web/web.go
func withStackTracer(h http.Handler, l log.Logger) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if err := recover(); err != nil {
				const size = 64 << 10
				buf := make([]byte, size)
				buf = buf[:runtime.Stack(buf, false)]
				level.Error(l).Log("msg", "panic while serving request", "client", r.RemoteAddr, "url", r.URL, "err", err, "stack", buf)
				panic(err)
			}
		}()
		h.ServeHTTP(w, r)
	})
}
func withStackTracer(h http.Handler, l log.Logger) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if err := recover(); err != nil {
				const size = 64 << 10
				buf := make([]byte, size)
				buf = buf[:runtime.Stack(buf, false)]
				level.Error(l).Log("msg", "panic while serving request", "client", r.RemoteAddr, "url", r.URL, "err", err, "stack", buf)
				panic(err)
			}
		}()
		h.ServeHTTP(w, r)
	})
}
// withStackTrace logs the stack trace in case the request panics. The function
// will re-raise the error which will then be handled by the net/http package.
// It is needed because the go-kit log package doesn't manage properly the
// panics from net/http (see https://github.com/go-kit/kit/issues/233).