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)

middleware/kubernetes/msg/service_test.go

@@ -0,0 +1,125 @@
+package msg
+
+import "testing"
+
+func TestSplit255(t *testing.T) {
+	xs := split255("abc")
+	if len(xs) != 1 && xs[0] != "abc" {
+		t.Errorf("Failure to split abc")
+	}
+	s := ""
+	for i := 0; i < 255; i++ {
+		s += "a"
+	}
+	xs = split255(s)
+	if len(xs) != 1 && xs[0] != s {
+		t.Errorf("failure to split 255 char long string")
+	}
+	s += "b"
+	xs = split255(s)
+	if len(xs) != 2 || xs[1] != "b" {
+		t.Errorf("failure to split 256 char long string: %d", len(xs))
+	}
+	for i := 0; i < 255; i++ {
+		s += "a"
+	}
+	xs = split255(s)
+	if len(xs) != 3 || xs[2] != "a" {
+		t.Errorf("failure to split 510 char long string: %d", len(xs))
+	}
+}
+
+func TestGroup(t *testing.T) {
+	// Key are in the wrong order, but for this test it does not matter.
+	sx := Group(
+		[]Service{
+			{Host: "127.0.0.1", Group: "g1", Key: "b/sub/dom1/skydns/test"},
+			{Host: "127.0.0.2", Group: "g2", Key: "a/dom1/skydns/test"},
+		},
+	)
+	// Expecting to return the shortest key with a Group attribute.
+	if len(sx) != 1 {
+		t.Fatalf("failure to group zeroth set: %v", sx)
+	}
+	if sx[0].Key != "a/dom1/skydns/test" {
+		t.Fatalf("failure to group zeroth set: %v, wrong Key", sx)
+	}
+
+	// Groups disagree, so we will not do anything.
+	sx = Group(
+		[]Service{
+			{Host: "server1", Group: "g1", Key: "region1/skydns/test"},
+			{Host: "server2", Group: "g2", Key: "region1/skydns/test"},
+		},
+	)
+	if len(sx) != 2 {
+		t.Fatalf("failure to group first set: %v", sx)
+	}
+
+	// Group is g1, include only the top-level one.
+	sx = Group(
+		[]Service{
+			{Host: "server1", Group: "g1", Key: "a/dom/region1/skydns/test"},
+			{Host: "server2", Group: "g2", Key: "a/subdom/dom/region1/skydns/test"},
+		},
+	)
+	if len(sx) != 1 {
+		t.Fatalf("failure to group second set: %v", sx)
+	}
+
+	// Groupless services must be included.
+	sx = Group(
+		[]Service{
+			{Host: "server1", Group: "g1", Key: "a/dom/region1/skydns/test"},
+			{Host: "server2", Group: "g2", Key: "a/subdom/dom/region1/skydns/test"},
+			{Host: "server2", Group: "", Key: "b/subdom/dom/region1/skydns/test"},
+		},
+	)
+	if len(sx) != 2 {
+		t.Fatalf("failure to group third set: %v", sx)
+	}
+
+	// Empty group on the highest level: include that one also.
+	sx = Group(
+		[]Service{
+			{Host: "server1", Group: "g1", Key: "a/dom/region1/skydns/test"},
+			{Host: "server1", Group: "", Key: "b/dom/region1/skydns/test"},
+			{Host: "server2", Group: "g2", Key: "a/subdom/dom/region1/skydns/test"},
+		},
+	)
+	if len(sx) != 2 {
+		t.Fatalf("failure to group fourth set: %v", sx)
+	}
+
+	// Empty group on the highest level: include that one also, and the rest.
+	sx = Group(
+		[]Service{
+			{Host: "server1", Group: "g5", Key: "a/dom/region1/skydns/test"},
+			{Host: "server1", Group: "", Key: "b/dom/region1/skydns/test"},
+			{Host: "server2", Group: "g5", Key: "a/subdom/dom/region1/skydns/test"},
+		},
+	)
+	if len(sx) != 3 {
+		t.Fatalf("failure to group fith set: %v", sx)
+	}
+
+	// One group.
+	sx = Group(
+		[]Service{
+			{Host: "server1", Group: "g6", Key: "a/dom/region1/skydns/test"},
+		},
+	)
+	if len(sx) != 1 {
+		t.Fatalf("failure to group sixth set: %v", sx)
+	}
+
+	// No group, once service
+	sx = Group(
+		[]Service{
+			{Host: "server1", Key: "a/dom/region1/skydns/test"},
+		},
+	)
+	if len(sx) != 1 {
+		t.Fatalf("failure to group seventh set: %v", sx)
+	}
+}