BK8s datasource middleware -- PoC for A records (#153)

* Laying down kubernetes middleware foundation

* Duplicated a bunch of code form etcd middleware
* Duplicated code hacked to compile and load as a separate middleware

* Adding verbose build option to Makefile

* Removing stubzone and tls support

tls and stubzone support was carried over from base etcd middleware code.
Removing to simplify the kube middleware implementation. (For now.)

* Adding conf directory for sample conf files

* Removing stubzone support from query handler

* Remove upstream and proxy from k8s corefile.

Not sure that upstream or proxy makes sense for a k8s backed zone.

* Comment out use of singleflight serialization

* Removing parsing support for "upstream" directive from k8s

* Removing upstream directive parsing code

* Removing CNAME and TXT lookup implementation

* Create README.md

Brain-dump of DNS record name assembly and open work items.

* Adding notes about wildcard handling

* Adding basic k8s API client

* Fleshing out methods on k8s connector

* Remove PathPrefix from middleware init

* Removing incorrect plural

* Adding brute-force k8s service lookup functions

* Initializing k8s API connector during startup

* Hacking around to call k8s connector

* Parsing incoming domain name into serviceName and namespace

* Improving and simplifying k8s zone matching and label segmentation

* Removing unused functions carried over from etcd middleware

* Adding basic return of k8s data to DNS client

* updated debugging println statements to flag with "[debug]"
* removed code in kubernetes.go::Records that was a hold-over from etcd middleware.
* Removed some random exploratory hacking.

* Minior README.md updates

* Updating with demo instructions

* Updating README.md with CoreFile and removing completed TODO items

* Updating conf file and README to reflect DNS response cache works

* Disabling DNS response caching

* Adding debug statement on entry to Records()

* Changing port number in exampes to port 53.

* Misc style and clarity changes

* Removing empty function definitions

* Adding comment to track future cleanup

* Refactoring README to follow style of other middleware

* Exposing dataobject field (typo)

1 files changed, 166 insertions, 0 deletions

diff --git a/middleware/kubernetes/msg/service.go b/middleware/kubernetes/msg/service.go
new file mode 100644
index 000000000..588e7b33c
--- /dev/null
+++ b/middleware/kubernetes/msg/service.go
@@ -0,0 +1,166 @@
+package msg
+
+import (
+	"net"
+	"strings"
+
+	"github.com/miekg/dns"
+)
+
+// This *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:"-"`
+}
+
+// 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)}
+}
+
+// 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
+}