Update federation target to etcd/clientv3 (#6119)

With CoreDNS now supporting etcdv3 as the DNS backend, we
can update our federation target to etcdv3. Users will now be
able to use etcdv3 server as the federation backbone.

Minio will update bucket data to etcdv3 and CoreDNS can pick
that data up and serve it as bucket style DNS path.

vendor/github.com/golang/protobuf/proto/message_set.go

@@ -42,6 +42,7 @@ import (
 	"fmt"
 	"reflect"
 	"sort"
+	"sync"
 )
 
 // errNoMessageTypeID occurs when a protocol buffer does not have a message type ID.
@@ -94,10 +95,7 @@ func (ms *messageSet) find(pb Message) *_MessageSet_Item {
 }
 
 func (ms *messageSet) Has(pb Message) bool {
-	if ms.find(pb) != nil {
-		return true
-	}
-	return false
+	return ms.find(pb) != nil
 }
 
 func (ms *messageSet) Unmarshal(pb Message) error {
@@ -150,46 +148,42 @@ func skipVarint(buf []byte) []byte {
 // MarshalMessageSet encodes the extension map represented by m in the message set wire format.
 // It is called by generated Marshal methods on protocol buffer messages with the message_set_wire_format option.
 func MarshalMessageSet(exts interface{}) ([]byte, error) {
-	var m map[int32]Extension
+	return marshalMessageSet(exts, false)
+}
+
+// marshaMessageSet implements above function, with the opt to turn on / off deterministic during Marshal.
+func marshalMessageSet(exts interface{}, deterministic bool) ([]byte, error) {
 	switch exts := exts.(type) {
 	case *XXX_InternalExtensions:
-		if err := encodeExtensions(exts); err != nil {
-			return nil, err
-		}
-		m, _ = exts.extensionsRead()
+		var u marshalInfo
+		siz := u.sizeMessageSet(exts)
+		b := make([]byte, 0, siz)
+		return u.appendMessageSet(b, exts, deterministic)
+
 	case map[int32]Extension:
-		if err := encodeExtensionsMap(exts); err != nil {
-			return nil, err
+		// This is an old-style extension map.
+		// Wrap it in a new-style XXX_InternalExtensions.
+		ie := XXX_InternalExtensions{
+			p: &struct {
+				mu           sync.Mutex
+				extensionMap map[int32]Extension
+			}{
+				extensionMap: exts,
+			},
 		}
-		m = exts
+
+		var u marshalInfo
+		siz := u.sizeMessageSet(&ie)
+		b := make([]byte, 0, siz)
+		return u.appendMessageSet(b, &ie, deterministic)
+
 	default:
 		return nil, errors.New("proto: not an extension map")
 	}
-
-	// Sort extension IDs to provide a deterministic encoding.
-	// See also enc_map in encode.go.
-	ids := make([]int, 0, len(m))
-	for id := range m {
-		ids = append(ids, int(id))
-	}
-	sort.Ints(ids)
-
-	ms := &messageSet{Item: make([]*_MessageSet_Item, 0, len(m))}
-	for _, id := range ids {
-		e := m[int32(id)]
-		// Remove the wire type and field number varint, as well as the length varint.
-		msg := skipVarint(skipVarint(e.enc))
-
-		ms.Item = append(ms.Item, &_MessageSet_Item{
-			TypeId:  Int32(int32(id)),
-			Message: msg,
-		})
-	}
-	return Marshal(ms)
 }
 
 // UnmarshalMessageSet decodes the extension map encoded in buf in the message set wire format.
-// It is called by generated Unmarshal methods on protocol buffer messages with the message_set_wire_format option.
+// It is called by Unmarshal methods on protocol buffer messages with the message_set_wire_format option.
 func UnmarshalMessageSet(buf []byte, exts interface{}) error {
 	var m map[int32]Extension
 	switch exts := exts.(type) {
@@ -235,7 +229,15 @@ func MarshalMessageSetJSON(exts interface{}) ([]byte, error) {
 	var m map[int32]Extension
 	switch exts := exts.(type) {
 	case *XXX_InternalExtensions:
-		m, _ = exts.extensionsRead()
+		var mu sync.Locker
+		m, mu = exts.extensionsRead()
+		if m != nil {
+			// Keep the extensions map locked until we're done marshaling to prevent
+			// races between marshaling and unmarshaling the lazily-{en,de}coded
+			// values.
+			mu.Lock()
+			defer mu.Unlock()
+		}
 	case map[int32]Extension:
 		m = exts
 	default:
@@ -253,15 +255,16 @@ func MarshalMessageSetJSON(exts interface{}) ([]byte, error) {
 
 	for i, id := range ids {
 		ext := m[id]
-		if i > 0 {
-			b.WriteByte(',')
-		}
-
 		msd, ok := messageSetMap[id]
 		if !ok {
 			// Unknown type; we can't render it, so skip it.
 			continue
 		}
+
+		if i > 0 && b.Len() > 1 {
+			b.WriteByte(',')
+		}
+
 		fmt.Fprintf(&b, `"[%s]":`, msd.name)
 
 		x := ext.value