fs.go
func NewPathPrefixStripper(prefixSize int) PathRewriteFunc {
	return func(ctx *RequestCtx) []byte {
		path := ctx.Path()
		if len(path) >= prefixSize {
			path = path[prefixSize:]
		}
		return path
	}
}
func NewPathPrefixStripper(prefixSize int) PathRewriteFunc {
	return func(ctx *RequestCtx) []byte {
		path := ctx.Path()
		if len(path) >= prefixSize {
			path = path[prefixSize:]
		}
		return path
	}
}
// 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 .