Fix for zero-sized content throwing off toChannelBuffer(). Also

short-circuit writeTo(..) accordingly to avoid unnecessary work.

Fixes #5543

src/main/java/org/elasticsearch/common/bytes/PagedBytesReference.java

@@ -84,6 +84,11 @@ public final class PagedBytesReference implements BytesReference {
 
     @Override
     public void writeTo(OutputStream os) throws IOException {
+        // nothing to do
+        if (length == 0) {
+            return;
+        }
+
         BytesRef ref = new BytesRef();
         int written = 0;
         
@@ -108,6 +113,11 @@ public final class PagedBytesReference implements BytesReference {
 
     @Override
     public void writeTo(GatheringByteChannel channel) throws IOException {
+        // nothing to do
+        if (length == 0) {
+            return;
+        }
+
         ByteBuffer[] buffers;
         ByteBuffer currentBuffer = null;
         BytesRef ref = new BytesRef();
@@ -201,6 +211,11 @@ public final class PagedBytesReference implements BytesReference {
 
     @Override
     public ChannelBuffer toChannelBuffer() {
+        // nothing to do
+        if (length == 0) {
+            return ChannelBuffers.EMPTY_BUFFER;
+        }
+
         ChannelBuffer[] buffers;
         ChannelBuffer currentBuffer = null;
         BytesRef ref = new BytesRef();

src/main/java/org/elasticsearch/common/io/stream/BytesStreamOutput.java

@@ -19,9 +19,8 @@
 
 package org.elasticsearch.common.io.stream;
 
-import org.apache.lucene.util.BytesRef;
-import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.bytes.PagedBytesReference;
 import org.elasticsearch.common.io.BytesStream;
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.common.util.ByteArray;
@@ -154,9 +153,7 @@ public class BytesStreamOutput extends StreamOutput implements BytesStream {
 
     @Override
     public BytesReference bytes() {
-        BytesRef bref = new BytesRef();
-        bytes.get(0, count, bref);
-        return new BytesArray(bref, false);
+        return new PagedBytesReference(bigarrays, bytes, count);
     }
 
     private void ensureCapacity(int offset) {

src/test/java/org/elasticsearch/common/bytes/PagedBytesReferenceTest.java

@@ -283,6 +283,14 @@ public class PagedBytesReferenceTest extends ElasticsearchTestCase {
         assertArrayEquals(pbr.toBytes(), bufferBytes);
     }
 
+    public void testEmptyToChannelBuffer() {
+        BytesReference pbr = getRandomizedPagedBytesReference(0);
+        ChannelBuffer cb = pbr.toChannelBuffer();
+        assertNotNull(cb);
+        assertEquals(0, pbr.length());
+        assertEquals(0, cb.capacity());
+    }
+
     public void testSliceToChannelBuffer() {
         int length = randomIntBetween(10, PAGE_SIZE * randomIntBetween(2,8));
         BytesReference pbr = getRandomizedPagedBytesReference(length);