I am using the request module to send requests to a URL
var req = require('request');
when the response is received, I would like to write that file on the node server, so I am piping it to crateWriteStream
req.get(myUrl)
.on('error', function(err) {
console.log('there is an error');
})
.pipe(fs.createWriteStream('userdir/abc.png'));
This works fine if there is no error returned by req.get. In case req.get, fails I would like to not write the file locally and instead do something else.
I introduced .on('error'..) for this but the on('error') code never gets executed and .pipe tries to write the file that does not exist.
How can catch an error returned by req.get() and only write when there is no error.
I think you are using streams but normally you can use the callback to receive the all information and then check if there is any error.
Personally I would do something like:
var req = require('request');
req.get(myUrl, function (error, response, body) {
if (error || response.statusCode != 200) {
console.log(error) // Do something with your error
}
// If no errors, this code will be executed
// Write in file
})
Related
I have this snippet of code:
app.post('/pst', function(req, res) {
var data = req.body.convo;
res.render('waiting.ejs'); //ADDED THIS
myFunc(data).then(result => {
res.render('success.ejs'); //THEN THIS
//---------------------------------
//clever way to send text file to client from the memory of the server
var fileContents = Buffer.from(result, 'ascii');
var readStream = new stream.PassThrough();
readStream.end(fileContents);
res.set('Content-disposition', 'attachment; filename=' + fileName);
res.set('Content-Type', 'text/plain');
readStream.pipe(res);
//--------------------------------------
}).catch( .....
The code i commented as 'clever way to send file from memory of the server' comes from this post:
Node Express.js - Download file from memory - 'filename must be a string'
What this does is is takes a string from the memory and serves it to the client as a .txt file.
This code used to work.
Then i decided to add the res.render('waiting.ejs'); line and i got this error:
Error: Can't set headers after they are sent.
I then experimented with adding another res.render() [in this case res.render('success.ejs');] before and after the code tht sends the .txt file to the client.
The error remained. Also, there is no redirect to success.ejs, in other words the res.render('success.ejs'); never worked, despite whether it is placed before ofr after that piece of code.
app.post('/pst', function(req, res) {
var data = req.body.convo;
myFunc(data).then(result => {
//---------------------------------
//clever way to send text file to client from the memory of the server
var fileContents = Buffer.from(result, 'ascii');
var readStream = new stream.PassThrough();
readStream.end(fileContents);
res.set('Content-disposition', 'attachment; filename=' + fileName);
res.set('Content-Type', 'text/plain');
readStream.pipe(res);
res.redirect(`/success`); //THEN THIS
//--------------------------------------
}).catch( .....
When you add middleware to express (which is built on connect) using the app.use method, you're appending items to Server.prototype.stack in connect.
When the server gets a request, it iterates over the stack, calling the (request, response, next) method.
The problem is, if in one of the middleware items writes to the response body or headers (it looks like it's either/or for some reason), but doesn't call response.end() and you call next() then as the core Server.prototype.handle method completes, it's going to notice that:
there are no more items in the stack, and/or
that response.headerSent is true.
So, it throws an error. But the error it throws is just this basic response (from the connect http.js source code:
res.statusCode = 404;
res.setHeader('Content-Type', 'text/plain');
res.end('Cannot ' + req.method + ' ' + req.url);
The problematic middleware sets the response header without calling response.end() and calls next(), which confuses express's server.
so you set the header through res.render() .Now if you will try to render again it will throw you an error.
app.get('/success',(req,res)=> {
res.render("container/index",{waiting:"waiting",......});
//handle your task then in client side index.ejs with appropriate setTimeout(()=>{},2000) for the waiting div , show waiting div for 2 seconds
});
//then your actual success gets render
You would have to check express.js source code (here):
res.render = function render(view, options, callback) {
var app = this.req.app;
var done = callback;
var opts = options || {};
var req = this.req;
var self = this;
// support callback function as second arg
if (typeof options === 'function') {
done = options;
opts = {};
}
// merge res.locals
opts._locals = self.locals;
// default callback to respond
done = done || function (err, str) {
if (err) return req.next(err);
self.send(str);
};
// render
app.render(view, opts, done);
};
You can see that when You use res.render() method, it will pass the done callback to app.render(...) (source code), it will then pass done to tryInitView etc.
At the end, it will invoke done callback with str in case of success or err in case of failure. It then triggers res.send() inside done callback which simply blocks You from setting headers after that.
res.render() function compiles your template, inserts locals there, and creates html output out of those two things. that's why error comes.
don't use it twice coz it send response.
I'm new to nodejs and javascript in general. I believe this is an issue with the scope that I'm not understanding.
Given this example:
...
...
if (url == '/'){
var request = require('request');
var body_text = "";
request('http://www.google.com', function (error, response, body) {
console.log('error:', error);
console.log('statusCode:', response && response.statusCode);
console.log('body:', body);
body_text=body;
});
console.log('This is the body:', body_text)
//I need the value of body returned from the request here..
}
//OUTPUT
This is the body: undefined
I need to be able to get the body from response back and then do some manipulation and I do not want to do all the implementation within the request function. Of course, if I move the log line into:
request( function { //here })
It works. But I need to return the body in some way outside the request. Any help would be appreciated.
You can't do that with callbacks because this will works asynchronously.
Work with callbacks is kind of normal in JS. But you can do better with Promises.
You can use the request-promise-native to do what you want with async/await.
async function requestFromClient(req, res) {
const request = require('request-promise-native');
const body_text = await request('http://www.google.com').catch((err) => {
// always use catches to log errors or you will be lost
})
if (!body_text) {
// sometimes you won't have a body and one of this case is when you get a request error
}
console.log('This is the body:', body_text)
//I need the value of body returned from the request here..
}
As you see, you always must be in a function scope to use the async/await in promises.
Recommendations:
JS the right way
ES6 Fetures
JS clean coding
More best practices...
Using promises
I have the following code. Where i upload the file first and then i read the file and console the output like console.log(obj). But the response comes first and the python scripts runs behind the scene. How can i make code to wait for the python script to run then proceed?
router.post(`${basePath}/file`, (req, res) => {
//Upload file first
PythonShell.run('calculations.py', { scriptPath: '/Path/to/python/script' }, function (err) {
console.log(err);
let obj = fs.readFileSync('Path/to/file', 'utf8');
console.log(obj);
});
return res.status(200).send({
message : 'Success',
});
});
I cannot get console.log(obj); output because it runs after the response. How can i make it wait for the python script to run and get console.log(obj) output on console.
To return the result after some async operation, you should call res.send inside the done-callback.
router.post(`${basePath}/file`, (req, res) => {
//Upload file first
PythonShell.run('calculations.py', { scriptPath: '/Path/to/python/script' }, function (err) {
console.log('The script work has been finished.'); // (*)
if(err) {
res.status(500).send({
error: err,
});
console.log(err);
return;
}
let obj = fs.readFileSync('Path/to/file', 'utf8');
console.log(obj); // (**)
res.status(200).send({
message : 'Success',
});
});
});
Then if you will not see the log (*) in the console, then it would mean that the script does not work or works improperly. The callback is not being called. First of all, you need to be sure that the script (PythonShell.run) works and the callback is being called. The POST handler will wait until you call res.send (with no matter of delay value), so that callback is the main point.
Also readFileSync could fail. In case of readFileSync failure you should see an exception. If it's ok then you'll see the next log (**) and the response will be sent.
I see PythonShell in your code. I have no experience with it, but after some reading I think that the problem could be in how you are using it. It seems the python-shell npm package, so following it's documentation you may try to to instantiate a python shell for your script and then to use listeners:
let pyshell = new PythonShell('calculations.py');
router.post(`${basePath}/file`, (req, res) => {
pyshell.send(settings); // path, args etc
pyshell.end(function (err) {
console.log('The script work has been finished.');
if(err) { res.status(200).send({ error: err }); }
else { res.status(200).send({ message : 'Success' }); }
});
});
This approach could be more appropriate because the pyton shell is kept open between different POST requests. This depends on your needs. But I guess it does not solve the problem of script running. If you are sure that the script itself is fine, then you need just to run it properly in the Node environment. There are some points:
path to script
arguments
other settings
Try to remove all arguments (create some new test script), cleanup settings object (keep only path) and execute it from Node. Handle its result in Node. You should be able to run the simplest script by correct path! Research how to setup correct scriptPath. Then add an argument to your script and run it with an argument. Hanlde the result again. There are not so many options, but each of them could be the cause of improper call.
I have an Express server with a simple error handler. All the err object passed to it are Error objects.
const errorHandler = (err, req, res, next) => {
logError(`Express Error Handler: ${err}`);
res.status(500).json(err);
};
I am calling the server's routes using request:
request
.post(
{
uri: url,
timeout,
json: true,
form: {
currentStepUid,
sourceStepUid: previousStepUid,
config,
},
},
(error, response, body) => {
// Handle errors
}
)
});
My problem is that the error are not coming through as error objects, but rather as an error property on the body object.
How should I have Express set up so that I get error objects back?
A 500 status is NOT reported by request.post() as an error. The http server was contacted and a response was supplied. That is not what it considers an error. It is up to your own code to detect that condition from the http response and then treat it as an error in your own code.
You will need to look at the actual response to see the http 500 status code. The error object IS the http response body so that's where it should be. That's where you need to get it from.
If you have to do this same logic in multiple places, you could make your own wrapper function for request.post() that would examine the http status code and if it's in a range that you consider an error, then get the http response body and make that into an error.
I am wondering how to properly handle errors with Meteor when using async methods. I have tried the following, but the error is being returned in the result parameter on the client callback instead of the error parameter.
Server code:
Future = Npm.require('fibers/future');
Meteor.methods({
'myServerMethod': function(){
var future = new Future();
// URL to some remote API
var url = UrlOfTheApiIWantToCall;
HTTP.get(url, {//other params as a hash},
function (error, result) {
if (!error) {
future.return(result);
} else {
future.return(error);
}
}
);
return future.wait();
}
});
Client code:
Meteor.call('myServerMethod', function (error, result) {
if(error){
console.warn(error);
}
console.log('result', result);
});
As I was saying above, 'error' is always undefined on the client side event when the HTTP.get() on the server side returned an error. I also tried replacing future.return(error); with future.throw(error); on the server side, but this really throws an error on the server side. The client side error parameter then gets a 500 Server Error, although the error thrown on the server was a 401 Unauthorized error.
So, is it possible to use Fiber's Future properly so that the client callback receives the same error parameter as the server callback?
According to the Meteor.Error docs at http://docs.meteor.com/#/full/meteor_error
Methods can throw any kind of exception. But Meteor.Error is the only kind of error that a server will send to the client. If a method function throws a different exception, then it will be mapped to a sanitized version on the wire. Specifically, if the sanitizedError field on the thrown error is set to a Meteor.Error, then that error will be sent to the client. Otherwise, if no sanitized version is available, the client gets Meteor.Error(500, 'Internal server error').
Which is why you are receiving the 500 Server Error on the client. If you want to preserve the error message and have it be sent to the client, you can do something like this:
Future = Npm.require('fibers/future');
Meteor.methods({
'myServerMethod': function(){
var future = new Future();
// URL to some remote API
var url = UrlOfTheApiIWantToCall;
HTTP.get(url, {//other params as a hash},
function (error, result) {
if (!error) {
future.return(result);
} else {
future.throw(error);
}
}
);
try {
return future.wait();
}
catch(err) {
// Replace this with whatever you want sent to the client.
throw new Meteor.Error("http-error", err);
}
}
});