[Java]: add a means for a custom appVersion validation scheme to be u…

…sed for appVersion compatibility checking.

aeron-cluster/src/main/java/io/aeron/cluster/AppVersionValidator.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2014-2022 Real Logic Limited.
+ *
+ * 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
+ *
+ * https://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.aeron.cluster;
+
+import org.agrona.SemanticVersion;
+
+/**
+ * Class to be used for determining AppVersion compatibility.
+ *
+ * Default is to use {@link org.agrona.SemanticVersion} semantics for check.
+ */
+public class AppVersionValidator
+{
+    /**
+     * Check version compatibility between configured context appVersion and appVersion in
+     * new leadership term or snapshot.
+     *
+     * @param contextAppVersion configured appVersion value from context.
+     * @param appVersionUnderTest to check against configured appVersion.
+     * @return true for compatible or false for not compatible.
+     */
+    public boolean isVersionCompatible(final int contextAppVersion, final int appVersionUnderTest)
+    {
+        return SemanticVersion.major(contextAppVersion) == SemanticVersion.major(appVersionUnderTest);
+    }
+}

aeron-cluster/src/main/java/io/aeron/cluster/ConsensusModule.java

@@ -1295,6 +1295,7 @@ public static final class Context implements Cloneable
         private LogPublisher logPublisher;
         private EgressPublisher egressPublisher;
         private DutyCycleTracker dutyCycleTracker;
+        private AppVersionValidator appVersionValidator;
         private boolean isLogMdc;
 
         /**
@@ -1354,6 +1355,11 @@ public void conclude()
                 epochClock = SystemEpochClock.INSTANCE;
             }
 
+            if (null == appVersionValidator)
+            {
+                appVersionValidator = new AppVersionValidator();
+            }
+
             if (null == clusterTimeConsumerSupplier)
             {
                 clusterTimeConsumerSupplier = (ctx) -> (timestamp) -> {};
@@ -1696,6 +1702,32 @@ public int appVersion()
             return appVersion;
         }
 
+        /**
+         * User assigned application version validator implementation used to check version compatibility.
+         *
+         * The default validator uses {@link org.agrona.SemanticVersion} semantics.
+         *
+         * @param appVersionValidator for user application.
+         * @return this for fluent API.
+         */
+        public Context appVersionValidator(final AppVersionValidator appVersionValidator)
+        {
+            this.appVersionValidator = appVersionValidator;
+            return this;
+        }
+
+        /**
+         * User assigned application version validator implementation used to check version compatibility.
+         *
+         * The default validator uses {@link org.agrona.SemanticVersion} semantics.
+         *
+         * @return AppVersionValidator in use.
+         */
+        public AppVersionValidator appVersionValidator()
+        {
+            return appVersionValidator;
+        }
+
         /**
          * Get level at which files should be sync'ed to disk.
          * <ul>

aeron-cluster/src/main/java/io/aeron/cluster/ConsensusModuleAgent.java

@@ -700,7 +700,7 @@ void onNewLeadershipTerm(
             appVersion,
             isStartup);
 
-        if (SemanticVersion.major(ctx.appVersion()) != SemanticVersion.major(appVersion))
+        if (!ctx.appVersionValidator().isVersionCompatible(ctx.appVersion(), appVersion))
         {
             ctx.errorHandler().onError(new ClusterException(
                 "incompatible version: " + SemanticVersion.toString(ctx.appVersion()) +
@@ -1324,7 +1324,7 @@ void onReplayNewLeadershipTermEvent(
             unexpectedTermination();
         }
 
-        if (SemanticVersion.major(ctx.appVersion()) != SemanticVersion.major(appVersion))
+        if (!ctx.appVersionValidator().isVersionCompatible(ctx.appVersion(), appVersion))
         {
             ctx.countedErrorHandler().onError(new ClusterException(
                 "incompatible version: " + SemanticVersion.toString(ctx.appVersion()) +
@@ -2708,7 +2708,7 @@ private void loadSnapshot(final RecordingLog.Snapshot snapshot, final AeronArchi
             }
 
             final int appVersion = snapshotLoader.appVersion();
-            if (SemanticVersion.major(ctx.appVersion()) != SemanticVersion.major(appVersion))
+            if (!ctx.appVersionValidator().isVersionCompatible(ctx.appVersion(), appVersion))
             {
                 throw new ClusterException(
                     "incompatible version: " + SemanticVersion.toString(ctx.appVersion()) +

aeron-cluster/src/main/java/io/aeron/cluster/service/ClusteredServiceAgent.java

@@ -468,7 +468,7 @@ void onNewLeadershipTermEvent(
         final TimeUnit timeUnit,
         final int appVersion)
     {
-        if (SemanticVersion.major(ctx.appVersion()) != SemanticVersion.major(appVersion))
+        if (!ctx.appVersionValidator().isVersionCompatible(ctx.appVersion(), appVersion))
         {
             ctx.errorHandler().onError(new ClusterException(
                 "incompatible version: " + SemanticVersion.toString(ctx.appVersion()) +
@@ -807,7 +807,7 @@ private void loadState(final Image image, final AeronArchive archive)
         }
 
         final int appVersion = snapshotLoader.appVersion();
-        if (SemanticVersion.major(ctx.appVersion()) != SemanticVersion.major(appVersion))
+        if (!ctx.appVersionValidator().isVersionCompatible(ctx.appVersion(), appVersion))
         {
             throw new ClusterException(
                 "incompatible app version: " + SemanticVersion.toString(ctx.appVersion()) +

aeron-cluster/src/main/java/io/aeron/cluster/service/ClusteredServiceContainer.java

@@ -17,6 +17,7 @@
 
 import io.aeron.*;
 import io.aeron.archive.client.AeronArchive;
+import io.aeron.cluster.AppVersionValidator;
 import io.aeron.cluster.client.ClusterException;
 import io.aeron.cluster.codecs.mark.ClusterComponentType;
 import io.aeron.cluster.codecs.mark.MarkFileHeaderEncoder;
@@ -616,6 +617,7 @@ public static final class Context implements Cloneable
         private String aeronDirectoryName = CommonContext.getAeronDirectoryName();
         private Aeron aeron;
         private DutyCycleTracker dutyCycleTracker;
+        private AppVersionValidator appVersionValidator;
         private boolean ownsAeronClient;
 
         private ClusteredService clusteredService;
@@ -666,6 +668,11 @@ public void conclude()
                 idleStrategySupplier = Configuration.idleStrategySupplier(null);
             }
 
+            if (null == appVersionValidator)
+            {
+                appVersionValidator = new AppVersionValidator();
+            }
+
             if (null == epochClock)
             {
                 epochClock = SystemEpochClock.INSTANCE;
@@ -832,6 +839,32 @@ public int appVersion()
             return appVersion;
         }
 
+        /**
+         * User assigned application version validator implementation used to check version compatibility.
+         *
+         * The default validator uses {@link org.agrona.SemanticVersion} semantics.
+         *
+         * @param appVersionValidator for user application.
+         * @return this for fluent API.
+         */
+        public Context appVersionValidator(final AppVersionValidator appVersionValidator)
+        {
+            this.appVersionValidator = appVersionValidator;
+            return this;
+        }
+
+        /**
+         * User assigned application version validator implementation used to check version compatibility.
+         *
+         * The default validator uses {@link org.agrona.SemanticVersion} semantics.
+         *
+         * @return AppVersionValidator in use.
+         */
+        public AppVersionValidator appVersionValidator()
+        {
+            return appVersionValidator;
+        }
+
         /**
          * Set the id for this cluster instance. This must match with the Consensus Module.
          *