koa-better-error-handler

A better error-handler for Lad and Koa. Makes ctx.throw awesome (best used with koa-404-handler)

Index

Features
Install
Usage
- API
- Web App
User-Friendly Responses
HTML Error Lists
License

Features

Detects Node.js DNS errors (e.g. ETIMEOUT and EBADFAMILY) and sends 408 Client Timeout error
Detects Mongoose errors and sends 408 Client Timeout error
Detects common programmer mistakes by detecting errors of TypeError, SyntaxError, ReferenceError, RangeError, URIError, and EvalError and yields generic "Internal Server Error" (only applies to production mode)
Detects Redis errors (e.g. ioredis' MaxRetriesPerRequestError) and sends 408 Client Timeout error
Uses Boom for making error messages beautiful (see User Friendly Responses below)
Simply a better error handler (doesn't remove all headers like the built-in one does)
Doesn't make all status codes 500 (like the built-in Koa error handler does)
Supports Flash messages and preservation of newly set session object
Fixes annoying redirect issue where flash messages were lost upon an error being thrown
Supports HTML Error Lists using <ul> for Mongoose validation errors with more than one message
Makes ctx.throw beautiful messages (e.g. ctx.throw(404) will output a beautiful error object 🌺)
Supports text/html, application/json, and text response types
Supports and recommends use of mongoose-beautiful-unique-validation

Install

npm install --save koa-better-error-handler

Usage

You should probably be using this in combination with koa-404-handler too!

The package exports a function which accepts four arguments (in order):

cookiesKey - defaults to false
logger - defaults to console
useCtxLogger - defaults to true
stringify - defaults to fast-safe-stringify (you can also use JSON.stringify or another option here if preferred)

If you pass a cookiesKey then support for sessions will be added. You should always set this argument's value if you are using cookies and sessions (e.g. web server).

We recommend to use Cabin for your logger and also you should use its middleware too, as it will auto-populate ctx.logger for you to make context-based logs easy.

Note that this package only supports koa-generic-session, and does not yet support koa-session-store (see the code in index.js for more insight, pull requests are welcome).

API

No support for sessions, cookies, or flash messaging:

const errorHandler = require('koa-better-error-handler');
const Koa = require('koa');
const Router = require('koa-router');
const koa404Handler = require('koa-404-handler');

// initialize our app
const app = new Koa();

// override koa's undocumented error handler
app.context.onerror = errorHandler();

// specify that this is our api
app.context.api = true;

// use koa-404-handler
app.use(koa404Handler);

// set up some routes
const router = new Router();

// throw an error anywhere you want!
router.get('/404', ctx => ctx.throw(404));
router.get('/500', ctx => ctx.throw(500));

// initialize routes on the app
app.use(router.routes());

// start the server
app.listen(3000);
console.log('listening on port 3000');

Web App

Built-in support for sessions, cookies, and flash messaging:

const errorHandler = require('koa-better-error-handler');
const Koa = require('koa');
const redis = require('redis');
const RedisStore = require('koa-redis');
const session = require('koa-generic-session');
const flash = require('koa-connect-flash');
const convert = require('koa-convert');
const Router = require('koa-router');
const koa404Handler = require('koa-404-handler');

// initialize our app
const app = new Koa();

// define keys used for signing cookies
app.keys = ['foo', 'bar'];

// initialize redis store
const redisClient = redis.createClient();
redisClient.on('connect', () => app.emit('log', 'info', 'redis connected'));
redisClient.on('error', err => app.emit('error', err));

// define our storage
const redisStore = new RedisStore({
  client: redisClient
});

// add sessions to our app
const cookiesKey = 'lad.sid';
app.use(
  convert(
    session({
      key: cookiesKey,
      store: redisStore
    })
  )
);

// add support for flash messages (e.g. `req.flash('error', 'Oops!')`)
app.use(convert(flash()));

// override koa's undocumented error handler
app.context.onerror = errorHandler(cookiesKey);

// use koa-404-handler
app.use(koa404Handler);

// set up some routes
const router = new Router();

// throw an error anywhere you want!
router.get('/404', ctx => ctx.throw(404));
router.get('/500', ctx => ctx.throw(500));

// initialize routes on the app
app.use(router.routes());

// start the server
app.listen(3000);
console.log('listening on port 3000');

User-Friendly Responses

Example Request:

curl -H "Accept: application/json" http://localhost/some-page-does-not-exist

Example Response:

{
  "statusCode": 404,
  "error": "Not Found",
  "message":"Not Found"
}

Prevent Errors From Being Automatically Translated

As of v3.0.5, you can prevent an error from being automatically translated by setting the error property of no_translate to have a value of true:

function middleware(ctx) {
  const err = Boom.badRequest('Uh oh!');
  err.no_translate = true; // <----
  ctx.throw(err);
}

HTML Error Lists

If you specify app.context.api = true or set ctx.api = true, and if a Mongoose validation error message occurs that has more than one message (e.g. multiple fields were invalid) – then err.message will be joined by a comma instead of by <li>.

Therefore if you DO want your API error messages to return HTML formatted error lists for Mongoose validation, then set app.context.api = false, ctx.api = false, or simply make sure to not set them before using this error handler.

try {
  // trigger manual validation
  // (this allows us to have a 400 error code instead of 500)
  await company.validate();
} catch (err) {
  ctx.throw(Boom.badRequest(err));
}

With error lists:

{
  "statusCode": 400,
  "error": "Bad Request",
  "message": "<ul class=\"text-left mb-0\"><li>Path `company_logo` is required.</li><li>Gig description must be 100-300 characters.</li></ul>"
}

Without error lists:

{
  "statusCode":400,
  "error":"Bad Request",
  "message":"Path `company_logo` is required., Gig description must be 100-300 characters."
}

API Friendly Messages

By default if ctx.api is true, then html-to-text will be invoked upon the err.message, thus converting all the HTML markup into text format.

You can also specify a base URI in the environment variable for rendering as process.env.ERROR_HANDLER_BASE_URL, e.g. ERROR_HANDLER_BASE_URL=https://example.com (omit trailing slash), and any HTML links such as <a href="/foo/bar/baz">Click here</a> will be converted to [Click here][1] with a [1] link appended of https://example.com/foo/bar/baz.

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