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.
Related
This bit of code, after connecting, does some stuff
controller.connect((response)=>{ does some stuff })
Down deep in the guts of the connect method this async function gets called, which returns a promise by way of the callback
async function ServerSend(endpoint,params,callback) {
const response = axios.get(host+endpoint, {params})
callback(response);
}
If the server is not available it correctly throws: UnhandledPromiseRejectionWarning: Error: connect ECONNREFUSED 127.0.0.1:8088
What is the correct way to handle this exception? I could possibly add a catch in the async method and rewrite all the call backs to return an err. But I'd rather catch it at the caller. I have not been able to get either method to work.
axios.get(host+endpoint, {params}) // this is a promise
so if it resolves it will be ok, but if it rejects (and yuou dont have any try .. catch, any .catch attached - it will throw error that exception is unhandled.
Why way would be to:
async function ServerSend(endpoint,params,callback) {
try {
const response = await axios.get(host+endpoint, {params})
callback(null, response);
} catch (err) {
callback(err, null);
}
}
OR
function ServerSend(endpoint,params,callback) {
// most callbacks are two parameters - 1st erro or null, second data if no error is present.
axios.get(host+endpoint, {params}).then(data => callback(null, data)).catch(err => callback(err, null));
}
The sequelize create statement has an error and I would like to handle that error. Since the create statement has the error I need to handle promise rejection. How do I do that in code? Tried to look at the sequelize documents but unable to work it out.
db.Employee.create(empData,
{
include:[
{
model: db.EmployeeDetails
}
]
}).then(function(newEmployee){
res.json(newEmployee);
}).catch(function(err){
return next(err);
});
The error is on the create and so the webpage just gives an internal server error. I was under the impression that the catch was something that handled the promise rejection and failure. In this case, how can I handle the promise rejection in code. An example would be greatly appreciated.
By doing next(err), by default, you send a 500 Internal Server Error message. If you use Express, and want to show a custom error, just append a status code which is not 5xx to the error:
General Usage:
const err = new Error("my custom error")
err.statusCode = 400
next(err)
In your snippet, do:
db.Employee.create(empData, {
include:[
{
model: db.EmployeeDetails
}
]
}).then(function(newEmployee){
res.json(newEmployee);
}).catch(function(err){
err.statusCode = 400
next(err);
});
If you haven't set your error handler in Express you will need to add somewhere at the end of the main file this:
// Error Handler
app.use(function(err, req, res, next) {
console.error(err)
if (!err.statusCode) err.statusCode = 500;
let msg = err.message
// Do not expose 500 error messages in production, to the client
if (process.env.NODE_ENV === "production" && err.statusCode === 500) {
msg = "Internal Server Error"
}
res.status(err.statusCode).send(msg)
})
Your webpage showing a 500 error means the issue was caught / working as intended. What you need to do is figure out how to handle displaying that error in a pretty format - this being a UI task. If you want a 'patch' for hiding the issue, change your return to a res. This will trick your browser with a 200 status and hide the error.
I do want to add, I recommend trying async/await for sequelize. There's a good amount of usage examples with it.
Promise
db.Employee.create(empData,
{
include:[
{
model: db.EmployeeDetails
}
]
}).then(function(newEmployee){
res.json(newEmployee);
}).catch(function(err){
// Temporary patch
res.json("pretty error message");
});
Async/Await version
async function createEmployee(empData) {
try {
return await db.Employee.create(empData, {
include:[ { model: db.EmployeeDetails } ]
});
} catch (err) {
// Handle error here
return err;
}
}
I want to test the saveRecords function for the failure and before that, I have to authenticate and connect the MongoDB. This is the code.
before(() => {
sinon.stub(Authentication, 'authenticate').returns(true);
sinon.stub(mongodb, 'connect').resolves("connected");
sinon.stub(models, 'saveRecords').throws(new Error("Error while saving record"));
});
it('Should error out if record is not inserted into the mongodb
collection', () => {
orderWebhook(req, res)
expect(res.result).to.contain("Error while saving record");
});
Here is the code I am testing.
exports.orderWebhook = async (req, res) => {
try {
const isAuthenticated = Authentication.authenticate(req);
if (isAuthenticated) {
await mongodb.connect();
await models.saveRecords(req.body");
res.status(200).send('Saved Successfully!');
} else {
res.status(403).send('Error! Auth failed!');
}
} catch (error) {
res.status(400).send(error.message);
}
}
I am assuming that this code will stub the authenticate then connect MongoDB and then try to insert the record and throw the error. But it is running two times when I debug with the VSCode debugger.
The first time it is returning true for the authenticate function and not resolving the MongoDB connect and return to expect immediately.
The second time it is running all three properly and throwing the expected error.
It is failing when I run the test in the terminal, What could be the issue?
Update: I noticed that the problem is related to the promise. Sinon is resolving the request and I am using await mongodb.connect(); but it is not working as expected, and if I remove await and return value instead of promise then it works.
I've got this code below that fetches once from firebase on nodejs. I'm purposely throwing an error and attempting to catch it, however, the error isn't being handled and my server keeps crashing and my catch statement isn't being executed.
FIREBASE WARNING: Exception was thrown by user callback. Error:
Article is not found
var ref = fdb.ref("Emojis");
ref.once("value", function (data) {
// do some stuff once
throw Error('Article is not found');
console.log(data.val());
}).catch(error => {
console.log('an error happenned')
});
I also tried this code and the error is still not handled:
ref.once("value", function (snapshot) {
throw Error('Article is not found');
console.log(snapshot.val());
}, function (errorObject) {
console.log("The read failed: " + errorObject.code);
});
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