Add default namespace to client

Adds a default namespace to the client.
Intercepts client requests to add namespace to context.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

grpc.go

@@ -0,0 +1,35 @@
+package containerd
+
+import (
+	"github.com/containerd/containerd/namespaces"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+)
+
+type namespaceInterceptor struct {
+	namespace string
+}
+
+func (ni namespaceInterceptor) unary(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+	_, ok := namespaces.Namespace(ctx)
+	if !ok {
+		ctx = namespaces.WithNamespace(ctx, ni.namespace)
+	}
+	return invoker(ctx, method, req, reply, cc, opts...)
+}
+
+func (ni namespaceInterceptor) stream(ctx context.Context, desc *grpc.StreamDesc, cc *grpc.ClientConn, method string, streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream, error) {
+	_, ok := namespaces.Namespace(ctx)
+	if !ok {
+		ctx = namespaces.WithNamespace(ctx, ni.namespace)
+	}
+
+	return streamer(ctx, desc, cc, method, opts...)
+}
+
+func newNSInterceptors(ns string) (grpc.UnaryClientInterceptor, grpc.StreamClientInterceptor) {
+	ni := namespaceInterceptor{
+		namespace: ns,
+	}
+	return grpc.UnaryClientInterceptor(ni.unary), grpc.StreamClientInterceptor(ni.stream)
+}