Provided by: libasr-dev_1.0.2-2_amd64 bug


       asr_run, asr_run_sync, asr_abort, res_send_async, res_query_async, res_search_async,
       getrrsetbyname_async, gethostbyname_async, gethostbyname2_async, gethostbyaddr_async,
       getnetbyname_async, getnetbyaddr_async, getaddrinfo_async, getnameinfo_async -
       asynchronous resolver functions


       #include <sys/types.h> #include <sys/socket.h> #include <netdb.h> #include <asr.h>
       asr_run(struct asr_query *aq, struct asr_result *ar);
       asr_run_sync(struct asr_query *aq, struct asr_result *ar);
       asr_abort(struct asr_query *aq);
       struct asr_query *
       res_send_async(const unsigned char *pkt, int pktlen, void *asr);
       struct asr_query *
       res_query_async(const char *name, int class, int type, void *asr);
       struct asr_query *
       res_search_async(const char *name, int class, int type, void *asr);
       struct asr_query *
       getrrsetbyname_async(const char *hostname, unsigned int rdclass, unsigned int rdtype,
       unsigned int flags, void *asr);
       struct asr_query *
       gethostbyname_async(const char *name, void *asr);
       struct asr_query *
       gethostbyname2_async(const char *name, int af, void *asr);
       struct asr_query *
       gethostbyaddr_async(const void *addr, socklen_t len, int af, void *asr);
       struct asr_query *
       getnetbyname_async(const char *name, void *asr);
       struct asr_query *
       getnetbyaddr_async(in_addr_t net, int type, void *asr);
       struct asr_query *
       getaddrinfo_async(const char *hostname, const char *servname,
       const struct addrinfo *hints, void *asr);
       struct asr_query *
       getnameinfo_async(const struct sockaddr *sa, socklen_t salen, char *host, size_t hostlen,
       char *serv, size_t servlen, int flags, void *asr);


       The asr functions provide a simple interface for asynchronous address resolution and
       nameserver querying.  They should be used in place of the classical resolver functions of
       libc when blocking is not desirable.

       The principle of operation is as follows: All async requests are made against an asr
       context which basically defines a list of sources to query and a strategy to do so.  The
       user creates a query through one of the dedicated functions, and gets a handle
       representing the internal query.  A query is a state-machine that can be run to try to
       fulfill a particular request.  This is done by calling in a generic API that performs the
       state transitions until it needs to give the control back to the user, either because a
       result is available, or because the next transition implies a blocking call (a file
       descriptor needs to be read from or written to).  The user is responsible for dealing with
       the situation: either get the result, or wait until the fd conditions are met, and then
       call back into the resolving machinery when it is ready to proceed.

       The asr_run() function drives the resolving process.  It runs the asynchronous query
       represented by the handle until a result is available, or until it cannot continue without
       blocking.  The results are returned to the user through the parameter, which must be a
       valid pointer to user allocated memory.  is defined as:
           struct asr_result {
                /* Fields set if the query is not done yet (asr_run returns 0) */
                int   ar_cond; /* ASR_WANT_READ or ASR_WANT_WRITE */
                int   ar_fd;        /* the fd waiting for io condition */
                int   ar_timeout;   /* time to wait for in milliseconds */
                /* Error fields.  Depends on the query type. */
                int   ar_errno;
                int   ar_h_errno;
                int   ar_gai_errno;
                int   ar_rrset_errno;
                /* Result for res_*_async() calls */
                int   ar_count;     /* number of answers in the dns reply */
                int   ar_rcode;     /* response code in the dns reply */
                void *ar_data; /* raw reply packet (must be freed) */
                int   ar_datalen;   /* reply packet length */
                struct sockaddr_storage ar_ns; /* nameserver that responded */
                /* Result for other calls. Must be freed properly. */
                struct addrinfo      *ar_addrinfo;
                struct rrsetinfo *ar_rrsetinfo;
                struct hostent  *ar_hostent;
                struct netent   *ar_netent;

       The function returns one of the following values:

            0      The query cannot be processed further until a specific condition on a
                   file descriptor becomes true.
                   The following members of the
                   structure are filled:

                 one of ASR_WANT_READ or ASR_WANT_WRITE,

                 the file descriptor waiting for an IO operation,

                 the amount of time to wait for in milliseconds.

            The caller is expected to call
            again once the condition holds or the timeout expires.

            1      The query is completed.
                   The members relevant to the actual async query type are set accordingly,
                   including error conditions.
                   In any case, the query is cleared and its handle is invalidated.

       Note that although the query itself may fail (the error being properly reported
       in the
       structure), the
       function itself cannot fail and it always preserves errno.

       function is a wrapper around
       that handles the read/write conditions, thus falling back to a blocking
       It only returns 1.
       It also preserves errno.

       function clears a running query.
       It can be called when the query is waiting on a file descriptor.
       Note that a completed query is already cleared when
       returns, so
       must not be called in this case.

       The remaining functions are used to initiate different kinds of query
       on the
       resolver context.
       The specific operational details for each of them are described below.
       All functions return a handle to an internal query, or NULL if they could
       not allocate the necessary resources to initiate the query.
       All other errors (especially invalid parameters) are reported when calling
       They usually have the same interface as an existing resolver function, with
       an additional
       argument, which specifies the context to use for this request.
       For now, the argument must always be NULL, which will use the default
       context for the current thread.

       functions are asynchronous versions of the standard libc resolver routines.
       Their interface is very similar, except that the response buffer is always
       allocated internally.
       The return value is found upon completion in the
       member of the response structure.
       In addition, the
       structure contains the address of the DNS server that sent the response,
       contains the code returned by the server in the DNS response packet, and
       contains the number of answers in the packet.
       If a response is received it is placed in a newly allocated buffer
       and returned as
       This buffer must be freed by the caller.
       On error, the
       members are set accordingly.

       function is an asynchronous version of
       Upon completion, the return code is found in
       and the address to the newly allocated result set is set in
       As for the blocking function, it must be freed by calling

       functions provide an asynchronous version of the network host entry functions.
       Upon completion,
       is set and the resulting hostent address, if found, is set
       in the
       Note that unlike their blocking counterparts, these functions always return a
       pointer to newly allocated memory, which must be released by the caller using

       Similarly, the
       functions provide an asynchronous version of the network entry functions.
       Upon completion,
       is set and the resulting netent address, if found, is set
       in the
       The memory there is also allocated for the request, and it must be freed by

       function is an asynchronous version of the
       It provides a chain of addrinfo structures with all valid combinations of
       socket address for the given
       Those three parameters have the same meaning as for the blocking counterpart.
       Upon completion the return code is set in
       member may also be set.
       On success, the
       member points to a newly allocated list of addrinfo.
       This list must be freed with


       This implementation of the asynchronous resolver interface is thread-safe and lock-free
       internally, but the following restriction applies: Two different threads must not create
       queries on the same context or run queries originating from the same context at the same
       time.  If they want to do that, all calls must be protected by a mutex around that

       It is generally not a problem since the main point of the asynchronous resolver is to
       multiplex queries within a single thread of control, so sharing a resolver among threads
       is not useful.


       getaddrinfo(3), gethostbyname(3), getnameinfo(3), getnetbyname(3), getrrsetbyname(3),
       res_send(3), resolv.conf(5)


       This DNS resolver implementation doesn't support the EDNS0 protocol extension yet.

                                    $Mdocdate: March 26 2014 $                         ASR_RUN(3)