public boolean isConnected() {
        synchronized (lock) {
            return content != null;
        }
    }
<p>Returns whether or not {@link #connectTo(ContentChannel)} has been called. Even if this method returns false,
calling {@link #connectTo(ContentChannel)} might still throw an IllegalStateException if there is a race.</p>

@return True if {@link #connectTo(ContentChannel)} has been called.
jdisc_core/src/main/java/com/yahoo/jdisc/handler/BufferedContentChannel.java