Extract multiple commit prevention in DNS writers into a base class

This still retains the DnsWriter interface itself for better integration
with Dagger and to preserve the option of having a DNS writer that does
not have this requirement (e.g. because it is idempotent).

This also makes the commit check thread-safe, which is a nice-to-have.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=168451114

java/google/registry/dns/writer/BaseDnsWriter.java

@@ -0,0 +1,36 @@
+// Copyright 2017 The Nomulus 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 google.registry.dns.writer;
+
+import static com.google.common.base.Preconditions.checkState;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * A base implementation of {@link DnsWriter} that protects against multiple calls to commit().
+ */
+public abstract class BaseDnsWriter implements DnsWriter {
+
+  private final AtomicBoolean committedAlready = new AtomicBoolean(false);
+
+  @Override
+  public final void commit() {
+    checkState(committedAlready.compareAndSet(false, true), "commit() has already been called");
+    commitUnchecked();
+  }
+
+  /** Commits DNS updates. This can never be called more than once. */
+  protected abstract void commitUnchecked();
+}

java/google/registry/dns/writer/VoidDnsWriter.java

@@ -14,8 +14,6 @@
 
 package google.registry.dns.writer;
 
-import static com.google.common.base.Preconditions.checkState;
-
 import com.google.common.base.Joiner;
 import java.util.HashSet;
 import java.util.Set;
@@ -27,7 +25,7 @@ import javax.inject.Inject;
  *
  * <p>All this class does is write its displeasure to the logs.
  */
-public final class VoidDnsWriter implements DnsWriter {
+public final class VoidDnsWriter extends BaseDnsWriter {
 
   /**
    * The name of the pricing engine, as used in {@code Registry.dnsWriter}. Remember to change
@@ -37,8 +35,6 @@ public final class VoidDnsWriter implements DnsWriter {
 
   private static final Logger logger = Logger.getLogger(VoidDnsWriter.class.getName());
 
-  private boolean committed = false;
-
   private final Set<String> names = new HashSet<>();
 
   @Inject
@@ -55,10 +51,7 @@ public final class VoidDnsWriter implements DnsWriter {
   }
 
   @Override
-  public void commit() {
-    checkState(!committed, "commit() has already been called");
-    committed = true;
-
+  protected void commitUnchecked() {
     logger.warning("Ignoring DNS zone updates! No DnsWriterFactory implementation specified!\n"
         + Joiner.on('\n').join(names));
   }

java/google/registry/dns/writer/clouddns/CloudDnsWriter.java

@@ -15,7 +15,6 @@
 package google.registry.dns.writer.clouddns;
 
 import static com.google.common.base.Preconditions.checkArgument;
-import static com.google.common.base.Preconditions.checkState;
 import static google.registry.model.EppResourceUtils.loadByForeignKey;
 
 import com.google.api.client.googleapis.json.GoogleJsonError.ErrorInfo;
@@ -33,6 +32,7 @@ import com.google.common.collect.ImmutableSet.Builder;
 import com.google.common.net.InternetDomainName;
 import com.google.common.util.concurrent.RateLimiter;
 import google.registry.config.RegistryConfig.Config;
+import google.registry.dns.writer.BaseDnsWriter;
 import google.registry.dns.writer.DnsWriter;
 import google.registry.dns.writer.DnsWriterZone;
 import google.registry.model.domain.DomainResource;
@@ -59,7 +59,7 @@ import org.joda.time.Duration;
  *
  * @see <a href="https://cloud.google.com/dns/docs/">Google Cloud DNS Documentation</a>
  */
-public class CloudDnsWriter implements DnsWriter {
+public class CloudDnsWriter extends BaseDnsWriter {
 
   /**
    * The name of the pricing engine, as used in {@code Registry.dnsWriter}. Remember to change
@@ -85,8 +85,6 @@ public class CloudDnsWriter implements DnsWriter {
   private final ImmutableMap.Builder<String, ImmutableSet<ResourceRecordSet>>
       desiredRecordsBuilder = new ImmutableMap.Builder<>();
 
-  private boolean committed = false;
-
   @Inject
   CloudDnsWriter(
       Dns dnsConnection,
@@ -273,15 +271,9 @@ public class CloudDnsWriter implements DnsWriter {
    * representation built via this writer.
    */
   @Override
-  public void commit() {
-    checkState(!committed, "commit() has already been called");
-    committed = true;
-    commit(desiredRecordsBuilder.build());
-  }
-
-  @VisibleForTesting
-  void commit(ImmutableMap<String, ImmutableSet<ResourceRecordSet>> desiredRecords) {
-    retrier.callWithRetry(getMutateZoneCallback(desiredRecords), ZoneStateException.class);
+  protected void commitUnchecked() {
+    retrier.callWithRetry(
+        getMutateZoneCallback(desiredRecordsBuilder.build()), ZoneStateException.class);
     logger.info("Wrote to Cloud DNS");
   }
 

java/google/registry/dns/writer/dnsupdate/DnsUpdateWriter.java

@@ -14,7 +14,6 @@
 
 package google.registry.dns.writer.dnsupdate;
 
-import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.base.Verify.verify;
 import static com.google.common.collect.Sets.intersection;
 import static com.google.common.collect.Sets.union;
@@ -26,7 +25,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.net.InternetDomainName;
 import google.registry.config.RegistryConfig.Config;
-import google.registry.dns.writer.DnsWriter;
+import google.registry.dns.writer.BaseDnsWriter;
 import google.registry.dns.writer.DnsWriterZone;
 import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.secdns.DelegationSignerData;
@@ -76,7 +75,7 @@ import org.xbill.DNS.Update;
  * message, as required by RFC 2136. Care must be taken to make sure the SOA serial number does not
  * go backwards if the entire TLD (zone) is "reset" to empty and republished.
  */
-public class DnsUpdateWriter implements DnsWriter {
+public class DnsUpdateWriter extends BaseDnsWriter {
 
   /**
    * The name of the pricing engine, as used in {@code Registry.dnsWriter}. Remember to change
@@ -92,12 +91,12 @@ public class DnsUpdateWriter implements DnsWriter {
   private final Update update;
   private final String zoneName;
 
-  private boolean committed = false;
-
   /**
    * Class constructor.
    *
-   * @param dnsTimeToLive TTL used for any created resource records
+   * @param dnsDefaultATtl TTL used for any created resource records
+   * @param dnsDefaultNsTtl TTL used for any created nameserver records
+   * @param dnsDefaultDsTtl TTL used for any created DS records
    * @param transport the transport used to send/receive the UPDATE messages
    * @param clock a source of time
    */
@@ -168,10 +167,7 @@ public class DnsUpdateWriter implements DnsWriter {
   }
 
   @Override
-  public void commit() {
-    checkState(!committed, "commit() has already been called");
-    committed = true;
-
+  protected void commitUnchecked() {
     try {
       Message response = transport.send(update);
       verify(