code: func (c *CompressResponseWriter) prepareHeaders() {
  	if c.compressionType != "" {
  		responseMime := ""
  		if t := c.Header.Get("Content-Type"); len(t) > 0 {
  			responseMime = t[0]
  		}
  		responseMime = strings.TrimSpace(strings.SplitN(responseMime, ";", 2)[0])
  		shouldEncode := false
  
  		if len(c.Header.Get("Content-Encoding")) == 0 {
  			for _, compressableMime := range compressableMimes {
  				if responseMime == compressableMime {
  					shouldEncode = true
  					c.Header.Set("Content-Encoding", c.compressionType)
  					c.Header.Del("Content-Length")
  					break
  				}
  			}
  		}
  
  		if !shouldEncode {
  			c.compressWriter = nil
  			c.compressionType = ""
  		}
  	}
  	c.Header.Release()
  }
docs: // Prepare the headers