noir-exception

Middleware for displaying noir style exceptions in the browser.

We missed noir exceptions. noir-exception brings back noir styled back traces for the browser. You will easily find problems with your code because noir-exception highlights your namespaces with a diferent color. The exception will be displayed along with the request that caused it.

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Install

Add the following dependency to your project.clj file:

Usage

The library provides two middleware functions called wrap-exceptions and wrap-internal-error.

The wrap-exceptions function will create styled stack traces to highlight local namespaces. This is useful for quickly identifying what matters most in stack traces during development.

If you have, as an example, development and production profiles, use the quiet? optional flag to set the profile - #(wrap-exceptions % quiet?). If you always want to show the stack traces, just use wrap-exceptions.

(ns my.ns
  (:require [noir-exception.core :refer [wrap-exceptions]]
            ...))

(def quiet? (not (= (System/getenv "PROFILE") "dev")))

(def app
  (app-handler [routes]
    :middleware [#(wrap-exceptions % quiet?)]))

The wrap-internal-error function allows catching errors and producing a standard error page. This function should be used for handling errors in production, where you do not wish to expose the internals of the application to the user. The function will print the stack trace and request to standard out by default.

The function accepts two keyword arguments, named :log and :error-response. The first allows providing a custom log function for the exceptions and the second can be used to supply a custom error response.

Alternatively to :error-response, it's possible to supply the :error-response-handler key that points to a function which can accept :request and :error as parameters and return a string response that will be returned to the client. This can be useful for generating contextual errors based on the contents of the request.

(ns my.ns
  (:require [taoensso.timbre :as timbre]
            [noir-exception.core :refer [wrap-internal-error]]
            ...))

(def app
  (app-handler [routes]
    :middleware [#(wrap-internal-error %
                    :log (fn [{:keys [error]}] (timbre/error error))
                    :error-response {:status 500
                                     :headers {"Content-Type" "text/html"}
                                     :body "something bad happened!"})]))

It's possible to reuse the error page in your handler like this:

(noir-exception.core/dev-page :error error :request request)

e.g., to send the error page to the developer by email.

It's also possible to reuse the production page:

(noir-exception.core/prod-page :h "We did something dumb"
                               :msg "Trained monkeys are fixing this mess")
(noir-exception.core/prod-page) ; uses library default messages

e.g., to present a custom message to your users.