core: Opaque: provide helper method to instantiate from ByteBuffer

We can construct an Opaque instance from the bytes provided in a
ByteBuffer. This saves us one clone() in Inode.

Related: #149
Signed-off-by: Christian Kohlschütter <[email protected]>

Author: kohlschuetter

core/src/main/java/org/dcache/nfs/util/Opaque.java

@@ -19,6 +19,7 @@
  */
 package org.dcache.nfs.util;
 
+import java.nio.ByteBuffer;
 import java.util.Arrays;
 import java.util.Base64;
 
@@ -31,6 +32,22 @@ public static Opaque forBytes(byte[] bytes) {
         return new OpaqueImpl(bytes.clone());
     }
 
+    /**
+     * Returns an {@link Opaque} instance based on a copy of the {@code length} bytes from the given {@link ByteBuffer}
+     * starting from the current {@link ByteBuffer#position()} plus the given {@code offset}.
+     * 
+     * @param buf The buffer.
+     * @param offset The offset (relative to the current position).
+     * @param length The number of bytes.
+     * @return The {@link Opaque} instance.
+     */
+    public static Opaque forBytes(ByteBuffer buf, int offset, int length) {
+        byte[] bytes = new byte[length];
+        buf.get(bytes, offset, length);
+
+        return new OpaqueImpl(bytes);
+    }
+
     byte[] toBytes();
 
     String toBase64();

core/src/main/java/org/dcache/nfs/vfs/Inode.java

@@ -109,9 +109,7 @@ public Inode(byte[] bytes) {
         exportIdx = b.getInt();
         type = (int) b.get();
         int olen = (int) b.get();
-        byte[] fs_opaque = new byte[olen];
-        b.get(fs_opaque);
-        this.opaqueKey = Opaque.forBytes(fs_opaque);
+        this.opaqueKey = Opaque.forBytes(b, 0, olen);
 
         this.nfsHandle = bytes.clone();
     }