Such a ReadableByteChannel should throw an IllegalArgumentException. This may be demonstrated by modifying java/nio/channels/Channels/Basic.java as:

@@ -296,6 +296,12 @@ public class Basic {
         byte data[] = new byte[messageSize+1];
         ByteBuffer bb = ByteBuffer.wrap(data);
 
+ try {
+ rbc.read(bb.asReadOnlyBuffer());
+ } catch (IllegalArgumentException expected) {
+ // ignore it
+ }
+
         int bytesRead = 0;
         int totalRead = 0;
         while (bytesRead != -1) {