From 5cb1e0b342f52a96cbe7f31667d98e999e167230 Mon Sep 17 00:00:00 2001
From: Gyuho Lee <leegyuho@amazon.com>
Date: Mon, 9 Mar 2020 14:35:26 -0700
Subject: [PATCH] clientv3: fix metadata overwrites in "WithRequireLeader"

Signed-off-by: Gyuho Lee <leegyuho@amazon.com>
---
 clientv3/client.go   |  8 -------
 clientv3/ctx.go      | 35 ++++++++++++++++++++++++++++++
 clientv3/ctx_test.go | 51 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+), 8 deletions(-)
 create mode 100644 clientv3/ctx.go
 create mode 100644 clientv3/ctx_test.go

diff --git a/clientv3/client.go b/clientv3/client.go
index ddaed0f66..3a4341b22 100644
--- a/clientv3/client.go
+++ b/clientv3/client.go
@@ -37,7 +37,6 @@ import (
 	"google.golang.org/grpc/codes"
 	grpccredentials "google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/keepalive"
-	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
 )
 
@@ -393,13 +392,6 @@ func (c *Client) dialWithBalancerCreds(ep string) grpccredentials.TransportCrede
 	return creds
 }
 
-// WithRequireLeader requires client requests to only succeed
-// when the cluster has a leader.
-func WithRequireLeader(ctx context.Context) context.Context {
-	md := metadata.Pairs(rpctypes.MetadataRequireLeaderKey, rpctypes.MetadataHasLeader)
-	return metadata.NewOutgoingContext(ctx, md)
-}
-
 func newClient(cfg *Config) (*Client, error) {
 	if cfg == nil {
 		cfg = &Config{}
diff --git a/clientv3/ctx.go b/clientv3/ctx.go
new file mode 100644
index 000000000..c1e8be6fe
--- /dev/null
+++ b/clientv3/ctx.go
@@ -0,0 +1,35 @@
+// Copyright 2020 The etcd Authors
+//
+// 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
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// 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 clientv3
+
+import (
+	"context"
+
+	"go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"
+	"google.golang.org/grpc/metadata"
+)
+
+// WithRequireLeader requires client requests to only succeed
+// when the cluster has a leader.
+func WithRequireLeader(ctx context.Context) context.Context {
+	md, ok := metadata.FromOutgoingContext(ctx)
+	if !ok { // no outgoing metadata ctx key, create one
+		md = metadata.Pairs(rpctypes.MetadataRequireLeaderKey, rpctypes.MetadataHasLeader)
+		return metadata.NewOutgoingContext(ctx, md)
+	}
+	// overwrite/add 'hasleader' key/value
+	md.Set(rpctypes.MetadataRequireLeaderKey, rpctypes.MetadataHasLeader)
+	return metadata.NewOutgoingContext(ctx, md)
+}
diff --git a/clientv3/ctx_test.go b/clientv3/ctx_test.go
new file mode 100644
index 000000000..d87728a98
--- /dev/null
+++ b/clientv3/ctx_test.go
@@ -0,0 +1,51 @@
+// Copyright 2020 The etcd Authors
+//
+// 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
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// 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 clientv3
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"
+	"google.golang.org/grpc/metadata"
+)
+
+func TestMetadataWithRequireLeader(t *testing.T) {
+	ctx := context.TODO()
+	md, ok := metadata.FromOutgoingContext(ctx)
+	if ok {
+		t.Fatal("expected no outgoing metadata ctx key")
+	}
+
+	// add a conflicting key with some other value
+	md = metadata.Pairs(rpctypes.MetadataRequireLeaderKey, "invalid")
+	// add a key, and expect not be overwritten
+	md.Set("hello", "1", "2")
+	ctx = metadata.NewOutgoingContext(ctx, md)
+
+	// expect overwrites but still keep other keys
+	ctx = WithRequireLeader(ctx)
+	md, ok = metadata.FromOutgoingContext(ctx)
+	if !ok {
+		t.Fatal("expected outgoing metadata ctx key")
+	}
+	if ss := md.Get("hasleader"); !reflect.DeepEqual(ss, []string{"true"}) {
+		t.Fatalf("unexpected metadata for 'hasleader' %v", ss)
+	}
+	if ss := md.Get("hello"); !reflect.DeepEqual(ss, []string{"1", "2"}) {
+		t.Fatalf("unexpected metadata for 'hello' %v", ss)
+	}
+}