AsyncResolv library

asynchronous DNS query library

by Aleksey Krivoshey krivoshey@users.sourceforge.net

1. Introduction

   1. Licensing

   2. Download

2. Using library

   1. initialization

   2. Prepare query

   3. Asynchronously resolve query and/or wait for completion

   4. Get reply

   5. Get all question fields from reply

   6. Get all headers from reply

   7. Get all answers (answer RR's)

   8. Get all authoritative answers

   9. Additional answers

   10. Print __all__ resource records

   11. Get all RR's of some type

   12. Cleanup before next query

1. Introduction.
   AsyncResolv is an asynchronous DNS query library written in C++.
   Resolver is capable of most RFC1035 resource records parsing, supports queries over UDP and over TCP (if UDP failed)

   1. Library is licensed under GNU Lesser ( Library ) General Public License (LGPL)

   2. Download
      Latest version is available from
      http://sourceforge.net/projects/asyncresolv/
      http://www.foss.kharkov.ua/~voodoo/

2. Using library

   1. Initialization

      1. Create resolver object:
         
         AsyncDNSResolver * resolver = new AsyncDNSResolver();

      2. Initialize it
         
         if(resolver->initialize() == -1){
           return -1;
         }

   2. Prepare query

      1. set query type (recursive, status/normal/inverse query)
         
         if(resolver->prepareQuery(RFC1035_OPCODE_QUERY, RFC1035_RESOLVE_RECURSIVE) == -1){
           return -1;
         }
         
         Possible values for opcode are:
         - RFC1035_OPCODE_QUERY
         - RFC1035_OPCODE_IQUERY
         - RFC1035_OPCODE_STATUS
         
         Possible values for recursive behavior are:
         - RFC1035_RESOLVE_RECURSIVE
         - 0

      2. set query ( query name, resource record type, class)
         
         if(resolver->addQuery("aol.com", RFC1035_TYPE_MX, RFC1035_CLASS_IN) == -1){
           return -1;
         }

   3. Asynchronously resolve query and/or wait for completion

      1. Using resolver->wait(msec) function
         
         while(resolver->resolveQueries() == EAGAIN){
           if(resolver->wait(10000) != 0){
             if(resolver->timedout() == -1){
               break;
             }
           }
         }

      2. Using own poll() loop
         
         while(resolver->resolveQueries() == EAGAIN){
           int e = poll(resolver->getPollfd(), 1, 10000);
             if(e == -1){
             perror(“poll() failed”);
             break;
           }
           if(e == 0){
             if(resolver->timedout() == -1){
               break;
             }
           }
         }

   4. Get reply
      
      const AsyncDNSReply * reply = resolver->getReply();

   5. Get all question fields from reply
      
      const RFC1035_MessageQuestion * question = reply->getQuestion();
      printf("Questions:\n");
      int i = 0;
      while((question = reply->getQuestion(i++)) != NULL){
        printf("qname=%s, qtype=%d, qclass=%d, header_id=%d\n", question->qname, question->qtype, question->qclass, question->header_id);
      }

   6. Get all headers from reply
      
      const RFC1035_MessageHeader * header = NULL;
      size_t i = 0;
      printf("Headers:\n");
      while((header = reply->getHeader(i++)) != NULL){
        printf("ID=%d, RCODE=%d, %s\n", header->id, header->get_rcode(), header->get_aa()?"Authoritative answer":"Not authoritative answer");
      }

   7. Get all answers (answer RR's)
      
      const RFC1035_RR * answer = NULL;
      i = 0;
      while((answer = reply->getAnswer(i++)) != NULL){
        dump(answer);
      }
      
      --- dump() function is defined in example/test.cc ---

   8. Get all authoritative answers
      
      const RFC1035_RR * answer = NULL;
      int i = 0;
      while((answer = reply->getAuthority(i++)) != NULL){
        dump(answer);
      }
      --- dump() function is defined in example/test.cc ---

   9. Additional answers
      
      const RFC1035_RR * answer = NULL;
      int i = 0;
      while((answer = reply->getAdditional(i++)) != NULL){
        dump(answer);
      }
      --- dump() function is defined in example/test.cc ---

   10. Print __all__ resource records
       
       const RFC1035_RR * answer = NULL;
       int i = 0;
       while((answer = reply->getRR(i++)) != NULL){
         dump(answer);
       }

   11. Get all RR's of some type
       Resource records of the same type are linked in the reverse unidirectional list:
       
       // All MX resource records
       const RFC1035_RR * answer = NULL;
       answer = reply->getLastRRByType(RFC1035_TYPE_MX);
       while(answer){
         dump(answer);
         answer = answer->prevRR;
       }

   12. Cleanup before next query
       
       resolver->cleanup(); //must be called after each call to resolveQueries