Introduced class ByteBufferPool.Lease to keep track of buffers with

associated information of whether they have been borrowed from the
ByteBufferPool or not.

jetty-fcgi/fcgi-client/src/main/java/org/eclipse/jetty/fcgi/generator/Generator.java

@@ -80,6 +80,7 @@ public class Generator
         return result;
     }
 
+    // TODO: rewrite this class in light of ByteBufferPool.Lease.
     public static class Result implements Callback
     {
         private final List<Callback> callbacks = new ArrayList<>(2);

jetty-hpack/src/main/java/org/eclipse/jetty/hpack/HpackEncoder.java

@@ -19,26 +19,20 @@
 
 package org.eclipse.jetty.hpack;
 
-import java.nio.ByteBuffer;
-import java.util.Collections;
-import java.util.List;
-
 import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.io.ByteBufferPool;
 
-
-/* ------------------------------------------------------------ */
-/**
- */
 public class HpackEncoder
 {
-    public HpackEncoder(ByteBufferPool pool)
+    private final ByteBufferPool byteBufferPool;
-    {
 
+    public HpackEncoder(ByteBufferPool byteBufferPool)
+    {
+        this.byteBufferPool = byteBufferPool;
     }
     
-    public List<ByteBuffer> encode(HttpFields fields)
+    public ByteBufferPool.Lease encode(HttpFields fields)
     {
-        return Collections.emptyList();
+        return new ByteBufferPool.Lease(byteBufferPool);
     }
 }

jetty-io/src/main/java/org/eclipse/jetty/io/ByteBufferPool.java

@@ -19,6 +19,8 @@
 package org.eclipse.jetty.io;
 
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
 
 /**
  * <p>A {@link ByteBuffer} pool.</p>
@@ -48,4 +50,55 @@ public interface ByteBufferPool
      * @see #acquire(int, boolean)
      */
     public void release(ByteBuffer buffer);
+
+    public static class Lease
+    {
+        private final ByteBufferPool byteBufferPool;
+        private final List<ByteBuffer> buffers;
+        private final List<Boolean> recycles;
+
+        public Lease(ByteBufferPool byteBufferPool)
+        {
+            this.byteBufferPool = byteBufferPool;
+            this.buffers = new ArrayList<>();
+            this.recycles = new ArrayList<>();
+        }
+
+        public void add(ByteBuffer buffer, boolean recycle)
+        {
+            buffers.add(buffer);
+            recycles.add(recycle);
+        }
+
+        public List<ByteBuffer> getByteBuffers()
+        {
+            return buffers;
+        }
+
+        public Lease merge(Lease that)
+        {
+            assert byteBufferPool == that.byteBufferPool;
+            buffers.addAll(that.buffers);
+            recycles.addAll(that.recycles);
+            return this;
+        }
+
+        public long getTotalLength()
+        {
+            long length = 0;
+            for (int i = 0; i < buffers.size(); ++i)
+                length += buffers.get(i).remaining();
+            return length;
+        }
+
+        public void recycle()
+        {
+            for (int i = 0; i < buffers.size(); ++i)
+            {
+                ByteBuffer buffer = buffers.get(i);
+                if (recycles.get(i))
+                    byteBufferPool.release(buffer);
+            }
+        }
+    }
 }