Add a caching channel factory.

src/Lib/CachedChannelFactory.cs

@@ -0,0 +1,97 @@
+// Copyright 2019 Google LLC
+//
+// 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.
+
+using Google.Ads.GoogleAds.Config;
+using Grpc.Auth;
+using Grpc.Core;
+using System;
+using System.Collections.Generic;
+
+namespace Google.Ads.GoogleAds.Lib
+{
+    /// <summary>
+    /// A channel factory that uses internal caching when possible.
+    /// </summary>
+    internal class CachedChannelFactory
+    {
+        /// <summary>
+        /// The cache to store existing channels.
+        /// </summary>
+        private static Dictionary<string, Channel> cache = new Dictionary<string, Channel>();
+
+
+        /// <summary>
+        /// Gets the channel for the specified configuration.
+        /// </summary>
+        /// <param name="config">The configuration.</param>
+        /// <returns>The channel.</returns>
+        internal static Channel GetChannel(GoogleAdsConfig config)
+        {
+            Channel retval = null;
+
+            // Channels with unique (credentials, Url) combination should be unique.
+            string key = string.Join("~", new object[] {
+                config.OAuth2Mode,
+                config.OAuth2ClientId,
+                config.OAuth2ClientSecret,
+                config.OAuth2RefreshToken,
+                config.OAuth2PrivateKey,
+                config.OAuth2PrnEmail,
+                config.ServerUrl
+            });
+
+            lock (cache)
+            {
+                if (cache.ContainsKey(key))
+                {
+                    retval = cache[key];
+                    if (retval.State == ChannelState.Shutdown)
+                    {
+                        // If the channel is shut down, then remove it from cache.
+                        lock (cache)
+                        {
+                            cache.Remove(key);
+                            retval = null;
+                        }
+                    }
+                }
+
+                if (retval == null)
+                {
+                    // Create a new channel.
+                    lock (cache)
+                    {
+                        retval = CreateChannel(config);
+                        cache[key] = retval;
+                    }
+                }
+            }
+
+            return retval;
+        }
+
+        /// <summary>
+        /// Creates the channel.
+        /// </summary>
+        /// <param name="config">The configuration.</param>
+        /// <returns>The channel.</returns>
+        private static Channel CreateChannel(GoogleAdsConfig config)
+        {
+            ChannelCredentials channelCredentials =
+                GoogleGrpcCredentials.ToChannelCredentials(config.Credentials);
+            Uri uri = new Uri(config.ServerUrl);
+            return new Channel(uri.Host, uri.Port, channelCredentials);
+        }
+    }
+}