Handle StatelessHandlerFn
		// OutCapacity is the output capacity on the caller.
		// If <= 0 capacity will be 1.
		OutCapacity int
	}

	// StreamHandlerFn must process a request with an optional initial payload.
	// It must keep consuming from 'in' until it returns.
	// 'in' and 'out' are independent.
	// The handler should never close out.
	// Buffers received from 'in'  can be recycled with PutByteBuffer.