Meteor.call does not wait for the result - javascript

The Async callback in Meteor.call does not wait for the result from the Meteor.method.This is the code.
Meteor.call("fetchData",function (err,res) {
if (err){
console.log("error ", err);
}else {
console.log("success ", res);
return res;
}
});//calling this from onRendered of client/somejs.js
Here is the method
fetchData :function(){
HTTP.call("POST","http://localhost:8080",{
data:'{"apple":"grape"}'
},function (err,res) {
if (err){
console.log("error ", err);
}else {
console.log("success ", res);
return res;
}
})
}//Server/methods.js
When Meteor.call is triggered,i get a log on the Server as success with its result.
On the client i get success undefined .
The call on the client does not wait for the result.Also i tried Fibers and Synchronous execution on the server.It does not work for me.In this case a publish is blocked(i guess due to the API call).
Another thing is that i tried the same with a DB query instead of API call.That works fine.I get the result from the Method.
Where am i going wrong.Help.
Thanks

Sanjith.
You were on the right path with futures. By default, Meteor's methods are async, so some "waiting" mechanism is needed on the client. For this, I'd recommend either using Meteor.wrapAsync or Promises. Here are two detailed explanations on implementing both:
https://themeteorchef.com/snippets/synchronous-methods/#tmc-using-wrapasync
https://themeteorchef.com/snippets/promise-based-modules/#tmc-calling-our-promise-based-module-from-the-client
The second link is more focused on structuring your code using promises, but gives a nice demo of how to call a method that relies on a Promise's response.

Related

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to client [duplicate]

I'm facing this weird issue in NodeJS when using with Passport.js, Express and Mongoose. Basically, I get an error saying "Cannot set headers after they are sent to the client" even though I don't send more than one header.
I've read other posts and tried them out as well, and none of them worked.
app.get - is there any difference between res.send vs return res.send
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Cannot set headers after they are sent to the client
I've dug through github issues and I can't seem to find a solution. I get the problem that this error is triggered when I send multiple response headers, but the fact is that I am not sending multiple headers. It seems just weird.
This is my stack trace:
(node:9236) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
Server Running on port 5000
MongoDB Connected Error
[ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the
client
at validateHeader (_http_outgoing.js:503:11)
at ServerResponse.setHeader (_http_outgoing.js:510:3)
at ServerResponse.header (/Users/lourdesroashan/code/github/devlog/node_modules/express/lib/response.js:767:10)
at ServerResponse.json (/Users/lourdesroashan/code/github/devlog/node_modules/express/lib/response.js:264:10)
at Profile.findOne.then.profile (/Users/lourdesroashan/code/github/devlog/routes/api/profile.js:27:30)
at <anonymous>
This is my server code:
router.get("/userprofile", passport.authenticate('jwt', { session: false }), (req, res) => {
Profile.findOne({ user: req.user.id }).then(profile => {
if (!profile) {
return res.status(404).json({ error: "No Profile Found" });
}
else {
res.json(profile);
}
}).catch(err => {
console.log(err);
})
});
I understand what the error means, but from what I know, I don't think I am sending multiple headers, I even checked by console.log that only one of the blocks is run.
Thank you so much in advance! :)
Full Code at: https://github.com/lourdesr/devlog
EDIT:
I figured it out. It was a problem in my passport.js while trying to get the authenticated user. I forgot to use 'return' on the 'done' method, which had caused it. Just added the return statement and it worked!
That particular error occurs whenever your code attempts to send more than one response to the same request. There are a number of different coding mistakes that can lead to this:
Improperly written asynchronous code that allows multiple branches to send a response.
Not returning from the request handler to stop further code in the request handler from running after you've sent a response.
Calling next() when you've already sent a response.
Improper logic branching that allows multiple code paths to execute attempt to send a response.
The code you show in your question does not appear like it would cause that error, but I do see code in a different route here that would cause that error.
Where you have this:
if (!user) {
errors.email = "User not found";
res.status(404).json({ errors });
}
You need to change it to:
if (!user) {
errors.email = "User not found";
res.status(404).json({ errors });
// stop further execution in this callback
return;
}
You don't want the code to continue after you've done res.status(404).json({ errors }); because it will then try to send another response.
In addition, everywhere you have this:
if (err) throw err;
inside an async callback, you need to replace that with something that actually sends an error response such as:
if (err) {
console.log(err);
res.sendStatus(500);
return;
}
throwing inside an async callback just goes back into the node.js event system and isn't thrown to anywhere that you can actually catch it. Further, it doesn't send a response to the http request. In otherwords, it doesn't really do what the server is supposed to do. So, do yourself a favor and never write that code in your server. When you get an error, send an error response.
Since it looks like you may be new here, I wanted to compliment you on including a link to your full source code at https://github.com/lourdesr/devlog because it's only by looking at that that I was able to see this place where the error is occuring.
I was receiving this error because of a foolish mistake on my part. I need to be more careful when referencing my other working code. The truly embarrassing part is how long I spent trying to figure out the cause of the error. Ouf!
Bad:
return res
.send(C.Status.OK)
.json({ item });
Good:
return res
.status(C.Status.OK)
.json({ item });
Use ctrl + F hotkey and find all 'res.' keywords
then replace them with 'return res.',
change all 'res.' to 'return res.'
something like this:
res.send() change to --> return res.send()
maybe you have 'res.' in some block, like if() statement
Sorry for the Late response,
As per the mongoose documentation "Mongoose queries are not promises. They have a .then() function for co and async/await as a convenience. However, unlike promises, calling a query's .then() can execute the query multiple time"
so to use promises
mongoose.Promise = global.Promise //To use the native js promises
Then
var promise = Profile.findOne({ user: req.user.id }).exec()
promise.then(function (profile){
if (!profile) {
throw new Error("User profile not found") //reject promise with error
}
return res.status(200).json(profile) //return user profile
}).catch(function (err){
console.log(err); //User profile not found
return res.status(404).json({ err.message }) //return your error msg
})
here is an nice article about switching out callbacks with promises in Mongoose
and this answer on mongooses promise rejection handling Mongoose right promise rejection handling
There is a simple fix for the node error [ERR_HTTP_HEADERS_SET]. You need to add a return statement in front of your responses to make sure your router exits correctly on error:
router.post("/", async (req, res) => {
let user = await User.findOne({email: req.body.email});
if (!user) **return** res.status(400).send("Wrong user");
});
Because of multiple response sending in your request. if you use return key word in your else condition your code will run properly
if (!profile) {
return res.status(404).json({ error: "No Profile Found" });
}
else {
**return** res.json(profile);
}
This also happen when you tries to send the multiple response for a same request !!
So make sure you always use return keyword to send response to client inorder to stop the further processing !!
Where you have this:
if (!user) { errors.email = "User not found"; res.status(404).json({ errors }); }
You need to change it to:
if (!user) { errors.email = "User not found"; return res.status(404).json({ errors }); }
I got the same error using express and mongoose with HBS template engine. I went to Expressjs and read the docs for res.render, and it says // if a callback is specified, the rendered HTML string has to be sent explicitly. So I wasnt originally sending my html explicitly in the callback,. This is only for a contact form btw, not login info, albeit GET
//Original
let { username, email } = req.query; //My get query data easier to read
res.status(200).render('index', { username, email });
//Solution without error. Second param sending data to views, Third param callback
res.status(200).render('index', { username, email }, (err, html)=>{
res.send(html);
});
In react, if your are calling the function in useEffect hook, make sure to add a dependency to the dependency Array.
I had this error from an if statement not having an else block.
if(someCondition) {
await () => { }
}
await () => { }
I changed the above to this below and solved my issue
if(someCondition) {
await () => { }
} else {
await () => { }
}
For me, I accidentally put a res.status inside of a for loop. So my server would trigger the error the second time a res.status was returned. I needed to put the res.status outside of the for loop so it would only trigger once within the function.
First of all : make sure you didn't miss any asynchronous action without an async/await or use promises/callbacks.
Then attach any res with the return keyword : return res.status(..).json({});
And finally which was my problem: don't use return res.sendStatus if you always have some return res... inside a callback function, but you can always do a retun res.status();
in my case it was :
users.save((err,savedDoc){
if(err) return res.status(501).json({})
res.status(200).json({});
});
return res.status(500); // instead ofdoing return res.sendStatus(500)
you have to enable Promises in your programm, in my case i enabled it in my mongoose schema by using mongoose.Promise = global.Promise .
This enables using native js promises.
other alternatives to this soloution is :
var mongoose = require('mongoose');
// set Promise provider to bluebird
mongoose.Promise = require('bluebird');
and
// q
mongoose.Promise = require('q').Promise;
but you need to install these packages first.
My problem besides not returning, i was forgetting to await an asynchronous function in the handler. So handler was returning and after a bit the async function did its thing. 🤦🏻‍♀️
Before:
req.session.set('x', {...});
req.session.save();
return req.status(200).end();
When i needed to await:
req.session.set('x', {...});
await req.session.save();
return req.status(200).end();
I'm putting this here for anyone else who has the same problem as me- this happened to me because I'm using the next() function without a return preceding it. Just like a lot of the other answers state, not using return with your response will / can cause / allow other code in the function to execute. In my case, I had this:
app.get("/customerDetails", async (req, res, next) => {
// check that our custom header from the app is present
if (req.get('App-Source') !== 'A Customer Header') next();
var customerID = req.query.CustomerID
var rows = await get_customer_details(customerID);
return res.json(rows);
});
In my case, I forgot to include the header in my request, so the conditional statement failed and next() was called. Another middleware function must have then been executed. After the middleware finishes, without a return, the rest of the code in the original middleware function is then executed. So I simply added a return before my next() call:
// serve customer details payload
app.get("/customerDetails", async (req, res, next) => {
// check that our custom header from the app is present
if (req.get('App-Source') !== 'A Customer Header') return next();
var customerID = req.query.CustomerID
var rows = await get_customer_details(customerID);
return res.json(rows);
});

How can i execute a promise after the endpoint response?

I need to keep a promise executing after the response has already been returned to the browser. In my case, I only want to convert a video and keep the output file at the OS without using await, for performance reasons. For example:
function endPointHandler(req, res) {
// ... sync stuff ...
processVideoConvertion(req); // this method will return a promise that needs to be executed after the response.
return res.json({ message: 'Success' });
}
As it shows above, I don't need any data of the returning value of the processVideoConvertion method, there is a way that I can do that?
You can .then and .catch to check status, the process will be running in the background after sending a response.
Note: Don't use async/await it will wait until the video is converted(process done).
function endPointHandler(req, res) {
// ... sync stuff ...
processVideoConvertion(req)
.then((data) => console.log("Video Converted", data))
.catch((e) => console.error("Video Conversion Failed", e));
return res.json({ message: "Success" });
}

NodeJS async function that wont work

I read many posts on how to create async functions in NodeJS but i cant figure it out! I know this is the most asked topic, but look at this sample code here:
function test2(){
console.log("Check x");
}
function test(callback){
for(var i=0;i<1000000000000;i++){}
callback();
}
console.log("Check 1");
test(test2);
console.log("Check 2");
console.log("Check 3");
Now shouldnt NodeJS consider test to be a sync function !?
and if not then how do i create it so that i can reach the logging of check 2 and 3 without waiting for the loop to end ?
Not everything in Node.js is asynchronous.
Asynchronous process only happens when I/O or Event are involved like accessing file system, handling network request, reading data from database, etc.
Example:
var fs = require('fs); //node.js built-in file system which requires I/O from storage
function getDataFromFile(callback) {
//fs.readFile is asynchronous process
fs.readFile('path/to/file', (err, data) => {
if (err) throw err;
callback(data);
});
}
getDataFromFile(function(data) {
//this is asynchronous callback from getDataFromFile()
console.log('data ' + data);
});

Is this async or blocking code?

Is this blocking code if I have JSON.stringify inside writeFile.Lets say it is big file. Is this why I am getting error conection refused when I push button multiple times in second which triggers this api endpoint?
app.patch('/', function(req, res) {
...some query
fs.writeFile(path.join(__dirname, "../../") + 'Data/deals.json', JSON.stringify(tickets), function (err) {
if (err) {
console.log(err);
return res.status(400).json({error: err});
}
return res.status(200).json({success: true, message: 'Deal Updated successfully'});
});
})
Edit #1:
JSON.stringify parsing object to string synchronously. but you missing that you called JSON.stringify inside the patch function and not inside the writeFIle.
Original:
It's Async. if you want to write a file synchronously you have to use writeFileSync.
For more information visit Node.js fs Docs
Example
// Async callback will called after finish
// Non-Blocking
fs.writeFile(file, data[, options], callback)
// write to file with return the result, may throw exception
// Blocking
fs.writeFileSync(file, data[, options])

Meteor method with HTTP request does not return callback

I am trying to create a Meteor method with a HTTP get request. I am getting back a result, but I can't get my callback on the client side to return the result. The callback needs to wait for the HTTP request to get back a result before it returns the callback. I am getting the data successfully from the HTTP request, so that is not the problem.
Any suggestions on how to get this working?
Meteor.methods({
getYouTubeVideo: function (id) {
check(id, String);
var params = {
part:'snippet, status, contentDetails',
id:id,
key:Meteor.settings.youtube.apiKey
};
HTTP.get('https://www.googleapis.com/youtube/v3/videos', {timeout:5000, params:params}, function(error, result){
if (error) {
throw new Meteor.Error(404, "Error: " + error);
return;
}
console.log(result);
return result;
});
}
});
You need to use the synchronous version of HTTP.get, just like this :
var result=HTTP.get('https://www.googleapis.com/youtube/v3/videos', {timeout:5000, params:params});
return result;
If you use the asynchronous version with a callback like you did, you're facing the common problem of having to try returning the result in the callback (which won't work) instead of in the method, which is what you should do.
Note that synchronous HTTP.get is only available in the server-environment, so put your method declaration under server/

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