plugin/metadata: add metadata plugin (#1894)

* plugin/metadata: add metadata plugin

* plugin/metadata: Add MD struct, refactor code, fix doc

* plugin/metadata: simplify metadata key

* plugin/metadata: improve setup_test

* Support of metadata by rewrite plugin. Move calculated variables to metadata.

* Move variables from metadata to pkg, add UTs, READMEs change, metadata small fixes

* Add client port validation to variables_test

* plugin/metadata: improve README

* plugin/metadata: rename methods

* plugin/metadata: Update Metadataer interface, update doc, cosmetic code changes

* plugin/metadata: move colllisions check to OnStartup(). Fix default variables metadataer.

* plugin/metadata: Fix comment for method setValue

* plugin/metadata: change variables order to fix linter warning

* plugin/metadata: rename Metadataer to Provider

plugin/metadata/setup_test.go

@@ -0,0 +1,70 @@
+package metadata
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+func TestSetup(t *testing.T) {
+	tests := []struct {
+		input     string
+		zones     []string
+		shouldErr bool
+	}{
+		{"metadata", []string{}, false},
+		{"metadata example.com.", []string{"example.com."}, false},
+		{"metadata example.com. net.", []string{"example.com.", "net."}, false},
+
+		{"metadata example.com. { some_param }", []string{}, true},
+		{"metadata\nmetadata", []string{}, true},
+	}
+
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.input)
+		err := setup(c)
+
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %d: Setup call expected error but found none for input %s", i, test.input)
+		}
+
+		if !test.shouldErr && err != nil {
+			t.Errorf("Test %d: Setup call expected no error but found one for input %s. Error was: %v", i, test.input, err)
+		}
+	}
+}
+
+func TestSetupHealth(t *testing.T) {
+	tests := []struct {
+		input     string
+		zones     []string
+		shouldErr bool
+	}{
+		{"metadata", []string{}, false},
+		{"metadata example.com.", []string{"example.com."}, false},
+		{"metadata example.com. net.", []string{"example.com.", "net."}, false},
+
+		{"metadata example.com. { some_param }", []string{}, true},
+		{"metadata\nmetadata", []string{}, true},
+	}
+
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.input)
+		m, err := metadataParse(c)
+
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %d: Expected error but found none for input %s", i, test.input)
+		}
+
+		if !test.shouldErr && err != nil {
+			t.Errorf("Test %d: Expected no error but found one for input %s. Error was: %v", i, test.input, err)
+		}
+
+		if !test.shouldErr && err == nil {
+			if !reflect.DeepEqual(test.zones, m.Zones) {
+				t.Errorf("Test %d: Expected zones %s. Zones were: %v", i, test.zones, m.Zones)
+			}
+		}
+	}
+}