diff -r fcb5b835bf32 -r 4f830b447edf src/jdk.incubator.httpclient/share/classes/jdk/incubator/http/RequestPublishers.java
--- a/src/jdk.incubator.httpclient/share/classes/jdk/incubator/http/RequestPublishers.java	Thu Dec 21 10:26:03 2017 +0100
+++ b/src/jdk.incubator.httpclient/share/classes/jdk/incubator/http/RequestPublishers.java	Thu Dec 21 16:58:51 2017 +0000
@@ -46,6 +46,7 @@
 import java.util.Objects;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.Flow;
+import java.util.concurrent.Flow.Publisher;
 import java.util.function.Supplier;
 import jdk.incubator.http.HttpRequest.BodyPublisher;
 import jdk.incubator.http.internal.common.Utils;
@@ -349,4 +350,26 @@
             return -1;
         }
     }
+
+    static final class PublisherAdapter implements BodyPublisher {
+
+        private final Publisher<? extends ByteBuffer> publisher;
+        private final long contentLength;
+
+        PublisherAdapter(Publisher<? extends ByteBuffer> publisher,
+                         long contentLength) {
+            this.publisher = Objects.requireNonNull(publisher);
+            this.contentLength = contentLength;
+        }
+
+        @Override
+        public final long contentLength() {
+            return contentLength;
+        }
+
+        @Override
+        public final void subscribe(Flow.Subscriber<? super ByteBuffer> subscriber) {
+            publisher.subscribe(subscriber);
+        }
+    }
 }