feat(ric): Cut response copies on the invocation success path from 4 to 1

A successful response of size S was copied four times before being posted:
toByteArray() on the Java heap, then GetByteArrayElements, the std::string
construction, and the by-value success() argument in native memory.

- toNativeString copies with GetByteArrayRegion straight into a presized
  std::string, dropping the JVM's temporary copy.
- The payload is moved into invocation_response::success instead of copied.
- New NativeClient.postInvocationResponseWithLength posts the first N bytes of
  an array, so AWSLambda passes the response buffer's backing array and size
  instead of a toByteArray() copy. It has its own JNI name, so the existing
  postInvocationResponse symbol and behavior are unchanged.
- LambdaRuntimeApiClient gets a default reportInvocationSuccess overload taking
  a length, which falls back to an exact-size copy for other implementations.
- The per-thread response buffer is a LambdaByteArrayOutputStream, which exposes
  its backing array.

The remaining copy into std::string is required by aws-lambda-cpp's
invocation_response::success(std::string, ...).

Author: darklight3it

aws-lambda-java-runtime-interface-client/src/main/java/com/amazonaws/services/lambda/runtime/api/client/AWSLambda.java

@@ -327,7 +327,13 @@ private static void startRuntimeLoop(LambdaRequestHandler lambdaRequestHandler,
 
                 try {
                     ByteArrayOutputStream payload = lambdaRequestHandler.call(request);
-                    runtimeClient.reportInvocationSuccess(request.getId(), payload.toByteArray(), request.getInvocationId());
+                    // Post straight from the backing array: toByteArray() would copy the whole response.
+                    ResponseBufferViewer view = ResponseBufferViewer.of(payload);
+                    if (view.isComplete()) {
+                        runtimeClient.reportInvocationSuccess(request.getId(), view.array(), view.length(), request.getInvocationId());
+                    } else {
+                        runtimeClient.reportInvocationSuccess(request.getId(), payload.toByteArray(), request.getInvocationId());
+                    }
                     // clear interrupted flag in case if it was set by user's code
                     Thread.interrupted();
                 } catch (Throwable t) {

aws-lambda-java-runtime-interface-client/src/main/java/com/amazonaws/services/lambda/runtime/api/client/ResponseBufferViewer.java

@@ -0,0 +1,60 @@
+/*
+Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package com.amazonaws.services.lambda.runtime.api.client;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+
+/**
+ * Gets the backing array of a ByteArrayOutputStream without copying it. ByteArrayOutputStream.writeTo(out) is
+ * specified to call out.write(buf, 0, count) with its own array, under the stream's lock, so this stream keeps that
+ * reference instead of writing anywhere. If writeTo does anything else (a subclass that overrides it, for example),
+ * the view is not complete and the caller falls back to toByteArray().
+ */
+final class ResponseBufferViewer extends OutputStream {
+    private byte[] array;
+    private int length;
+    private int arrayWrites;
+    private boolean otherWrites;
+
+    /** Runs payload.writeTo on a new view. */
+    static ResponseBufferViewer of(ByteArrayOutputStream payload) throws IOException {
+        ResponseBufferViewer view = new ResponseBufferViewer();
+        payload.writeTo(view);
+        return view;
+    }
+
+    @Override
+    public void write(byte[] b, int off, int len) {
+        if (off != 0) {
+            otherWrites = true;
+            return;
+        }
+        arrayWrites++;
+        array = b;
+        length = len;
+    }
+
+    @Override
+    public void write(int b) {
+        otherWrites = true;
+    }
+
+    /** True when writeTo passed a single array from offset 0: array() then holds the whole content. */
+    boolean isComplete() {
+        return arrayWrites == 1 && !otherWrites;
+    }
+
+    /** The captured array. Only the first length() bytes are the content. */
+    byte[] array() {
+        return array;
+    }
+
+    int length() {
+        return length;
+    }
+}

aws-lambda-java-runtime-interface-client/src/main/java/com/amazonaws/services/lambda/runtime/api/client/runtimeapi/LambdaRuntimeApiClient.java

@@ -7,6 +7,7 @@
 import com.amazonaws.services.lambda.runtime.api.client.logging.LambdaContextLogger;
 import com.amazonaws.services.lambda.runtime.api.client.runtimeapi.dto.InvocationRequest;
 import java.io.IOException;
+import java.util.Arrays;
 
 /**
  * Java interface for 
@@ -38,6 +39,17 @@ public interface LambdaRuntimeApiClient {
      */
     void reportInvocationSuccess(String requestId, byte[] response, String invocationId) throws IOException;
 
+    /**
+     * Report invocation success with the first responseLength bytes of response
+     * @param requestId request id
+     * @param response byte array whose first responseLength bytes are the response
+     * @param responseLength number of bytes of response to send
+     * @param invocationId invocation id for cross-wiring protection (may be null)
+     */
+    default void reportInvocationSuccess(String requestId, byte[] response, int responseLength, String invocationId) throws IOException {
+        reportInvocationSuccess(requestId, Arrays.copyOf(response, responseLength), invocationId);
+    }
+
     /**
      * Report invocation error
      * @param requestId request id

aws-lambda-java-runtime-interface-client/src/main/java/com/amazonaws/services/lambda/runtime/api/client/runtimeapi/LambdaRuntimeApiClientImpl.java

@@ -130,6 +130,12 @@ public void reportInvocationSuccess(String requestId, byte[] response, String in
         NativeClient.postInvocationResponse(requestId.getBytes(UTF_8), response, invocationIdBytes);
     }
 
+    @Override
+    public void reportInvocationSuccess(String requestId, byte[] response, int responseLength, String invocationId) {
+        byte[] invocationIdBytes = invocationId != null ? invocationId.getBytes(UTF_8) : null;
+        NativeClient.postInvocationResponseWithLength(requestId.getBytes(UTF_8), response, responseLength, invocationIdBytes);
+    }
+
     @Override
     public void reportInvocationError(String requestId, LambdaError error, String invocationId) throws IOException {
         String endpoint = invocationEndpoint + requestId + "/error";

aws-lambda-java-runtime-interface-client/src/main/java/com/amazonaws/services/lambda/runtime/api/client/runtimeapi/NativeClient.java

@@ -23,4 +23,7 @@ static void init(String awsLambdaRuntimeApi) {
 
     static native void postInvocationResponse(byte[] requestId, byte[] response, byte[] invocationId);
 
+    /** Posts the first responseLength bytes of response, so callers can pass a buffer's backing array without copying it. */
+    static native void postInvocationResponseWithLength(byte[] requestId, byte[] response, int responseLength, byte[] invocationId);
+
 }

aws-lambda-java-runtime-interface-client/src/main/jni/com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient.cpp

@@ -64,15 +64,19 @@ static void throwLambdaRuntimeClientException(JNIEnv *env, std::string message,
   env->Throw(lambdaRuntimeException);
 }
 
-static std::string toNativeString(JNIEnv *env, jbyteArray jArray) {
-  int length = env->GetArrayLength(jArray);
-  jbyte* bytes = env->GetByteArrayElements(jArray, NULL);
-  std::string nativeString = std::string((char *)bytes, length);
-  env->ReleaseByteArrayElements(jArray, bytes, JNI_ABORT);
+// Copies the first length bytes of the array straight into the string. GetByteArrayElements would usually make a
+// temporary copy first. A length outside the array raises ArrayIndexOutOfBoundsException; callers check for it.
+static std::string toNativeString(JNIEnv *env, jbyteArray jArray, jsize length) {
+  std::string nativeString(length > 0 ? length : 0, '\0');
+  env->GetByteArrayRegion(jArray, 0, length, reinterpret_cast<jbyte*>(&nativeString[0]));
   env->DeleteLocalRef(jArray);
   return nativeString;
 }
 
+static std::string toNativeString(JNIEnv *env, jbyteArray jArray) {
+  return toNativeString(env, jArray, env->GetArrayLength(jArray));
+}
+
 JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient_initializeClient(JNIEnv *env, jobject thisObject, jbyteArray userAgent, jbyteArray awsLambdaRuntimeApi) {
   std::string user_agent = toNativeString(env, userAgent);
   std::string endpoint = toNativeString(env, awsLambdaRuntimeApi);
@@ -129,12 +133,7 @@ JNIEXPORT jobject JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_
       return NULL;
 }
 
-JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient_postInvocationResponse
-  (JNIEnv *env, jobject thisObject, jbyteArray jrequestId, jbyteArray jresponseArray, jbyteArray jinvocationId) {
-  std::string payload = toNativeString(env, jresponseArray);
-  if ((env)->ExceptionOccurred()){
-    return;
-  }
+static void postInvocationResponse(JNIEnv *env, jbyteArray jrequestId, std::string payload, jbyteArray jinvocationId) {
   std::string requestId =  toNativeString(env, jrequestId);
   if ((env)->ExceptionOccurred()){
     return;
@@ -148,10 +147,28 @@ JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_run
     }
   }
 
-  auto response = aws::lambda_runtime::invocation_response::success(payload, "application/json");
+  auto response = aws::lambda_runtime::invocation_response::success(std::move(payload), "application/json");
   auto outcome = CLIENT->post_success(requestId, response, invocationId);
   if (!outcome.is_success()) {
     std::string errorMessage("Failed to post invocation response.");
     throwLambdaRuntimeClientException(env, errorMessage, outcome.get_failure());
   }
 }
+
+JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient_postInvocationResponse
+  (JNIEnv *env, jobject thisObject, jbyteArray jrequestId, jbyteArray jresponseArray, jbyteArray jinvocationId) {
+  std::string payload = toNativeString(env, jresponseArray);
+  if ((env)->ExceptionOccurred()){
+    return;
+  }
+  postInvocationResponse(env, jrequestId, std::move(payload), jinvocationId);
+}
+
+JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient_postInvocationResponseWithLength
+  (JNIEnv *env, jobject thisObject, jbyteArray jrequestId, jbyteArray jresponseArray, jint responseLength, jbyteArray jinvocationId) {
+  std::string payload = toNativeString(env, jresponseArray, responseLength);
+  if ((env)->ExceptionOccurred()){
+    return;
+  }
+  postInvocationResponse(env, jrequestId, std::move(payload), jinvocationId);
+}

aws-lambda-java-runtime-interface-client/src/main/jni/com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient.h

@@ -19,6 +19,9 @@ JNIEXPORT jobject JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_
 JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient_postInvocationResponse
   (JNIEnv *, jobject, jbyteArray, jbyteArray, jbyteArray);
 
+JNIEXPORT void JNICALL Java_com_amazonaws_services_lambda_runtime_api_client_runtimeapi_NativeClient_postInvocationResponseWithLength
+  (JNIEnv *, jobject, jbyteArray, jbyteArray, jint, jbyteArray);
+
 #ifdef __cplusplus
 }
 #endif

aws-lambda-java-runtime-interface-client/src/test/java/com/amazonaws/services/lambda/runtime/api/client/AWSLambdaTest.java

@@ -8,12 +8,14 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.*;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOError;
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -242,7 +244,7 @@ void testConcurrentRunWithPlatformThreads() throws Throwable {
         AWSLambda.startRuntimeLoops(lambdaRequestHandler, lambdaLogger, concurrencyConfig, runtimeClient);
 
         // Success Reports Must Equal number of tasks that ran successfully.
-        verify(runtimeClient, times(7)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), any());
+        verify(runtimeClient, times(7)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), anyInt(), any());
         // Hashmap keys should equal the number of threads (runtime loops).
         assertEquals(4, SampleHandler.hashMap.size());
         // Hashmap total count should equal all tasks that ran * number of iterations per task
@@ -284,7 +286,7 @@ void testConcurrentRunWithPlatformThreadsWithFailures() throws Throwable {
         verify(runtimeClient).reportInvocationError(eq(UserFaultID), any(), any());
 
         // Success Reports Must Equal number of tasks that ran successfully.
-        verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), any());
+        verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), anyInt(), any());
 
         // Hashmap keys should equal the minumum between(number of threads (runtime loops) AND number of tasks that ran successfully).
         assertEquals(2, SampleHandler.hashMap.size());
@@ -331,7 +333,7 @@ void testConcurrentModeLoopDoesNotExitExceptForLambdaRuntimeClientMaxRetriesExce
          verify(runtimeClient).reportInvocationError(eq(IOErrorID), any(), any());
 
          // Success Reports Must Equal number of tasks that ran successfully.
-         verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), any());
+         verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), anyInt(), any());
 
          // Hashmap keys should equal the minumum between(number of threads (runtime loops) AND number of tasks that ran successfully).
          assertEquals(1, SampleHandler.hashMap.size());
@@ -520,7 +522,7 @@ void testSequentialWithFatalUserFaultErrorStopsLoop() throws Throwable {
         verify(runtimeClient).reportInvocationError(eq(UserFaultID), any(), any());
 
         // Success Reports Must Equal number of tasks that ran successfully. And only 2 Error reports for failImmediatelyRequest and userFaultRequest.
-        verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), any());
+        verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), anyInt(), any());
         verify(runtimeClient, times(2)).reportInvocationError(any(), any(), any());
 
         // Hashmap keys should equal one as it is not multithreaded.
@@ -566,7 +568,7 @@ void testSequentialWithVirtualMachineErrorStopsLoop() throws Throwable {
         verify(runtimeClient).reportInvocationError(eq(IOErrorID), any(), any());
 
         // Success Reports Must Equal number of tasks that ran successfully. And only 2 Error reports for failImmediatelyRequest and virtualMachineErrorRequest.
-        verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), any());
+        verify(runtimeClient, times(2)).reportInvocationSuccess(eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), anyInt(), any());
         verify(runtimeClient, times(2)).reportInvocationError(any(), any(), any());
 
         // Hashmap keys should equal one as it is not multithreaded.
@@ -671,7 +673,68 @@ void testInvocationIdIsPassedToReportSuccess() throws Throwable {
         AWSLambda.startRuntimeLoops(lambdaRequestHandler, lambdaLogger, concurrencyConfig, runtimeClient);
 
         verify(runtimeClient).reportInvocationSuccess(
-                eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), eq("test-inv-uuid-1234"));
+                eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), any(), anyInt(), eq("test-inv-uuid-1234"));
+    }
+
+    /** Exposes the backing array so tests can check that it is posted as is. */
+    private static final class InspectableByteArrayOutputStream extends ByteArrayOutputStream {
+        byte[] backingArray() {
+            return buf;
+        }
+    }
+
+    /** Overrides writeTo the way a subclass could, one byte at a time, so the backing array cannot be captured. */
+    private static final class BytewiseWriteToByteArrayOutputStream extends ByteArrayOutputStream {
+        @Override
+        public synchronized void writeTo(java.io.OutputStream out) throws IOException {
+            for (byte b : toByteArray()) {
+                out.write(b);
+            }
+        }
+    }
+
+    private void runOneInvocation(LambdaRequestHandler handler) throws Throwable {
+        when(concurrencyConfig.isMultiConcurrent()).thenReturn(false);
+
+        InvocationRequest request = getFakeInvocationRequest(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE);
+        request.setInvocationId("test-inv-uuid-1234");
+
+        // Fatal error to stop the loop after one successful invocation
+        InvocationRequest fatalRequest = mock(InvocationRequest.class);
+        when(fatalRequest.getId()).thenThrow(UserFault.makeUserFault(new IOError(new Throwable()), true)).thenReturn("fatal");
+
+        when(runtimeClient.nextInvocation())
+                .thenReturn(request)
+                .thenReturn(fatalRequest);
+
+        AWSLambda.startRuntimeLoops(handler, lambdaLogger, concurrencyConfig, runtimeClient);
+    }
+
+    @Test
+    @Timeout(value = 1, unit = TimeUnit.MINUTES)
+    void testResponseBackingArrayIsPostedWithoutCopy() throws Throwable {
+        InspectableByteArrayOutputStream output = new InspectableByteArrayOutputStream();
+        output.write("\"success\"".getBytes());
+
+        runOneInvocation(request -> output);
+
+        // The backing array itself is passed, with the content length, instead of a toByteArray() copy.
+        verify(runtimeClient).reportInvocationSuccess(
+                eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), same(output.backingArray()), eq(9), eq("test-inv-uuid-1234"));
+        verify(runtimeClient, never()).reportInvocationSuccess(anyString(), any(), any());
+    }
+
+    @Test
+    @Timeout(value = 1, unit = TimeUnit.MINUTES)
+    void testResponseIsCopiedWhenWriteToDoesNotPassTheBackingArray() throws Throwable {
+        ByteArrayOutputStream output = new BytewiseWriteToByteArrayOutputStream();
+        output.write("\"success\"".getBytes());
+
+        runOneInvocation(request -> output);
+
+        verify(runtimeClient).reportInvocationSuccess(
+                eq(SampleHandler.ADD_ENTRY_TO_MAP_ID_OP_MODE), eq("\"success\"".getBytes()), eq("test-inv-uuid-1234"));
+        verify(runtimeClient, never()).reportInvocationSuccess(anyString(), any(), anyInt(), any());
     }
 
     @Test