How to change the default error output in restify - node.js

Question

Is there any way that I can change the default error output? Say I'm going to change the rest error output:
{
"code": "InvalidArgumentError",
"message": "blah blah..."
}
to:
{
"code": 10001,
"message": "blah blah",
"extraMsg": "blah blah"
}
Here are some of my ideas:
Listen to the error events.
It seems like not all the RestError have emitted extra events (like NotFound, MethodNotAllowed, VersionNotAllowed... do). So I can't catch all the errors to rewrite them.
Listen to an event before response data sent.
I look through the official documents and have found nothing relative.
Modify the implementation of the RestError class.
Well it's obviously not a good approach.
Any other ideas?

Answer 1

Finally I provide a customized JSON formatter to get what I want:
var server = restify.createServer( {
formatters: {
'application/json': function customizedFormatJSON( req, res, body ) {
// Copied from restify/lib/formatters/json.js
if ( body instanceof Error ) {
// snoop for RestError or HttpError, but don't rely on
// instanceof
res.statusCode = body.statusCode || 500;
if ( body.body ) {
body = {
code: 10001,
scode: body.body.code,
msg: body.body.message
};
} else {
body = {
code: 10001,
msg: body.message
};
}
} else if ( Buffer.isBuffer( body ) ) {
body = body.toString( 'base64' );
}
var data = JSON.stringify( body );
res.setHeader( 'Content-Length', Buffer.byteLength( data ) );
return data;
}
}
} );

Answer 2

While the answers above might work, the easiest way to add a custom field to the error body is to call the restify error constructor with an object (hash) instead of a string. The object has to contain the body key which is what you will see in the browser.
For example:
return next(new restify.InvalidArgumentError({body: {field: 'password', message: 'Password has to be at least 6 characters long'}}));
or
return next(new restify.UnauthorizedError({body: {foo: 'bar', name: 'john doe', message: 'whatever error message'}}));

Answer 3

Restify offer many ways to implement error management : http://mcavage.github.io/node-restify/#Error-handling
Why don't you create a new error type "myError" just like sample code :
var restify = require('restify');
var util = require('util');
function MyError(message) {
restify.RestError.call(this, {
restCode : 'MyError',
statusCode : 418,
message : message,
constructorOpt: MyError
});
this.name = 'MyError';
}
util.inherits(MyError, restify.RestError);
For common errors I think that overloading methods is not such a bad idea... (I don't speak about modifying restify, just overloading functions using prototype)
(edited)

Answer 4

I was able to provide additional data adding a property to the body object.
Notice the this.body.errors = errors line
var restify = require('restify');
var util = require('util');
function ValidationError(message, errors) {
restify.RestError.call(this, {
restCode: 'ValidationError',
statusCode: 400,
message: message,
constructorOpt: ValidationError
});
this.name = 'ValidationError';
this.body.errors = errors; //<---
}
util.inherits(ValidationError, restify.RestError);
`

Answer 5

You can use restify-errors-options
Your example simply becomes:
const restify = require('restify');
const errors = require('restify-errors');
const errorsOptions = require('restify-errors-options');
errorsOptions.add('extraMsg');
const err = new errors.BadRequestError({extraMsg: 'whatever you want'});
err.toJSON();
//=> {code: 'BadRequest', message: '', extraMsg: 'whatever you want'}
Please also note that the solution provided was only tested on restify 5.x
Follow this issue for more information.