fix(mdns): answer hostname A queries after TTL (#96)

* fix(mdns): answer hostname A queries after TTL

Zeroconf answers only service queries. The A record for <alias>.local
expired from the OS cache after 120 seconds and lookups then failed.

Vendor zeroconf v1.0.0 with one change: it now answers A and AAAA
queries for the registered hostname. Fixes #95.

* fix(deps): update golang.org/x/net to v0.60.0

govulncheck reports several x/net advisories fixed in v0.60.0.
The Security Scan job fails on them.

third_party/zeroconf/service.go

@@ -0,0 +1,109 @@
+package zeroconf
+
+import (
+	"fmt"
+	"net"
+	"sync"
+)
+
+// ServiceRecord contains the basic description of a service, which contains instance name, service type & domain
+type ServiceRecord struct {
+	Instance string `json:"name"`   // Instance name (e.g. "My web page")
+	Service  string `json:"type"`   // Service name (e.g. _http._tcp.)
+	Domain   string `json:"domain"` // If blank, assumes "local"
+
+	// private variable populated on ServiceRecord creation
+	serviceName         string
+	serviceInstanceName string
+	serviceTypeName     string
+}
+
+// ServiceName returns a complete service name (e.g. _foobar._tcp.local.), which is composed
+// of a service name (also referred as service type) and a domain.
+func (s *ServiceRecord) ServiceName() string {
+	return s.serviceName
+}
+
+// ServiceInstanceName returns a complete service instance name (e.g. MyDemo\ Service._foobar._tcp.local.),
+// which is composed from service instance name, service name and a domain.
+func (s *ServiceRecord) ServiceInstanceName() string {
+	return s.serviceInstanceName
+}
+
+// ServiceTypeName returns the complete identifier for a DNS-SD query.
+func (s *ServiceRecord) ServiceTypeName() string {
+	return s.serviceTypeName
+}
+
+// NewServiceRecord constructs a ServiceRecord.
+func NewServiceRecord(instance, service, domain string) *ServiceRecord {
+	s := &ServiceRecord{
+		Instance:    instance,
+		Service:     service,
+		Domain:      domain,
+		serviceName: fmt.Sprintf("%s.%s.", trimDot(service), trimDot(domain)),
+	}
+
+	// Cache service instance name
+	if instance != "" {
+		s.serviceInstanceName = fmt.Sprintf("%s.%s", trimDot(s.Instance), s.ServiceName())
+	}
+
+	// Cache service type name domain
+	typeNameDomain := "local"
+	if len(s.Domain) > 0 {
+		typeNameDomain = trimDot(s.Domain)
+	}
+	s.serviceTypeName = fmt.Sprintf("_services._dns-sd._udp.%s.", typeNameDomain)
+
+	return s
+}
+
+// LookupParams contains configurable properties to create a service discovery request
+type LookupParams struct {
+	ServiceRecord
+	Entries chan<- *ServiceEntry // Entries Channel
+
+	stopProbing chan struct{}
+	once        sync.Once
+}
+
+// NewLookupParams constructs a LookupParams.
+func NewLookupParams(instance, service, domain string, entries chan<- *ServiceEntry) *LookupParams {
+	return &LookupParams{
+		ServiceRecord: *NewServiceRecord(instance, service, domain),
+		Entries:       entries,
+
+		stopProbing: make(chan struct{}),
+	}
+}
+
+// Notify subscriber that no more entries will arrive. Mostly caused
+// by an expired context.
+func (l *LookupParams) done() {
+	close(l.Entries)
+}
+
+func (l *LookupParams) disableProbing() {
+	l.once.Do(func() { close(l.stopProbing) })
+}
+
+// ServiceEntry represents a browse/lookup result for client API.
+// It is also used to configure service registration (server API), which is
+// used to answer multicast queries.
+type ServiceEntry struct {
+	ServiceRecord
+	HostName string   `json:"hostname"` // Host machine DNS name
+	Port     int      `json:"port"`     // Service Port
+	Text     []string `json:"text"`     // Service info served as a TXT record
+	TTL      uint32   `json:"ttl"`      // TTL of the service record
+	AddrIPv4 []net.IP `json:"-"`        // Host machine IPv4 address
+	AddrIPv6 []net.IP `json:"-"`        // Host machine IPv6 address
+}
+
+// NewServiceEntry constructs a ServiceEntry.
+func NewServiceEntry(instance, service, domain string) *ServiceEntry {
+	return &ServiceEntry{
+		ServiceRecord: *NewServiceRecord(instance, service, domain),
+	}
+}