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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
3. 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/
4. 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