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85 lines
3.3 KiB
Go
85 lines
3.3 KiB
Go
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package mdns
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import "github.com/miekg/dns"
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// DNSSDService is a service that complies with the DNS-SD (RFC 6762) and MDNS
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// (RFC 6762) specs for local, multicast-DNS-based discovery.
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//
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// DNSSDService implements the Zone interface and wraps an MDNSService instance.
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// To deploy an mDNS service that is compliant with DNS-SD, it's recommended to
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// register only the wrapped instance with the server.
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//
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// Example usage:
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// service := &mdns.DNSSDService{
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// MDNSService: &mdns.MDNSService{
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// Instance: "My Foobar Service",
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// Service: "_foobar._tcp",
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// Port: 8000,
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// }
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// }
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// server, err := mdns.NewServer(&mdns.Config{Zone: service})
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// if err != nil {
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// log.Fatalf("Error creating server: %v", err)
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// }
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// defer server.Shutdown()
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type DNSSDService struct {
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MDNSService *MDNSService
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}
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// Records returns DNS records in response to a DNS question.
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//
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// This function returns the DNS response of the underlying MDNSService
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// instance. It also returns a PTR record for a request for "
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// _services._dns-sd._udp.<Domain>", as described in section 9 of RFC 6763
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// ("Service Type Enumeration"), to allow browsing of the underlying MDNSService
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// instance.
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func (s *DNSSDService) Records(q dns.Question) []dns.RR {
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var recs []dns.RR
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if q.Name == "_services._dns-sd._udp."+s.MDNSService.Domain+"." {
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recs = s.dnssdMetaQueryRecords(q)
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}
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return append(recs, s.MDNSService.Records(q)...)
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}
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// dnssdMetaQueryRecords returns the DNS records in response to a "meta-query"
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// issued to browse for DNS-SD services, as per section 9. of RFC6763.
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//
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// A meta-query has a name of the form "_services._dns-sd._udp.<Domain>" where
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// Domain is a fully-qualified domain, such as "local."
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func (s *DNSSDService) dnssdMetaQueryRecords(q dns.Question) []dns.RR {
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// Intended behavior, as described in the RFC:
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// ...it may be useful for network administrators to find the list of
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// advertised service types on the network, even if those Service Names
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// are just opaque identifiers and not particularly informative in
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// isolation.
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//
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// For this purpose, a special meta-query is defined. A DNS query for PTR
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// records with the name "_services._dns-sd._udp.<Domain>" yields a set of
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// PTR records, where the rdata of each PTR record is the two-abel
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// <Service> name, plus the same domain, e.g., "_http._tcp.<Domain>".
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// Including the domain in the PTR rdata allows for slightly better name
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// compression in Unicast DNS responses, but only the first two labels are
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// relevant for the purposes of service type enumeration. These two-label
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// service types can then be used to construct subsequent Service Instance
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// Enumeration PTR queries, in this <Domain> or others, to discover
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// instances of that service type.
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return []dns.RR{
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&dns.PTR{
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Hdr: dns.RR_Header{
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Name: q.Name,
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Rrtype: dns.TypePTR,
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Class: dns.ClassINET,
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Ttl: defaultTTL,
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},
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Ptr: s.MDNSService.serviceAddr,
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},
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}
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}
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// Announcement returns DNS records that should be broadcast during the initial
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// availability of the service, as described in section 8.3 of RFC 6762.
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// TODO(reddaly): Add this when Announcement is added to the mdns.Zone interface.
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//func (s *DNSSDService) Announcement() []dns.RR {
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// return s.MDNSService.Announcement()
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//}
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