Fixed the issue where S3 multipart client failed to download zero-byt…

.changes/next-release/bugfix-AmazonS3-33f2ede.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "Amazon S3",
+    "contributor": "",
+    "description": "Fixed the issue where S3 multipart client failed to download zero-byte file, causing `Content range header is missing` exception to throw."
+}

core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/async/FileAsyncResponseTransformerPublisher.java

@@ -104,11 +104,21 @@ public void onResponse(T response) {
             if (!contentRangeOpt.isPresent()) {
                 contentRangeOpt = response.sdkHttpResponse().firstMatchingHeader("content-range");
                 if (!contentRangeOpt.isPresent()) {
-                    // Bad state! This is intended to cancel everything
-                    if (subscriber != null) {
+                    Optional<String> contentLength = response.sdkHttpResponse().firstMatchingHeader("content-length");
+                    long transformerCount = FileAsyncResponseTransformerPublisher.this.transformerCount.get();
+                    // Error out if content range header is missing and this is not the initial request
+                    if (subscriber != null && transformerCount > 0) {
                         subscriber.onError(new IllegalStateException("Content range header is missing"));
+                        return;
                     }
-                    return;
+
+                    if (!contentLength.isPresent()) {
+                        subscriber.onError(new IllegalStateException("Content length header is missing"));
+                        return;
+                    }
+                    String totalLength = contentLength.get();
+                    long endByte = Long.parseLong(totalLength) - 1;
+                    contentRangeOpt = Optional.of("bytes 0-" + endByte + "/" + totalLength);
                 }
             }
 

core/sdk-core/src/test/java/software/amazon/awssdk/core/internal/async/FileAsyncResponseTransformerPublisherTest.java

@@ -51,6 +51,7 @@
 import software.amazon.awssdk.core.async.SdkPublisher;
 import software.amazon.awssdk.http.SdkHttpResponse;
 import software.amazon.awssdk.utils.CompletableFutureUtils;
+import software.amazon.awssdk.utils.ContentRangeParser;
 
 class FileAsyncResponseTransformerPublisherTest {
 
@@ -239,11 +240,17 @@ public void onComplete() {
     }
 
     private SdkResponse createMockResponseWithRange(String contentRange) {
+        return createMockResponseWithRange(contentRange,
+                                           ContentRangeParser.totalBytes(contentRange).getAsLong());
+    }
+
+    private SdkResponse createMockResponseWithRange(String contentRange, Long contentLength) {
         SdkResponse mockResponse = mock(SdkResponse.class);
         SdkHttpResponse mockHttpResponse = mock(SdkHttpResponse.class);
 
         when(mockResponse.sdkHttpResponse()).thenReturn(mockHttpResponse);
-        when(mockHttpResponse.firstMatchingHeader("x-amz-content-range")).thenReturn(Optional.of(contentRange));
+        when(mockHttpResponse.firstMatchingHeader("content-length")).thenReturn(Optional.ofNullable(String.valueOf(contentLength)));
+        when(mockHttpResponse.firstMatchingHeader("x-amz-content-range")).thenReturn(Optional.ofNullable(contentRange));
 
         return mockResponse;
     }
@@ -298,7 +305,101 @@ void createOrAppendToExisting_shouldThrowException() {
         assertThatThrownBy(() -> new FileAsyncResponseTransformerPublisher<>((FileAsyncResponseTransformer<?>) initialTransformer))
             .isInstanceOf(IllegalArgumentException.class)
             .hasMessageContaining("CREATE_OR_APPEND_TO_EXISTING");
+    }
+
+    @Test
+    void singleDemand_contentRangeMissing_shouldSucceed() throws Exception {
+        AsyncResponseTransformer<SdkResponse, SdkResponse> initialTransformer = AsyncResponseTransformer.toFile(testFile);
+        FileAsyncResponseTransformerPublisher<SdkResponse> publisher =
+            new FileAsyncResponseTransformerPublisher<>((FileAsyncResponseTransformer<SdkResponse>) initialTransformer);
+
+        CountDownLatch latch = new CountDownLatch(1);
+        AtomicReference<AsyncResponseTransformer<SdkResponse, SdkResponse>> receivedTransformer = new AtomicReference<>();
+        CompletableFuture<SdkResponse> future = new CompletableFuture<>();
 
+        publisher.subscribe(new Subscriber<AsyncResponseTransformer<SdkResponse, SdkResponse>>() {
+            private Subscription subscription;
+
+            @Override
+            public void onSubscribe(Subscription s) {
+                this.subscription = s;
+                s.request(1);
+            }
+
+            @Override
+            public void onNext(AsyncResponseTransformer<SdkResponse, SdkResponse> transformer) {
+                receivedTransformer.set(transformer);
+
+                // Simulate response with content-range header
+                SdkResponse mockResponse = createMockResponseWithRange(null, 0L);
+                CompletableFuture<SdkResponse> prepareFuture = transformer.prepare();
+                CompletableFutureUtils.forwardResultTo(prepareFuture, future);
+                transformer.onResponse(mockResponse);
+
+                // Simulate stream data
+                SdkPublisher<ByteBuffer> mockPublisher = createMockPublisher();
+                transformer.onStream(mockPublisher);
+
+                latch.countDown();
+            }
+
+            @Override
+            public void onError(Throwable t) {
+                fail("Unexpected error with exception: " + t.getMessage());
+            }
+
+            @Override
+            public void onComplete() {
+                latch.countDown();
+            }
+        });
+
+        assertThat(latch.await(5, TimeUnit.SECONDS)).isTrue();
+        assertThat(receivedTransformer.get()).isNotNull();
+        assertThat(Files.exists(testFile)).isTrue();
+        assertThat(future).succeedsWithin(10, TimeUnit.SECONDS);
+    }
+
+    @Test
+    void multipleTransformers_contentRangeMissingOnSecondRequest_shouldFail() throws Exception {
+        AsyncResponseTransformer<SdkResponse, SdkResponse> initialTransformer = AsyncResponseTransformer.toFile(testFile);
+        FileAsyncResponseTransformerPublisher<SdkResponse> publisher =
+            new FileAsyncResponseTransformerPublisher<>((FileAsyncResponseTransformer<SdkResponse>) initialTransformer);
+
+        CountDownLatch latch = new CountDownLatch(1);
+        CompletableFuture<SdkResponse> future = new CompletableFuture<>();
+        AtomicReference<Throwable> exception = new AtomicReference<>();
+
+        publisher.subscribe(new Subscriber<AsyncResponseTransformer<SdkResponse, SdkResponse>>() {
+
+            @Override
+            public void onSubscribe(Subscription s) {
+                s.request(2);
+            }
+
+            @Override
+            public void onNext(AsyncResponseTransformer<SdkResponse, SdkResponse> transformer) {
+                SdkResponse mockResponse = createMockResponseWithRange(null, 0L);
+
+                CompletableFuture<SdkResponse> prepareFuture = transformer.prepare();
+                CompletableFutureUtils.forwardResultTo(prepareFuture, future);
+                transformer.onResponse(mockResponse);
+            }
+
+            @Override
+            public void onError(Throwable t) {
+                exception.set(t);
+                latch.countDown();
+            }
+
+            @Override
+            public void onComplete() {
+                fail("Unexpected onComplete");
+            }
+        });
+
+        assertThat(latch.await(5, TimeUnit.SECONDS)).isTrue();
+        assertThat(exception.get()).hasMessageContaining("Content range header is missing");
     }
 
 }

services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3MultipartClientFileDownloadIntegrationTest.java

@@ -55,6 +55,7 @@ public class S3MultipartClientFileDownloadIntegrationTest extends S3IntegrationT
     private static final int MIB = 1024 * 1024;
     private static final String TEST_BUCKET = temporaryBucketName(S3MultipartClientFileDownloadIntegrationTest.class);
     private static final String TEST_KEY = "testfile.dat";
+    private static final String ZERO_BYTE_KEY = "zero.dat";
     private static final int OBJ_SIZE = 100 * MIB;
     private static final long PART_SIZE = 5 * MIB;
 
@@ -108,6 +109,22 @@ void download_defaultCreateNewFile_shouldSucceed() throws Exception {
         path.toFile().delete();
     }
 
+    @Test
+    void download_emptyFile_shouldSucceed() throws Exception {
+        Path path = tmpPath().resolve(UUID.randomUUID().toString());
+        s3Client.putObject(b -> b.bucket(TEST_BUCKET).key(ZERO_BYTE_KEY), AsyncRequestBody.empty()).join();
+        CompletableFuture<GetObjectResponse> future = s3Client.getObject(
+            req -> req.bucket(TEST_BUCKET).key(ZERO_BYTE_KEY),
+            AsyncResponseTransformer.toFile(path, FileTransformerConfiguration.defaultCreateNew()));
+        future.join();
+        MessageDigest md = MessageDigest.getInstance("SHA-256");
+        byte[] downloadedHash = md.digest(Files.readAllBytes(path));
+        md.reset();
+        byte[] originalHash = md.digest(new byte[0]);
+        assertThat(downloadedHash).isEqualTo(originalHash);
+    }
+
+
     private Path tmpPath() {
         return Paths.get(JavaSystemSetting.TEMP_DIRECTORY.getStringValueOrThrow());
     }