Add server-side communications channel

pkg/analyzer_plugin/lib/channel/channel.dart

Index: pkg/analyzer_plugin/lib/channel/channel.dart
diff --git a/pkg/analyzer_plugin/lib/channel/channel.dart b/pkg/analyzer_plugin/lib/channel/channel.dart
index 44f065efea583a7cd1ed2a5f6be41db134cd6be6..0d385e4f6c55df5e71de767d1c00dcdbd1de8214 100644
--- a/pkg/analyzer_plugin/lib/channel/channel.dart
+++ b/pkg/analyzer_plugin/lib/channel/channel.dart
@@ -5,8 +5,9 @@
 import 'package:analyzer_plugin/protocol/protocol.dart';
 
 /**
- * The object that allows a [ServerPlugin] to receive [Request]s and to return
- * both [Response]s and [Notification]s.
+ * A communication channel that allows a [ServerPlugin] to receive [Request]s
+ * from, and to return both [Response]s and [Notification]s to, an analysis
+ * server.
  *
  * Clients may not extend, implement or mix-in this class.
  */
@@ -36,3 +37,33 @@ abstract class PluginCommunicationChannel {
    */
   void sendResponse(Response response);
 }
+
+/**
+ * A communication channel that allows an analysis server to send [Request]s
+ * to, and to receive both [Response]s and [Notification]s from, a plugin.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class ServerCommunicationChannel {
+  /**
+   * Close the communication channel.
+   */
+  void close();
+
+  /**
+   * Listen to the channel for responses and notifications. If a response is
+   * received, invoke the [onResponse] function. If a notification is received,
+   * invoke the [onNotification] function. If an error is encountered while
+   * trying to read from the socket, invoke the [onError] function. If the
+   * socket is closed by the client, invoke the [onDone] function. Only one

[scheglov, 2017/02/02 18:25:04]

Is "the client" here code that uses ServerCommunicationChannel, or the plugin
this channel is used to talk to?

[Brian Wilkerson, 2017/02/02 18:46:39]

The plugin. I'll fix the wording, thanks.

+   * listener is allowed per channel.
+   */
+  void listen(void onResponse(Response response),
+      void onNotification(Notification notification),
+      {Function onError, void onDone()});
+
+  /**
+   * Send the given [request] to the plugin.
+   */
+  void sendRequest(Request request);
+}