DNSServiceQueryRecord

- query records from DNS

Synopsis

cc [ flag ... ] file ... -ldns_sd [ library ... ]
#include <dns_sd.h>

DNSServiceErrorType DNSServiceQueryRecord(DNSServiceRef *sdRef,
     DNSServiceFlags flags, uint32_t interfaceIndex, const char *fullname,
     uint16_t rrtype, uint16_t rrclass,
     DNSServiceServiceQueryRecordReply callBack, void *context);

typedef void(*DNSServiceQueryRecordReply)(DNSServiceRef DNSServiceRef,
     DNSServiceFlags flags, uint32_t interfaceIndex,
     DNSServiceErrorType errorCode, const char *fullname,
     uint16_t rrtype, uint16_t rrclass, uint16_t rdlen,
     const void *rdata, uint32_t ttl, void *context);

Description

The DNSServiceQueryRecord() function is used to query the daemon for any DNS resource record type. The callback argument to DNSServiceQueryRecord() points to a function of type DNSServiceQueryRecordReply() listed above. The sdRef parameter in DNSServiceQueryRecord() points to an uninitialized DNSServiceRef. The DNSServiceQueryRecord() function returns kDNSServiceErr_NoError and initializes sdRef on success. The query runs indefinitely until the client terminates by passing the initialized sdRef from the query call to DNSServiceRefDeallocate().

The flag kDNSServiceFlagsLongLivedQuery should be passed in the flags argument of DNSServiceQueryRecord() to create a “long-lived” unicast query in a non-local domain. This flag has no effect on link local multicast queries. Without this flag, unicast queries will be one-shot and only the results that are available at the time of the query will be returned. With long-lived queries, add or remove events that are available after the first call generate callbacks. The interfaceIndex argument specifies the interface on which to issue the query. Most applications will pass a 0 as the interfaceIndex to make the query on all interfaces. See the section “Constants for specifying an interface index” in <dns_sd.h>. The fullname argument indicates the full domain name of the resource record to be queried. The rrtype argument indicates the resource record type: kDNSServiceType_PTR, for example. The rrclass argument holds the class of the resource record to be queried (kDNSServiceClass_IN). The context argument can be NULL and points to a value passed to the callback function.

The sdRef argument passed to the callback function is initialized by the call to DNSServiceQueryRecord(). Possible values for the flags parameter to the callback function are kDNSServiceFlagsMoreComing and kDNSServiceFlagsAdd. The kDNSServiceFlagsMoreComing value is set to indicate that additional results are immediately available. The kDNSServiceFlagsAdd value indicates that the results returned to the callback function are for a valid DNS record. If kDNSServiceFlagsAdd is not set, the results returned are for a delete event. The errorCode passed to the callback is kDNSServiceErr_NoError on success. Otherwise, failure is indicated and other parameter values are undefined. The fullname parameter indicates the full domain name of the resource record . The rrtype indicates the resource record type. The rrclass indicates the class of the DNS resource record. The rdlen parameter indicates the length of the resource record rdata in bytes. The rdata parameter points to raw rdata of the resource record. The ttl parameter indicates the time to live of the resource record in seconds. The context parameter points to the value passed by the application in the context argument to the DNSServiceQueryRecord() call.

Return Values

The DNSServiceQueryRecord function returns kDNSServiceErr_NoError on success. Otherwise, an error code defined in <dns_sd.h> is returned to indicate the specific failure that occurred.

Attributes

See attributes(5) for description of the following attributes:

See Also

DNSServiceBrowse(3DNS_SD), DNSServiceRegister(3DNS_SD), DNSServiceResolve(3DNS_SD), attributes(5)