provides final tuple bytebuf implementation (#614)

Signed-off-by: Oleh Dokuka <[email protected]>

Author: OlegDokuka

rsocket-core/src/main/java/io/rsocket/buffer/AbstractTupleByteBuf.java

@@ -0,0 +1,78 @@
+package io.rsocket.buffer;
+
+import java.lang.reflect.Field;
+import java.nio.Buffer;
+import java.nio.ByteBuffer;
+import java.security.AccessController;
+import java.security.PrivilegedExceptionAction;
+import sun.misc.Unsafe;
+
+abstract class BufferUtil {
+
+  private static final Unsafe UNSAFE;
+
+  static {
+    Unsafe unsafe;
+    try {
+      final PrivilegedExceptionAction<Unsafe> action =
+          () -> {
+            final Field f = Unsafe.class.getDeclaredField("theUnsafe");
+            f.setAccessible(true);
+
+            return (Unsafe) f.get(null);
+          };
+
+      unsafe = AccessController.doPrivileged(action);
+    } catch (final Exception ex) {
+      throw new RuntimeException(ex);
+    }
+
+    UNSAFE = unsafe;
+  }
+
+  private static final long BYTE_BUFFER_ADDRESS_FIELD_OFFSET;
+
+  static {
+    try {
+      BYTE_BUFFER_ADDRESS_FIELD_OFFSET =
+          UNSAFE.objectFieldOffset(Buffer.class.getDeclaredField("address"));
+    } catch (final Exception ex) {
+      throw new RuntimeException(ex);
+    }
+  }
+
+  /**
+   * Allocate a new direct {@link ByteBuffer} that is aligned on a given alignment boundary.
+   *
+   * @param capacity required for the buffer.
+   * @param alignment boundary at which the buffer should begin.
+   * @return a new {@link ByteBuffer} with the required alignment.
+   * @throws IllegalArgumentException if the alignment is not a power of 2.
+   */
+  static ByteBuffer allocateDirectAligned(final int capacity, final int alignment) {
+    if (alignment == 0) {
+      return ByteBuffer.allocateDirect(capacity);
+    }
+
+    if (!isPowerOfTwo(alignment)) {
+      throw new IllegalArgumentException("Must be a power of 2: alignment=" + alignment);
+    }
+
+    final ByteBuffer buffer = ByteBuffer.allocateDirect(capacity + alignment);
+
+    final long address = UNSAFE.getLong(buffer, BYTE_BUFFER_ADDRESS_FIELD_OFFSET);
+    final int remainder = (int) (address & (alignment - 1));
+    final int offset = alignment - remainder;
+
+    buffer.limit(capacity + offset);
+    buffer.position(offset);
+
+    return buffer.slice();
+  }
+
+  private static boolean isPowerOfTwo(final int value) {
+    return value > 0 && ((value & (~value + 1)) == value);
+  }
+
+  private BufferUtil() {}
+}