code: func NewPathPrefixStripper(prefixSize int) PathRewriteFunc {
  	return func(ctx *RequestCtx) []byte {
  		path := ctx.Path()
  		if len(path) >= prefixSize {
  			path = path[prefixSize:]
  		}
  		return path
  	}
  }
docs: // NewPathPrefixStripper returns path rewriter, which removes prefixSize bytes
  // from the path prefix.
  //
  // Examples:
  //
  //   * prefixSize = 0, original path: "/foo/bar", result: "/foo/bar"
  //   * prefixSize = 3, original path: "/foo/bar", result: "o/bar"
  //   * prefixSize = 7, original path: "/foo/bar", result: "r"
  //
  // The returned path rewriter may be used as FS.PathRewrite .