plugin/metadata: some cleanups (#1906)

* plugin/metadata: some cleanups

Name to provider.go as that's what being defined right now in the file.
Use request.Request because that's done in variables.go anyway. Name the
main storage M, because there is no further meaning behind.

Remove superfluous methods

Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix test

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/metadata/metadata.go

@@ -24,15 +24,16 @@ func (m *Metadata) Name() string { return "metadata" }
 // ServeDNS implements the plugin.Handler interface.
 func (m *Metadata) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
 
-	md, ctx := newMD(ctx)
+	ctx = context.WithValue(ctx, metadataKey{}, M{})
+	md, _ := FromContext(ctx)
 
 	state := request.Request{W: w, Req: r}
 	if plugin.Zones(m.Zones).Matches(state.Name()) != "" {
-		// Go through all Providers and collect metadata
+		// Go through all Providers and collect metadata.
 		for _, provider := range m.Providers {
 			for _, varName := range provider.MetadataVarNames() {
-				if val, ok := provider.Metadata(ctx, w, r, varName); ok {
-					md.setValue(varName, val)
+				if val, ok := provider.Metadata(ctx, state, varName); ok {
+					md.SetValue(varName, val)
 				}
 			}
 		}
@@ -47,8 +48,8 @@ func (m *Metadata) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Ms
 func (m *Metadata) MetadataVarNames() []string { return variables.All }
 
 // Metadata implements the plugin.Provider interface.
-func (m *Metadata) Metadata(ctx context.Context, w dns.ResponseWriter, r *dns.Msg, varName string) (interface{}, bool) {
-	if val, err := variables.GetValue(varName, w, r); err == nil {
+func (m *Metadata) Metadata(ctx context.Context, state request.Request, varName string) (interface{}, bool) {
+	if val, err := variables.GetValue(state, varName); err == nil {
 		return val, true
 	}
 	return nil, false

plugin/metadata/metadata_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
 )
@@ -20,12 +21,12 @@ func (m testProvider) MetadataVarNames() []string {
 	return keys
 }
 
-func (m testProvider) Metadata(ctx context.Context, w dns.ResponseWriter, r *dns.Msg, key string) (val interface{}, ok bool) {
+func (m testProvider) Metadata(ctx context.Context, state request.Request, key string) (val interface{}, ok bool) {
 	value, ok := m[key]
 	return value, ok
 }
 
-// testHandler implements plugin.Handler
+// testHandler implements plugin.Handler.
 type testHandler struct{ ctx context.Context }
 
 func (m *testHandler) Name() string { return "testHandler" }
@@ -35,7 +36,7 @@ func (m *testHandler) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns
 	return 0, nil
 }
 
-func TestMetadataServDns(t *testing.T) {
+func TestMetadataServeDNS(t *testing.T) {
 	expectedMetadata := []testProvider{
 		testProvider{"testkey1": "testvalue1"},
 		testProvider{"testkey2": 2, "testkey3": "testvalue3"},
@@ -45,9 +46,8 @@ func TestMetadataServDns(t *testing.T) {
 	for _, e := range expectedMetadata {
 		providers = append(providers, e)
 	}
-	// Fake handler which stores the resulting context
-	next := &testHandler{}
 
+	next := &testHandler{} // fake handler which stores the resulting context
 	metadata := Metadata{
 		Zones:     []string{"."},
 		Providers: providers,

plugin/metadata/provider.go

@@ -3,7 +3,7 @@ package metadata
 import (
 	"context"
 
-	"github.com/miekg/dns"
+	"github.com/coredns/coredns/request"
 )
 
 // Provider interface needs to be implemented by each plugin willing to provide
@@ -16,38 +16,32 @@ type Provider interface {
 	// Metadata is expected to return a value with metadata information by the key
 	// from 4th argument. Value can be later retrieved from context by any other plugin.
 	// If value is not available by some reason returned boolean value should be false.
-	Metadata(context.Context, dns.ResponseWriter, *dns.Msg, string) (interface{}, bool)
+	Metadata(ctx context.Context, state request.Request, variable string) (interface{}, bool)
 }
 
-// MD is metadata information storage
-type MD map[string]interface{}
+// M is metadata information storage.
+type M map[string]interface{}
 
-// metadataKey defines the type of key that is used to save metadata into the context
-type metadataKey struct{}
-
-// newMD initializes MD and attaches it to context
-func newMD(ctx context.Context) (MD, context.Context) {
-	m := MD{}
-	return m, context.WithValue(ctx, metadataKey{}, m)
-}
-
-// FromContext retrieves MD struct from context.
-func FromContext(ctx context.Context) (md MD, ok bool) {
+// FromContext retrieves the metadata from the context.
+func FromContext(ctx context.Context) (M, bool) {
 	if metadata := ctx.Value(metadataKey{}); metadata != nil {
-		if md, ok := metadata.(MD); ok {
-			return md, true
+		if m, ok := metadata.(M); ok {
+			return m, true
 		}
 	}
-	return MD{}, false
+	return M{}, false
 }
 
 // Value returns metadata value by key.
-func (m MD) Value(key string) (value interface{}, ok bool) {
+func (m M) Value(key string) (value interface{}, ok bool) {
 	value, ok = m[key]
 	return value, ok
 }
 
-// setValue adds metadata value.
-func (m MD) setValue(key string, val interface{}) {
+// SetValue sets the metadata value under key.
+func (m M) SetValue(key string, val interface{}) {
 	m[key] = val
 }
+
+// metadataKey defines the type of key that is used to save metadata into the context.
+type metadataKey struct{}

plugin/metadata/provider_test.go

@@ -25,23 +25,24 @@ func TestMD(t *testing.T) {
 
 	// Using one same md and ctx for all test cases
 	ctx := context.TODO()
-	md, ctx := newMD(ctx)
+	ctx = context.WithValue(ctx, metadataKey{}, M{})
+	m, _ := FromContext(ctx)
 
 	for i, tc := range tests {
 		for k, v := range tc.addValues {
-			md.setValue(k, v)
+			m.SetValue(k, v)
 		}
-		if !reflect.DeepEqual(tc.expectedValues, map[string]interface{}(md)) {
-			t.Errorf("Test %d: Expected %v but got %v", i, tc.expectedValues, md)
+		if !reflect.DeepEqual(tc.expectedValues, map[string]interface{}(m)) {
+			t.Errorf("Test %d: Expected %v but got %v", i, tc.expectedValues, m)
 		}
 
-		// Make sure that MD is recieved from context successfullly
-		mdFromContext, ok := FromContext(ctx)
+		// Make sure that md is recieved from context successfullly
+		mFromContext, ok := FromContext(ctx)
 		if !ok {
-			t.Errorf("Test %d: MD is not recieved from the context", i)
+			t.Errorf("Test %d: md is not recieved from the context", i)
 		}
-		if !reflect.DeepEqual(md, mdFromContext) {
-			t.Errorf("Test %d: MD recieved from context differs from initial. Initial: %v, from context: %v", i, md, mdFromContext)
+		if !reflect.DeepEqual(m, mFromContext) {
+			t.Errorf("Test %d: md recieved from context differs from initial. Initial: %v, from context: %v", i, m, mFromContext)
 		}
 	}
 }