Add ttrpc namespace support

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

namespaces/ttrpc.go

@@ -0,0 +1,41 @@
+/*
+   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"
+
+	"github.com/containerd/ttrpc"
+)
+
+const (
+	// TTRPCHeader defines the header name for specifying a containerd namespace
+	TTRPCHeader = "containerd-namespace-ttrpc"
+)
+
+func withTTRPCNamespaceHeader(ctx context.Context, namespace string) context.Context {
+	md, ok := ttrpc.GetMetadata(ctx)
+	if !ok {
+		md = ttrpc.Metadata{}
+	}
+	md.Set(TTRPCHeader, namespace)
+	return ttrpc.WithMetadata(ctx, md)
+}
+
+func fromTTRPCHeader(ctx context.Context) (string, bool) {
+	return ttrpc.GetMetadataValue(ctx, TTRPCHeader)
+}