DNSServiceRegister

DNSServiceRegister is a function in Apple's DNS Service Discovery (DNS-SD) API, commonly known as Bonjour. It is used to publish a network service instance on the local network via multicast DNS (mDNS) and DNS-SD. The function registers a service with a specific name, type, domain, and port, and can include TXT records to convey additional metadata.

The API signature (in C) includes parameters for a DNSServiceRef, flags, network interface index, the instance name, service type (regtype), domain, host, port, TXT record data, a callback, and user context. Through this call, a client can advertise a service such as "_http._tcp" on port 80, optionally providing TXT data with key-value pairs. The domain is typically the local DNS-SD domain (often "local."), and the host is optional. The port must be provided in network byte order. TXT records are supplied as a length/byte array.

The registration is asynchronous. A completion callback informs success or failure and may supply the finalized name, regtype, and domain. The function returns immediately with an error code, and the service appears on the network once registration completes. The DNSServiceRef returned by the call must be kept alive for the duration of the registration and deallocated when no longer needed.

Usage typically involves integrating the DNSServiceRef with a run loop or dispatch mechanism to handle callbacks. DNSServiceRegister is commonly used alongside DNSServiceBrowse and DNSServiceResolve to discover and advertise services on local networks. It is available on Apple platforms and other systems implementing the DNS-SD API.