netty: prepare NettySocketSupport for internal import (#4311)

Delegate the actual heavy lifting to a helper class that can be easily swapped
at runtime.

3 files changed, 62 insertions, 13 deletions

diff --git a/netty/src/main/java/io/grpc/netty/InternalNettySocketSupport.java b/netty/src/main/java/io/grpc/netty/InternalNettySocketSupport.java
new file mode 100644
index 000000000..069fc3fb3
--- /dev/null
+++ b/netty/src/main/java/io/grpc/netty/InternalNettySocketSupport.java
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2018, gRPC Authors All rights reserved.
+ *
+ * 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 io.grpc.netty;
+
+import io.grpc.Internal;
+
+/**
+ * An internal accessor. Do not use.
+ */
+@Internal
+public final class InternalNettySocketSupport {
+
+  public interface InternalHelper extends NettySocketSupport.Helper { }
+
+  public static void setHelper(InternalHelper helper) {
+    NettySocketSupport.setHelper(helper);
+  }
+
+  private InternalNettySocketSupport() {}
+}
diff --git a/netty/src/main/java/io/grpc/netty/NettySocketSupport.java b/netty/src/main/java/io/grpc/netty/NettySocketSupport.java
index 597927b6f..e4de364a8 100644
--- a/netty/src/main/java/io/grpc/netty/NettySocketSupport.java
+++ b/netty/src/main/java/io/grpc/netty/NettySocketSupport.java
@@ -20,7 +20,6 @@ import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableMap;
 import io.grpc.internal.Channelz.TcpInfo;
 import io.netty.channel.Channel;
-import java.util.HashMap;
 import java.util.Map;
 import javax.annotation.Nullable;
 
@@ -28,22 +27,22 @@ import javax.annotation.Nullable;
  * An class for getting low level socket info.
  */
 final class NettySocketSupport {
+  private static volatile Helper INSTANCE = new NettySocketHelperImpl();
 
-  /**
-   * Returns the info on the socket if possible. Returns null if the info can not be discovered.
-   */
-  @Nullable
-  public static NativeSocketOptions getNativeSocketOptions(Channel ch) {
-    // TODO(zpencer): if netty-epoll, use reflection to call EpollSocketChannel.tcpInfo()
-    // And/or if some other low level socket support library is available, call it now.
-    return null;
+  interface Helper {
+    /**
+     * Returns the info on the socket if possible. Returns null if the info can not be discovered.
+     */
+    @Nullable
+    NativeSocketOptions getNativeSocketOptions(Channel ch);
   }
 
   /**
    * A TcpInfo and additional other info that will be turned into channelz socket options.
    */
   public static final class NativeSocketOptions {
-    @Nullable public final TcpInfo tcpInfo;
+    @Nullable
+    public final TcpInfo tcpInfo;
     public final ImmutableMap<String, String> otherInfo;
 
     /** Creates an instance. */
@@ -52,9 +51,24 @@ final class NettySocketSupport {
         Map<String, String> otherInfo) {
       Preconditions.checkNotNull(otherInfo);
       this.tcpInfo = tcpInfo;
-      this.otherInfo = ImmutableMap.copyOf(new HashMap<String, String>(otherInfo));
+      this.otherInfo = ImmutableMap.copyOf(otherInfo);
     }
   }
 
-  private NettySocketSupport() {}
+  public static NativeSocketOptions getNativeSocketOptions(Channel ch) {
+    return INSTANCE.getNativeSocketOptions(ch);
+  }
+
+  static void setHelper(Helper helper) {
+    INSTANCE = Preconditions.checkNotNull(helper);
+  }
+
+  private static final class NettySocketHelperImpl implements Helper {
+    @Override
+    public NativeSocketOptions getNativeSocketOptions(Channel ch) {
+      // TODO(zpencer): if netty-epoll, use reflection to call EpollSocketChannel.tcpInfo()
+      // And/or if some other low level socket support library is available, call it now.
+      return null;
+    }
+  }
 }
diff --git a/netty/src/main/java/io/grpc/netty/Utils.java b/netty/src/main/java/io/grpc/netty/Utils.java
index fc2203c9c..abd3c5dd4 100644
--- a/netty/src/main/java/io/grpc/netty/Utils.java
+++ b/netty/src/main/java/io/grpc/netty/Utils.java
@@ -237,7 +237,8 @@ class Utils {
       b.addOption(key.name(), String.valueOf(value));
     }
 
-    NativeSocketOptions nativeOptions = NettySocketSupport.getNativeSocketOptions(channel);
+    NativeSocketOptions nativeOptions
+        = NettySocketSupport.getNativeSocketOptions(channel);
     if (nativeOptions != null) {
       b.setTcpInfo(nativeOptions.tcpInfo); // may be null
       for (Entry<String, String> entry : nativeOptions.otherInfo.entrySet()) {