code: func (h *ResponseHeader) SetContentRange(startPos, endPos, contentLength int) {
  	b := h.bufKV.value[:0]
  	b = append(b, strBytes...)
  	b = append(b, ' ')
  	b = AppendUint(b, startPos)
  	b = append(b, '-')
  	b = AppendUint(b, endPos)
  	b = append(b, '/')
  	b = AppendUint(b, contentLength)
  	h.bufKV.value = b
  
  	h.SetCanonical(strContentRange, h.bufKV.value)
  }
docs: // SetContentRange sets 'Content-Range: bytes startPos-endPos/contentLength'
  // header.