Add streaming service

Adds a service capable of streaming Any objects bi-directionally.
This can be used by services to send data, received data, or to
initiate requests from server to client.

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

pkg/streaming/streaming.go

@@ -0,0 +1,47 @@
+/*
+   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 streaming
+
+import (
+	"context"
+
+	"github.com/containerd/typeurl"
+)
+
+type StreamManager interface {
+	StreamGetter
+	Register(context.Context, string, Stream) error
+}
+
+type StreamGetter interface {
+	Get(context.Context, string) (Stream, error)
+}
+
+type StreamCreator interface {
+	Create(context.Context, string) (Stream, error)
+}
+
+type Stream interface {
+	// Send sends the object on the stream
+	Send(typeurl.Any) error
+
+	// Recv receives an object on the stream
+	Recv() (typeurl.Any, error)
+
+	// Close closes the stream
+	Close() error
+}