Method ReadLast

agent/immortalstreams/backedpipe/ring_buffer.go:94–129

ReadLast returns the last n bytes from the buffer. If n is greater than the available data, returns an error. If n is negative, returns an error.

(n int)

// If n is greater than the available data, returns an error.
// If n is negative, returns an error.
func (rb *ringBuffer) ReadLast(n int) ([]byte, error) {
	if n < 0 {
		return nil, xerrors.New("cannot read negative number of bytes")
	}

	if n == 0 {
		return nil, nil
	}

	size := rb.Size()

	// If requested more than available, return error
	if n > size {
		return nil, xerrors.Errorf("requested %d bytes but only %d available", n, size)
	}

	result := make([]byte, n)
	capacity := len(rb.buffer)

	// Calculate where to start reading from (n bytes before the end)
	startOffset := size - n
	actualStart := (rb.start + startOffset) % capacity

	// Copy the last n bytes
	if actualStart+n <= capacity {
		// No wrap needed
		copy(result, rb.buffer[actualStart:actualStart+n])
	} else {
		// Need to wrap around
		firstChunk := capacity - actualStart
		copy(result[0:firstChunk], rb.buffer[actualStart:capacity])
		copy(result[firstChunk:], rb.buffer[0:n-firstChunk])
	}

	return result, nil
}