DNSServiceGetAddrInfo

DNSServiceGetAddrInfo is a function in Apple's DNSServiceDiscovery (Bonjour) API used to retrieve address information for a given host name or a DNS-SD service. It provides asynchronous, callback-based resolution of IPv4 and/or IPv6 addresses, allowing applications to discover network endpoints without blocking.

The function starts an address lookup and delivers results through a callback of type DNSServiceGetAddrInfoReply. The callback receives the service reference, flags, the network interface index, an error code, the host name, the address (as a sockaddr structure), and a time-to-live value. The caller specifies which interfaces to query via an interfaceIndex parameter (0 for all interfaces) and which protocol families to return via a protocol flag (IPv4, IPv6, or both). The host parameter supplies the hostname to resolve.

Usage is asynchronous: a client creates a DNSServiceRef, calls DNSServiceGetAddrInfo with the desired flags, interface index, protocol, and host, and then runs a run loop or dispatch source to process incoming callback events. Results are delivered as they become available and can include multiple addresses. When the lookup is no longer needed, the client deallocates the DNSServiceRef to cancel the query and free resources.

The function returns a DNSServiceErrorType to indicate success or failure of initiating the query. Typical values include kDNSServiceErr_NoError on success, with other codes signaling issues such as invalid parameters or internal errors. DNSServiceGetAddrInfo complements other DNS-SD operations like DNSServiceBrowse and DNSServiceResolve by providing address information needed to establish connections to discovered services.