errMap

lightweight middleware for error filtering

Impetus

errMap was created to help control which errors I sent allowed out of an API I was building: i.e. I didn't want sensitive information leaking out to the client in the form of error messages, but I also wanted an easy interface for managing which errors I did allow.

Bad: SQL failure: INSERT id = 3, password_hash = 'fkdsljfa', mismatched_field = 2 INTO USERS

Good: Error: validation error: please check your fields

Installation

$ npm install err-map

Quick Start

var ErrMap = require('err-map');
var initialErrors = {
  'firstErr': {
    status: 400,
    message: 'you goofed it up!'
  }
};

//Will only be called if the error is raised via errMap.
var handler = function(errMapObj, req, res, next) {
  res.status(errMapObj.status).json({message: errMapObj.message});
}

var errMap = new ErrMap(initialErrors, handler);

//Add another error:
errMap.register('second error message', 402, '2ndAlias');


var app = require('express')();

//register a route:
app.get('/err', function() {
  throw errMap.raise('2ndAlias');
});

//instantiate errMap middleware, and the base (catch-all) error:
app.use(errMap.activate({
  status: 500,
  message: 'Internal Server Error'
}));



app.listen(3000);

API

Constructor: function ([map,] [handler])

Instantiate a new instance of errmap with a predetermined error map and handler function.

defaults:

map = {};
handler = function(errMapObj, req, res, next) {
    res.status(errMapObj.status).json({
      message: errMapObj.message
    });
  }

example:

var errMap = new ErrMap(initialErrors, handler);

Methods

activate: function([baseError])

Activate the middleware. Generally, this is the last piece of middleware used.

defaults:

baseError = {
    status: 500,
    message: 'Internal Server Error'
  };

example:

app.use(middleware1);
app.use(middleware2);
//etc
app.use(errMap.activate(baseError))

raise: function(message || alias)

Throw an error from a message or alias.

example:

app.get('/restricted', function() {
  throw errMap.raise('not allowed');
});

***NOTE: If you prefer, errors may also be raised with the standard syntax (It will still work :)):

throw new Error([alias || key])

register: function(message, status, [alias])

Attach a new error to the map, optionally accessed through the alias.

example:

errMap.register('API requires authentication', 401, 'noAuth')

contributors/feedback welcome.