Move namespaces to pkg/namespaces

Signed-off-by: Derek McGowan <derek@mcg.dev>

pkg/namespaces/grpc.go

@@ -0,0 +1,61 @@
+/*
+   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"
+
+	"google.golang.org/grpc/metadata"
+)
+
+const (
+	// GRPCHeader defines the header name for specifying a containerd namespace.
+	GRPCHeader = "containerd-namespace"
+)
+
+// NOTE(stevvooe): We can stub this file out if we don't want a grpc dependency here.
+
+func withGRPCNamespaceHeader(ctx context.Context, namespace string) context.Context {
+	// also store on the grpc headers so it gets picked up by any clients that
+	// are using this.
+	nsheader := metadata.Pairs(GRPCHeader, namespace)
+	md, ok := metadata.FromOutgoingContext(ctx) // merge with outgoing context.
+	if !ok {
+		md = nsheader
+	} else {
+		// order ensures the latest is first in this list.
+		md = metadata.Join(nsheader, md)
+	}
+
+	return metadata.NewOutgoingContext(ctx, md)
+}
+
+func fromGRPCHeader(ctx context.Context) (string, bool) {
+	// try to extract for use in grpc servers.
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		// TODO(stevvooe): Check outgoing context?
+		return "", false
+	}
+
+	values := md[GRPCHeader]
+	if len(values) == 0 {
+		return "", false
+	}
+
+	return values[0], true
+}