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/google.golang.org/grpc/metadata/metadata.go

@@ -1,38 +1,24 @@
 /*
  *
- * Copyright 2014, Google Inc.
- * All rights reserved.
+ * Copyright 2014 gRPC authors.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
  *
- *     * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above
- * copyright notice, this list of conditions and the following disclaimer
- * in the documentation and/or other materials provided with the
- * distribution.
- *     * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
+ *     http://www.apache.org/licenses/LICENSE-2.0
  *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
  *
  */
 
 // Package metadata define the structure of the metadata supported by gRPC library.
-// Please refer to http://www.grpc.io/docs/guides/wire.html for more information about custom-metadata.
+// Please refer to https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
+// for more information about custom-metadata.
 package metadata // import "google.golang.org/grpc/metadata"
 
 import (
@@ -42,7 +28,9 @@ import (
 	"golang.org/x/net/context"
 )
 
-// DecodeKeyValue returns k, v, nil.  It is deprecated and should not be used.
+// DecodeKeyValue returns k, v, nil.
+//
+// Deprecated: use k and v directly instead.
 func DecodeKeyValue(k, v string) (string, string, error) {
 	return k, v, nil
 }
@@ -51,8 +39,17 @@ func DecodeKeyValue(k, v string) (string, string, error) {
 // two convenience functions New and Pairs to generate MD.
 type MD map[string][]string
 
-// New creates a MD from given key-value map.
-// Keys are automatically converted to lowercase.
+// New creates an MD from a given key-value map.
+//
+// Only the following ASCII characters are allowed in keys:
+//  - digits: 0-9
+//  - uppercase letters: A-Z (normalized to lower)
+//  - lowercase letters: a-z
+//  - special characters: -_.
+// Uppercase letters are automatically converted to lowercase.
+//
+// Keys beginning with "grpc-" are reserved for grpc-internal use only and may
+// result in errors if set in metadata.
 func New(m map[string]string) MD {
 	md := MD{}
 	for k, val := range m {
@@ -64,7 +61,16 @@ func New(m map[string]string) MD {
 
 // Pairs returns an MD formed by the mapping of key, value ...
 // Pairs panics if len(kv) is odd.
-// Keys are automatically converted to lowercase.
+//
+// Only the following ASCII characters are allowed in keys:
+//  - digits: 0-9
+//  - uppercase letters: A-Z (normalized to lower)
+//  - lowercase letters: a-z
+//  - special characters: -_.
+// Uppercase letters are automatically converted to lowercase.
+//
+// Keys beginning with "grpc-" are reserved for grpc-internal use only and may
+// result in errors if set in metadata.
 func Pairs(kv ...string) MD {
 	if len(kv)%2 == 1 {
 		panic(fmt.Sprintf("metadata: Pairs got the odd number of input pairs for metadata: %d", len(kv)))
@@ -91,9 +97,33 @@ func (md MD) Copy() MD {
 	return Join(md)
 }
 
-// Join joins any number of MDs into a single MD.
+// Get obtains the values for a given key.
+func (md MD) Get(k string) []string {
+	k = strings.ToLower(k)
+	return md[k]
+}
+
+// Set sets the value of a given key with a slice of values.
+func (md MD) Set(k string, vals ...string) {
+	if len(vals) == 0 {
+		return
+	}
+	k = strings.ToLower(k)
+	md[k] = vals
+}
+
+// Append adds the values to key k, not overwriting what was already stored at that key.
+func (md MD) Append(k string, vals ...string) {
+	if len(vals) == 0 {
+		return
+	}
+	k = strings.ToLower(k)
+	md[k] = append(md[k], vals...)
+}
+
+// Join joins any number of mds into a single MD.
 // The order of values for each key is determined by the order in which
-// the MDs containing those values are presented to Join.
+// the mds containing those values are presented to Join.
 func Join(mds ...MD) MD {
 	out := MD{}
 	for _, md := range mds {
@@ -107,38 +137,74 @@ func Join(mds ...MD) MD {
 type mdIncomingKey struct{}
 type mdOutgoingKey struct{}
 
-// NewContext is a wrapper for NewOutgoingContext(ctx, md).  Deprecated.
-func NewContext(ctx context.Context, md MD) context.Context {
-	return NewOutgoingContext(ctx, md)
-}
-
 // NewIncomingContext creates a new context with incoming md attached.
 func NewIncomingContext(ctx context.Context, md MD) context.Context {
 	return context.WithValue(ctx, mdIncomingKey{}, md)
 }
 
-// NewOutgoingContext creates a new context with outgoing md attached.
+// NewOutgoingContext creates a new context with outgoing md attached. If used
+// in conjunction with AppendToOutgoingContext, NewOutgoingContext will
+// overwrite any previously-appended metadata.
 func NewOutgoingContext(ctx context.Context, md MD) context.Context {
-	return context.WithValue(ctx, mdOutgoingKey{}, md)
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md})
 }
 
-// FromContext is a wrapper for FromIncomingContext(ctx).  Deprecated.
-func FromContext(ctx context.Context) (md MD, ok bool) {
-	return FromIncomingContext(ctx)
+// AppendToOutgoingContext returns a new context with the provided kv merged
+// with any existing metadata in the context. Please refer to the
+// documentation of Pairs for a description of kv.
+func AppendToOutgoingContext(ctx context.Context, kv ...string) context.Context {
+	if len(kv)%2 == 1 {
+		panic(fmt.Sprintf("metadata: AppendToOutgoingContext got an odd number of input pairs for metadata: %d", len(kv)))
+	}
+	md, _ := ctx.Value(mdOutgoingKey{}).(rawMD)
+	added := make([][]string, len(md.added)+1)
+	copy(added, md.added)
+	added[len(added)-1] = make([]string, len(kv))
+	copy(added[len(added)-1], kv)
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md, added: added})
 }
 
-// FromIncomingContext returns the incoming MD in ctx if it exists.  The
-// returned md should be immutable, writing to it may cause races.
-// Modification should be made to the copies of the returned md.
+// FromIncomingContext returns the incoming metadata in ctx if it exists.  The
+// returned MD should not be modified. Writing to it may cause races.
+// Modification should be made to copies of the returned MD.
 func FromIncomingContext(ctx context.Context) (md MD, ok bool) {
 	md, ok = ctx.Value(mdIncomingKey{}).(MD)
 	return
 }
 
-// FromOutgoingContext returns the outgoing MD in ctx if it exists.  The
-// returned md should be immutable, writing to it may cause races.
-// Modification should be made to the copies of the returned md.
-func FromOutgoingContext(ctx context.Context) (md MD, ok bool) {
-	md, ok = ctx.Value(mdOutgoingKey{}).(MD)
-	return
+// FromOutgoingContextRaw returns the un-merged, intermediary contents
+// of rawMD. Remember to perform strings.ToLower on the keys. The returned
+// MD should not be modified. Writing to it may cause races. Modification
+// should be made to copies of the returned MD.
+//
+// This is intended for gRPC-internal use ONLY.
+func FromOutgoingContextRaw(ctx context.Context) (MD, [][]string, bool) {
+	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
+	if !ok {
+		return nil, nil, false
+	}
+
+	return raw.md, raw.added, true
+}
+
+// FromOutgoingContext returns the outgoing metadata in ctx if it exists.  The
+// returned MD should not be modified. Writing to it may cause races.
+// Modification should be made to copies of the returned MD.
+func FromOutgoingContext(ctx context.Context) (MD, bool) {
+	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
+	if !ok {
+		return nil, false
+	}
+
+	mds := make([]MD, 0, len(raw.added)+1)
+	mds = append(mds, raw.md)
+	for _, vv := range raw.added {
+		mds = append(mds, Pairs(vv...))
+	}
+	return Join(mds...), ok
+}
+
+type rawMD struct {
+	md    MD
+	added [][]string
 }