Catch express bodyParser error

Question

I want to catch the error from the bodyParser() middleware when I send a json object and it is invalid because I want to send a custom response instead of a generic 400 error.

This is what I have and it works:

app.use (express.bodyParser ());
app.use (function (error, req, res, next){
    //Catch bodyParser error
    if (error.message === "invalid json"){
        sendError (res, myCustomErrorMessage);
    }else{
        next ();
    }
});

But this seems to me a very ugly approach because I'm comparing the error message which could change in future express versions. There's any other way to catch bodyParser() errors?

EDIT:

This is the error when the request body has an invalid json:

{
  stack: 'Error: invalid json\n    at Object.exports.error (<path>/node_modules/express/node_modules/connect/lib/utils.js:55:13)\n    at IncomingMessage.<anonymous> (<path>/node_modules/express/node_modules/connect/lib/middleware/json.js:74:71)\n    at IncomingMessage.EventEmitter.emit (events.js:92:17)\n    at _stream_readable.js:872:14\n    at process._tickDomainCallback (node.js:459:13)',
  arguments: undefined,
  type: undefined,
  message: 'invalid json',
  status: 400
}

Pretty printed stack:

Error: invalid json
    at Object.exports.error (<path>/node_modules/express/node_modules/connect/lib/utils.js:55:13)
    at IncomingMessage.<anonymous> (<path>/node_modules/express/node_modules/connect/lib/middleware/json.js:74:71)
    at IncomingMessage.EventEmitter.emit (events.js:92:17)
    at _stream_readable.js:872:14
    at process._tickDomainCallback (node.js:459:13)

Answer 1

I think your best bet is to check for SyntaxError:

app.use(function (error, req, res, next) {
  if (error instanceof SyntaxError) {
    sendError(res, myCustomErrorMessage);
  } else {
    next();
  }
});

Answer 2

From the answer of @alexander but with an example of usage

app.use((req, res, next) => {
    bodyParser.json({
        verify: addRawBody,
    })(req, res, (err) => {
        if (err) {
            console.log(err);
            res.sendStatus(400);
            return;
        }
        next();
    });
});

function addRawBody(req, res, buf, encoding) {
    req.rawBody = buf.toString();
}

Answer 3

Ok, found it:

bodyParser() is a convenience function for json(), urlencoded() and multipart(). I just need to call to json(), catch the error and call to urlencoded() and multipart().

bodyParser source

app.use (express.json ());
app.use (function (error, req, res, next){
    //Catch json error
    sendError (res, myCustomErrorMessage);
});

app.use (express.urlencoded ());
app.use (express.multipart ());

Answer 4

what I did was just:

app.use(bodyParser.json({ limit: '10mb' }))
// body parser error catcher
app.use((err, req, res, next) => {
  if (err) {
    res.status(400).send('error parsing data')
  } else {
    next()
  }
})

Answer 5

All errors include a type property from 1.18.0 release onwards. For parse failure, err.type === 'entity.parse.failed'.

app.use(function (error, req, res, next) {
if (error.type === 'entity.parse.failed') {
 sendError(res, myCustomErrorMessage);
} else {
 next();
}
});

Answer 6

I found checking for SyntaxError to be not enough, therefore I do:

if (err instanceof SyntaxError &&
  err.status >= 400 && err.status < 500 &&
  err.message.indexOf('JSON') !== -1) {
    // process filtered exception here
}