This package is an error handler for use in both development (debug) and production environments.
In production mode, strong-error-handler
omits details from error responses to prevent leaking sensitive information:
- For 5xx errors, the output contains only the status code and the status name from the HTTP specification.
- For 4xx errors, the output contains the full error message (
error.message
) and the contents of thedetails
property (error.details
) thatValidationError
typically uses to provide machine-readable details about validation problems. It also includeserror.code
to allow a machine-readable error code to be passed through which could be used, for example, for translation.
In debug mode, strong-error-handler
returns full error stack traces and internal details of any error objects to the client in the HTTP responses.
Current | Long Term Support | Maintenance |
---|---|---|
3.x | 2.x | 1.x |
Learn more about our LTS plan in docs.
$ npm install --save strong-error-handler
In an Express-based application:
var express = require('express');
var errorHandler = require('strong-error-handler');
var app = express();
// setup your routes
// `options` are set to default values. For more info, see `options` below.
// app.use(errorHandler({ /* options, see below */ }));
app.use(errorHandler({
debug: app.get('env') === 'development',
log: true,
}));
app.listen(3000);
The module also exports writeErrorToResponse
, a non-middleware flavor of the
error handler:
const http = require('http');
const writeErrorToResponse = require('strong-error-handler')
.writeErrorToResponse;
const errHandlingOptions = {debug: process.env.NODE_ENV === 'development'}
http
.createServer((req, res) => {
if (errShouldBeThrown) {
writeErrorToResponse(
new Error('something went wrong'),
req,
res,
errHandlingOptions,
);
}
})
.listen(3000);
In LoopBack applications, add the following entry to server/middleware.json
:
{
"final:after": {
"strong-error-handler": {
"params": {
"debug": false,
"log": true
}
}
}
}
In general, strong-error-handler
must be the last middleware function registered.
The above configuration will log errors to the server console, but not return stack traces in HTTP responses. For details on configuration options, see below.
The strong-error-handler
package supports JSON, HTML and XML responses:
- When the object is a standard Error object, it returns the string provided by the stack property in HTML/text responses.
- When the object is a non-Error object, it returns the result of
util.inspect
in HTML/text responses. - For JSON responses, the result is an object with all enumerable properties from the object in the response.
The content type of the response depends on the request's Accepts
header.
- For Accepts header
json
orapplication/json
, the response content type is JSON. - For Accepts header
html
ortext/html
, the response content type is HTML. - For Accepts header
xml
ortext/xml
, the response content type is XML.
There are plans to support other formats such as Plain-text.
Option | Type | Default | Description |
---|---|---|---|
debug | Boolean | false |
If true , HTTP responses include all error properties, including sensitive data such as file paths, URLs and stack traces. See Example output below. |
log | Boolean | true |
If true , all errors are printed via console.error , including an array of fields (custom error properties) that are safe to include in response messages (both 4xx and 5xx). If false , sends only the error back in the response. |
safeFields | [String] | [] |
Specifies property names on errors that are allowed to be passed through in 4xx and 5xx responses. See Safe error fields below. |
defaultType | String | "json" |
Specify the default response content type to use when the client does not provide any Accepts header. |
negotiateContentType | Boolean | true | Negotiate the response content type via Accepts request header. When disabled, strong-error-handler will always use the default content type when producing responses. Disabling content type negotiation is useful if you want to see JSON-formatted error responses in browsers, because browsers usually prefer HTML and XML over other content types. |
Express
To use a different log format, add your own custom error-handling middleware then disable errorHandler.log
.
For example, in an Express application:
app.use(myErrorLogger());
app.use(errorHandler({ log: false }));
In general, add strong-error-handler
as the last middleware function, just before calling app.listen()
.
LoopBack
For LoopBack applications, put custom error-logging middleware in a separate file; for example, server/middleware/error-logger.js
:
module.exports = function(options) {
return function logError(err, req, res, next) {
console.log('unhandled error' ,err);
next(err);
};
};
Then in server/middleware.json
, specify your custom error logging function as follows:
{
// ...
"final:after": {
"./middleware/error-logger": {},
"strong-error-handler": {
"params": {
"log": false
}
}
}
The default middleware.development.json
file explicitly enables logging in strong-error-handler params, so you will need to change that file too.
By default, strong-error-handler
will only pass through the name
, message
and details
properties of an error. Additional error
properties may be allowed through on 4xx and 5xx status code errors using the safeFields
option to pass in an array of safe field names:
{
"final:after": {
"strong-error-handler": {
"params": {
"safeFields": ["errorCode"]
}
}
}
Using the above configuration, an error containing an errorCode
property will produce the following response:
{
"error": {
"statusCode": 500,
"message": "Internal Server Error",
"errorCode": "INTERNAL_SERVER_ERROR"
}
}
NOTE: This is only required for applications scaffolded with old versions of the slc loopback
tool.
To migrate a LoopBack 2.x application to use strong-error-handler
:
- In
package.json
dependencies, remove"errorhandler": "^x.x.x”,
- Install the new error handler by entering the command:
npm install --save strong-error-handler
- In
server/config.json
, remove:"remoting": { ... "errorHandler": { "disableStackTrace": false }
and replace it with:"remoting": { ..., "rest": { "handleErrors": false }
- In
server/middleware.json
, remove:"final:after": { "loopback#errorHandler": {} }
and replace it with:"final:after": { "strong-error-handler": {} }
- Delete
server/middleware.production.json
. - Create
server/middleware.development.json
containing:"final:after": { "strong-error-handler": { "params": { "debug": true, "log": true } } }
For more information, see Migrating apps to LoopBack 3.0.
5xx error generated when debug: false
:
{ error: { statusCode: 500, message: 'Internal Server Error' } }
The same error generated when debug: true
:
{ error:
{ statusCode: 500,
name: 'Error',
message: 'a test error message',
stack: 'Error: a test error message
at Context.<anonymous> (User/strong-error-handler/test/handler.test.js:220:21)
at callFnAsync (User/strong-error-handler/node_modules/mocha/lib/runnable.js:349:8)
at Test.Runnable.run (User/strong-error-handler/node_modules/mocha/lib/runnable.js:301:7)
at Runner.runTest (User/strong-error-handler/node_modules/mocha/lib/runner.js:422:10)
at User/strong-error-handler/node_modules/mocha/lib/runner.js:528:12
at next (User/strong-error-handler/node_modules/mocha/lib/runner.js:342:14)
at User/strong-error-handler/node_modules/mocha/lib/runner.js:352:7
at next (User/strong-error-handler/node_modules/mocha/lib/runner.js:284:14)
at Immediate._onImmediate (User/strong-error-handler/node_modules/mocha/lib/runner.js:320:5)
at tryOnImmediate (timers.js:543:15)
at processImmediate [as _immediateCallback] (timers.js:523:5)' }}
4xx error generated when debug: false
:
{ error:
{ statusCode: 422,
name: 'Unprocessable Entity',
message: 'Missing required fields',
code: 'MISSING_REQUIRED_FIELDS' }}