namespace: Copy ttrpc metadata before setting header

If there are multiple goroutines calling `namespace.WithNamespace` on a
ctx that already had namespace, there will be a data race when
`withTTRPCNamespaceHeader` calling `MD.Set()`. So we have to copy the md
before using it.

Signed-off-by: Li Yuxuan <[email protected]>

namespaces/ttrpc.go

@@ -27,10 +27,20 @@ const (
 	TTRPCHeader = "containerd-namespace-ttrpc"
 )
 
+func copyMetadata(src ttrpc.MD) ttrpc.MD {
+	md := ttrpc.MD{}
+	for k, v := range src {
+		md[k] = append(md[k], v...)
+	}
+	return md
+}
+
 func withTTRPCNamespaceHeader(ctx context.Context, namespace string) context.Context {
 	md, ok := ttrpc.GetMetadata(ctx)
 	if !ok {
 		md = ttrpc.MD{}
+	} else {
+		md = copyMetadata(md)
 	}
 	md.Set(TTRPCHeader, namespace)
 	return ttrpc.WithMetadata(ctx, md)

namespaces/ttrpc_test.go

@@ -0,0 +1,52 @@
+/*
+   Copyright The containerd 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 namespaces
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"github.com/containerd/ttrpc"
+)
+
+func TestCopyTTRPCMetadata(t *testing.T) {
+	src := ttrpc.MD{}
+	src.Set("key", "a", "b", "c", "d")
+	md := copyMetadata(src)
+
+	if !reflect.DeepEqual(src, md) {
+		t.Fatalf("metadata is copied incorrectly")
+	}
+
+	slice, _ := src.Get("key")
+	slice[0] = "z"
+	if reflect.DeepEqual(src, md) {
+		t.Fatalf("metadata is copied incorrectly")
+	}
+}
+
+func TestTTRPCNamespaceHeader(t *testing.T) {
+	ctx := context.Background()
+	namespace := "test-namepace"
+	ctx = withTTRPCNamespaceHeader(ctx, namespace)
+
+	header, ok := fromTTRPCHeader(ctx)
+	if !ok || header != namespace {
+		t.Fatalf("ttrp namespace header is set incorrectly")
+	}
+}