MLE-27509 No longer using ByteArrayDataSource on a multipart response

marklogic-client-api/build.gradle

@@ -76,6 +76,9 @@ dependencies {
 
 	testImplementation 'org.skyscreamer:jsonassert:1.5.3'
 
+	// ArchUnit for verifying certain classes aren't used
+	testImplementation 'com.tngtech.archunit:archunit-junit5:1.4.1'
+
 	// Automatic loading of test framework implementation dependencies is deprecated.
 	// https://docs.gradle.org/current/userguide/upgrading_version_8.html#test_framework_implementation_dependencies
 	// Without this, once using JUnit 5.12 or higher, Gradle will not find any tests and report an error of:

marklogic-client-api/src/main/java/com/marklogic/client/impl/OkHttpServices.java

@@ -37,8 +37,8 @@
 import jakarta.mail.internet.ContentDisposition;
 import jakarta.mail.internet.MimeMultipart;
 import jakarta.mail.internet.ParseException;
-import jakarta.mail.util.ByteArrayDataSource;
 import jakarta.xml.bind.DatatypeConverter;
+import com.marklogic.client.impl.okhttp.InputStreamDataSource;
 import okhttp3.*;
 import okhttp3.MultipartBody.Part;
 import okhttp3.logging.HttpLoggingInterceptor;
@@ -5305,7 +5305,9 @@ static private <T> T getEntity(ResponseBody body, Class<T> as) {
 			} else if (as == MimeMultipart.class) {
 				MediaType mediaType = body.contentType();
 				String contentType = (mediaType != null) ? mediaType.toString() : "application/x-unknown-content-type";
-				ByteArrayDataSource dataSource = new ByteArrayDataSource(body.byteStream(), contentType);
+				// Use custom DataSource to avoid reading document into memory. Allows a user to use an
+				// InputStreamHandle to fetch the content without being surprised that all the data is in memory already.
+				InputStreamDataSource dataSource = new InputStreamDataSource(body.byteStream(), contentType);
 				return (T) new MimeMultipart(dataSource);
 			} else if (as == File.class) {
 				// write out the response body to a temp file in the system temp folder
@@ -6055,12 +6057,10 @@ void setResponse(Response response) {
 					setNull(true);
 					return;
 				}
-				ByteArrayDataSource dataSource = new ByteArrayDataSource(
-					responseBody.byteStream(), contentType.toString()
-				);
+				// Use custom DataSource to avoid reading document into memory. Allows a user to use an
+				// InputStreamHandle to fetch the content without being surprised that all the data is in memory already.
+				InputStreamDataSource dataSource = new InputStreamDataSource(responseBody.byteStream(), contentType.toString());
 				setMultipart(new MimeMultipart(dataSource));
-			} catch (IOException e) {
-				throw new MarkLogicIOException(e);
 			} catch (MessagingException e) {
 				throw new MarkLogicIOException(e);
 			}

marklogic-client-api/src/main/java/com/marklogic/client/impl/okhttp/InputStreamDataSource.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2010-2026 Progress Software Corporation and/or its subsidiaries or affiliates. All Rights Reserved.
+ */
+package com.marklogic.client.impl.okhttp;
+
+import jakarta.activation.DataSource;
+
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * A streaming DataSource implementation that wraps an InputStream without buffering it into memory.
+ * This is a critical component for enabling true streaming of large documents from MarkLogic,
+ * avoiding OutOfMemoryErrors when processing large result sets.
+ * <p>
+ * Unlike ByteArrayDataSource (which loads the entire stream into a byte array), this implementation
+ * preserves the streaming nature of the underlying InputStream, allowing documents to be processed
+ * incrementally as they are read from the network.
+ * <p>
+ * Note: This DataSource is read-only. The getOutputStream() method throws UnsupportedOperationException.
+ */
+public class InputStreamDataSource implements DataSource {
+
+	private final InputStream inputStream;
+	private final String contentType;
+
+	/**
+	 * Creates a new InputStreamDataSource.
+	 *
+	 * @param inputStream the InputStream to wrap (will not be buffered into memory)
+	 * @param contentType the MIME type of the data
+	 */
+	public InputStreamDataSource(InputStream inputStream, String contentType) {
+		this.inputStream = inputStream;
+		this.contentType = contentType;
+	}
+
+	@Override
+	public InputStream getInputStream() {
+		return inputStream;
+	}
+
+	@Override
+	public OutputStream getOutputStream() {
+		throw new UnsupportedOperationException("InputStreamDataSource is read-only");
+	}
+
+	@Override
+	public String getContentType() {
+		return contentType;
+	}
+
+	@Override
+	public String getName() {
+		return null;
+	}
+}

marklogic-client-api/src/test/java/com/marklogic/client/test/VerifyByteArrayDataSourceIsNotUsedTest.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2010-2026 Progress Software Corporation and/or its subsidiaries or affiliates. All Rights Reserved.
+ */
+package com.marklogic.client.test;
+
+import com.marklogic.client.impl.okhttp.PartIterator;
+import com.tngtech.archunit.core.domain.JavaClasses;
+import com.tngtech.archunit.core.importer.ClassFileImporter;
+import com.tngtech.archunit.core.importer.ImportOption;
+import com.tngtech.archunit.lang.ArchRule;
+import jakarta.mail.util.ByteArrayDataSource;
+import org.junit.jupiter.api.Test;
+
+import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.noClasses;
+
+/**
+ * Architecture tests to ensure streaming best practices are followed.
+ * <p>
+ * ByteArrayDataSource defeats streaming by loading entire InputStreams into memory.
+ * We use InputStreamDataSource instead to enable true streaming for large documents.
+ */
+class VerifyByteArrayDataSourceIsNotUsedTest {
+
+	private final JavaClasses classes = new ClassFileImporter()
+		.withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS)
+		.importPackages("com.marklogic.client");
+
+	@Test
+	void shouldNotUseByteArrayDataSourceInProduction() {
+		ArchRule rule = noClasses()
+			// PartIterator can use ByteArrayDataSource because for an eval/invoke use case, it's very likely the user
+			// wants the results in memory so they can perform some operation on them. If this proves false in the
+			// future, PartIterator can be adjusted to use InputStreamDataSource instead.
+			.that().doNotHaveSimpleName(PartIterator.class.getSimpleName())
+
+			.should().dependOnClassesThat().haveSimpleName(ByteArrayDataSource.class.getSimpleName())
+			.because("MLE-27509 identifies a problem where a multipart response was having each part " +
+				"processed with the ByteArrayDataSource, which loads the entire stream into memory. This is " +
+				"surprising to any user using InputStreamHandle to access the content of a document, as that user " +
+				"is likely expecting to stream document from MarkLogic to some target. The InputStreamDataSource " +
+				"class was created to avoiding reading the contents of the document into an in-memory byte " +
+				"array, thus allowing for streaming reads to occur via a multipart response.");
+
+		rule.check(classes);
+	}
+}