Irrespective of the type of database, I can't get a clear picture of best way of handling db errors without crashing the application.
e.g connecting with sql
pool.getConnection(function(err, connection) {
if (err) {
throw err
}
connection.execute('select * ...' , values, function(err, result) {
if (err) {
throw err;
}
});
});
In both cases above I am throwing errors which causes node server to crash.
I want to register the error and respond to the request in a most elegant fashion. Can anyone point in the right direction ?
When you are throwing an error, someone needs to catch them. If you don't catch them anywhere in your code, it will cause the program to crush.
So basically what you need to do is to wrap the call to your functions with try/catch, and in case you catch- log it and return an apporopriate response to the requester.
Something like:
try {
pool.getConnection(function(err, connection) {
if (err) {
throw err
}
connection.execute('select * ...' , values, function(err, result) {
if (err) {
throw err;
}
});
});
} catch (error) {
log(error);
res.status(500).body("failed to get ... " + err).send();
}
I also recommend reading this blog post, has good explanation about the subject
Related
how can I catch an error in NodeJS or create own error code and send it to the frontend to inform the user?
In the following code I am looking into the database result if there were any data deleted and try to send an error code. How can I send the error code to my react frontend? Maybe using response.json("Not deleted any user"). Tried it already out.
How can I prevent my server from crashing? If the sql is not correcting because there was no id send to delete it is crashing.
Thanks for the answers for this two cases.
db.getConnection((err, connection) => {
if (err) throw err;
connection.query(
"DELETE FROM users where users_id = ?",
[2],
(err, rows) => {
connection.release();
if (rows.affectedRows == 0) {
throw err;
}
if (err) throw err;
if (!err) {
res.redirect("/");
} else {
console.log(err);
}
console.log("Daten gelöscht", rows.affectedRows);
}
);
});
You should use a try, catch block. If you want to throw a custom exception, you can do something like
throw new NotFoundException("Record with the given id Not Found...!!!"):
I use it in nestjs I am not fully sure that this will work for you but you can try :)
the answer to this question: How to get node to exit when mongo connect fails contains async/wait code for a connection
however, my code (running on node v11.5.0 and mongodb v3.1.13) is failing to catch:
(async function() {
let db;
try {
db = await MongoClient.connect(uri, { useNewUrlParser: true });
console.log("RETURN", db);
} catch (err) {
console.log('EXITING');
process.exit(1);
}
}());
to prove the point I intentionally give a uri without credentials:
mongodb://undefined#cluster0-shard-00-00-z4j9e.azure.mongodb.net:27017,cluster0-shard-00-01-z4j9e.azure.mongodb.net:27017,cluster0-shard-00-02-z4j9e.azure.mongodb.net:27017/test?ssl=true&replicaSet=Cluster0-shard-0&authSource=admin&retryWrites=true
and what I get is output like this:
/Users/ekkis/dev/mongo/node_modules/mongodb/lib/topologies/replset.js:346
throw err;
^
MongoError: password must be a string
at passwordDigest (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/auth/scram.js:63:43)
at ScramSHA1.ScramSHA.auth (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/auth/scram.js:175:25)
at authenticate (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/connection/pool.js:232:17)
at authenticateLiveConnections (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/connection/pool.js:819:7)
at /Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/connection/pool.js:864:5
at waitForLogout (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/connection/pool.js:855:34)
at Pool.auth (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/connection/pool.js:862:3)
at Server.auth (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/topologies/server.js:931:20)
at auth (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/topologies/replset.js:1474:19)
at ReplSet.auth (/Users/ekkis/dev/mongo/node_modules/mongodb-core/lib/topologies/replset.js:1492:5)
so if the error had been caught, the console should have displayed the word 'EXITING', but does not. additionally, I contend an exception was thrown because otherwise the returned value would have been printed, which it was not
how can this be? what do I need to do to get it to work?
* Appendix I *
In fact, the promises version of this exhibits the same odd behaviour, it doesn't catch:
MongoClient
.connect(uri, { useNewUrlParser: true })
.then(dbc => {
console.log('SUCCESS');
})
.catch(err => {
console.log('EXITING');
process.exit(1);
});
and yes, I tested the callback version, which also suffers the same malady. Incidentally, passing an empty string for the uri works well. I don't get it
* Appendix II *
In fact, the problem seems to be particular to the credentials passed i.e. if I pass:
mongodb://x:y#cluster0-shard-[...]
I catch a "MongoError: authentication fail" as expected. passing:
mongodb://#cluster0-shard-[...]
interestingly returns a connection but credentials missing a ":" fail in this odd way, so:
mongodb://ekkis#cluster0-shard-[...]
fails to catch
Looks to me like it's a bug with however MongoClient is setting up its connections. You won't be able to use try & catch to handle asynchronously thrown errors within MongoClient code.
const {MongoClient} = require("mongodb");
process.on("uncaughtException", (err) => {
console.log("process err", err);
process.exit(1)
})
async function run () {
let db;
try {
// connection url will throw because password isn't provided
db = await MongoClient.connect("mongodb://myUsername:#localhost", { useNewUrlParser: true });
} catch (err) {
console.log('Exiting from thrown error', err);
process.exit(1);
}
}
run();
Here's a simplified example of what's happening -- the error will end up "uncaught" and caught by the uncaughtException handler
process.on("uncaughtException", (err) => console.log("uncaught", err));
try {
setTimeout(() => {
throw new Error("asynchronously thrown error");
})
} catch (err) {
console.log("Error will not be caught here")
}
When I was using mongo version 3.6.1, it was not an issue and i was able to handle the thrown exception using catch. But after a few days on another project this type of error occurred and was showing as the error thrown from
%project_folder%/node_modules/mongodb/lib/utils.js:668
(Don't mind about the slash in the path string.)
The mongodb version this time is 3.6.3. Upon checking the code in that file at the mentioned line I found the below piece of code. where the caught error is again being thrown.
fn(function(err, res) {
if (err != null) {
try {
callback(err);
} catch (error) {
return process.nextTick(() => {
throw error;
});
}
return;
}
callback(err, res);
});
I changed the throw error to console.error(error) and the problem got resolved. But still you need to be caught somewhere in our code where connect function is called.
I think this is because the above piece of code is checking for the presence of error and passing it to the callback function and then again throwing the same error again. I suppose it is the MongoDB driver developer community's responsibility to resolve this issue.
I'm curious if there's a good way to handle this with express 4.0.
There are times where there is a problem with either Stripe, or my connection to Stripe that needs to be addressed. However, I obviously do not want users to know about this. I want to display a message 'There was a problem completing your order, please contact support.' while safely logging the message with some information for me to handle it.
I suspect I can do this in middleware. However, I'm not sure how. I would like to catch these errors as they are happening and dump them to a logfile of some kind (suggestions would be great) so I can handle it.
Is there a standard way of doing this? How would I accomplish this?
Thank you!
You're thinking about this the wrong way. Instead of exposing 3rd party errors, explicitly define each possible failure case in your route.
// bad
app.use(function (err, req, res, next) {
res.status(err.status).json({ error: err.message })
})
Instead mark errors to be exposed:
app.use(function (err, req, res, next) {
if (err.expose) {
res.status(err.status).json({ code: err.code, error: err.message })
} else {
reportError(err, req)
res.status(500).json({ code: "unknown", error: "unknown error" })
}
})
You need to re-throw actual api errors.
function createError(status, message) {
var err = new Error(message)
err.expose = true
err.status = status
return err
}
function changeCard(user, data) {
return postStripeCards(user, data)
.catch({ type: "card_error" }, function (err) {
throw createError(400, "invalid card")
})
}
Uncaught errors are programmer mistakes which should be reported and fixed. Anything that makes it through is a bug.
function reportError (err, req) {
// log error
console.error(err.stack)
// send to rollbar
rollbar.handleError(err, req)
// maybe send an email
mailgun.send({
from: "bot#myapp.com",
to: "me#gmail.com",
subject: "My App: " + err.message,
text: err.stack + "\n\n" + JSON.stringify(req),
})
// pager duty, airbrake, etc
}
It takes work, but it means your API is well-defined.
I'm creating an API using Restify and Mongoose, and I'm completely new to both. I can't seem to figure out the proper way to handle errors in Mongoose / Node.
As of now, I'm trying to do something like this:
Submission.findById(req.params.submission_id, function(err, data) {
if (err)
return next(err);
res.send(data);
});
I'm attempting to call a GET on this (for a user that not exist). And rather than sending back a simple error message, it causes my entire node application to fail. I'm a bit confused on the user of return next(err) and what that exactly should do.
Any help is greatly appreciated.
A findById query that doesn't find a match isn't an error at the Mongoose level, so you if you want it treated that way you have to do it yourself:
Submission.findById(req.params.submission_id, function(err, data) {
if (err)
return next(err);
else if (!data)
return next(new Error("User not found"));
res.send(data);
});
I am using node-mongodb-native driver. I tried
collection.findOne({email: 'a#mail.com'}, function(err, result) {
if (!result) throw new Error('Record not found!');
});
But the error is caught by mongodb driver and the express server is terminated.
What's the correct way for this case?
=== Edit===
I have the code below in app.js
app.configure('development', function() {
app.use(express.errorHandler({dumpExceptions: true, showStack: true}));
});
app.configure('production', function() {
app.use(express.errorHandler());
});
Related code in node_modules/mongodb/lib/mongodb/connection/server.js
connectionPool.on("message", function(message) {
try {
......
} catch (err) {
// Throw error in next tick
process.nextTick(function() {
throw err; // <-- here throws an uncaught error
})
}
});
The correct use is not to throw an error, but to pass it to next function. First you define the error handler:
app.error(function (err, req, res, next) {
res.render('error_page.jade');
})
(What's this talk about error being depracated? I don't know anything about that. But even if then you can just use use. The mechanism is still the same.).
Now in your route you pass the error to the handler like this:
function handler(req, res, next) {
collection.findOne({email: 'a#mail.com'}, function(err, result) {
if (!result) {
var myerr = new Error('Record not found!');
return next(myerr); // <---- pass it, not throw it
}
res.render('results.jade', { results: result });
});
};
Make sure that no other code (related to the response) is fired after next(myerr); (that's why I used return there).
Side note: Errors thrown in asynchronous operations are not handled well by Express (well, actually they somewhat are, but that's not what you need). This may crash your app. The only way to capture them is by using
process.on('uncaughtException', function(err) {
// handle it here, log or something
});
but this is a global exception handler, i.e. you cannot use it to send the response to the user.
I'm guessing that the error is not caught. Are you using an Express error handler? Something like:
app.error(function (err, req, res, next) {
res.render('error-page', {
status: 404
});
More on error handling in Express: http://expressjs.com/guide.html#error-handling
In terms of checking for errors off mongodb, use '!error' for success as opposed to '!result' for errors.
collection.findOne({email: 'a#mail.com'}, function(err, result) {
if (!error) {
// do good stuff;
} else {
throw new Error('Record not found!');
}
});
As for the custom 404, I've yet to do that in node and express, but I would imagine it would involve "app.router".