aeron-client/src/main/java/io/aeron/command/CounterMessageFlyweight.java
public CounterMessageFlyweight keyBuffer(final DirectBuffer keyBuffer, final int keyOffset, final int keyLength)
    {
        buffer.putInt(KEY_LENGTH_OFFSET, keyLength);
        if (null != keyBuffer && keyLength > 0)
        {
            buffer.putBytes(keyBufferOffset(), keyBuffer, keyOffset, keyLength);
        }

        return this;
    }
public CounterMessageFlyweight keyBuffer(final DirectBuffer keyBuffer, final int keyOffset, final int keyLength)
    {
        buffer.putInt(KEY_LENGTH_OFFSET, keyLength);
        if (null != keyBuffer && keyLength > 0)
        {
            buffer.putBytes(keyBufferOffset(), keyBuffer, keyOffset, keyLength);
        }

        return this;
    }
Fill the key buffer.

@param keyBuffer containing the optional key for the counter.
@param keyOffset within the keyBuffer at which the key begins.
@param keyLength of the key in the keyBuffer.
@return flyweight