// Users should either catch ErrShortDst and allow dst to grow or have dst be at
// least of size MaxTransformChunkSize to be guaranteed of progress.
func (f Form) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
	// Cap the maximum number of src bytes to check.
	b := src
	eof := atEOF
	if ns := len(dst); ns < len(b) {
		err = transform.ErrShortDst
		eof = false
		b = b[:ns]
	}

// Users should either catch ErrShortDst and allow dst to grow or have dst be at
// least of size MaxTransformChunkSize to be guaranteed of progress.
func (f Form) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
	// Cap the maximum number of src bytes to check.
	b := src
	eof := atEOF
	if ns := len(dst); ns < len(b) {
		err = transform.ErrShortDst
		eof = false
		b = b[:ns]
	}

	if len(c.dst)-c.pDst < len(b) {
		c.err = transform.ErrShortDst
		return false
	}
	// This loop is faster than using copy.
	for _, ch := range b {
		c.dst[c.pDst] = ch
		c.pDst++
	}
	return true
}

// writeString writes the given string to dst.
func (c *context) writeString(s string) bool {
	if len(c.dst)-c.pDst < len(s) {
		c.err = transform.ErrShortDst
		return false
	}

// needs to be reset between uses.
func (t *Transformer) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
	if len(dst) < len(src) {
		src = src[:len(dst)]
		atEOF = false
		err = transform.ErrShortDst
	}
	n, err1 := t.Span(src, atEOF)
	copy(dst, src[:n])
	if err == nil || err1 != nil && err1 != transform.ErrShortSrc {
		err = err1
	}
	return n, n, err
}