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service.go
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service.go
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// Package msg defines the Service structure which is used for service discovery.
package msg
import (
"fmt"
"net"
"strings"
"github.com/miekg/dns"
)
// Service defines a discoverable service in etcd. It is the rdata from a SRV
// record, but with a twist. Host (Target in SRV) must be a domain name, but
// if it looks like an IP address (4/6), we will treat it like an IP address.
type Service struct {
Host string `json:"host,omitempty"`
Port int `json:"port,omitempty"`
Priority int `json:"priority,omitempty"`
Weight int `json:"weight,omitempty"`
Text string `json:"text,omitempty"`
Mail bool `json:"mail,omitempty"` // Be an MX record. Priority becomes Preference.
TTL uint32 `json:"ttl,omitempty"`
// When a SRV record with a "Host: IP-address" is added, we synthesize
// a srv.Target domain name. Normally we convert the full Key where
// the record lives to a DNS name and use this as the srv.Target. When
// TargetStrip > 0 we strip the left most TargetStrip labels from the
// DNS name.
TargetStrip int `json:"targetstrip,omitempty"`
// Group is used to group (or *not* to group) different services
// together. Services with an identical Group are returned in the same
// answer.
Group string `json:"group,omitempty"`
// Etcd key where we found this service and ignored from json un-/marshalling
Key string `json:"-"`
}
// RR returns an RR representation of s. It is in a condensed form to minimize space
// when this is returned in a DNS message.
// The RR will look like:
// 1.rails.production.east.skydns.local. 300 CH TXT "service1.example.com:8080(10,0,,false)[0,]"
// etcd Key Ttl Host:Port < see below >
// between parens: (Priority, Weight, Text (only first 200 bytes!), Mail)
// between blockquotes: [TargetStrip,Group]
// If the record is synthesised by CoreDNS (i.e. no lookup in etcd happened):
//
// TODO(miek): what to put here?
//
func (s *Service) RR() *dns.TXT {
l := len(s.Text)
if l > 200 {
l = 200
}
t := new(dns.TXT)
t.Hdr.Class = dns.ClassCHAOS
t.Hdr.Ttl = s.TTL
t.Hdr.Rrtype = dns.TypeTXT
t.Hdr.Name = Domain(s.Key)
t.Txt = make([]string, 1)
t.Txt[0] = fmt.Sprintf("%s:%d(%d,%d,%s,%t)[%d,%s]",
s.Host, s.Port,
s.Priority, s.Weight, s.Text[:l], s.Mail,
s.TargetStrip, s.Group)
return t
}
// NewSRV returns a new SRV record based on the Service.
func (s *Service) NewSRV(name string, weight uint16) *dns.SRV {
host := targetStrip(dns.Fqdn(s.Host), s.TargetStrip)
return &dns.SRV{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: s.TTL},
Priority: uint16(s.Priority), Weight: weight, Port: uint16(s.Port), Target: dns.Fqdn(host)}
}
// NewMX returns a new MX record based on the Service.
func (s *Service) NewMX(name string) *dns.MX {
host := targetStrip(dns.Fqdn(s.Host), s.TargetStrip)
return &dns.MX{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeMX, Class: dns.ClassINET, Ttl: s.TTL},
Preference: uint16(s.Priority), Mx: host}
}
// NewA returns a new A record based on the Service.
func (s *Service) NewA(name string, ip net.IP) *dns.A {
return &dns.A{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: s.TTL}, A: ip}
}
// NewAAAA returns a new AAAA record based on the Service.
func (s *Service) NewAAAA(name string, ip net.IP) *dns.AAAA {
return &dns.AAAA{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: s.TTL}, AAAA: ip}
}
// NewCNAME returns a new CNAME record based on the Service.
func (s *Service) NewCNAME(name string, target string) *dns.CNAME {
return &dns.CNAME{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeCNAME, Class: dns.ClassINET, Ttl: s.TTL}, Target: dns.Fqdn(target)}
}
// NewTXT returns a new TXT record based on the Service.
func (s *Service) NewTXT(name string) *dns.TXT {
return &dns.TXT{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: s.TTL}, Txt: split255(s.Text)}
}
// NewPTR returns a new PTR record based on the Service.
func (s *Service) NewPTR(name string, target string) *dns.PTR {
return &dns.PTR{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypePTR, Class: dns.ClassINET, Ttl: s.TTL}, Ptr: dns.Fqdn(target)}
}
// NewNS returns a new NS record based on the Service.
func (s *Service) NewNS(name string) *dns.NS {
host := targetStrip(dns.Fqdn(s.Host), s.TargetStrip)
return &dns.NS{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: s.TTL}, Ns: host}
}
// Group checks the services in sx, it looks for a Group attribute on the shortest
// keys. If there are multiple shortest keys *and* the group attribute disagrees (and
// is not empty), we don't consider it a group.
// If a group is found, only services with *that* group (or no group) will be returned.
func Group(sx []Service) []Service {
if len(sx) == 0 {
return sx
}
// Shortest key with group attribute sets the group for this set.
group := sx[0].Group
slashes := strings.Count(sx[0].Key, "/")
length := make([]int, len(sx))
for i, s := range sx {
x := strings.Count(s.Key, "/")
length[i] = x
if x < slashes {
if s.Group == "" {
break
}
slashes = x
group = s.Group
}
}
if group == "" {
return sx
}
ret := []Service{} // with slice-tricks in sx we can prolly save this allocation (TODO)
for i, s := range sx {
if s.Group == "" {
ret = append(ret, s)
continue
}
// Disagreement on the same level
if length[i] == slashes && s.Group != group {
return sx
}
if s.Group == group {
ret = append(ret, s)
}
}
return ret
}
// Split255 splits a string into 255 byte chunks.
func split255(s string) []string {
if len(s) < 255 {
return []string{s}
}
sx := []string{}
p, i := 0, 255
for {
if i <= len(s) {
sx = append(sx, s[p:i])
} else {
sx = append(sx, s[p:])
break
}
p, i = p+255, i+255
}
return sx
}
// targetStrip strips "targetstrip" labels from the left side of the fully qualified name.
func targetStrip(name string, targetStrip int) string {
if targetStrip == 0 {
return name
}
offset, end := 0, false
for i := 0; i < targetStrip; i++ {
offset, end = dns.NextLabel(name, offset)
}
if end {
// We overshot the name, use the orignal one.
offset = 0
}
name = name[offset:]
return name
}