fix idempotency when only string

Author: jeromevdl

powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/internal/IdempotencyHandler.java

@@ -127,6 +127,8 @@ private Object handleForStatus(DataRecord record) {
         Class<?> returnType = ((MethodSignature) pjp.getSignature()).getReturnType();
         try {
             LOG.debug("Response for key '{}' retrieved from idempotency store, skipping the function", record.getIdempotencyKey());
+            if (returnType.equals(String.class))
+                return record.getResponseData();
             return JsonConfig.get().getObjectMapper().reader().readValue(record.getResponseData(), returnType);
         } catch (Exception e) {
             throw new IdempotencyPersistenceLayerException("Unable to get function response as " + returnType.getSimpleName(), e);

powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/BasePersistenceStore.java

@@ -108,7 +108,12 @@ public void configure(IdempotencyConfig config, String functionName) {
     public void saveSuccess(JsonNode data, Object result, Instant now) {
         ObjectWriter writer = JsonConfig.get().getObjectMapper().writer();
         try {
-            String responseJson = writer.writeValueAsString(result);
+            String responseJson;
+            if (result instanceof String) {
+                responseJson = (String) result;
+            } else {
+                responseJson = writer.writeValueAsString(result);
+            }
             DataRecord record = new DataRecord(
                     getHashedIdempotencyKey(data),
                     DataRecord.Status.COMPLETED,

powertools-idempotency/src/test/java/software/amazon/lambda/powertools/idempotency/handlers/IdempotencyStringFunction.java

@@ -0,0 +1,22 @@
+package software.amazon.lambda.powertools.idempotency.handlers;
+
+import com.amazonaws.services.lambda.runtime.Context;
+import com.amazonaws.services.lambda.runtime.RequestHandler;
+import software.amazon.lambda.powertools.idempotency.Idempotent;
+import software.amazon.lambda.powertools.idempotency.model.Product;
+
+public class IdempotencyStringFunction implements RequestHandler<Product, String> {
+
+    private boolean handlerCalled = false;
+
+    public boolean handlerCalled() {
+        return handlerCalled;
+    }
+
+    @Override
+    @Idempotent
+    public String handleRequest(Product input, Context context) {
+        handlerCalled = true;
+        return input.getName();
+    }
+}

powertools-idempotency/src/test/java/software/amazon/lambda/powertools/idempotency/internal/IdempotencyAspectTest.java

@@ -114,6 +114,36 @@ public void secondCall_notExpired_shouldGetFromStore() throws JsonProcessingExce
         assertThat(function.handlerCalled()).isFalse();
     }
 
+    @Test
+    public void secondCall_notExpired_shouldGetStringFromStore() {
+        // GIVEN
+        Idempotency.config()
+                .withPersistenceStore(store)
+                .withConfig(IdempotencyConfig.builder()
+                        .withEventKeyJMESPath("id")
+                        .build()
+                ).configure();
+
+        doThrow(IdempotencyItemAlreadyExistsException.class).when(store).saveInProgress(any(), any());
+
+        Product p = new Product(42, "fake product", 12);
+        DataRecord record = new DataRecord(
+                "42",
+                DataRecord.Status.COMPLETED,
+                Instant.now().plus(356, SECONDS).getEpochSecond(),
+                p.getName(),
+                null);
+        doReturn(record).when(store).getRecord(any(), any());
+
+        // WHEN
+        IdempotencyStringFunction function = new IdempotencyStringFunction();
+        String name = function.handleRequest(p, context);
+
+        // THEN
+        assertThat(name).isEqualTo(p.getName());
+        assertThat(function.handlerCalled()).isFalse();
+    }
+
     @Test
     public void secondCall_inProgress_shouldThrowIdempotencyAlreadyInProgressException() throws JsonProcessingException {
         // GIVEN