Add ChannelBase, change client base argument

src/csharp/Grpc.Core.Api/ChannelBase.cs

@@ -0,0 +1,52 @@
+#region Copyright notice and license
+
+// Copyright 2019 The gRPC 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.
+
+#endregion
+
+using System;
+using Grpc.Core.Utils;
+
+namespace Grpc.Core
+{
+    /// <summary>
+    /// Base class for gRPC channel. Channels are an abstraction of long-lived connections to remote servers.
+    /// </summary>
+    public abstract class ChannelBase
+    {
+        private readonly string target;
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="ChannelBase"/> class that connects to a specific host.
+        /// </summary>
+        /// <param name="target">Target of the channel.</param>
+        protected ChannelBase(string target)
+        {
+            this.target = GrpcPreconditions.CheckNotNull(target, nameof(target));
+        }
+
+        /// <summary>The original target used to create the channel.</summary>
+        public string Target
+        {
+            get { return this.target; }
+        }
+
+        /// <summary>
+        /// Create a new <see cref="CallInvoker"/> for the channel.
+        /// </summary>
+        /// <returns>A new <see cref="CallInvoker"/>.</returns>
+        public abstract CallInvoker CreateCallInvoker();
+    }
+}

src/csharp/Grpc.Core/Channel.cs

@@ -30,7 +30,7 @@ namespace Grpc.Core
     /// More client objects can reuse the same channel. Creating a channel is an expensive operation compared to invoking
     /// a remote call so in general you should reuse a single channel for as many calls as possible.
     /// </summary>
-    public class Channel
+    public class Channel : ChannelBase
     {
         static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<Channel>();
 
@@ -38,7 +38,6 @@ namespace Grpc.Core
         readonly AtomicCounter activeCallCounter = new AtomicCounter();
         readonly CancellationTokenSource shutdownTokenSource = new CancellationTokenSource();
 
-        readonly string target;
         readonly GrpcEnvironment environment;
         readonly CompletionQueueSafeHandle completionQueue;
         readonly ChannelSafeHandle handle;
@@ -64,9 +63,8 @@ namespace Grpc.Core
         /// <param name="target">Target of the channel.</param>
         /// <param name="credentials">Credentials to secure the channel.</param>
         /// <param name="options">Channel options.</param>
-        public Channel(string target, ChannelCredentials credentials, IEnumerable<ChannelOption> options)
+        public Channel(string target, ChannelCredentials credentials, IEnumerable<ChannelOption> options) : base(target)
         {
-            this.target = GrpcPreconditions.CheckNotNull(target, "target");
             this.options = CreateOptionsDictionary(options);
             EnsureUserAgentChannelOption(this.options);
             this.environment = GrpcEnvironment.AddRef();
@@ -179,15 +177,6 @@ namespace Grpc.Core
             }
         }
 
-        /// <summary>The original target used to create the channel.</summary>
-        public string Target
-        {
-            get
-            {
-                return this.target;
-            }
-        }
-
         /// <summary>
         /// Returns a token that gets cancelled once <c>ShutdownAsync</c> is invoked.
         /// </summary>
@@ -257,6 +246,15 @@ namespace Grpc.Core
             await GrpcEnvironment.ReleaseAsync().ConfigureAwait(false);
         }
 
+        /// <summary>
+        /// Create a new <see cref="CallInvoker"/> for the channel.
+        /// </summary>
+        /// <returns>A new <see cref="CallInvoker"/>.</returns>
+        public override CallInvoker CreateCallInvoker()
+        {
+            return new DefaultCallInvoker(this);
+        }
+
         internal ChannelSafeHandle Handle
         {
             get

src/csharp/Grpc.Core/ClientBase.cs

@@ -51,7 +51,7 @@ namespace Grpc.Core
         /// Initializes a new instance of <c>ClientBase</c> class.
         /// </summary>
         /// <param name="channel">The channel to use for remote call invocation.</param>
-        public ClientBase(Channel channel) : base(channel)
+        public ClientBase(ChannelBase channel) : base(channel)
         {
         }
 
@@ -113,7 +113,7 @@ namespace Grpc.Core
         /// Initializes a new instance of <c>ClientBase</c> class.
         /// </summary>
         /// <param name="channel">The channel to use for remote call invocation.</param>
-        public ClientBase(Channel channel) : this(new DefaultCallInvoker(channel))
+        public ClientBase(ChannelBase channel) : this(channel.CreateCallInvoker())
         {
         }