core: permanently store authority at channel creation (#4886)

Getting the authority must not rely on the name resolver being
non-null, because that can trivially happen if the channel is shut
down.

core/src/main/java/io/grpc/internal/ManagedChannelImpl.java

@@ -576,7 +576,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
     this.retryEnabled = builder.retryEnabled && !builder.temporarilyDisableRetry;
     serviceConfigInterceptor = new ServiceConfigInterceptor(
         retryEnabled, builder.maxRetryAttempts, builder.maxHedgedAttempts);
-    Channel channel = new RealChannel();
+    Channel channel = new RealChannel(nameResolver.getServiceAuthority());
     channel = ClientInterceptors.intercept(channel, serviceConfigInterceptor);
     if (builder.binlog != null) {
       channel = builder.binlog.wrapChannel(channel);
@@ -810,6 +810,14 @@ final class ManagedChannelImpl extends ManagedChannel implements
   }
 
   private class RealChannel extends Channel {
+    // Set when the NameResolver is initially created. When we create a new NameResolver for the
+    // same target, the new instance must have the same value.
+    private final String authority;
+
+    private RealChannel(String authority) {
+      this.authority =  checkNotNull(authority, "authority");
+    }
+
     @Override
     public <ReqT, RespT> ClientCall<ReqT, RespT> newCall(MethodDescriptor<ReqT, RespT> method,
         CallOptions callOptions) {
@@ -828,8 +836,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
 
     @Override
     public String authority() {
-      String authority = nameResolver.getServiceAuthority();
-      return checkNotNull(authority, "authority");
+      return authority;
     }
   }
 

core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java

@@ -2801,6 +2801,14 @@ public class ManagedChannelImplTest {
     mychannel.shutdownNow();
   }
 
+  @Test
+  public void getAuthorityAfterShutdown() throws Exception {
+    createChannel();
+    assertEquals(SERVICE_NAME, channel.authority());
+    channel.shutdownNow().awaitTermination(1, TimeUnit.SECONDS);
+    assertEquals(SERVICE_NAME, channel.authority());
+  }
+
   private static final class ChannelBuilder
       extends AbstractManagedChannelImplBuilder<ChannelBuilder> {