DNS Service Discovery C Reference

Declared in
dns_sd.h

Overview

Included Headers

  • <sys/types.h>

  • <sys/types.h>

  • "Tiano.h"

  • <windows.h>

  • <stdint.h>

  • <dispatch/dispatch.h>

Functions by Task

See the Overview section above for header-level documentation.

Version checking

Unix Domain Socket access, DNSServiceRef deallocation, and data processing functions

Unified lookup of both IPv4 and IPv6 addresses for a fully qualified hostname

TXT Record Parsing Functions

A typical calling sequence for TXT record parsing is something like:

Receive TXT record data in DNSServiceResolve callback

 
 if (TXTRecordContainsKey(txtLen, txtRecord, "key")) then do something
 val1ptr = TXTRecordGetValuePtr(txtLen, txtRecord, "key1", &len1);
 val2ptr = TXTRecordGetValuePtr(txtLen, txtRecord, "key2", &len2);
 ...
 memcpy(myval1, val1ptr, len1);
 memcpy(myval2, val2ptr, len2);
 ...
 return;
 

If you wish to retain the values after return from the DNSServiceResolve callback, then you need to copy the data to your own storage using memcpy() or similar, as shown in the example above.

If for some reason you need to parse a TXT record you built yourself using the TXT record construction functions above, then you can do that using TXTRecordGetLength and TXTRecordGetBytesPtr calls: TXTRecordGetValue(TXTRecordGetLength(x), TXTRecordGetBytesPtr(x), key, &len);

Most applications only fetch keys they know about from a TXT record and ignore the rest. However, some debugging tools wish to fetch and display all keys. To do that, use the TXTRecordGetCount() and TXTRecordGetItemAtIndex() calls.

TXT Record Construction Functions

Special Purpose Calls

DNSServiceCreateConnection, DNSServiceRegisterRecord, DNSServiceReconfirmRecord (most applications will not use these)

Service Registration

Service Discovery

Querying Individual Specific Records

NAT Port Mapping

General Utility Functions

Domain Enumeration

Functions

DNSServiceAddRecord

Adds a record to a registered service.

DNSServiceErrorType DNSServiceAddRecord (
   DNSServiceRef sdRef,
   DNSRecordRef *RecordRef,
   DNSServiceFlags flags,
   uint16_t rrtype,
   uint16_t rdlen,
   const void *rdata,
   uint32_t ttl
);
Parameters
sdRef

A DNSServiceRef initialized by DNSServiceRegister.

RecordRef

A pointer to an uninitialized DNSRecordRef. Upon succesfull completion of this call, this ref may be passed to DNSServiceUpdateRecord or DNSServiceRemoveRecord. If the above DNSServiceRef is passed to DNSServiceRefDeallocate, RecordRef is also invalidated and may not be used further.

flags

Currently ignored, reserved for future use.

rrtype

The type of the record (e.g. kDNSServiceType_TXT, kDNSServiceType_SRV, and so on).

rdlen

The length, in bytes, of the rdata.

rdata

The raw rdata to be contained in the added resource record.

ttl

The time to live of the resource record, in seconds. Most clients should pass 0 to indicate that the system should select a sensible default value.

Return Value

Returns kDNSServiceErr_NoError on success, otherwise returns an error code indicating the error that occurred (the RecordRef is not initialized).

Discussion

The name of the record will be the same as the registered service's name. The record can later be updated or deregistered by passing the RecordRef initialized by this function to DNSServiceUpdateRecord or DNSServiceRemoveRecord.

Note that the DNSServiceAddRecord/UpdateRecord/RemoveRecord are *NOT* thread-safe with respect to a single DNSServiceRef. If you plan to have multiple threads in your program simultaneously add, update, or remove records from the same DNSServiceRef, then it's the caller's responsibility to use a mutext lock or take similar appropriate precautions to serialize those calls.

DNSServiceBrowse

Browses for available services.

DNSServiceErrorType DNSServiceBrowse (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   const char *regtype,
   const char *domain, /* may be NULL */
   DNSServiceBrowseReply callBack,
   void *context /* may be NULL */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the browse operation will run indefinitely until the client terminates it by passing this DNSServiceRef to DNSServiceRefDeallocate.

flags

Currently ignored, reserved for future use.

interfaceIndex

If non-zero, specifies the interface on which to browse for services (the index for a given interface is determined via the if_nametoindex() family of calls.) Most applications will pass 0 to browse on all available interfaces. See "Constants for specifying an interface index" for more details.

regtype

The service type being browsed for followed by the protocol, separated by a dot (e.g. "_ftp._tcp"). The transport protocol must be "_tcp" or "_udp". A client may optionally specify a single subtype to perform filtered browsing: e.g. browsing for "_primarytype._tcp,_subtype" will discover only those instances of "_primarytype._tcp" that were registered specifying "_subtype" in their list of registered subtypes. Additionally, a group identifier may also be specified before the subtype e.g., _primarytype._tcp:GroupID, which will discover only the members that register the service with GroupID. See DNSServiceRegister for more details.

domain

If non-NULL, specifies the domain on which to browse for services. Most applications will not specify a domain, instead browsing on the default domain(s).

callBack

The function to be called when an instance of the service being browsed for is found, or if the call asynchronously fails.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred (the callback is not invoked and the DNSServiceRef is not initialized).

DNSServiceConstructFullName

Concatenates a three-part domain name (as returned by the above callbacks) into a properly-escaped full domain name.

DNSServiceErrorType DNSServiceConstructFullName (
   char *const fullName,
   const char *const service, /* may be NULL */
   const char *const regtype,
   const char *const domain
);
Parameters
fullName

A pointer to a buffer that where the resulting full domain name is to be written. The buffer must be kDNSServiceMaxDomainName (1009) bytes in length to accommodate the longest legal domain name without buffer overrun.

service

The service name - any dots or backslashes must NOT be escaped. May be NULL (to construct a PTR record name, e.g. "_ftp._tcp.apple.com.").

regtype

The service type followed by the protocol, separated by a dot (e.g. "_ftp._tcp").

domain

The domain name, e.g. "apple.com.". Literal dots or backslashes, if any, must be escaped, e.g. "1st\. Floor.apple.com."

Return Value

Returns kDNSServiceErr_NoError (0) on success, kDNSServiceErr_BadParam on error.

Discussion

Note that callbacks in the above functions ALREADY ESCAPE strings where necessary.

DNSServiceCreateConnection

Creates a connection to the daemon, allowing efficient registration of multiple individual records.

DNSServiceErrorType DNSServiceCreateConnection (
   DNSServiceRef *sdRef
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. Deallocating the reference (via DNSServiceRefDeallocate) severs the connection and deregisters all records registered on this connection.

Return Value

Returns kDNSServiceErr_NoError on success, otherwise returns an error code indicating the specific failure that occurred (in which case the DNSServiceRef is not initialized).

DNSServiceCreateDelegateConnection

Create a delegate connection to the daemon allowing efficient registration of multiple individual records.

DNSServiceErrorType DNSServiceCreateDelegateConnection (
   DNSServiceRef *sdRef,
   int32_t pid,
   uuid_t uuid
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. Deallocating the reference (via DNSServiceRefDeallocate()) severs the connection and deregisters all records registered on this connection.

pid

Process ID of the delegate

uuid

UUID of the delegate

Note that only one of the two arguments (pid or uuid) can be specified. If pid is zero, uuid will be assumed to be a valid value; otherwise pid will be used.

Return Value

Returns kDNSServiceErr_NoError on success, otherwise returns an error code indicating the specific failure that occurred (in which case the DNSServiceRef is not initialized). kDNSServiceErr_NotAuth is returned to indicate that the calling process does not have entitlements to use this API.

DNSServiceEnumerateDomains

Enumerates domains that are recommended for registration and browsing.

DNSServiceErrorType DNSServiceEnumerateDomains (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceDomainEnumReply callBack,
   void *context /* may be NULL */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the enumeration operation will run indefinitely until the client terminates it by passing this DNSServiceRef to DNSServiceRefDeallocate.

flags

Possible values are: kDNSServiceFlagsBrowseDomains to enumerate domains recommended for browsing. kDNSServiceFlagsRegistrationDomains to enumerate domains recommended for registration.

interfaceIndex

If non-zero, specifies the interface on which to look for domains. (the index for a given interface is determined via the if_nametoindex() family of calls.) Most applications will pass 0 to enumerate domains on all interfaces. See "Constants for specifying an interface index" for more details.

callBack

The function to be called when a domain is found or the call asynchronously fails.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred (the callback is not invoked and the DNSServiceRef is not initialized).

Discussion

The enumeration MUST be cancelled via DNSServiceRefDeallocate when no more domains are to be found.

Note that the names returned are (like all of DNS-SD) UTF-8 strings, and are escaped using standard DNS escaping rules. (See "Notes on DNS Name Escaping" earlier in this file for more details.) A graphical browser displaying a hierarchical tree-structured view should cut the names at the bare dots to yield individual labels, then de-escape each label according to the escaping rules, and then display the resulting UTF-8 text.

DNSServiceGetAddrInfo

Queries for the IP address of a hostname by using either Multicast or Unicast DNS.

DNSServiceErrorType DNSServiceGetAddrInfo (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceProtocol protocol,
   const char *hostname,
   DNSServiceGetAddrInfoReply callBack,
   void *context /* may be NULL */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the query begins and will last indefinitely until the client terminates the query by passing this DNSServiceRef to DNSServiceRefDeallocate.

flags

kDNSServiceFlagsForceMulticast or kDNSServiceFlagsLongLivedQuery. Pass kDNSServiceFlagsLongLivedQuery to create a "long-lived" unicast query to a unicast DNS server that implements the protocol. This flag has no effect on link-local multicast queries.

interfaceIndex

The interface on which to issue the query. Passing 0 causes the query to be sent on all active interfaces via Multicast or the primary interface via Unicast.

protocol

Pass in kDNSServiceProtocol_IPv4 to look up IPv4 addresses, or kDNSServiceProtocol_IPv6 to look up IPv6 addresses, or both to look up both kinds. If neither flag is set, the system will apply an intelligent heuristic, which is (currently) that it will attempt to look up both, except:

* If "hostname" is a wide-area unicast DNS hostname (i.e. not a ".local." name) but this host has no routable IPv6 address, then the call will not try to look up IPv6 addresses for "hostname", since any addresses it found would be unlikely to be of any use anyway. Similarly, if this host has no routable IPv4 address, the call will not try to look up IPv4 addresses for "hostname".

hostname

The fully qualified domain name of the host to be queried for.

callBack

The function to be called when the query succeeds or fails asynchronously.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred.

DNSServiceGetPID

Maps the source port of the local UDP socket that was opened for sending the DNS query to the process ID of the application that triggered the DNS resolution.

DNSServiceErrorType DNSServiceGetPID (
   uint16_t srcport,
   int32_t *pid
);
Parameters
srcport

Source port (in network byte order) of the UDP socket that was created by mDNSResponder to send the DNS query on the wire.

pid

Process ID of the application that started the name resolution which triggered mDNSResponder to send the query on the wire. The value can be -1 if the srcport cannot be mapped.

Return Value

Returns kDNSServiceErr_NoError on success, or kDNSServiceErr_ServiceNotRunning if the daemon is not running. The value of the pid is undefined if the return value has error.

DNSServiceGetProperty

Gets the specified property of a service.

DNSServiceErrorType DNSServiceGetProperty (
   const char *property, /* Requested property (e.g. {@link kDNSServiceProperty_DaemonVersion}) */
   void *result, /* Pointer to place to store result */
   uint32_t *size /* size of result location */
);
Parameters
property

The requested property. Currently the only property defined is kDNSServiceProperty_DaemonVersion.

result

Place to store result. For retrieving DaemonVersion, this should be the address of a uint32_t.

size

Pointer to uint32_t containing size of the result location. For retrieving DaemonVersion, this should be sizeof(uint32_t). On return the uint32_t is updated to the size of the data returned. For DaemonVersion, the returned size is always sizeof(uint32_t), but future properties could be defined which return variable-sized results.

Return Value

Returns kDNSServiceErr_NoError on success, or kDNSServiceErr_ServiceNotRunning if the daemon (or "system service" on Windows) is not running.

DNSServiceNATPortMappingCreate

Requests a port mapping in the NAT gateway, which maps a port on the local machine to an external port on the NAT.

DNSServiceErrorType DNSServiceNATPortMappingCreate (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceProtocol protocol, /* TCP and/or UDP          */
   uint16_t internalPort, /* network byte order      */
   uint16_t externalPort, /* network byte order      */
   uint32_t ttl, /* time to live in seconds */
   DNSServiceNATPortMappingReply callBack,
   void *context /* may be NULL             */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the nat port mapping will last indefinitely until the client terminates the port mapping request by passing this DNSServiceRef to DNSServiceRefDeallocate.

flags

Currently ignored, reserved for future use.

interfaceIndex

The interface on which to create port mappings in a NAT gateway. Passing 0 causes the port mapping request to be sent on the primary interface.

protocol

To request a port mapping, pass in kDNSServiceProtocol_UDP, or kDNSServiceProtocol_TCP, or (kDNSServiceProtocol_UDP | kDNSServiceProtocol_TCP) to map both. The local listening port number must also be specified in the internalPort parameter. To just discover the NAT gateway's external IP address, pass zero for protocol, internalPort, externalPort and ttl.

internalPort

The port number in network byte order on the local machine which is listening for packets.

externalPort

The requested external port in network byte order in the NAT gateway that you would like to map to the internal port. Pass 0 if you don't care which external port is chosen for you.

ttl

The requested renewal period of the NAT port mapping, in seconds. If the client machine crashes, suffers a power failure, is disconnected from the network, or suffers some other unfortunate demise which causes it to vanish unexpectedly without explicitly removing its NAT port mappings, then the NAT gateway will garbage-collect old stale NAT port mappings when their lifetime expires. Requesting a short TTL causes such orphaned mappings to be garbage-collected more promptly, but consumes system resources and network bandwidth with frequent renewal packets to keep the mapping from expiring. Requesting a long TTL is more efficient on the network, but in the event of the client vanishing, stale NAT port mappings will not be garbage-collected as quickly. Most clients should pass 0 to use a system-wide default value.

callBack

The function to be called when the port mapping request succeeds or fails asynchronously.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred.

If you don't actually want a port mapped, and are just calling the API because you want to find out the NAT's external IP address (e.g. for UI display) then pass zero for protocol, internalPort, externalPort and ttl.

Discussion

The NAT should support either the NAT-PMP or the UPnP IGD for this API to create a successful mapping. Note that this API currently supports IPv4 addresses/mappings only. If the NAT gateway supports PCP and returns an IPv6 address (incorrectly, since this API specifically requests IPv4 addresses), the DNSServiceNATPortMappingReply callback is invoked with errorCode kDNSServiceErr_NATPortMappingUnsupported.

The port mapping will be renewed indefinitely until the client process exits, or explicitly terminates the port mapping request by calling DNSServiceRefDeallocate. The client callback will be invoked, informing the client of the NAT gateway's external IP address and the external port that has been allocated for this client. The client should then record this external IP address and port using whatever directory service mechanism it is using to enable peers to connect to it. (Clients advertising services using Wide-Area DNS-SD DO NOT need to use this API; when a client calls DNSServiceRegister NAT mappings are automatically created, and the external IP address and port for the service are recorded in the global DNS. Only clients using some directory mechanism other than Wide-Area DNS-SD need to use this API to explicitly map their own ports.)

It's possible that the client callback could be called multiple times, for example if the NAT gateway's IP address changes, or if a configuration change results in a different external port being mapped for this client. Over the lifetime of any long-lived port mapping, the client should be prepared to handle these notifications of changes in the environment, and should update its recorded address and/or port as appropriate.

NOTE: There are two unusual aspects of how the DNSServiceNATPortMappingCreate API works, which were intentionally designed to help simplify client code:

1. It's not an error to request a NAT mapping when the machine is not behind a NAT gateway. In other NAT mapping APIs, if you request a NAT mapping and the machine is not behind a NAT gateway, then the API returns an error code -- it can't get you a NAT mapping if there's no NAT gateway. The DNSServiceNATPortMappingCreate API takes a different view. Working out whether or not you need a NAT mapping can be tricky and non-obvious, particularly on a machine with multiple active network interfaces. Rather than make every client recreate this logic for deciding whether a NAT mapping is required, the PortMapping API does that work for you. If the client calls the PortMapping API when the machine already has a routable public IP address, then instead of complaining about it and giving an error, the PortMapping API just invokes your callback, giving the machine's public address and your own port number. This means you don't need to write code to work out whether your client needs to call the PortMapping API -- just call it anyway, and if it wasn't necessary, no harm is done: - If the machine already has a routable public IP address, then your callback will just be invoked giving your own address and port.

- If a NAT mapping is required and obtained, then your callback will be invoked giving you the external address and port.

- If a NAT mapping is required but not obtained from the local NAT gateway, or the machine has no network connectivity, then your callback will be invoked giving zero address and port.

2. In other NAT mapping APIs, if a laptop computer is put to sleep and woken up on a new network, it's the client's job to notice this, and work out whether a NAT mapping is required on the new network, and make a new NAT mapping request if necessary. The DNSServiceNATPortMappingCreate API does this for you, automatically. The client just needs to make one call to the PortMapping API, and its callback will be invoked any time the mapping state changes. This property complements point (1) above. If the client didn't make a NAT mapping request just because it determined that one was not required at that particular moment in time, the client would then have to monitor for network state changes to determine if a NAT port mapping later became necessary. By unconditionally making a NAT mapping request, even when a NAT mapping not to be necessary, the PortMapping API will then begin monitoring network state changes on behalf of the client, and if a NAT mapping later becomes necessary, it will automatically create a NAT mapping and inform the client with a new callback giving the new address and port information.

DNSServiceProcessResult

Reads a reply from the daemon, calling the appropriate application callback.

DNSServiceErrorType DNSServiceProcessResult (
   DNSServiceRef sdRef
);
Parameters
sdRef

A DNSServiceRef initialized by any of the DNSService calls that take a callback parameter.

Return Value

Returns kDNSServiceErr_NoError on success, otherwise returns an error code indicating the specific failure that occurred.

Discussion

This call blocks until the daemon's response is received. Use DNSServiceRefSockFD in conjunction with a run loop or select() to determine the presence of a response from the server before calling this function to process the reply without blocking. Call this function at any point if it is acceptable to block until the daemon's response arrives. Note that the client is responsible for ensuring that DNSServiceProcessResult is called whenever there is a reply from the daemon - the daemon may terminate its connection with a client that does not process the daemon's responses.

DNSServiceQueryRecord

Query for an arbitrary DNS record.

DNSServiceErrorType DNSServiceQueryRecord (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   const char *fullname,
   uint16_t rrtype,
   uint16_t rrclass,
   DNSServiceQueryRecordReply callBack,
   void *context /* may be NULL */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the query operation will run indefinitely until the client terminates it by passing this DNSServiceRef to DNSServiceRefDeallocate.

flags

kDNSServiceFlagsForceMulticast or kDNSServiceFlagsLongLivedQuery. Pass kDNSServiceFlagsLongLivedQuery to create a "long-lived" unicast query to a unicast DNS server that implements the protocol. This flag has no effect on link-local multicast queries.

interfaceIndex

If non-zero, specifies the interface on which to issue the query (the index for a given interface is determined via the if_nametoindex() family of calls.) Passing 0 causes the name to be queried for on all interfaces. See "Constants for specifying an interface index" for more details.

fullname

The full domain name of the resource record to be queried for.

rrtype

The numerical type of the resource record to be queried for (e.g. kDNSServiceType_PTR, kDNSServiceType_SRV, and so on).

rrclass

The class of the resource record (usually kDNSServiceClass_IN).

callBack

The function to be called when a result is found, or if the call asynchronously fails.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred (the callback is never invoked and the DNSServiceRef is not initialized).

DNSServiceReconfirmRecord

Instructs the daemon to verify the validity of a resource record that appears to be out of date (for example, because TCP connection to a service's target failed).

DNSServiceErrorType DNSServiceReconfirmRecord (
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   const char *fullname,
   uint16_t rrtype,
   uint16_t rrclass,
   uint16_t rdlen,
   const void *rdata
);
Parameters
flags

Not currently used.

interfaceIndex

Specifies the interface of the record in question. The caller must specify the interface. This API (by design) causes increased network traffic, so it requires the caller to be precise about which record should be reconfirmed. It is not possible to pass zero for the interface index to perform a "wildcard" reconfirmation, where *all* matching records are reconfirmed.

fullname

The resource record's full domain name.

rrtype

The resource record's type (e.g. kDNSServiceType_PTR, kDNSServiceType_SRV, and so on).

rrclass

The class of the resource record (usually kDNSServiceClass_IN).

rdlen

The length, in bytes, of the resource record rdata.

rdata

The raw rdata of the resource record.

Discussion

Causes the record to be flushed from the daemon's cache (as well as all other daemons' caches on the network) if the record is determined to be invalid.

DNSServiceRefDeallocate

Terminates a connection with the daemon and frees memory associated with the DNSServiceRef.

void DNSServiceRefDeallocate (
   DNSServiceRef sdRef
);
Parameters
sdRef

A DNSServiceRef initialized by any of the DNSService calls.

Discussion

Any services or records registered with this DNSServiceRef will be deregistered. Any Browse, Resolve, or Query operations called with this reference will be terminated.

Note: If the reference's underlying socket is used in a run loop or select() call, it should be removed BEFORE DNSServiceRefDeallocate is called, as this function closes the reference's socket.

Note: If the reference was initialized with DNSServiceCreateConnection, any DNSRecordRefs created via this reference will be invalidated by this call - the resource records are deregistered, and their DNSRecordRefs may not be used in subsequent functions. Similarly, if the reference was initialized with DNSServiceRegister, and an extra resource record was added to the service via DNSServiceAddRecord, the DNSRecordRef created by the add call is invalidated when this function is called - the DNSRecordRef may not be used in subsequent functions.

Note: This call is to be used only with the DNSServiceRef defined by this API.

DNSServiceRefSockFD

Accesses underlying Unix domain socket for an initialized DNSServiceRef.

int DNSServiceRefSockFD (
   DNSServiceRef sdRef
);
Parameters
sdRef

A DNSServiceRef initialized by any of the DNSService calls.

Return Value

The DNSServiceRef's underlying socket descriptor, or -1 on error.

Discussion

The DNS Service Discovery implementation uses this socket to communicate between the client and the mDNSResponder daemon. The application MUST NOT directly read from or write to this socket. Access to the socket is provided so that it can be used as a kqueue event source, a CFRunLoop event source, in a select() loop, etc. When the underlying event management subsystem (kqueue/ select/CFRunLoop etc.) indicates to the client that data is available for reading on the socket, the client should call DNSServiceProcessResult, which will extract the daemon's reply from the socket, and pass it to the appropriate application callback. By using a run loop or select(), results from the daemon can be processed asynchronously. Alternatively, a client can choose to fork a thread and have it loop calling "DNSServiceProcessResult(ref);" If DNSServiceProcessResult is called when no data is available for reading on the socket, it will block until data does become available, and then process the data and return to the caller. When data arrives on the socket, the client is responsible for calling DNSServiceProcessResult(ref) in a timely fashion -- if the client allows a large backlog of data to build up the daemon may terminate the connection.

DNSServiceRegister

Registers a service.

DNSServiceErrorType DNSServiceRegister (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   const char *name, /* may be NULL */
   const char *regtype,
   const char *domain, /* may be NULL */
   const char *host, /* may be NULL */
   uint16_t port, /* In network byte order */
   uint16_t txtLen,
   const void *txtRecord, /* may be NULL */
   DNSServiceRegisterReply callBack, /* may be NULL */
   void *context /* may be NULL */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the registration will remain active indefinitely until the client terminates it by passing this DNSServiceRef to DNSServiceRefDeallocate.

interfaceIndex

If non-zero, specifies the interface on which to register the service (the index for a given interface is determined via the if_nametoindex() family of calls.) Most applications will pass 0 to register on all available interfaces. See "Constants for specifying an interface index" for more details.

flags

Indicates the renaming behavior on name conflict (most applications will pass 0). See flag definitions above for details.

name

If non-NULL, specifies the service name to be registered. Most applications will not specify a name, in which case the computer name is used (this name is communicated to the client via the callback). If a name is specified, it must be 1-63 bytes of UTF-8 text. If the name is longer than 63 bytes it will be automatically truncated to a legal length, unless the NoAutoRename flag is set, in which case kDNSServiceErr_BadParam will be returned.

regtype

The service type followed by the protocol, separated by a dot (e.g. "_ftp._tcp"). The service type must be an underscore, followed by 1-15 characters, which may be letters, digits, or hyphens. The transport protocol must be "_tcp" or "_udp". New service types should be registered at http://www.dns-sd.org/ServiceTypes.html.

Additional subtypes of the primary service type (where a service type has defined subtypes) follow the primary service type in a comma-separated list, with no additional spaces, e.g. "_primarytype._tcp,_subtype1,_subtype2,_subtype3" Subtypes provide a mechanism for filtered browsing: A client browsing for "_primarytype._tcp" will discover all instances of this type; a client browsing for "_primarytype._tcp,_subtype2" will discover only those instances that were registered with "_subtype2" in their list of registered subtypes.

The subtype mechanism can be illustrated with some examples using the dns-sd command-line tool:

% dns-sd -R Simple _test._tcp "" 1001 & % dns-sd -R Better _test._tcp,HasFeatureA "" 1002 & % dns-sd -R Best _test._tcp,HasFeatureA,HasFeatureB "" 1003 &

Now: % dns-sd -B _test._tcp # will find all three services % dns-sd -B _test._tcp,HasFeatureA # finds "Better" and "Best" % dns-sd -B _test._tcp,HasFeatureB # finds only "Best"

Subtype labels may be up to 63 bytes long, and may contain any eight- bit byte values, including zero bytes. However, due to the nature of using a C-string-based API, conventional DNS escaping must be used for dots ('.'), commas (','), backslashes ('\') and zero bytes, as shown below:

% dns-sd -R Test '_test._tcp,s\.one,s\,two,s\\three,s\000four' local 123

When a service is registered, all the clients browsing for the registered type ("regtype") will discover it. If the discovery should be restricted to a smaller set of well known peers, the service can be registered with additional data (group identifier) that is known only to a smaller set of peers. The group identifier should follow primary service type using a colon (":") as a delimeter. If subtypes are also present, it should be given before the subtype as shown below.

% dns-sd -R _test1 _http._tcp:mygroup1 local 1001 % dns-sd -R _test2 _http._tcp:mygroup2 local 1001 % dns-sd -R _test3 _http._tcp:mygroup3,HasFeatureA local 1001

Now: % dns-sd -B _http._tcp:"mygroup1" # will discover only test1 % dns-sd -B _http._tcp:"mygroup2" # will discover only test2 % dns-sd -B _http._tcp:"mygroup3",HasFeatureA # will discover only test3

By specifying the group information, only the members of that group are discovered.

The group identifier itself is not sent in clear. Only a hash of the group identifier is sent and the clients discover them anonymously. The group identifier may be up to 256 bytes long and may contain any eight bit values except comma which should be escaped.

domain

If non-NULL, specifies the domain on which to advertise the service. Most applications will not specify a domain, instead automatically registering in the default domain(s).

host

If non-NULL, specifies the SRV target host name. Most applications will not specify a host, instead automatically using the machine's default host name(s). Note that specifying a non-NULL host does NOT create an address record for that host - the application is responsible for ensuring that the appropriate address record exists, or creating it via DNSServiceRegisterRecord.

port

The port, in network byte order, on which the service accepts connections. Pass 0 for a "placeholder" service (i.e. a service that will not be discovered by browsing, but will cause a name conflict if another client tries to register that same name). Most clients will not use placeholder services.

txtLen

The length of the txtRecord, in bytes. Must be zero if the txtRecord is NULL.

txtRecord

The TXT record rdata. A non-NULL txtRecord MUST be a properly formatted DNS TXT record, i.e. <length byte> <data> <length byte> <data> ... Passing NULL for the txtRecord is allowed as a synonym for txtLen=1, txtRecord="", i.e. it creates a TXT record of length one containing a single empty string. RFC 1035 doesn't allow a TXT record to contain *zero* strings, so a single empty string is the smallest legal DNS TXT record. As with the other parameters, the DNSServiceRegister call copies the txtRecord data; e.g. if you allocated the storage for the txtRecord parameter with malloc() then you can safely free that memory right after the DNSServiceRegister call returns.

callBack

The function to be called when the registration completes or asynchronously fails. The client MAY pass NULL for the callback - The client will NOT be notified of the default values picked on its behalf, and the client will NOT be notified of any asynchronous errors (e.g. out of memory errors, etc.) that may prevent the registration of the service. The client may NOT pass the NoAutoRename flag if the callback is NULL. The client may still deregister the service at any time via DNSServiceRefDeallocate.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred (the callback is never invoked and the DNSServiceRef is not initialized).

DNSServiceRegisterRecord

Registers an individual resource record on a connected DNSServiceRef.

DNSServiceErrorType DNSServiceRegisterRecord (
   DNSServiceRef sdRef,
   DNSRecordRef *RecordRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   const char *fullname,
   uint16_t rrtype,
   uint16_t rrclass,
   uint16_t rdlen,
   const void *rdata,
   uint32_t ttl,
   DNSServiceRegisterRecordReply callBack,
   void *context /* may be NULL */
);
Parameters
sdRef

A DNSServiceRef initialized by DNSServiceCreateConnection.

RecordRef

A pointer to an uninitialized DNSRecordRef. Upon succesfull completion of this call, this ref may be passed to DNSServiceUpdateRecord or DNSServiceRemoveRecord. (To deregister ALL records registered on a single connected DNSServiceRef and deallocate each of their corresponding DNSServiceRecordRefs, call DNSServiceRefDeallocate).

flags

Possible values are kDNSServiceFlagsShared or kDNSServiceFlagsUnique (see flag type definitions for details).

interfaceIndex

If non-zero, specifies the interface on which to register the record (the index for a given interface is determined via the if_nametoindex() family of calls.) Passing 0 causes the record to be registered on all interfaces. See "Constants for specifying an interface index" for more details.

fullname

The full domain name of the resource record.

rrtype

The numerical type of the resource record (e.g. kDNSServiceType_PTR, kDNSServiceType_SRV, and so on).

rrclass

The class of the resource record (usually kDNSServiceClass_IN)

rdlen

Length, in bytes, of the rdata.

rdata

A pointer to the raw rdata, as it is to appear in the DNS record.

ttl

The time to live of the resource record, in seconds. Most clients should pass 0 to indicate that the system should select a sensible default value.

callBack

The function to be called when a result is found, or if the call asynchronously fails (e.g. because of a name conflict.)

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred (the callback is never invoked and the DNSRecordRef is not initialized).

Discussion

Note that name conflicts occurring for records registered via this call must be handled by the client in the callback.

DNSServiceRemoveRecord

Removes a record previously added to a service record set via DNSServiceAddRecord, or deregister an record registered individually via DNSServiceRegisterRecord.

DNSServiceErrorType DNSServiceRemoveRecord (
   DNSServiceRef sdRef,
   DNSRecordRef RecordRef,
   DNSServiceFlags flags
);
Parameters
sdRef

A DNSServiceRef initialized by DNSServiceRegister (if the record being removed was registered via DNSServiceAddRecord) or by DNSServiceCreateConnection (if the record being removed was registered via DNSServiceRegisterRecord).

RecordRef

A DNSRecordRef initialized by a successful call to DNSServiceAddRecord or DNSServiceRegisterRecord.

flags

Currently ignored, reserved for future use.

Return Value

Returns kDNSServiceErr_NoError on success, otherwise returns an error code indicating the error that occurred.

DNSServiceResolve

DNSServiceErrorType DNSServiceResolve (
   DNSServiceRef *sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   const char *name,
   const char *regtype,
   const char *domain,
   DNSServiceResolveReply callBack,
   void *context /* may be NULL */
);
Parameters
sdRef

A pointer to an uninitialized DNSServiceRef. If the call succeeds then it initializes the DNSServiceRef, returns kDNSServiceErr_NoError, and the resolve operation will run indefinitely until the client terminates it by passing this DNSServiceRef to DNSServiceRefDeallocate.

flags

Specifying kDNSServiceFlagsForceMulticast will cause query to be performed with a link-local mDNS query, even if the name is an apparently non-local name (i.e. a name not ending in ".local.")

interfaceIndex

The interface on which to resolve the service. If this resolve call is as a result of a currently active DNSServiceBrowse operation, then the interfaceIndex should be the index reported in the DNSServiceBrowseReply callback. If this resolve call is using information previously saved (e.g. in a preference file) for later use, then use interfaceIndex 0, because the desired service may now be reachable via a different physical interface. See "Constants for specifying an interface index" for more details.

name

The name of the service instance to be resolved, as reported to the DNSServiceBrowseReply callback.

regtype

The type of the service instance to be resolved, as reported to the DNSServiceBrowseReply callback.

domain

The domain of the service instance to be resolved, as reported to the DNSServiceBrowseReply callback.

callBack

The function to be called when a result is found, or if the call asynchronously fails.

context

An application context pointer which is passed to the callback function (may be NULL).

Return Value

Returns kDNSServiceErr_NoError on success (any subsequent, asynchronous errors are delivered to the callback), otherwise returns an error code indicating the error that occurred (the callback is never invoked and the DNSServiceRef is not initialized).

DNSServiceSetDispatchQueue

Allows you to schedule a DNSServiceRef on a serial dispatch queue for receiving asynchronous callbacks.

DNSServiceErrorType DNSServiceSetDispatchQueue (
   DNSServiceRef service,
   dispatch_queue_t queue
);
Parameters
service

DNSServiceRef that was allocated and returned to the application, when the application calls one of the DNSService API.

queue

dispatch queue where the application callback will be scheduled

Return Value

Returns kDNSServiceErr_NoError on success. Returns kDNSServiceErr_NoMemory if it cannot create a dispatch source Returns kDNSServiceErr_BadParam if the service param is invalid or the queue param is invalid

Discussion

It is the client's responsibility to ensure that the provided dispatch queue is running.

A typical application that uses CFRunLoopRun or dispatch_main on its main thread will usually schedule DNSServiceRefs on its main queue (which is always a serial queue) using "DNSServiceSetDispatchQueue(sdref, dispatch_get_main_queue());"

If there is any error during the processing of events, the application callback will be called with an error code. For shared connections, each subordinate DNSServiceRef will get its own error callback. Currently these error callbacks only happen if the mDNSResponder daemon is manually terminated or crashes, and the error code in this case is kDNSServiceErr_ServiceNotRunning. The application must call DNSServiceRefDeallocate to free the DNSServiceRef when it gets such an error code. These error callbacks are rare and should not normally happen on customer machines, but application code should be written defensively to handle such error callbacks gracefully if they occur.

After using DNSServiceSetDispatchQueue on a DNSServiceRef, calling DNSServiceProcessResult on the same DNSServiceRef will result in undefined behavior and should be avoided.

Once the application successfully schedules a DNSServiceRef on a serial dispatch queue using DNSServiceSetDispatchQueue, it cannot remove the DNSServiceRef from the dispatch queue, or use DNSServiceSetDispatchQueue a second time to schedule the DNSServiceRef onto a different serial dispatch queue. Once scheduled onto a dispatch queue a DNSServiceRef will deliver events to that queue until the application no longer requires that operation and terminates it using DNSServiceRefDeallocate.

DNSServiceUpdateRecord

Updates a registered resource record.

DNSServiceErrorType DNSServiceUpdateRecord (
   DNSServiceRef sdRef,
   DNSRecordRef RecordRef, /* may be NULL */
   DNSServiceFlags flags,
   uint16_t rdlen,
   const void *rdata,
   uint32_t ttl
);
Parameters
sdRef

A DNSServiceRef that was initialized by DNSServiceRegister or DNSServiceCreateConnection.

RecordRef

A DNSRecordRef initialized by DNSServiceAddRecord, or NULL to update the service's primary txt record.

flags

Currently ignored, reserved for future use.

rdlen

The length, in bytes, of the new rdata.

rdata

The new rdata to be contained in the updated resource record.

ttl

The time to live of the updated resource record, in seconds. Most clients should pass 0 to indicate that the system should select a sensible default value.

Return Value

Returns kDNSServiceErr_NoError on success, otherwise returns an error code indicating the error that occurred.

Discussion

The record must either be:

- The primary txt record of a service registered via DNSServiceRegister

- A record added to a registered service via DNSServiceAddRecord

- An individual record registered by DNSServiceRegisterRecord

PeerConnectionRelease

Releases P2P connection resources associated with the service instance.

DNSServiceErrorType PeerConnectionRelease (
   DNSServiceFlags flags,
   const char *name,
   const char *regtype,
   const char *domain
);
Discussion

When a service is resolved over a P2P interface, a connection is brought up to the peer advertising the service instance. This call will free the resources associated with that connection. Note that the reference to the service instance will only be maintained by the mDNSResponder daemon while the browse for the service type is still running. Thus the sequence of calls to discover, resolve, and then terminate the connection associated with a given P2P service instance would be:

DNSServiceRef BrowseRef, ResolveRef; DNSServiceBrowse(&BrowseRef, ...) // browse for all instances of the service DNSServiceResolve(&ResolveRef, ...) // resolving a service instance creates a // connection to the peer device advertising that service DNSServiceRefDeallocate(ResolveRef) // Stop the resolve, which does not close the peer connection

// Communicate with the peer application.

PeerConnectionRelease() // release the connection to the peer device for the specified service instance

DNSServiceRefDeallocate(BrowseRef) // stop the browse // Any further calls to PeerConnectionRelease() will have no affect since the // service instance to peer connection relationship is only maintained by the // mDNSResponder daemon while the browse is running.

flags: Not currently used.

name: The name of the service instance to be resolved, as reported to the DNSServiceBrowseReply callback.

regtype: The type of the service instance to be resolved, as reported to the DNSServiceBrowseReply callback.

domain: The domain of the service instance to be resolved, as reported to the DNSServiceBrowseReply callback.

return value: Returns kDNSServiceErr_NoError on success or the error that occurred.

TXTRecordContainsKey

Allows you to determine if a given TXT Record contains a specified key.

int TXTRecordContainsKey (
   uint16_t txtLen,
   const void *txtRecord,
   const char *key
);
Parameters
txtLen

The size of the received TXT Record.

txtRecord

Pointer to the received TXT Record bytes.

key

A null-terminated ASCII string containing the key name.

Return Value

Returns 1 if the TXT Record contains the specified key. Otherwise, it returns 0.

TXTRecordCreate

Creates a new empty TXTRecordRef referencing the specified storage.

void TXTRecordCreate (
   TXTRecordRef *txtRecord,
   uint16_t bufferLen,
   void *buffer
);
Parameters
txtRecord

A pointer to an uninitialized TXTRecordRef.

bufferLen

The size of the storage provided in the "buffer" parameter.

buffer

Optional caller-supplied storage used to hold the TXTRecord data. This storage must remain valid for as long as the TXTRecordRef.

Discussion

If the buffer parameter is NULL, or the specified storage size is not large enough to hold a key subsequently added using TXTRecordSetValue(), then additional memory will be added as needed using malloc().

On some platforms, when memory is low, malloc() may fail. In this case, TXTRecordSetValue() will return kDNSServiceErr_NoMemory, and this error condition will need to be handled as appropriate by the caller.

You can avoid the need to handle this error condition if you ensure that the storage you initially provide is large enough to hold all the key/value pairs that are to be added to the record. The caller can precompute the exact length required for all of the key/value pairs to be added, or simply provide a fixed-sized buffer known in advance to be large enough.

A no-value (key-only) key requires (1 + key length) bytes.

A key with empty value requires (1 + key length + 1) bytes.

A key with non-empty value requires (1 + key length + 1 + value length).

For most applications, DNS-SD TXT records are generally less than 100 bytes, so in most cases a simple fixed-sized 256-byte buffer will be more than sufficient.

Recommended size limits for DNS-SD TXT Records are discussed in dns-sd.org

Note: When passing parameters to and from these TXT record APIs, the key name does not include the '=' character. The '=' character is the separator between the key and value in the on-the-wire packet format; it is not part of either the key or the value.

TXTRecordDeallocate

Releases resources associated with a TXT record.

void TXTRecordDeallocate (
   TXTRecordRef *txtRecord
);
Parameters
txtRecord

A TXTRecordRef initialized by calling TXTRecordCreate().

Discussion

Releases any resources allocated in the course of preparing a TXT Record using TXTRecordCreate()/TXTRecordSetValue()/TXTRecordRemoveValue(). Ownership of the buffer provided in TXTRecordCreate() returns to the client.

TXTRecordGetBytesPtr

Allows you to retrieve a pointer to the raw bytes within a TXTRecordRef.

const void * TXTRecordGetBytesPtr (
   const TXTRecordRef *txtRecord
);
Parameters
txtRecord

A TXTRecordRef initialized by calling TXTRecordCreate().

Return Value

Returns a pointer to the raw bytes inside the TXTRecordRef which you can pass directly to DNSServiceRegister or to DNSServiceUpdateRecord.

TXTRecordGetCount

Returns the number of keys stored in the TXT Record.

uint16_t TXTRecordGetCount (
   uint16_t txtLen,
   const void *txtRecord
);
Parameters
txtLen

The size of the received TXT Record.

txtRecord

Pointer to the received TXT Record bytes.

Return Value

Returns the total number of keys in the TXT Record.

Discussion

The count can be used with TXTRecordGetItemAtIndex() to iterate through the keys.

TXTRecordGetItemAtIndex

Allows you to retrieve a key name and value pointer, given an index into a TXT Record.

DNSServiceErrorType TXTRecordGetItemAtIndex (
   uint16_t txtLen,
   const void *txtRecord,
   uint16_t itemIndex,
   uint16_t keyBufLen,
   char *key,
   uint8_t *valueLen,
   const void **value
);
Parameters
txtLen

The size of the received TXT Record.

txtRecord

Pointer to the received TXT Record bytes.

itemIndex

An index into the TXT Record.

keyBufLen

The size of the string buffer being supplied.

key

A string buffer used to store the key name. On return, the buffer contains a null-terminated C string giving the key name. DNS-SD TXT keys are usually 9 characters or fewer. To hold the maximum possible key name, the buffer should be 256 bytes long.

valueLen

On output, will be set to the size of the "value" data.

value

On output, *value is set to point to location within TXT Record bytes that holds the value data.

Return Value

Returns kDNSServiceErr_NoError on success. Returns kDNSServiceErr_NoMemory if keyBufLen is too short. Returns kDNSServiceErr_Invalid if index is greater than TXTRecordGetCount()-1.

Discussion

Legal index values range from zero to TXTRecordGetCount()-1. It's also possible to iterate through keys in a TXT record by simply calling TXTRecordGetItemAtIndex() repeatedly, beginning with index zero and increasing until TXTRecordGetItemAtIndex() returns kDNSServiceErr_Invalid.

On return:

For keys with no value, *value is set to NULL and *valueLen is zero.

For keys with empty value, *value is non-NULL and *valueLen is zero.

For keys with non-empty value, *value is non-NULL and *valueLen is non-zero.

TXTRecordGetLength

Allows you to determine the length of the raw bytes within a TXTRecordRef.

uint16_t TXTRecordGetLength (
   const TXTRecordRef *txtRecord
);
Parameters
txtRecord

A TXTRecordRef initialized by calling TXTRecordCreate().

Return Value

Returns the size of the raw bytes inside a TXTRecordRef which you can pass directly to DNSServiceRegister or to DNSServiceUpdateRecord. Returns 0 if the TXTRecordRef is empty.

TXTRecordGetValuePtr

Allows you to retrieve the value for a given key from a TXT Record.

const void * TXTRecordGetValuePtr (
   uint16_t txtLen,
   const void *txtRecord,
   const char *key,
   uint8_t *valueLen
);
Parameters
txtLen

The size of the received TXT Record

txtRecord

Pointer to the received TXT Record bytes.

key

A null-terminated ASCII string containing the key name.

valueLen

On output, will be set to the size of the "value" data.

Return Value

Returns NULL if the key does not exist in this TXT record, or exists with no value (to differentiate between these two cases use TXTRecordContainsKey()). Returns pointer to location within TXT Record bytes if the key exists with empty or non-empty value. For empty value, valueLen will be zero. For non-empty value, valueLen will be length of value data.

TXTRecordRemoveValue

Removes a key from a TXTRecordRef.

DNSServiceErrorType TXTRecordRemoveValue (
   TXTRecordRef *txtRecord,
   const char *key
);
Parameters
txtRecord

A TXTRecordRef initialized by calling TXTRecordCreate().

key

A key name. This value must be an ASCII string that exists in the TXTRecordRef.

Return Value

Returns kDNSServiceErr_NoError on success. Returns kDNSServiceErr_NoSuchKey if the "key" does not exist in the TXTRecordRef.

TXTRecordSetValue

Adds a key (optionally with value) to a TXTRecordRef.

DNSServiceErrorType TXTRecordSetValue (
   TXTRecordRef *txtRecord,
   const char *key,
   uint8_t valueSize, /* may be zero */
   const void *value /* may be NULL */
);
Parameters
txtRecord

A TXTRecordRef initialized by calling TXTRecordCreate().

key

A null-terminated string which only contains printable ASCII values (0x20-0x7E), excluding '=' (0x3D). Keys should be 9 characters or fewer (not counting the terminating null).

valueSize

The size of the value.

value

Any binary value. For values that represent textual data, UTF-8 is STRONGLY recommended. For values that represent textual data, valueSize should NOT include the terminating null (if any) at the end of the string. If NULL, then "key" will be added with no value. If non-NULL but valueSize is zero, then "key=" will be added with empty value.

Return Value

Returns kDNSServiceErr_NoError on success. Returns kDNSServiceErr_Invalid if the "key" string contains illegal characters. Returns kDNSServiceErr_NoMemory if adding this key would exceed the available storage.

Discussion

If the "key" already exists in the TXTRecordRef, then the current value will be replaced with the new value. Keys may exist in four states with respect to a given TXT record: - Absent (key does not appear at all) - Present with no value ("key" appears alone) - Present with empty value ("key=" appears in TXT record) - Present with non-empty value ("key=value" appears in TXT record) For more details refer to "Data Syntax for DNS-SD TXT Records" in dns-sd.org

Callbacks by Task

See the Overview section above for header-level documentation.

Unified lookup of both IPv4 and IPv6 addresses for a fully qualified hostname

Special Purpose Calls

DNSServiceCreateConnection, DNSServiceRegisterRecord, DNSServiceReconfirmRecord (most applications will not use these)

Service Registration

Service Discovery

Querying Individual Specific Records

NAT Port Mapping

Domain Enumeration

Callbacks

DNSServiceBrowseReply

Callback for handling the results of previous calls to DNSServiceBrowse.

typedef void ( *DNSServiceBrowseReply) (
   DNSServiceRef sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceErrorType errorCode,
   const char *serviceName,
   const char *regtype,
   const char *replyDomain,
   void *context );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceBrowse.

flags

Possible values are kDNSServiceFlagsMoreComing and kDNSServiceFlagsAdd. See flag definitions for details.

interfaceIndex

The interface on which the service is advertised. This index should be passed to DNSServiceResolve when resolving the service.

errorCode

Will be kDNSServiceErr_NoError (0) on success, otherwise will indicate the failure that occurred. Other parameters are undefined if the errorCode is nonzero.

serviceName

The discovered service name. This name should be displayed to the user, and stored for subsequent use in the DNSServiceResolve call.

regtype

The service type, which is usually (but not always) the same as was passed to DNSServiceBrowse. One case where the discovered service type may not be the same as the requested service type is when using subtypes: The client may want to browse for only those ftp servers that allow anonymous connections. The client will pass the string "_ftp._tcp,_anon" to DNSServiceBrowse, but the type of the service that's discovered is simply "_ftp._tcp". The regtype for each discovered service instance should be stored along with the name, so that it can be passed to DNSServiceResolve when the service is later resolved.

replyDomain

The domain of the discovered service instance. This may or may not be the same as the domain that was passed to DNSServiceBrowse. The domain for each discovered service instance should be stored along with the name, so that it can be passed to DNSServiceResolve when the service is later resolved.

context

The context pointer that was passed to the callout.

DNSServiceDomainEnumReply

Callback for handling the results of a previous call to DNSServiceEnumerateDomains.

typedef void ( *DNSServiceDomainEnumReply) (
   DNSServiceRef sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceErrorType errorCode,
   const char *replyDomain,
   void *context );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceEnumerateDomains.

flags

Possible values are:

kDNSServiceFlagsMoreComing

kDNSServiceFlagsAdd

kDNSServiceFlagsDefault

interfaceIndex

Specifies the interface on which the domain exists. (The index for a given interface is determined via the if_nametoindex() family of calls.)

errorCode

Will be kDNSServiceErr_NoError (0) on success, otherwise indicates the failure that occurred (other parameters are undefined if errorCode is nonzero).

replyDomain

The name of the domain.

context

The context pointer passed to DNSServiceEnumerateDomains.

DNSServiceGetAddrInfoReply

Callback for handling the results of a previous call to DNSServiceGetAddrInfo.

typedef void ( *DNSServiceGetAddrInfoReply) (
   DNSServiceRef sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceErrorType errorCode,
   const char *hostname,
   const struct sockaddr *address,
   uint32_t ttl,
   void *context );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceGetAddrInfo.

flags

Possible values are kDNSServiceFlagsMoreComing and kDNSServiceFlagsAdd.

interfaceIndex

The interface to which the answers pertain.

errorCode

Will be kDNSServiceErr_NoError on success, otherwise will indicate the failure that occurred. Other parameters are undefined if errorCode is nonzero.

hostname

The fully qualified domain name of the host to be queried for.

address

IPv4 or IPv6 address.

ttl

If the client wishes to cache the result for performance reasons, the TTL indicates how long the client may legitimately hold onto this result, in seconds. After the TTL expires, the client should consider the result no longer valid, and if it requires this data again, it should be re-fetched with a new query. Of course, this only applies to clients that cancel the asynchronous operation when they get a result. Clients that leave the asynchronous operation running can safely assume that the data remains valid until they get another callback telling them otherwise.

context

The context pointer that was passed to the callout.

DNSServiceNATPortMappingReply

Callback for handling the reply from a previous call to DNSServiceNATPortMappingReply.

typedef void ( *DNSServiceNATPortMappingReply) (
   DNSServiceRef sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceErrorType errorCode,
   uint32_t externalAddress, /* four byte IPv4 address in network byte order */
   DNSServiceProtocol protocol,
   uint16_t internalPort, /* In network byte order */
   uint16_t externalPort, /* In network byte order and may be different than the requested port */
   uint32_t ttl, /* may be different than the requested ttl */
   void *context );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceNATPortMappingCreate.

flags

Currently unused, reserved for future use.

interfaceIndex

The interface through which the NAT gateway is reached.

errorCode

Will be kDNSServiceErr_NoError on success. Will be kDNSServiceErr_DoubleNAT when the NAT gateway is itself behind one or more layers of NAT, in which case the other parameters have the defined values. For other failures, will indicate the failure that occurred, and the other parameters are undefined.

externalAddress

Four byte IPv4 address in network byte order.

protocol

Will be kDNSServiceProtocol_UDP or kDNSServiceProtocol_TCP or both.

internalPort

The port on the local machine that was mapped.

externalPort

The actual external port in the NAT gateway that was mapped. This is likely to be different than the requested external port.

ttl

The lifetime of the NAT port mapping created on the gateway. This controls how quickly stale mappings will be garbage-collected if the client machine crashes, suffers a power failure, is disconnected from the network, or suffers some other unfortunate demise which causes it to vanish without explicitly removing its NAT port mapping. It's possible that the ttl value will differ from the requested ttl value.

context

The context pointer that was passed to the callout.

Discussion

The NAT should support either the NAT-PMP or the UPnP IGD protocol for this API to create a successful mapping.

DNSServiceQueryRecordReply

Callback for handling the results of a previous call to DNSServiceQueryRecord.

typedef void ( *DNSServiceQueryRecordReply) (
   DNSServiceRef sdRef,
   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 );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceQueryRecord.

flags

Possible values are kDNSServiceFlagsMoreComing and kDNSServiceFlagsAdd. The Add flag is NOT set for PTR records with a ttl of 0, i.e. "Remove" events.

interfaceIndex

The interface on which the query was resolved (the index for a given interface is determined via the if_nametoindex() family of calls). See "Constants for specifying an interface index" for more details.

errorCode

Will be kDNSServiceErr_NoError on success, otherwise will indicate the failure that occurred. Other parameters are undefined if errorCode is nonzero.

fullname

The resource record's full domain name.

rrtype

The resource record's type (e.g. kDNSServiceType_PTR, kDNSServiceType_SRV, and so on).

rrclass

The class of the resource record (usually kDNSServiceClass_IN).

rdlen

The length, in bytes, of the resource record rdata.

rdata

The raw rdata of the resource record.

ttl

If the client wishes to cache the result for performance reasons, the TTL indicates how long the client may legitimately hold onto this result, in seconds. After the TTL expires, the client should consider the result no longer valid, and if it requires this data again, it should be re-fetched with a new query. Of course, this only applies to clients that cancel the asynchronous operation when they get a result. Clients that leave the asynchronous operation running can safely assume that the data remains valid until they get another callback telling them otherwise.

context

The context pointer that was passed to the callout.

DNSServiceRegisterRecordReply

Callback for handling the results of a previous call to DNSServiceRegisterRecord.

typedef void ( *DNSServiceRegisterRecordReply) (
   DNSServiceRef sdRef,
   DNSRecordRef RecordRef,
   DNSServiceFlags flags,
   DNSServiceErrorType errorCode,
   void *context );

Parameters
sdRef

The connected DNSServiceRef initialized by DNSServiceCreateConnection.

RecordRef

The DNSRecordRef initialized by DNSServiceRegisterRecord. If the above DNSServiceRef is passed to DNSServiceRefDeallocate, this DNSRecordRef is invalidated, and may not be used further.

flags

Currently unused, reserved for future use.

errorCode

Will be kDNSServiceErr_NoError on success, otherwise will indicate the failure that occurred (including name conflicts.) Other parameters are undefined if errorCode is nonzero.

context

The context pointer that was passed to the callout.

DNSServiceRegisterReply

Handler for the results from a previous call to DNSServiceRegister.

typedef void ( *DNSServiceRegisterReply) (
   DNSServiceRef sdRef,
   DNSServiceFlags flags,
   DNSServiceErrorType errorCode,
   const char *name,
   const char *regtype,
   const char *domain,
   void *context );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceRegister.

flags

When a name is successfully registered, the callback will be invoked with the kDNSServiceFlagsAdd flag set. When Wide-Area DNS-SD is in use, it is possible for a single service to get more than one success callback (e.g. one in the "local" multicast DNS domain, and another in a wide-area unicast DNS domain). If a successfully-registered name later suffers a name conflict or similar problem and has to be deregistered, the callback will be invoked with the kDNSServiceFlagsAdd flag not set. The callback is *not* invoked in the case where the caller explicitly terminates the service registration by calling DNSServiceRefDeallocate(ref);

errorCode

Will be kDNSServiceErr_NoError on success, otherwise will indicate the failure that occurred (including name conflicts, if the kDNSServiceFlagsNoAutoRename flag was used when registering.) Other parameters are undefined if errorCode is nonzero.

name

The service name registered (if the application did not specify a name in DNSServiceRegister, this indicates what name was automatically chosen).

regtype

The type of service registered, as it was passed to the callout.

domain

The domain on which the service was registered (if the application did not specify a domain in DNSServiceRegister, this indicates the default domain on which the service was registered).

context

The context pointer that was passed to the callout.

DNSServiceResolveReply

typedef void ( *DNSServiceResolveReply) (
   DNSServiceRef sdRef,
   DNSServiceFlags flags,
   uint32_t interfaceIndex,
   DNSServiceErrorType errorCode,
   const char *fullname,
   const char *hosttarget,
   uint16_t port, /* In network byte order */
   uint16_t txtLen,
   const unsigned char *txtRecord,
   void *context );

Parameters
sdRef

The DNSServiceRef initialized by DNSServiceResolve.

flags

Possible values: kDNSServiceFlagsMoreComing

interfaceIndex

The interface on which the service was resolved.

errorCode

Will be kDNSServiceErr_NoError (0) on success, otherwise will indicate the failure that occurred. Other parameters are undefined if the errorCode is nonzero.

fullname

The full service domain name, in the form <servicename>.<protocol>.<domain>. (This name is escaped following standard DNS rules, making it suitable for passing to standard system DNS APIs such as res_query(), or to the special-purpose functions included in this API that take fullname parameters. See "Notes on DNS Name Escaping" earlier in this file for more details.)

hosttarget

The target hostname of the machine providing the service. This name can be passed to functions like gethostbyname() to identify the host's IP address.

port

The port, in network byte order, on which connections are accepted for this service.

txtLen

The length of the txt record, in bytes.

txtRecord

The service's primary txt record, in standard txt record format.

context

The context pointer that was passed to the callout.

NOTE: In earlier versions of this header file, the txtRecord parameter was declared "const char *" This is incorrect, since it contains length bytes which are values in the range 0 to 255, not -128 to +127. Depending on your compiler settings, this change may cause signed/unsigned mismatch warnings. These should be fixed by updating your own callback function definition to match the corrected function signature using "const unsigned char *txtRecord". Making this change may also fix inadvertent bugs in your callback function, where it could have incorrectly interpreted a length byte with value 250 as being -6 instead, with various bad consequences ranging from incorrect operation to software crashes. If you need to maintain portable code that will compile cleanly with both the old and new versions of this header file, you should update your callback function definition to use the correct unsigned value, and then in the place where you pass your callback function to DNSServiceResolve, use a cast to eliminate the compiler warning, e.g.:

DNSServiceResolve(sd, flags, index, name, regtype, domain, (DNSServiceResolveReply)MyCallback, context);

This will ensure that your code compiles cleanly without warnings (and more importantly, works correctly) with both the old header and with the new corrected version.

Discussion

Resolve a service name discovered via DNSServiceBrowse to a target host name, port number, and txt record.

Note: Applications should NOT use DNSServiceResolve solely for txt record monitoring - use DNSServiceQueryRecord instead, as it is more efficient for this task.

Note: When the desired results have been returned, the client MUST terminate the resolve by calling DNSServiceRefDeallocate.

Note: DNSServiceResolve behaves correctly for typical services that have a single SRV record and a single TXT record. To resolve non-standard services with multiple SRV or TXT records, DNSServiceQueryRecord should be used.

Data Types

See the Overview section above for header-level documentation.

DNSServiceErrorType

typedef int32_t DNSServiceErrorType;
Discussion

Type declaration for DNS Service error type.

DNSServiceFlags

typedef uint32_t DNSServiceFlags;
Discussion

Type declaration for DNS Service flags.

DNSServiceProtocol

typedef uint32_t DNSServiceProtocol;
Discussion

Type declaration for DNS Service protocol.

TXTRecordRef

Opaque internal data type that represents a DNS-SD TXT record.

typedef union _TXTRecordRef_t {
   char PrivateData[16];
   char *ForceNaturalAlignment;
} TXTRecordRef;

Constants

See the Overview section above for header-level documentation.

Constants for specifying an interface index

   
#define kDNSServiceInterfaceIndexAny 0
#define kDNSServiceInterfaceIndexLocalOnly ((uint32_t)-1)
#define kDNSServiceInterfaceIndexP2P ((uint32_t)-3)
#define kDNSServiceInterfaceIndexUnicast ((uint32_t)-2)
Constants
kDNSServiceInterfaceIndexAny

Specific interface indexes are identified via a 32-bit unsigned integer returned by the if_nametoindex() family of calls.

If the client passes 0 for interface index, that means "do the right thing", which (at present) means, "if the name is in an mDNS local multicast domain (e.g. 'local.', '254.169.in-addr.arpa.', '{8,9,A,B}.E.F.ip6.arpa.') then multicast on all applicable interfaces, otherwise send via unicast to the appropriate DNS server." Normally, most clients will use 0 for interface index to automatically get the default sensible behaviour.

If the client passes a positive interface index, then for multicast names that indicates to do the operation only on that one interface. For unicast names the interface index is ignored unless kDNSServiceFlagsForceMulticast is also set.

If the client passes kDNSServiceInterfaceIndexLocalOnly when registering a service, then that service will be found *only* by other local clients on the same machine that are browsing using kDNSServiceInterfaceIndexLocalOnly or kDNSServiceInterfaceIndexAny. If a client has a 'private' service, accessible only to other processes running on the same machine, this allows the client to advertise that service in a way such that it does not inadvertently appear in service lists on all the other machines on the network.

If the client passes kDNSServiceInterfaceIndexLocalOnly when browsing then it will find *all* records registered on that same local machine. Clients explicitly wishing to discover *only* LocalOnly services can accomplish this by inspecting the interfaceIndex of each service reported to their DNSServiceBrowseReply callback function, and discarding those where the interface index is not kDNSServiceInterfaceIndexLocalOnly.

kDNSServiceInterfaceIndexP2P is meaningful only in Browse, QueryRecord, Register, and Resolve operations. It should not be used in other DNSService APIs.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceBrowse or DNSServiceQueryRecord, it restricts the operation to P2P.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceRegister, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceResolve, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set, because resolving a P2P service may create and/or enable an interface whose index is not known a priori. The resolve callback will indicate the index of the interface via which the service can be accessed.

If applications pass kDNSServiceInterfaceIndexAny to DNSServiceBrowse or DNSServiceQueryRecord, they must set the kDNSServiceFlagsIncludeP2P flag to include P2P. In this case, if a service instance or the record being queried is found over P2P, the resulting ADD event will indicate kDNSServiceInterfaceIndexP2P as the interface index.

kDNSServiceInterfaceIndexLocalOnly

Specific interface indexes are identified via a 32-bit unsigned integer returned by the if_nametoindex() family of calls.

If the client passes 0 for interface index, that means "do the right thing", which (at present) means, "if the name is in an mDNS local multicast domain (e.g. 'local.', '254.169.in-addr.arpa.', '{8,9,A,B}.E.F.ip6.arpa.') then multicast on all applicable interfaces, otherwise send via unicast to the appropriate DNS server." Normally, most clients will use 0 for interface index to automatically get the default sensible behaviour.

If the client passes a positive interface index, then for multicast names that indicates to do the operation only on that one interface. For unicast names the interface index is ignored unless kDNSServiceFlagsForceMulticast is also set.

If the client passes kDNSServiceInterfaceIndexLocalOnly when registering a service, then that service will be found *only* by other local clients on the same machine that are browsing using kDNSServiceInterfaceIndexLocalOnly or kDNSServiceInterfaceIndexAny. If a client has a 'private' service, accessible only to other processes running on the same machine, this allows the client to advertise that service in a way such that it does not inadvertently appear in service lists on all the other machines on the network.

If the client passes kDNSServiceInterfaceIndexLocalOnly when browsing then it will find *all* records registered on that same local machine. Clients explicitly wishing to discover *only* LocalOnly services can accomplish this by inspecting the interfaceIndex of each service reported to their DNSServiceBrowseReply callback function, and discarding those where the interface index is not kDNSServiceInterfaceIndexLocalOnly.

kDNSServiceInterfaceIndexP2P is meaningful only in Browse, QueryRecord, Register, and Resolve operations. It should not be used in other DNSService APIs.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceBrowse or DNSServiceQueryRecord, it restricts the operation to P2P.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceRegister, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceResolve, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set, because resolving a P2P service may create and/or enable an interface whose index is not known a priori. The resolve callback will indicate the index of the interface via which the service can be accessed.

If applications pass kDNSServiceInterfaceIndexAny to DNSServiceBrowse or DNSServiceQueryRecord, they must set the kDNSServiceFlagsIncludeP2P flag to include P2P. In this case, if a service instance or the record being queried is found over P2P, the resulting ADD event will indicate kDNSServiceInterfaceIndexP2P as the interface index.

kDNSServiceInterfaceIndexP2P

Specific interface indexes are identified via a 32-bit unsigned integer returned by the if_nametoindex() family of calls.

If the client passes 0 for interface index, that means "do the right thing", which (at present) means, "if the name is in an mDNS local multicast domain (e.g. 'local.', '254.169.in-addr.arpa.', '{8,9,A,B}.E.F.ip6.arpa.') then multicast on all applicable interfaces, otherwise send via unicast to the appropriate DNS server." Normally, most clients will use 0 for interface index to automatically get the default sensible behaviour.

If the client passes a positive interface index, then for multicast names that indicates to do the operation only on that one interface. For unicast names the interface index is ignored unless kDNSServiceFlagsForceMulticast is also set.

If the client passes kDNSServiceInterfaceIndexLocalOnly when registering a service, then that service will be found *only* by other local clients on the same machine that are browsing using kDNSServiceInterfaceIndexLocalOnly or kDNSServiceInterfaceIndexAny. If a client has a 'private' service, accessible only to other processes running on the same machine, this allows the client to advertise that service in a way such that it does not inadvertently appear in service lists on all the other machines on the network.

If the client passes kDNSServiceInterfaceIndexLocalOnly when browsing then it will find *all* records registered on that same local machine. Clients explicitly wishing to discover *only* LocalOnly services can accomplish this by inspecting the interfaceIndex of each service reported to their DNSServiceBrowseReply callback function, and discarding those where the interface index is not kDNSServiceInterfaceIndexLocalOnly.

kDNSServiceInterfaceIndexP2P is meaningful only in Browse, QueryRecord, Register, and Resolve operations. It should not be used in other DNSService APIs.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceBrowse or DNSServiceQueryRecord, it restricts the operation to P2P.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceRegister, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceResolve, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set, because resolving a P2P service may create and/or enable an interface whose index is not known a priori. The resolve callback will indicate the index of the interface via which the service can be accessed.

If applications pass kDNSServiceInterfaceIndexAny to DNSServiceBrowse or DNSServiceQueryRecord, they must set the kDNSServiceFlagsIncludeP2P flag to include P2P. In this case, if a service instance or the record being queried is found over P2P, the resulting ADD event will indicate kDNSServiceInterfaceIndexP2P as the interface index.

kDNSServiceInterfaceIndexUnicast

Specific interface indexes are identified via a 32-bit unsigned integer returned by the if_nametoindex() family of calls.

If the client passes 0 for interface index, that means "do the right thing", which (at present) means, "if the name is in an mDNS local multicast domain (e.g. 'local.', '254.169.in-addr.arpa.', '{8,9,A,B}.E.F.ip6.arpa.') then multicast on all applicable interfaces, otherwise send via unicast to the appropriate DNS server." Normally, most clients will use 0 for interface index to automatically get the default sensible behaviour.

If the client passes a positive interface index, then for multicast names that indicates to do the operation only on that one interface. For unicast names the interface index is ignored unless kDNSServiceFlagsForceMulticast is also set.

If the client passes kDNSServiceInterfaceIndexLocalOnly when registering a service, then that service will be found *only* by other local clients on the same machine that are browsing using kDNSServiceInterfaceIndexLocalOnly or kDNSServiceInterfaceIndexAny. If a client has a 'private' service, accessible only to other processes running on the same machine, this allows the client to advertise that service in a way such that it does not inadvertently appear in service lists on all the other machines on the network.

If the client passes kDNSServiceInterfaceIndexLocalOnly when browsing then it will find *all* records registered on that same local machine. Clients explicitly wishing to discover *only* LocalOnly services can accomplish this by inspecting the interfaceIndex of each service reported to their DNSServiceBrowseReply callback function, and discarding those where the interface index is not kDNSServiceInterfaceIndexLocalOnly.

kDNSServiceInterfaceIndexP2P is meaningful only in Browse, QueryRecord, Register, and Resolve operations. It should not be used in other DNSService APIs.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceBrowse or DNSServiceQueryRecord, it restricts the operation to P2P.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceRegister, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set.

- If kDNSServiceInterfaceIndexP2P is passed to DNSServiceResolve, it is mapped internally to kDNSServiceInterfaceIndexAny with the kDNSServiceFlagsIncludeP2P set, because resolving a P2P service may create and/or enable an interface whose index is not known a priori. The resolve callback will indicate the index of the interface via which the service can be accessed.

If applications pass kDNSServiceInterfaceIndexAny to DNSServiceBrowse or DNSServiceQueryRecord, they must set the kDNSServiceFlagsIncludeP2P flag to include P2P. In this case, if a service instance or the record being queried is found over P2P, the resulting ADD event will indicate kDNSServiceInterfaceIndexP2P as the interface index.

Discussion

This section describes the functions, callbacks, and data structures that make up the DNS Service Discovery API.

The DNS Service Discovery API is part of Bonjour, Apple's implementation of zero-configuration networking (ZEROCONF).

Bonjour allows you to register a network service, such as a printer or file server, so that it can be found by name or browsed for by service type and domain. Using Bonjour, applications can discover what services are available on the network, along with all the information -- such as name, IP address, and port -- necessary to access a particular service.

In effect, Bonjour combines the functions of a local DNS server and AppleTalk. Bonjour allows applications to provide user-friendly printer and server browsing, among other things, over standard IP networks. This behavior is a result of combining protocols such as multicast and DNS to add new functionality to the network (such as multicast DNS).

Bonjour gives applications easy access to services over local IP networks without requiring the service or the application to support an AppleTalk or a Netbeui stack, and without requiring a DNS server for the local network.

Notes on DNS Name Escaping

-- or --

"Why is kDNSServiceMaxDomainName 1009, when the maximum legal domain name is 256 bytes?"

All strings used in the DNS-SD APIs are UTF-8 strings. Apart from the exceptions noted below, the APIs expect the strings to be properly escaped, using the conventional DNS escaping rules:

  • '\\' represents a single literal '\' in the name

  • '\.' represents a single literal '.' in the name

  • '\ddd', where ddd is a three-digit decimal value from 000 to 255, represents a single literal byte with that value.

  • A bare unescaped '.' is a label separator, marking a boundary between domain and subdomain.

The exceptions, that do not use escaping, are the routines where the full DNS name of a resource is broken, for convenience, into servicename/regtype/domain. In these routines, the "servicename" is NOT escaped. It does not need to be, since it is, by definition, just a single literal string. Any characters in that string represent exactly what they are. The "regtype" portion is, technically speaking, escaped, but since legal regtypes are only allowed to contain letters, digits, and hyphens, there is nothing to escape, so the issue is moot. The "domain" portion is also escaped, though most domains in use on the public Internet today, like regtypes, don't contain any characters that need to be escaped. As DNS-SD becomes more popular, rich-text domains for service discovery will become common, so software should be written to cope with domains with escaping.

The servicename may be up to 63 bytes of UTF-8 text (not counting the C-String terminating NULL at the end). The regtype is of the form _service._tcp or _service._udp, where the "service" part is 1-15 characters, which may be letters, digits, or hyphens. The domain part of the three-part name may be any legal domain, providing that the resulting servicename+regtype+domain name does not exceed 256 bytes.

For most software, these issues are transparent. When browsing, the discovered servicenames should simply be displayed as-is. When resolving, the discovered servicename/regtype/domain are simply passed unchanged to DNSServiceResolve. When a DNSServiceResolve succeeds, the returned fullname is already in the correct format to pass to standard system DNS APIs such as res_query(). For converting from servicename/regtype/domain to a single properly-escaped full DNS name, the helper function DNSServiceConstructFullName is provided.

The following (highly contrived) example illustrates the escaping process. Suppose you have an service called "Dr. Smith\Dr. Johnson", of type "_ftp._tcp" in subdomain "4th. Floor" of subdomain "Building 2" of domain "apple.com." The full (escaped) DNS name of this service's SRV record would be: Dr\.\032Smith\\Dr\.\032Johnson._ftp._tcp.4th\.\032Floor.Building\0322.apple.com.

Miscellaneous Defines

   
#define _DNS_SD_H 5220111
#define kDNSServiceMaxDomainName 1009
#define kDNSServiceMaxServiceName 64
#define kDNSServiceOutputFlags (kDNSServiceFlagsValidate | kDNSServiceFlagsValidateOptional | kDNSServiceFlagsMoreComing | kDNSServiceFlagsAdd | kDNSServiceFlagsDefault)
#define kDNSServiceProperty_DaemonVersion "DaemonVersion"
Constants
_DNS_SD_H

API version number.

_DNS_SD_H contains the mDNSResponder version number for this header file, formatted as follows:

Major part of the build number * 10000 +

minor part of the build number * 100

For example, Mac OS X 10.4.9 has mDNSResponder-108.4, which would be represented as version 1080400. This allows C code to do simple greater-than and less-than comparisons: e.g. an application that requires the DNSServiceGetProperty call (new in mDNSResponder-126) can check:

 
   #if _DNS_SD_H+0 >= 1260000
   ... some C code that calls DNSServiceGetProperty() ...
   #endif
 

The version defined in this header file symbol allows for compile-time checking, so that C code building with earlier versions of the header file can avoid compile errors trying to use functions that aren't even defined in those earlier versions. Similar checks may also be performed at run-time:

  • weak linking -- to avoid link failures if run with an earlier version of the library that's missing some desired symbol, or

  • DNSServiceGetProperty(DaemonVersion) -- to verify whether the running daemon ("system service" on Windows) meets some required minimum functionality level.

kDNSServiceMaxDomainName

Maximum length, in bytes, of a domain name represented as an *escaped* C string including the final trailing dot, and the terminating NULL at the end.

kDNSServiceMaxServiceName

Maximum length, in bytes, of a service name represented as a literal C string, including the terminating NULL at the end.

kDNSServiceOutputFlags

All the output flags excluding the DNSSEC Status flags.

Typically used to check DNSSEC Status

kDNSServiceProperty_DaemonVersion

The daemon version property.

When requesting kDNSServiceProperty_DaemonVersion, the result pointer must point to a 32-bit unsigned integer, and the size parameter must be set to sizeof(uint32_t).

On return, the 32-bit unsigned integer contains the version number, formatted as follows:

Major part of the build number * 10000 +

minor part of the build number * 100

For example, Mac OS X 10.4.9 has mDNSResponder-108.4, which would be represented as version 1080400. This allows applications to do simple greater-than and less-than comparisons: e.g. an application that requires at least mDNSResponder-108.4 can check:

 
   if (version >= 1080400) ...
 

Example usage:

 
 
 uint32_t version;
 uint32_t size = sizeof(version);
 DNSServiceErrorType err = DNSServiceGetProperty(kDNSServiceProperty_DaemonVersion, &version, &size);
 if (!err) printf("Bonjour version is %d.%d\n", version / 10000, version / 100 % 100);
 
 

DNS Classes

enum {
   kDNSServiceClass_IN = 1 /*! Internet */
};
Constants
kDNSServiceClass_IN

Internet

Discussion

The values for DNS Classes and Types are listed in RFC 1035, and are available on every OS in its DNS header file. Unfortunately every OS does not have the same header file containing DNS Class and Type constants, and the names of the constants are not consistent. For example, BIND 8 uses "T_A", BIND 9 uses "ns_t_a", Windows uses "DNS_TYPE_A", etc. For this reason, these constants are also listed here, so that code using the DNS-SD programming APIs can use these constants, so that the same code can compile on all our supported platforms.

DNS Error Codes

enum {
   kDNSServiceErr_NoError = 0,
   /*! No error */
   kDNSServiceErr_Unknown = -65537, /* 0xFFFE FFFF */
   kDNSServiceErr_NoSuchName = -65538,
   kDNSServiceErr_NoMemory = -65539,
   /*! Out of memory. */
   kDNSServiceErr_BadParam = -65540,
   /*! Bad parameter value passed to function. */
   kDNSServiceErr_BadReference = -65541,
   kDNSServiceErr_BadState = -65542,
   kDNSServiceErr_BadFlags = -65543,
   kDNSServiceErr_Unsupported = -65544,
   kDNSServiceErr_NotInitialized = -65545,
   kDNSServiceErr_AlreadyRegistered = -65547,
   kDNSServiceErr_NameConflict = -65548,
   kDNSServiceErr_Invalid = -65549,
   /*! An invalid index or character was passed. */
   kDNSServiceErr_Firewall = -65550,
   kDNSServiceErr_Incompatible = -65551,
   /*! Client library incompatible with daemon */
   kDNSServiceErr_BadInterfaceIndex = -65552,
   kDNSServiceErr_Refused = -65553,
   kDNSServiceErr_NoSuchRecord = -65554,
   kDNSServiceErr_NoAuth = -65555,
   kDNSServiceErr_NoSuchKey = -65556,
   /*! The key does not exist in the TXT record. */
   kDNSServiceErr_NATTraversal = -65557,
   kDNSServiceErr_DoubleNAT = -65558,
   /*! More than one NAT gateway between source and destionation.
   */
   kDNSServiceErr_BadTime = -65559, /* Codes up to here existed in Tiger */
   kDNSServiceErr_BadSig = -65560,
   kDNSServiceErr_BadKey = -65561,
   kDNSServiceErr_Transient = -65562,
   kDNSServiceErr_ServiceNotRunning = -65563,
   /*! Background daemon not running */
   kDNSServiceErr_NATPortMappingUnsupported = -65564,
   /*! The NAT gateway doesn't support PCP,
   NAT-PMP or UPnP.
   */
   kDNSServiceErr_NATPortMappingDisabled = -65565,
   /*! The NAT gateway supports PCP,
   NAT-PMP or UPnP,
   but support is disabled by the administrator.
   */
   kDNSServiceErr_NoRouter = -65566,
   /*! No router is currently configured (probably no network connectivity).
   */
   kDNSServiceErr_PollingMode = -65567,
   kDNSServiceErr_Timeout = -65568 /*! A timeout occurred because the {@link kDNSServiceFlagsTimeout }
   */
   /* mDNS Error codes are in the range
   */
};
Constants
kDNSServiceErr_NoError

No error

kDNSServiceErr_NoMemory

Out of memory.

kDNSServiceErr_BadParam

Bad parameter value passed to function.

kDNSServiceErr_Invalid

An invalid index or character was passed.

kDNSServiceErr_Incompatible

Client library incompatible with daemon

kDNSServiceErr_NoSuchKey

The key does not exist in the TXT record.

kDNSServiceErr_DoubleNAT

More than one NAT gateway between source and destionation.

kDNSServiceErr_ServiceNotRunning

Background daemon not running

kDNSServiceErr_NATPortMappingUnsupported

The NAT gateway doesn't support PCP, NAT-PMP or UPnP.

kDNSServiceErr_NATPortMappingDisabled

The NAT gateway supports PCP, NAT-PMP or UPnP, but support is disabled by the administrator.

kDNSServiceErr_NoRouter

No router is currently configured (probably no network connectivity).

kDNSServiceErr_Timeout

A timeout occurred because the kDNSServiceFlagsTimeout + flag was passed.

Discussion

possible error code values

DNS Service Types

enum {
   kDNSServiceType_A = 1,
   /*! Host address. */
   kDNSServiceType_NS = 2,
   /*! Authoritative server. */
   kDNSServiceType_MD = 3,
   /*! Mail destination. */
   kDNSServiceType_MF = 4,
   /*! Mail forwarder. */
   kDNSServiceType_CNAME = 5,
   /*! Canonical name. */
   kDNSServiceType_SOA = 6,
   /*! Start of authority zone. */
   kDNSServiceType_MB = 7,
   /*! Mailbox domain name. */
   kDNSServiceType_MG = 8,
   /*! Mail group member. */
   kDNSServiceType_MR = 9,
   /*! Mail rename name. */
   kDNSServiceType_NULL = 10,
   /*! Null resource record. */
   kDNSServiceType_WKS = 11,
   /*! Well known service. */
   kDNSServiceType_PTR = 12,
   /*! Domain name pointer. */
   kDNSServiceType_HINFO = 13,
   /*! Host information. */
   kDNSServiceType_MINFO = 14,
   /*! Mailbox information. */
   kDNSServiceType_MX = 15,
   /*! Mail routing information. */
   kDNSServiceType_TXT = 16,
   /*! One or more text strings (NOT "zero or more..."). */
   kDNSServiceType_RP = 17,
   /*! Responsible person. */
   kDNSServiceType_AFSDB = 18,
   /*! AFS cell database. */
   kDNSServiceType_X25 = 19,
   /*! X_25 calling address. */
   kDNSServiceType_ISDN = 20,
   /*! ISDN calling address. */
   kDNSServiceType_RT = 21,
   /*! Router. */
   kDNSServiceType_NSAP = 22,
   /*! NSAP address. */
   kDNSServiceType_NSAP_PTR = 23,
   /*! Reverse NSAP lookup (deprecated). */
   kDNSServiceType_SIG = 24,
   /*! Security signature. */
   kDNSServiceType_KEY = 25,
   /*! Security key. */
   kDNSServiceType_PX = 26,
   /*! X.400 mail mapping. */
   kDNSServiceType_GPOS = 27,
   /*! Geographical position (withdrawn). */
   kDNSServiceType_AAAA = 28,
   /*! IPv6 Address. */
   kDNSServiceType_LOC = 29,
   /*! Location Information. */
   kDNSServiceType_NXT = 30,
   /*! Next domain (security). */
   kDNSServiceType_EID = 31,
   /*! Endpoint identifier. */
   kDNSServiceType_NIMLOC = 32,
   /*! Nimrod Locator. */
   kDNSServiceType_SRV = 33,
   /*! Server Selection. */
   kDNSServiceType_ATMA = 34,
   /*! ATM Address */
   kDNSServiceType_NAPTR = 35,
   /*! Naming Authority PoinTeR */
   kDNSServiceType_KX = 36,
   /*! Key Exchange */
   kDNSServiceType_CERT = 37,
   /*! Certification record */
   kDNSServiceType_A6 = 38,
   /*! IPv6 Address (deprecated) */
   kDNSServiceType_DNAME = 39,
   /*! Non-terminal DNAME (for IPv6) */
   kDNSServiceType_SINK = 40,
   /*! Kitchen sink (experimental) */
   kDNSServiceType_OPT = 41,
   /*! EDNS0 option (meta-RR) */
   kDNSServiceType_APL = 42,
   /*! Address Prefix List */
   kDNSServiceType_DS = 43,
   /*! Delegation Signer */
   kDNSServiceType_SSHFP = 44,
   /*! SSH Key Fingerprint */
   kDNSServiceType_IPSECKEY = 45,
   /*! IPSECKEY */
   kDNSServiceType_RRSIG = 46,
   /*! RRSIG */
   kDNSServiceType_NSEC = 47,
   /*! Denial of Existence */
   kDNSServiceType_DNSKEY = 48,
   /*! DNSKEY */
   kDNSServiceType_DHCID = 49,
   /*! DHCP Client Identifier */
   kDNSServiceType_NSEC3 = 50,
   /*! Hashed Authenticated Denial of Existence */
   kDNSServiceType_NSEC3PARAM = 51,
   /*! Hashed Authenticated Denial of Existence */
   kDNSServiceType_HIP = 55,
   /*! Host Identity Protocol */
   kDNSServiceType_SPF = 99,
   /*! Sender Policy Framework for E-Mail */
   kDNSServiceType_UINFO = 100,
   /*! IANA-Reserved */
   kDNSServiceType_UID = 101,
   /*! IANA-Reserved */
   kDNSServiceType_GID = 102,
   /*! IANA-Reserved */
   kDNSServiceType_UNSPEC = 103,
   /*! IANA-Reserved */
   kDNSServiceType_TKEY = 249,
   /*! Transaction key */
   kDNSServiceType_TSIG = 250,
   /*! Transaction signature. */
   kDNSServiceType_IXFR = 251,
   /*! Incremental zone transfer. */
   kDNSServiceType_AXFR = 252,
   /*! Transfer zone of authority. */
   kDNSServiceType_MAILB = 253,
   /*! Transfer mailbox records. */
   kDNSServiceType_MAILA = 254,
   /*! Transfer mail agent records. */
   kDNSServiceType_ANY = 255 /*! Wildcard match. */
};
Constants
kDNSServiceType_A

Host address.

kDNSServiceType_NS

Authoritative server.

kDNSServiceType_MD

Mail destination.

kDNSServiceType_MF

Mail forwarder.

kDNSServiceType_CNAME

Canonical name.

kDNSServiceType_SOA

Start of authority zone.

kDNSServiceType_MB

Mailbox domain name.

kDNSServiceType_MG

Mail group member.

kDNSServiceType_MR

Mail rename name.

kDNSServiceType_NULL

Null resource record.

kDNSServiceType_WKS

Well known service.

kDNSServiceType_PTR

Domain name pointer.

kDNSServiceType_HINFO

Host information.

kDNSServiceType_MINFO

Mailbox information.

kDNSServiceType_MX

Mail routing information.

kDNSServiceType_TXT

One or more text strings (NOT "zero or more...").

kDNSServiceType_RP

Responsible person.

kDNSServiceType_AFSDB

AFS cell database.

kDNSServiceType_X25

X_25 calling address.

kDNSServiceType_ISDN

ISDN calling address.

kDNSServiceType_RT

Router.

kDNSServiceType_NSAP

NSAP address.

kDNSServiceType_NSAP_PTR

Reverse NSAP lookup (deprecated).

kDNSServiceType_SIG

Security signature.

kDNSServiceType_KEY

Security key.

kDNSServiceType_PX

X.400 mail mapping.

kDNSServiceType_GPOS

Geographical position (withdrawn).

kDNSServiceType_AAAA

IPv6 Address.

kDNSServiceType_LOC

Location Information.

kDNSServiceType_NXT

Next domain (security).

kDNSServiceType_EID

Endpoint identifier.

kDNSServiceType_NIMLOC

Nimrod Locator.

kDNSServiceType_SRV

Server Selection.

kDNSServiceType_ATMA

ATM Address

kDNSServiceType_NAPTR

Naming Authority PoinTeR

kDNSServiceType_KX

Key Exchange

kDNSServiceType_CERT

Certification record

kDNSServiceType_A6

IPv6 Address (deprecated)

kDNSServiceType_DNAME

Non-terminal DNAME (for IPv6)

kDNSServiceType_SINK

Kitchen sink (experimental)

kDNSServiceType_OPT

EDNS0 option (meta-RR)

kDNSServiceType_APL

Address Prefix List

kDNSServiceType_DS

Delegation Signer

kDNSServiceType_SSHFP

SSH Key Fingerprint

kDNSServiceType_IPSECKEY

IPSECKEY

kDNSServiceType_RRSIG

RRSIG

kDNSServiceType_NSEC

Denial of Existence

kDNSServiceType_DNSKEY

DNSKEY

kDNSServiceType_DHCID

DHCP Client Identifier

kDNSServiceType_NSEC3

Hashed Authenticated Denial of Existence

kDNSServiceType_NSEC3PARAM

Hashed Authenticated Denial of Existence

kDNSServiceType_HIP

Host Identity Protocol

kDNSServiceType_SPF

Sender Policy Framework for E-Mail

kDNSServiceType_UINFO

IANA-Reserved

kDNSServiceType_UID

IANA-Reserved

kDNSServiceType_GID

IANA-Reserved

kDNSServiceType_UNSPEC

IANA-Reserved

kDNSServiceType_TKEY

Transaction key

kDNSServiceType_TSIG

Transaction signature.

kDNSServiceType_IXFR

Incremental zone transfer.

kDNSServiceType_AXFR

Transfer zone of authority.

kDNSServiceType_MAILB

Transfer mailbox records.

kDNSServiceType_MAILA

Transfer mail agent records.

kDNSServiceType_ANY

Wildcard match.

Discussion

The values for DNS Classes and Types are listed in RFC 1035, and are available on every OS in its DNS header file. Unfortunately every OS does not have the same header file containing DNS Class and Type constants, and the names of the constants are not consistent. For example, BIND 8 uses "T_A", BIND 9 uses "ns_t_a", Windows uses "DNS_TYPE_A", etc. For this reason, these constants are also listed here, so that code using the DNS-SD programming APIs can use these constants, so that the same code can compile on all our supported platforms.

General flags

Deprecated.

enum {
   /*! MoreComing indicates to a callback that at least one more result is
   */
   kDNSServiceFlagsMoreComing = 0x1,
   /*!
   */
   kDNSServiceFlagsAdd = 0x2,
   /*!
   */
   kDNSServiceFlagsDefault = 0x4,
   /*! Flag for specifying renaming behavior on name conflict when registering
   */
   kDNSServiceFlagsNoAutoRename = 0x8,
   /*!
   */
   kDNSServiceFlagsShared = 0x10,
   /*!
   */
   kDNSServiceFlagsUnique = 0x20,
   /*!
   */
   kDNSServiceFlagsBrowseDomains = 0x40,
   /*!
   */
   kDNSServiceFlagsRegistrationDomains = 0x80,
   /*! Flag for creating a long-lived unicast query for the DNSServiceQueryRecord call.
   */
   kDNSServiceFlagsLongLivedQuery = 0x100,
   /*! Flag for creating a record for which we will answer remote queries
   */
   kDNSServiceFlagsAllowRemoteQuery = 0x200,
   /*! Flag for signifying that a query or registration should be performed exclusively via multicast
   */
   kDNSServiceFlagsForceMulticast = 0x400,
   /*! @abstract Deprecated. */
   kDNSServiceFlagsForce = 0x800, // This flag is deprecated.
   /*!
   */
   kDNSServiceFlagsKnownUnique = 0x800,
   /*! Flag for returning intermediate results.
   */
   kDNSServiceFlagsReturnIntermediates = 0x1000,
   /*! A service registered with the NonBrowsable flag set can be resolved using
   */
   kDNSServiceFlagsNonBrowsable = 0x2000,
   /*! For efficiency,
   clients that perform many concurrent operations may want to use a
   */
   kDNSServiceFlagsShareConnection = 0x4000,
   /*!
   */
   kDNSServiceFlagsSuppressUnusable = 0x8000,
   /*!
   */
   kDNSServiceFlagsTimeout = 0x10000,
   /*!
   */
   kDNSServiceFlagsIncludeP2P = 0x20000,
   /*!
   */
   kDNSServiceFlagsWakeOnResolve = 0x40000,
   /*!
   */
   kDNSServiceFlagsBackgroundTrafficClass = 0x80000,
   /*!
   */
   kDNSServiceFlagsIncludeAWDL = 0x100000,
   /*!
   */
   kDNSServiceFlagsValidate = 0x200000,
   /*!
   */
   kDNSServiceFlagsSecure = 0x200010,
   /*!
   */
   kDNSServiceFlagsInsecure = 0x200020,
   /*!
   */
   kDNSServiceFlagsBogus = 0x200040,
   /*!
   */
   kDNSServiceFlagsIndeterminate = 0x200080,
   /*!
   */
   kDNSServiceFlagsUnicastResponse = 0x400000,
   /*!
   */
   kDNSServiceFlagsValidateOptional = 0x800000,
   /*!
   */
   kDNSServiceFlagsWakeOnlyService = 0x1000000,
   /*
   * This flag is meaningful only in DNSServiceBrowse. When set,
   * the system will stop issuing browse queries on the network once the number
   * of answers returned is one or more.  It will issue queries on the network
   * again if the number of answers drops to zero.
   * This flag is for Apple internal use only. Third party developers
   * should not rely on this behavior being supported in any given software release.
   */
   kDNSServiceFlagsThresholdOne = 0x2000000,
   /*
   * This flag is meaningful only in DNSServiceBrowse. When set,
   * the system will stop issuing browse queries on the network once the number
   * of answers has reached the threshold set for Finder.
   * It will issue queries on the network again if the number of answers drops below
   * this threshold.
   * This flag is for Apple internal use only. Third party developers
   * should not rely on this behavior being supported in any given software release.
   */
   kDNSServiceFlagsThresholdFinder = 0x4000000,
   /*
   * When this flag is set in the client callback add or remove event,
   * it indicates that the browse answer threshold has been reached and no
   * browse requests will be generated on the network until the number of answers falls
   * below the threshold value.  Add and remove events can still occur based
   * on incoming Bonjour traffic observed by the system.
   * The set of services return to the client is not guaranteed to represent the
   * entire set of services present on the network once the threshold has been reached.
   *
   * Note,
   while kDNSServiceFlagsThresholdReached and kDNSServiceFlagsThresholdOne
   * have the same value,
   there  isn't a conflict because kDNSServiceFlagsThresholdReached
   * is only set in the callbacks and kDNSServiceFlagsThresholdOne is only set on
   * input to a DNSServiceBrowse call.
   */
   kDNSServiceFlagsThresholdReached = kDNSServiceFlagsThresholdOne,
};
Constants
kDNSServiceFlagsMoreComing

MoreComing indicates to a callback that at least one more result is queued and will be delivered following immediately after this one. When the MoreComing flag is set, applications should not immediately update their UI, because this can result in a great deal of ugly flickering on the screen, and can waste a great deal of CPU time repeatedly updating the screen with content that is then immediately erased, over and over. Applications should wait until MoreComing is not set, and then update their UI when no more changes are imminent.

When MoreComing is not set, that doesn't mean there will be no more answers EVER, just that there are no more answers immediately available right now at this instant. If more answers become available in the future they will be delivered as usual.

kDNSServiceFlagsAdd

Indicates that the domain is newly discovered. If NOT set, indicates a "Remove", i.e. the domain is no longer valid. Used in domain enumeration and browse/query reply callbacks.

kDNSServiceFlagsDefault

Indicates that this domain should be selected by default. Applies only to enumeration and is only valid in conjunction with "Add".

kDNSServiceFlagsNoAutoRename

Flag for specifying renaming behavior on name conflict when registering non-shared records. By default, name conflicts are automatically handled by renaming the service. NoAutoRename overrides this behavior - with this flag set, name conflicts will result in a callback. The NoAutorename flag is only valid if a name is explicitly specified when registering a service (i.e. the default name is not used.)

kDNSServiceFlagsShared

Flag for registering individual records on a connected DNSServiceRef. Shared indicates that there may be multiple records with this name on the network (e.g. PTR records).

kDNSServiceFlagsUnique

Indicates that the record's name is to be unique on the network (e.g. SRV records).

kDNSServiceFlagsBrowseDomains

Enumerates domains recommended for browsing. Used for specifying domain enumeration type in DNSServiceEnumerateDomains.

kDNSServiceFlagsRegistrationDomains

Enumerates domains recommended for registration. Used for specifying domain enumeration type in DNSServiceEnumerateDomains.

kDNSServiceFlagsLongLivedQuery

Flag for creating a long-lived unicast query for the DNSServiceQueryRecord call.

kDNSServiceFlagsAllowRemoteQuery

Flag for creating a record for which we will answer remote queries (queries from hosts more than one hop away; hosts not directly connected to the local link).

kDNSServiceFlagsForceMulticast

Flag for signifying that a query or registration should be performed exclusively via multicast DNS, even for a name in a domain (e.g. foo.apple.com.) that would normally imply unicast DNS.

kDNSServiceFlagsKnownUnique

Client guarantees that record names are unique, so we can skip sending out initial probe messages. Standard name conflict resolution is still done if a conflict is discovered. Currently only valid for a DNSServiceRegister call.

kDNSServiceFlagsReturnIntermediates

Flag for returning intermediate results. For example, if a query results in an authoritative NXDomain (name does not exist) then that result is returned to the client. However the query is not implicitly cancelled -- it remains active and if the answer subsequently changes (e.g. because a VPN tunnel is subsequently established) then that positive result will still be returned to the client. Similarly, if a query results in a CNAME record, then in addition to following the CNAME referral, the intermediate CNAME result is also returned to the client. When this flag is not set, NXDomain errors are not returned, and CNAME records are followed silently without informing the client of the intermediate steps. (In earlier builds this flag was briefly called kDNSServiceFlagsReturnCNAME.)

kDNSServiceFlagsNonBrowsable

A service registered with the NonBrowsable flag set can be resolved using DNSServiceResolve, but will not be discoverable using DNSServiceBrowse. This is for cases where the name is actually a GUID; it is found by other means; there is no end-user benefit to browsing to find a long list of opaque GUIDs. Using the NonBrowsable flag creates SRV+TXT without the cost of also advertising an associated PTR record.

kDNSServiceFlagsShareConnection

For efficiency, clients that perform many concurrent operations may want to use a single Unix Domain Socket connection with the background daemon, instead of having a separate connection for each independent operation. To use this mode, clients first call DNSServiceCreateConnection(&MainRef) to initialize the main DNSServiceRef. For each subsequent operation that is to share that same connection, the client copies the MainRef, and then passes the address of that copy, setting the ShareConnection flag to tell the library that this DNSServiceRef is not a typical uninitialized DNSServiceRef; it's a copy of an existing DNSServiceRef whose connection information should be reused.

For example:

 
 DNSServiceErrorType error;
 DNSServiceRef MainRef;
 error = DNSServiceCreateConnection(&MainRef);
 if (error) ...
 DNSServiceRef BrowseRef = MainRef;  // Important: COPY the primary DNSServiceRef first...
 error = DNSServiceBrowse(&BrowseRef, kDNSServiceFlagsShareConnection, ...); // then use the copy
 if (error) ...
 ...
 DNSServiceRefDeallocate(BrowseRef); // Terminate the browse operation
 DNSServiceRefDeallocate(MainRef);   // Terminate the shared connection
 

Notes:

  1. Collective kDNSServiceFlagsMoreComing flag When callbacks are invoked using a shared DNSServiceRef, the kDNSServiceFlagsMoreComing flag applies collectively to *all* active operations sharing the same parent DNSServiceRef. If the MoreComing flag is set it means that there are more results queued on this parent DNSServiceRef, but not necessarily more results for this particular callback function. The implication of this for client programmers is that when a callback is invoked with the MoreComing flag set, the code should update its internal data structures with the new result, and set a variable indicating that its UI needs to be updated. Then, later when a callback is eventually invoked with the MoreComing flag not set, the code should update *all* stale UI elements related to that shared parent DNSServiceRef that need updating, not just the UI elements related to the particular callback that happened to be the last one to be invoked.

  2. Canceling operations and kDNSServiceFlagsMoreComing Whenever you cancel any operation for which you had deferred UI updates waiting because of a kDNSServiceFlagsMoreComing flag, you should perform those deferred UI updates. This is because, after cancelling the operation, you can no longer wait for a callback *without* MoreComing set, to tell you do perform your deferred UI updates (the operation has been canceled, so there will be no more callbacks). An implication of the collective kDNSServiceFlagsMoreComing flag for shared connections is that this guideline applies more broadly -- any time you cancel an operation on a shared connection, you should perform all deferred UI updates for all operations sharing that connection. This is because the MoreComing flag might have been referring to events coming for the operation you canceled, which will now not be coming because the operation has been canceled.

  3. Only share DNSServiceRef's created with DNSServiceCreateConnection Calling DNSServiceCreateConnection(&ref) creates a special shareable DNSServiceRef. DNSServiceRef's created by other calls like DNSServiceBrowse or DNSServiceResolve cannot be shared by copying them and using kDNSServiceFlagsShareConnection.

  4. Don't Double-Deallocate Calling DNSServiceRefDeallocate(ref) for a particular operation's DNSServiceRef terminates just that operation. Calling DNSServiceRefDeallocate(ref) for the main shared DNSServiceRef (the parent DNSServiceRef, originally created by DNSServiceCreateConnection(&ref)) automatically terminates the shared connection and all operations that were still using it. After doing this, DO NOT then attempt to deallocate any remaining subordinate DNSServiceRef's. The memory used by those subordinate DNSServiceRef's has already been freed, so any attempt to do a DNSServiceRefDeallocate (or any other operation) on them will result in accesses to freed memory, leading to crashes or other equally undesirable results.

  5. Thread Safety The dns_sd.h API does not presuppose any particular threading model, and consequently does no locking of its own (which would require linking some specific threading library). If client code calls API routines on the same DNSServiceRef concurrently from multiple threads, it is the client's responsibility to use a mutext lock or take similar appropriate precautions to serialize those calls.

kDNSServiceFlagsSuppressUnusable

This flag is meaningful only in DNSServiceQueryRecord which suppresses unusable queries on the wire. If "hostname" is a wide-area unicast DNS hostname (i.e. not a ".local." name) but this host has no routable IPv6 address, then the call will not try to look up IPv6 addresses for "hostname", since any addresses it found would be unlikely to be of any use anyway. Similarly, if this host has no routable IPv4 address, the call will not try to look up IPv4 addresses for "hostname".

kDNSServiceFlagsTimeout

When passed to DNSServiceQueryRecord or DNSServiceGetAddrInfo, the query is stopped after a certain number of seconds have elapsed. The time at which the query is stopped is determined by the system and cannot be configured by the user. The query is stopped irrespective of whether a response was given earlier or not. When the query is stopped, the callback is called with an error code of kDNSServiceErr_Timeout and a NULL sockaddr is returned for DNSServiceGetAddrInfo and zero length rdata is returned for DNSServiceQueryRecord.

kDNSServiceFlagsIncludeP2P

Include P2P interfaces when kDNSServiceInterfaceIndexAny is specified. By default, specifying kDNSServiceInterfaceIndexAny does not include P2P interfaces.

kDNSServiceFlagsWakeOnResolve

This flag is meaningful only in DNSServiceResolve. When set, it tries to send a magic packet to wake up the client.

kDNSServiceFlagsBackgroundTrafficClass

This flag is meaningful in DNSServiceBrowse, DNSServiceGetAddrInfo, DNSServiceQueryRecord, and DNSServiceResolve. When set, it uses the background traffic class for packets that service the request.

kDNSServiceFlagsIncludeAWDL

Include AWDL interface when kDNSServiceInterfaceIndexAny is specified.

kDNSServiceFlagsValidate

This flag is meaningful in DNSServiceGetAddrInfo and DNSServiceQueryRecord. This is the ONLY flag that is both valid as an input to the APIs and also as an output through the callbacks in the APIs.

When this flag is passed to DNSServiceQueryRecord and DNSServiceGetAddrInfo to resolve unicast names, the response is validated using DNSSEC. The validation results are delivered using the flags field in the callback and kDNSServiceFlagsValidate is marked in the flags to indicate that DNSSEC status is also available. When the callback is called to deliver the query results, the validation results may or may not be available. If it is not delivered along with the results, the validation status is delivered when the validation completes.

When the validation results are delivered in the callback, it is indicated by marking the flags with kDNSServiceFlagsValidate and kDNSServiceFlagsAdd along with the DNSSEC status flags (described below) and a NULL sockaddr is returned for DNSServiceGetAddrInfo and zero length rdata is returned for DNSServiceQueryRecord. DNSSEC validation results are for the whole RRSet and not just individual records delivered in the callback. When kDNSServiceFlagsAdd is not set in the flags, applications should implicitly assume that the DNSSEC status of the RRSet that has been delivered up until that point is not valid anymore, till another callback is called with kDNSServiceFlagsAdd and kDNSServiceFlagsValidate.

The kDNSServiceFlagsValidate, kDNSServiceFlagsSecure, kDNSServiceFlagsInsecure, and kDNSServiceFlagsBogus flags indicate the status of the DNSSEC validation and marked in the flags field of the callback. When any of these four flags is set, kDNSServiceFlagsValidate is also set. To check the validation status, the other applicable output flags should be masked. See kDNSServiceOutputFlags below.

kDNSServiceFlagsSecure

The response has been validated by verifying all the signaures in the response and was able to build a successful authentication chain starting from a known trust anchor.

kDNSServiceFlagsInsecure

A chain of trust cannot be built starting from a known trust anchor to the response.

kDNSServiceFlagsBogus

If the response cannot be verified to be secure due to expired signatures, missing signatures, and so on, then the results are considered to be bogus.

kDNSServiceFlagsIndeterminate

There is no valid trust anchor that can be used to determine whether a response is secure or not.

kDNSServiceFlagsUnicastResponse

Request unicast response to query.

kDNSServiceFlagsValidateOptional

This flag is identical to kDNSServiceFlagsValidate except for the case where the response cannot be validated. If this flag is set in DNSServiceQueryRecord or DNSServiceGetAddrInfo, the DNSSEC records will be requested for validation. If they cannot be received for some reason during the validation (e.g., zone is not signed, zone is signed but cannot be traced back to root, recursive server does not understand DNSSEC etc.), then this falls back to the default behavior where the validation is not performed and no DNSSEC results are provided.

If the zone is signed and there is a valid path to a known trust anchor configured in the system and the application requires DNSSEC validation irrespective of the DNSSEC awareness in the current network, then this option MUST not be used. This is only intended to be used during the transition period where the different nodes participating in the DNS resolution may not understand DNSSEC or managed properly (e.g. missing DS record) but still want to be able to resolve DNS successfully.

kDNSServiceFlagsWakeOnlyService

This flag is meaningful only in DNSServiceRegister. When set, the service is not registered with a sleep proxy server during sleep.

Discussion

Most DNS-SD API functions and callbacks include a DNSServiceFlags parameter. As a general rule, any given bit in the 32-bit flags field has a specific fixed meaning, regardless of the function or callback being used. For any given function or callback, typically only a subset of the possible flags are meaningful, and all others should be zero. The discussion section for each API call describes which flags are valid for that call and callback. In some cases, for a particular call, it may be that no flags are currently defined, in which case the DNSServiceFlags parameter exists purely to allow future expansion. In all cases, developers should expect that in future releases, it is possible that new flag values will be defined, and write code with this in mind. For example, code that tests

 
     if (flags == kDNSServiceFlagsAdd) ...
 

will fail if, in a future release, another bit in the 32-bit flags field is also set. The reliable way to test whether a particular bit is set is not with an equality test, but with a bitwise mask:

 
     if (flags & kDNSServiceFlagsAdd) ...
 

With the exception of kDNSServiceFlagsValidate, each flag can be valid(be set) EITHER only as an input to one of the DNSService*() APIs OR only as an output (provide status) through any of the callbacks used. For example, kDNSServiceFlagsAdd can be set only as an output in the callback, whereas kDNSServiceFlagsIncludeP2P can be set only as an input to the DNSService*() APIs. See comments on kDNSServiceFlagsValidate defined in this enum.

Port Mapping Protocols

Possible protocols for DNSServiceNATPortMappingCreate.

enum {
   /* for DNSServiceGetAddrInfo() */
   kDNSServiceProtocol_IPv4 = 0x01,
   /*! IPv4 protocol. */
   kDNSServiceProtocol_IPv6 = 0x02,
   /*! IPv6 protocol. */
   /* 0x04 and x08 reserved for future internetwork protocols */
   /* for DNSServiceNATPortMappingCreate() */
   kDNSServiceProtocol_UDP = 0x10,
   /*! UDP protocol. */
   kDNSServiceProtocol_TCP = 0x20 /*! TCP protocol. */
   /* 0x40 and x80 reserved for future transport protocols,
   e.g. SCTP [RFC 2960]
   * or DCCP [RFC 4340]. If future NAT gateways are created that support port
   * mappings for these protocols,
   new constants will be defined here.
   */
};
Constants
kDNSServiceProtocol_IPv4

IPv4 protocol.

kDNSServiceProtocol_IPv6

IPv6 protocol.

kDNSServiceProtocol_UDP

UDP protocol.

kDNSServiceProtocol_TCP

TCP protocol.