I am creating an application in SailsJS. I am getting errors, like, typeError or 500 errors when some error occurs in DB related queries.I am using MongoDB. Is there any way that I can catch this error in server-side.
Now, these errors are crashing my server. And the server stops. I have to restart the server again.
Please help me in fixing this issue.
Thanks in advance.
Most likely waterline is throwing an exception and you're not catching it. Here's some code to fix that:
controlleAction:function(req,res){
var invalidParams = {};//whatever's causing the error
Model
.create(invalidParams)
.exec(function(err,created){
if(err) res.json(err);
res.json(created);
});
}
you could also use the promise syntax
controlleAction:function(req,res){
var invalidParams = {};//whatever's causing the error
Model
.create(invalidParams)
.then(function(created){
res.json(created);
})
.catch(function(err){
res.json(err);
});
}
If you're trying to catch every global error in your entire application,
in your app.js, there's a line like this:
// Start server
sails.lift(rc('sails'));
surround that line with a try catch block like so:
try{
// Start server
sails.lift(rc('sails'));
}catch(e){
console.dir(e);
}
Please be careful there:
controlleAction:function(req,res){
var invalidParams = {};//whatever's causing the error
Model
.create(invalidParams)
.exec(function(err,created){
// return res.json()
if(err) return res.json(err);
return res.json(created);
});
}
// The difference is in the return
if(err) return res.json(err);
If you have an error, without the return, the server will crash because it would try to send two responses one with the error and another one with the created object.
If you are using Sails 0.10.x you can pass errors to next handler:
controlleAction:function(req,res, next){
var invalidParams = {};//whatever's causing the error
Model
.create(invalidParams)
.exec(function(err,created){
if(err) return next(err);
return res.json(created);
});
}
And then process errors in "Custom Responses"
Related
I am developing a NodeJS application. I had a problem saving an object to the database; the code in my controller was:
console.log("Before save: " + transaction);
transaction = await transaction.save();
console.log("After save");
In the terminal running the Node application, I saw:
Before save: {
_id: ...,
created: ...,
...
}
and nothing more, while the browser page looks like it's loading.
I tried wrapping it in a try-catch block:
try {
transaction = await transaction.save();
} catch (err) {
console.log(err);
}
and I get the same output in the terminal. I suppose that since I don't see the error in the console without the try-catch, I don't see it with it either.
One problem was that the MongoDB collection for that object did not exist (and I asked about it here). But I still have another error.
How can I enable MongoDB to show those errors (missing collection, and the error I am still looking for) in the terminal running NodeJS while I'm in development?
I found the problem: I had omitted a next(); in a pre-save hook:
SomeSchema.pre('save', function(next) {
// any logic you require
if (this.condition) {
// ...
}
next(); // <- this is required, else Mongo won't save nor return
});
So I was not getting an error because there was no error, only a break in the flow of calls.
I have a node.js service that is being called from a main application. I've had issues where an error occurs in the service and the service hangs preventing any other requests from being handled. I have code to catch errors in common places like after doing a mongodb query.
model.aggregate(
[
...
],function (err, result) {
if (err) {
next(err);
}
else {
//other code
}
I am also catching uncaught exceptions and killing the service in this case with the following code.
process.on('uncaughtException', function (er) {
console.error(er.stack);
logger.log('info','Cbt Dev Service crashed',er);
process.exit(1);
});
These seem to be working fine except I occasionally run into issues where an error occurs but isn't caught by either. An exmple of an error in this case is after getting a result from a mongodb query and getting an error like "Cannot read property 'subjectAreas' of undefined. This error seems to get caught by the mongodb middleware. The code looks like this.
function (err, result) {
if (err) {
res.send(errorHandler(err, req));
}
else {
var subjectAreas = result[0].subjectAreas.sort();
}
In this case result is an empty array so obviously throws an error. I understand that I can prevent this with better written code like using try/catch but if I'm not aware this issue exists and the service hangs up again, I don't know what the error is in order to fix it so that's why I need to log it.
Is there something else I can do that will catch these kinds of errors?
I am very aware of the problems with using uncaughtException in my code. I am also aware that the domains module is being deprecated so I do not want to use that. My question is what to do when I encounter an error that should not happen. For instance, if using mongo db and mongoose the following code example is give:
var kitty = new Cat({ name: 'Zildjian' });
kitty.save(function (err) {
if (err) {
console.log(err);
} else {
console.log('meow');
}
});
Here there is, what I assume is an inexplicable error. It is caught, but only uses console.log to log the error. Clearly more would have to happen to inform the user there is a problem, but I am wondering what should happen to the rest of the application.
Should it shutdown? Should something else happen? I have a good number of cases where I can catch errors like this, but if they happen they represent some very weird situation where something like the database has failed, or something else from another library has failed for no explicable reason and
I suggest you to return a json to your app showing the results of operation. Example:
if(err) {
res.status(500).json({saved: false, errormsg: 'Cannot save to database'});
} else {
res.json({saved: true, errormsg: null});
}
Handle the response in your app and show to the user that some bad think happened.
When an error occurs in NodeJS application, the server may crash and stop if an exception occurs.
How can I prevent this situation so that the server never stops on error, but returns and error code instead ?
--
EDIT
Here is a method which causes a server crash (table foo doesn't exist) :
app.get('/articles/list', function(req, res) {
connection.query('select * from foo', function(err, rows, fields) {
if (err) throw err;
res.send(JSON.stringify(rows));
});
});
-- BEST SOLUTION
Finally, I found the best solution for me :
http://rowanmanning.com/posts/node-cluster-and-express/
In summary, it consists in using a cluster of server, and to restart a server when it exits
If you are using express, you can use this
function clientErrorHandler (err, req, res, next) {
if (req.xhr) {
res.status(500).send({ error: 'Something failed!' })
} else {
next(err)
}
}
app.use(clientErrorHandler);
I suggest you to ready this article, it will clarify a lot for you.
JFK, be aware of async error catching, most common error, once you have async stuff which is wrapped in try-catch.
Also, avoid usage of
process.on("uncaughException", () => {....})
This is quite bad, because when an uncaught exception is thrown you can’t reliably continue your program at this point.Let it fail and restart with daemonizer's like pm2, forever and etc.
As general rule, you should handle all errors and promise rejects in your code to avoid uncaught Exceptions.
For errors: using try-catch statement
For promises: using .catch method
Btw Node permits you to intercept an uncaughtExceptions or unhandledRejection events, but is not a good practice to handle errors at this level and prevent program exits, because can generate unpredictable behaviours.
Use try catch... for parts of code, which throws exception
try{
//youre code here
}catch(error){
console.log(error)
}
I am running node.js with express. I wrote a node module with methods in it so when you go to
http://bla.com/module_name/method_name
it will run the method.
The method follows the typical style of
exports.method_name(req, res, next);
my main app does something like this:
app.all("*", resSetup, controller, render);
and controller is the thing that will call the method based on the path.
it seems that if there is an undefined variable error in the method, express will just hang there and not throw any error. Nothing will appear in the console log either. I can put a console message right before and after where the error occurs and the before will appear in the log, and after will not.
I can wrap it in a try/catch and get this:
[ReferenceError: blabla is not defined]
but no line numbers or anything.
My guess is that express is somehow preventing the errors from coming up. When I put the error in the function called "controller" that is directly in the route, it shows that error correctly.
It might not matter too much, but here is the code I am working on:
https://github.com/RobKohr/quick-site/blob/master/index.js
Line 189 is where the method call happens.
Building on Ruairi's comment above, I had this same issue with when using 'q' (https://github.com/kriskowal/q) and promises with express - node would hang and no error was generated.
By adding a catch to the end of the promise 'callback' chain I was able to see the error and print it to console etc.
The code ends up looking like:
export function index(req, res) {
//Create the 'promise'
var request = req.body;
var queryJobID = req.query.jobId;
console.log('queryJobID: ' + queryJobID);
var jobStatusPromsie = jobManager.job.getStatus(queryJobID);
Q.all([jobStatusPromsie])
.then(
function (result) {
var responseData = {};
console.log('Job Status Response received');
if (result != null) {
//Without the .catch below an error here will be 'silent'
console.log('jobStatus result: ' + util.inspect(result, false, null));
responseData['status'] = 'OK';
responseData['progress'] = result.progress;
res.json(responseData);
} else {
console.log('jobStatus Error');
responseData['status'] = 'Error';
}
res.json(responseData);
console.log('jobStatus Response data sent');
},
function (error) {
console.log('Error while getting job status:', error);
res.json("Error");
})
.catch(function(err) {
//handle errors
console.log('Promise error while getting job status:', err);
});
}
Express heavily relies on Nodes asynchronous nature. Seeing errors thrown like on line 30 would give me the creeps if I was maintaining this. Try refactoring your code to only use the next(err) pattern.
The reason that you app is hanging is that Express hasn't finished the HTTP response (eg: res.send()). This means you have broken plumbing where an Error has bubbled up the call stack but not redirected into the Express middleware pipeline. Try registering some error middleware to see if it gets called with your error.