1); //we have only 1 question dns->ans_count = 0; dns->auth_count = 0; dns->add_count = 0; //point to the query portion qname =(unsigned char*)&buf[sizeof( DNS_HEADER)]; ChangetoDnsNameFormat(qname , host); qinfo =( QUESTION*)&buf[sizeof( DNS_HEADER) + (strlen((const char*)qname) + 1)]; //fill it qinfo->qtype = htons( query_type ); //type of the query , A , MX , CNAME , NS etc qinfo->qclass = htons(1); //its internet (lol) printf("\nSending Packet..."); if( sendto(s,(char*)buf,sizeof( DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(QUESTION),0,(struct sockaddr*)&dest,sizeof(dest)) < 0) { perror("sendto failed"); } printf("Done"); //Receive the answer i = sizeof dest; printf("\nReceiving answer..."); if(recvfrom (s,(char*)buf , 65536 , 0 , (struct sockaddr*)&dest , (socklen_t*)&i ) < 0) { perror("recvfrom failed"); } printf("Done"); dns = (DNS_HEADER*) buf; //move ahead of the dns header and the query field reader = &buf[sizeof( DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof( QUESTION)]; printf("\nThe response contains : "); printf("\n %d Questions.",ntohs(dns->q_count)); printf("\n %d Answers.",ntohs(dns->ans_count)); printf("\n %d Authoritative Servers.",ntohs(dns->auth_count)); printf("\n %d Additional records.\n\n",ntohs(dns->add_count)); //Start reading answers stop=0; for(i=0;i<ntohs(dns->ans_count);i++) { answers[i].name=ReadName(reader,buf,&stop); reader = reader + stop; answers[i].resource = ( R_DATA*)(reader); reader = reader + sizeof( R_DATA); if(ntohs(answers[i].resource->type) == 1) //if its an ipv4 address { answers[i].rdata = (unsigned char*)malloc(ntohs(answers[i].resource->data_len)); for(j=0 ; j<ntohs(answers[i].resource->data_len) ; j++) { answers[i].rdata[j]=reader[j]; } answers[i].rdata[ntohs(answers[i].resource->data_len)] = '\0'; reader = reader + ntohs(answers[i].resource->data_len); } else { answers[i].rdata = ReadName(reader,buf,&stop); reader = reader + stop; } } //read authorities for(i=0;i<ntohs(dns->auth_count);i++) { auth[i].name=ReadName(reader,buf,&stop); reader+=stop; auth[i].resource=( R_DATA*)(reader); reader+=sizeof( R_DATA); auth[i].rdata=ReadName(reader,buf,&stop); reader+=stop; } //read additional for(i=0;i<ntohs(dns->add_count);i++) { addit[i].name=ReadName(reader,buf,&stop); reader+=stop; addit[i].resource=( R_DATA*)(reader); reader+=sizeof( R_DATA); if(ntohs(addit[i].resource->type)==1) { addit[i].rdata = (unsigned char*)malloc(ntohs(addit[i].resource->data_len)); for(j=0;j<ntohs(addit[i].resource->data_len);j++) addit[i].rdata[j]=reader[j]; addit[i].rdata[ntohs(addit[i].resource->data_len)]='\0'; reader+=ntohs(addit[i].resource->data_len); } else { addit[i].rdata=ReadName(reader,buf,&stop); reader+=stop; } } //print answers printf("\nAnswer Records : %d \n" , ntohs(dns->ans_count) ); for(i=0 ; i < ntohs(dns->ans_count) ; i++) { printf("Name : %s ",answers[i].name); if( ntohs(answers[i].resource->type) == T_A) //IPv4 address { long *p; p=(long*)answers[i].rdata; a.sin_addr.s_addr=(*p); //working without ntohl printf("has IPv4 address : %s",inet_ntoa(a.sin_addr)); } if(ntohs(answers[i].resource->type)==5) { //Canonical name for an alias printf("has alias name : %s",answers[i].rdata); } printf("\n"); } //print authorities printf("\nAuthoritive Records : %d \n" , ntohs(dns->auth_count) ); for( i=0 ; i < ntohs(dns->auth_count) ; i++) { printf("Name : %s ",auth[i].name); if(ntohs(auth[i].resource->type)==2) { printf("has nameserver : %s",auth[i].rdata); } printf("\n"); } //print additional resource records printf("\nAdditional Records : %d \n" , ntohs(dns->add_count) ); for(i=0; i < ntohs(dns->add_count) ; i++) { printf("Name : %s ",addit[i].name); if(ntohs(addit[i].resource->type)==1) { long *p; p=(long*)addit[i].rdata; a.sin_addr.s_addr=(*p); printf("has IPv4 address : %s",inet_ntoa(a.sin_addr)); } printf("\n"); } return;}/* * * */u_char* ReadName(unsigned char* reader,unsigned char* buffer,int* count){ unsigned char *name; unsigned int p=0,jumped=0,offset; int i , j; *count = 1; name = (unsigned char*)malloc(256); name[0]='\0'; //read the names in 3www6google3com format while(*reader!=0) { if(*reader>=192) { offset = (*reader)*256 + *(reader+1) - 49152; //49152 = 11000000 00000000 reader = buffer + offset - 1; jumped = 1; //we have jumped to another location so counting wont go up! } else { name[p++]=*reader; } reader = reader+1; if(jumped==0) { *count = *count + 1; //if we havent jumped to another location then we can count up } } name[p]='\0'; //string complete if(jumped==1) { *count = *count + 1; //number of steps we actually moved forward in the packet } //now convert 3www6google3com0 to www.google.com for(i=0;i<(int)strlen((const char*)name);i++) { p=name[i]; for(j=0;j<(int)p;j++) { name[i]=name[i+1]; i=i+1; } name[i]='.'; } name[i-1]='\0'; //remove the last dot return name;}/* * Get the DNS servers from /etc/resolv.conf file on Linux * */void get_dns_servers(){ FILE *fp; char line[200] ;//*p if((fp = fopen("/etc/resolv.conf" , "r")) == NULL) { printf("Failed opening /etc/resolv.conf file \n"); } while(fgets(line , 200 , fp)) { if(line[0] == '#') { continue; } if(strncmp(line , "nameserver" , 10) == 0) { // p = strtok(line , " "); // p = strtok(NULL , " "); //p now is the dns ip //? } } strcpy(dns_servers[0] , "8.8.8.8"); strcpy(dns_servers[1] , "208.67.220.220");}/* * This will convert www.google.com to 3www6google3com * got it * */void ChangetoDnsNameFormat(unsigned char* dns,unsigned char* host){ int lock = 0 , i; strcat((char*)host,"."); for(i = 0 ; i < strlen((char*)host) ; i++) { if(host[i]=='.') { *dns++ = i-lock; for(;lock<i;lock++) { *dns++=host[lock]; } lock++; //or lock=i+1; } } *dns++='\0';}
hi
