Add methods to ReadableBuffer to support returning read bytes via Byt…

…eBuffers.

core/src/main/java/io/grpc/internal/AbstractReadableBuffer.java

@@ -16,6 +16,9 @@
 
 package io.grpc.internal;
 
+import java.nio.ByteBuffer;
+import java.util.List;
+
 /**
  * Abstract base class for {@link ReadableBuffer} implementations.
  */
@@ -30,6 +33,16 @@ public final int readInt() {
     return (b1 << 24) | (b2 << 16) | (b3 << 8) | b4;
   }
 
+  @Override
+  public boolean shouldUseByteBuffer() {
+    return false;
+  }
+
+  @Override
+  public List<ByteBuffer> readByteBuffers(int length) {
+    throw new UnsupportedOperationException();
+  }
+
   @Override
   public boolean hasArray() {
     return false;

core/src/main/java/io/grpc/internal/ForwardingReadableBuffer.java

@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
+import java.util.List;
 
 /**
  * Base class for a wrapper around another {@link ReadableBuffer}.
@@ -81,6 +82,16 @@ public ReadableBuffer readBytes(int length) {
     return buf.readBytes(length);
   }
 
+  @Override
+  public boolean shouldUseByteBuffer() {
+    return buf.shouldUseByteBuffer();
+  }
+
+  @Override
+  public List<ByteBuffer> readByteBuffers(int length) {
+    return buf.readByteBuffers(length);
+  }
+
   @Override
   public boolean hasArray() {
     return buf.hasArray();

core/src/main/java/io/grpc/internal/ReadableBuffer.java

@@ -20,6 +20,7 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
+import java.util.List;
 
 /**
  * Interface for an abstract byte buffer. Buffers are intended to be a read-only, except for the
@@ -102,6 +103,22 @@ public interface ReadableBuffer extends Closeable {
    */
   ReadableBuffer readBytes(int length);
 
+  /**
+   * Indicates whether or not this buffer supports {@link #readByteBuffers} operation that returns
+   * buffer's content as {@link ByteBuffer}s without making an extra copy.
+   */
+  boolean shouldUseByteBuffer();
+
+  /**
+   * Reads {@code length} bytes as {@link ByteBuffer}s. This is an optional method, so callers
+   * should first check {@link #shouldUseByteBuffer}.
+   *
+   * @param length the total number of bytes to contain in the returned {@link ByteBuffer}s.
+   * @throws UnsupportedOperationException the buffer does not support this method
+   * @throws IndexOutOfBoundsException if required bytes are not readable
+   */
+  List<ByteBuffer> readByteBuffers(int length);
+
   /**
    * Indicates whether or not this buffer exposes a backing array.
    */