fix: make sure serialized result is deserialize-able

examples/src/main/java/software/amazon/lambda/durable/examples/general/CustomConfigExample.java

@@ -31,6 +31,7 @@
  *   <li>Automatic region detection with fallback to us-east-1 for testing environments
  *   <li>Environment variable credentials provider
  *   <li>Custom SerDes with snake_case property naming
+ *   <li>Optional round-trip validation toggle for performance-sensitive workloads
  * </ul>
  */
 public class CustomConfigExample extends DurableHandler<String, String> {
@@ -68,6 +69,8 @@ protected DurableConfig createConfiguration() {
         return DurableConfig.builder()
                 .withDurableExecutionClient(durableClient)
                 .withSerDes(customSerDes)
+                // Disable the extra deserialize pass if your workload is sensitive to the added validation cost.
+                .withSerializationRoundTripValidation(false)
                 .build();
     }
 

sdk/src/main/java/software/amazon/lambda/durable/DurableConfig.java

@@ -98,6 +98,7 @@ public final class DurableConfig {
     private final LoggerConfig loggerConfig;
     private final PollingStrategy pollingStrategy;
     private final Duration checkpointDelay;
+    private final boolean validateSerializationRoundTrip;
     private final PluginRunner pluginRunner;
 
     private DurableConfig(Builder builder) {
@@ -109,6 +110,7 @@ private DurableConfig(Builder builder) {
         this.loggerConfig = Objects.requireNonNullElseGet(builder.loggerConfig, LoggerConfig::defaults);
         this.pollingStrategy = Objects.requireNonNullElse(builder.pollingStrategy, PollingStrategies.Presets.DEFAULT);
         this.checkpointDelay = Objects.requireNonNullElseGet(builder.checkpointDelay, () -> Duration.ofSeconds(0));
+        this.validateSerializationRoundTrip = builder.validateSerializationRoundTrip;
         this.pluginRunner = builder.plugins.isEmpty() ? PluginRunner.noOp() : new PluginRunner(builder.plugins);
 
         validateConfiguration();
@@ -186,6 +188,19 @@ public Duration getCheckpointDelay() {
         return checkpointDelay;
     }
 
+    /**
+     * Gets whether serialized operation data should be immediately deserialized to verify round-trip compatibility.
+     *
+     * <p>When enabled, the SDK validates serialized operation results and exceptions before checkpointing them. This
+     * catches incompatible SerDes behavior early at the cost of an extra deserialize pass. Defaults to true, and custom
+     * SerDes implementations are still expected to be round-trip safe even if this validation is disabled.
+     *
+     * @return true when round-trip serialization validation is enabled
+     */
+    public boolean shouldValidateSerializationRoundTrip() {
+        return validateSerializationRoundTrip;
+    }
+
     /**
      * Gets the plugin runner that dispatches lifecycle events to registered plugins.
      *
@@ -293,6 +308,7 @@ public static final class Builder {
         private LoggerConfig loggerConfig;
         private PollingStrategy pollingStrategy;
         private Duration checkpointDelay;
+        private boolean validateSerializationRoundTrip = true;
         private List<DurableExecutionPlugin> plugins = new ArrayList<>();
 
         public Builder() {}
@@ -403,6 +419,22 @@ public Builder withCheckpointDelay(Duration duration) {
             return this;
         }
 
+        /**
+         * Controls whether the SDK immediately deserializes serialized results and exceptions to verify they can be
+         * read back before checkpointing.
+         *
+         * <p>This validation is enabled by default. Disable it only to avoid the extra deserialize pass when the
+         * additional safety check is too expensive for your workload. Custom SerDes implementations are still expected
+         * to round-trip SDK-managed values correctly.
+         *
+         * @param validateSerializationRoundTrip true to validate serialized data with an immediate deserialize pass
+         * @return This builder
+         */
+        public Builder withSerializationRoundTripValidation(boolean validateSerializationRoundTrip) {
+            this.validateSerializationRoundTrip = validateSerializationRoundTrip;
+            return this;
+        }
+
         /**
          * Registers one or more plugins for lifecycle event instrumentation.
          *

sdk/src/main/java/software/amazon/lambda/durable/DurableHandler.java

@@ -117,6 +117,7 @@ public DurableConfig getConfiguration() {
      *         .withDurableExecutionClient(durableClient)
      *         .withSerDes(customSerDes)  // Optional: custom SerDes for user data
      *         .withExecutorService(customExecutor)  // Optional: custom thread pool
+     *         .withSerializationRoundTripValidation(false)  // Optional: skip extra validation deserialize pass
      *         .build();
      * }
      * }</pre>

sdk/src/main/java/software/amazon/lambda/durable/operation/ChildContextOperation.java

@@ -149,6 +149,8 @@ private void executeChildContext() {
     }
 
     private void handleChildContextSuccess(T result) {
+        var serialized = serializeResult(result);
+
         if (replayChildren.get() || isVirtual || parentOperation != null && parentOperation.isOperationCompleted()) {
             // Skip checkpointing if
             // - parent ConcurrencyOperation has already completed, preventing race conditions where a child finishes
@@ -159,13 +161,11 @@ private void handleChildContextSuccess(T result) {
             cachedOperationResult.set(DeserializedOperationResult.succeeded(result));
             markAlreadyCompleted();
         } else {
-            checkpointSuccess(result);
+            checkpointSuccess(result, serialized);
         }
     }
 
-    private void checkpointSuccess(T result) {
-        var serialized = serializeResult(result);
-
+    private void checkpointSuccess(T result, String serialized) {
         if (serialized == null || serialized.getBytes(StandardCharsets.UTF_8).length < LARGE_RESULT_THRESHOLD) {
             sendOperationUpdate(
                     OperationUpdate.builder().action(OperationAction.SUCCEED).payload(serialized));

sdk/src/main/java/software/amazon/lambda/durable/operation/SerializableDurableOperation.java

@@ -101,7 +101,11 @@ protected T deserializeResult(String result) {
      * @return the serialized string
      */
     protected String serializeResult(T result) {
-        return resultSerDes.serialize(result);
+        var serialized = resultSerDes.serialize(result);
+        if (shouldValidateSerializationRoundTrip()) {
+            deserializeResult(serialized);
+        }
+        return serialized;
     }
 
     /**
@@ -110,8 +114,18 @@ protected String serializeResult(T result) {
      * @param throwable the exception to serialize
      * @return the serialized error object
      */
+    @SuppressWarnings("ThrowableNotThrown")
     protected ErrorObject serializeException(Throwable throwable) {
-        return ExceptionHelper.buildErrorObject(throwable, resultSerDes);
+        var error = ExceptionHelper.buildErrorObject(throwable, resultSerDes);
+        if (shouldValidateSerializationRoundTrip()) {
+            deserializeException(error);
+        }
+        return error;
+    }
+
+    private boolean shouldValidateSerializationRoundTrip() {
+        var config = getContext().getDurableConfig();
+        return config == null || config.shouldValidateSerializationRoundTrip();
     }
 
     /**

sdk/src/test/java/software/amazon/lambda/durable/DurableConfigTest.java

@@ -87,6 +87,24 @@ void testBuilder_WithCustomExecutorService() {
         assertNotNull(config.getSerDes());
     }
 
+    @Test
+    void testBuilder_SerializationRoundTripValidationDefaultsToTrue() {
+        var config =
+                DurableConfig.builder().withDurableExecutionClient(mockClient).build();
+
+        assertTrue(config.shouldValidateSerializationRoundTrip());
+    }
+
+    @Test
+    void testBuilder_WithSerializationRoundTripValidationDisabled() {
+        var config = DurableConfig.builder()
+                .withDurableExecutionClient(mockClient)
+                .withSerializationRoundTripValidation(false)
+                .build();
+
+        assertFalse(config.shouldValidateSerializationRoundTrip());
+    }
+
     @Test
     void testBuilder_WithAllCustomComponents() {
         var config = DurableConfig.builder()
@@ -131,6 +149,7 @@ void testBuilder_FluentAPI() {
         assertSame(builder, builder.withDurableExecutionClient(mockClient));
         assertSame(builder, builder.withSerDes(mockSerDes));
         assertSame(builder, builder.withExecutorService(mockExecutor));
+        assertSame(builder, builder.withSerializationRoundTripValidation(false));
     }
 
     @Test

sdk/src/test/java/software/amazon/lambda/durable/operation/ChildContextOperationTest.java

@@ -24,16 +24,30 @@
 import software.amazon.lambda.durable.context.DurableContextImpl;
 import software.amazon.lambda.durable.exception.ChildContextFailedException;
 import software.amazon.lambda.durable.exception.NonDeterministicExecutionException;
+import software.amazon.lambda.durable.exception.SerDesException;
 import software.amazon.lambda.durable.execution.ExecutionManager;
 import software.amazon.lambda.durable.execution.ThreadContext;
 import software.amazon.lambda.durable.execution.ThreadType;
 import software.amazon.lambda.durable.model.OperationIdentifier;
 import software.amazon.lambda.durable.model.OperationSubType;
 import software.amazon.lambda.durable.serde.JacksonSerDes;
+import software.amazon.lambda.durable.serde.SerDes;
 
 /** Unit tests for ChildContextOperation. */
 class ChildContextOperationTest {
 
+    private static final class SerializationOnlySerDes implements SerDes {
+        @Override
+        public String serialize(Object value) {
+            return "\"serialized\"";
+        }
+
+        @Override
+        public <T> T deserialize(String data, TypeToken<T> typeToken) {
+            throw new SerDesException("cannot deserialize");
+        }
+    }
+
     private static final JacksonSerDes SERDES = new JacksonSerDes();
 
     private DurableContextImpl durableContext;
@@ -49,29 +63,42 @@ void setUp() {
     }
 
     private DurableConfig createConfig() {
+        return createConfig(true);
+    }
+
+    private DurableConfig createConfig(boolean validateSerializationRoundTrip) {
         return DurableConfig.builder()
                 .withExecutorService(Executors.newCachedThreadPool())
+                .withSerializationRoundTripValidation(validateSerializationRoundTrip)
                 .build();
     }
 
     private static final OperationIdentifier OPERATION_IDENTIFIER =
             OperationIdentifier.of("1", "test-context", OperationSubType.RUN_IN_CHILD_CONTEXT);
 
     private ChildContextOperation<String> createOperation(Function<DurableContext, String> func) {
+        return createOperation(func, SERDES);
+    }
+
+    private ChildContextOperation<String> createOperation(Function<DurableContext, String> func, SerDes serDes) {
         return new ChildContextOperation<>(
                 OPERATION_IDENTIFIER,
                 func,
                 TypeToken.get(String.class),
-                RunInChildContextConfig.builder().serDes(SERDES).build(),
+                RunInChildContextConfig.builder().serDes(serDes).build(),
                 durableContext);
     }
 
     private ChildContextOperation<String> createVirtualOperation(Function<DurableContext, String> func) {
+        return createVirtualOperation(func, SERDES);
+    }
+
+    private ChildContextOperation<String> createVirtualOperation(Function<DurableContext, String> func, SerDes serDes) {
         return new ChildContextOperation<>(
                 OPERATION_IDENTIFIER,
                 func,
                 TypeToken.get(String.class),
-                RunInChildContextConfig.builder().serDes(SERDES).isVirtual(true).build(),
+                RunInChildContextConfig.builder().serDes(serDes).isVirtual(true).build(),
                 durableContext);
     }
 
@@ -311,6 +338,40 @@ void childSkipsSuccessCheckpointWhenParentAlreadyCompleted() throws Exception {
                 .sendOperationUpdate(argThat(update -> update.action() == OperationAction.SUCCEED));
     }
 
+    /** Virtual child still validates result round-trip before skipping a success checkpoint. */
+    @Test
+    void virtualChildFailsWhenResultCannotBeDeserialized() throws Exception {
+        when(executionManager.getOperationAndUpdateReplayState("1")).thenReturn(null);
+
+        var operation = createVirtualOperation(ctx -> "result", new SerializationOnlySerDes());
+        operation.execute();
+        Thread.sleep(200);
+
+        var thrown = assertThrows(ChildContextFailedException.class, operation::get);
+        assertTrue(thrown.getMessage().contains(SerDesException.class.getName()));
+        verify(executionManager, never())
+                .sendOperationUpdate(argThat(update -> update.action() == OperationAction.SUCCEED));
+        verify(executionManager, never())
+                .sendOperationUpdate(argThat(update -> update.action() == OperationAction.FAIL));
+    }
+
+    /** Virtual child can skip round-trip validation when disabled in DurableConfig. */
+    @Test
+    void virtualChildSucceedsWhenResultValidationDisabled() throws Exception {
+        when(executionManager.getOperationAndUpdateReplayState("1")).thenReturn(null);
+        when(durableContext.getDurableConfig()).thenReturn(createConfig(false));
+
+        var operation = createVirtualOperation(ctx -> "result", new SerializationOnlySerDes());
+        operation.execute();
+        Thread.sleep(200);
+
+        assertEquals("result", operation.get());
+        verify(executionManager, never())
+                .sendOperationUpdate(argThat(update -> update.action() == OperationAction.SUCCEED));
+        verify(executionManager, never())
+                .sendOperationUpdate(argThat(update -> update.action() == OperationAction.FAIL));
+    }
+
     /** Child skips failure checkpoint when parent operation has already completed. */
     @Test
     void childSkipsFailureCheckpointWhenParentAlreadyCompleted() throws Exception {