8299015: Ensure that HttpResponse.BodySubscribers.ofFile writes all bytes

Backport-of: a7d6de71bb83c8715654f61dd166aad6e8dab847

src/java.net.http/share/classes/jdk/internal/net/http/ResponseSubscribers.java

@@ -282,7 +282,10 @@ public class ResponseSubscribers {
         @Override
         public void onNext(List<ByteBuffer> items) {
             try {
-                out.write(items.toArray(Utils.EMPTY_BB_ARRAY));
+                ByteBuffer[] buffers = items.toArray(Utils.EMPTY_BB_ARRAY);
+                do {
+                    out.write(buffers);
+                } while (Utils.hasRemaining(buffers));
             } catch (IOException ex) {
                 close();
                 subscription.cancel();

src/java.net.http/share/classes/jdk/internal/net/http/common/Utils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -665,6 +665,14 @@ public final class Utils {
         return false;
     }
 
+    public static boolean hasRemaining(ByteBuffer[] bufs) {
+        for (ByteBuffer buf : bufs) {
+            if (buf.hasRemaining())
+                return true;
+        }
+        return false;
+    }
+
     public static long remaining(List<ByteBuffer> bufs) {
         long remain = 0;
         for (ByteBuffer buf : bufs) {

test/jdk/java/net/httpclient/PathSubscriber/BodySubscriberOfFileTest.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8237470
+ * @bug 8237470 8299015
  * @summary Confirm HttpResponse.BodySubscribers#ofFile(Path)
  *          works with default and non-default file systems
  *          when SecurityManager is enabled
@@ -66,11 +66,15 @@ import java.net.http.HttpRequest.BodyPublishers;
 import java.net.http.HttpResponse.BodyHandler;
 import java.net.http.HttpResponse.BodySubscriber;
 import java.net.http.HttpResponse.BodySubscribers;
+import java.nio.Buffer;
+import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.*;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.util.Map;
+import java.util.concurrent.Flow;
+import java.util.stream.IntStream;
 
 import static java.lang.System.out;
 import static java.net.http.HttpClient.Builder.NO_PROXY;
@@ -199,6 +203,30 @@ public class BodySubscriberOfFileTest implements HttpServerAdapters {
         }
     }
 
+    // A large enough number of buffers to gather from, in an attempt to provoke a partial
+    // write. Loosely based on the value of _SC_IOV_MAX, to trigger partial gathering write.
+    private static final int NUM_GATHERING_BUFFERS = 1024 + 1;
+
+    @Test
+    public void testSubscribersWritesAllBytes() throws Exception {
+        var buffers = IntStream.range(0, NUM_GATHERING_BUFFERS)
+                .mapToObj(i -> new byte[10])
+                .map(ByteBuffer::wrap).toList();
+        int expectedSize = buffers.stream().mapToInt(Buffer::remaining).sum();
+
+        var subscriber = BodySubscribers.ofFile(defaultFsPath);
+        subscriber.onSubscribe(new Flow.Subscription() {
+            @Override
+            public void request(long n) { }
+            @Override
+            public void cancel() { }
+        });
+        subscriber.onNext(buffers);
+        subscriber.onComplete();
+        buffers.forEach(b -> assertEquals(b.remaining(), 0) );
+        assertEquals(expectedSize, Files.size(defaultFsPath));
+    }
+
     @BeforeTest
     public void setup() throws Exception {
         sslContext = new SimpleSSLContext().get();