Promise.then not being invoked

Question

In continuation to my question, I have created JavaScript class that takes a remote url as parameter and then uploads the file to S3 (via axios). Here is the class:

const config = require('../config.json');

const stream = require('stream');
const axios = require('axios');
const AWS = require('aws-sdk');

class S3RemoteUploader {
    constructor(remoteAddr){
        this.remoteAddr = remoteAddr;
        this.stream = stream;
        this.axios = axios;
        this.config = config;
        this.AWS = AWS;
        this.AWS.config.update({
            accessKeyId: this.config.api_key,
            secretAccessKey: this.config.api_secret
        });
        this.spacesEndpoint = new this.AWS.Endpoint(this.config.endpoint);
        this.s3 = new this.AWS.S3({endpoint: this.spacesEndpoint});

        this.file_name = this.remoteAddr.substring(this.remoteAddr.lastIndexOf('/')+1);
        this.obj_key = this.config.subfolder+'/'+this.file_name;
        this.content_type = 'application/octet-stream';

        this.uploadStream();
    }

    uploadStream(){
        const pass = new this.stream.PassThrough();
        this.promise = this.s3.upload({
            Bucket: this.config.bucket,
            Key: this.obj_key,
            ACL: this.config.acl,
            Body: pass,
            ContentType: this.content_type
        }).promise();
        return pass;
    }

    initiateAxiosCall() {
        axios({
            method: 'get',
            url: this.remoteAddr,
            responseType: 'stream'
        }).then( (response) => {
            if(response.status===200){
                this.content_type = response.headers['content-type'];
                response.data.pipe(this.uploadStream());
            }
        });
    }

    dispatch() {
        this.initiateAxiosCall();
    }

    async finish(){
        //console.log(this.promise); /* return Promise { Pending } */
        return this.promise.then( (r) => {
            console.log(r.Location);
            return r.Location;
        }).catch( (e)=>{
            console.log(e);
        });
    }

    run() {
        this.dispatch();
        this.finish();
    }
}

As you can see, the promise property contains the S3 upload promise. However, then doesn't seem to be invoked in anyway. So far, I have tried these:

testUpload = new S3RemoteUploader('https://avatars2.githubusercontent.com/u/41177');
testUpload.run();
//console.log(testUpload.promise); /* Returns Promise { Pending } */
testUpload.promise.then(r => console.log); // does nothing

I suspect that the promise resolves before then is being called here.

Another reason would be that it throws and that you need to `.catch` instead. Do you have a reason to believe that it should not throw? — Lazar Ljubenović, Sep 25 '18 at 06:11
`testUpload.promise.then(r => console.log)` will produce a promise that will resolve to `console.log`. It will _not_ invoke `console.log`. Either `testUpload.promise.then(r => console.log(r))` or `testUpload.promise.then(console.log)` will. — Amadan, Sep 25 '18 at 06:13
@ShubhamGupta, `run` function does return due to `finish` being invoked, doesn't it? — abhisek, Sep 25 '18 at 06:22
@LazarLjubenović doesn't throw any error. Just doen't return anything. — abhisek, Sep 25 '18 at 06:22

score 0 · Answer 1 · answered Sep 25 '18 at 06:30

0

Your run should return a promise for .then to resolved. Update your code to following and check if .then is invoked.

finish(){
    return this.promise;
}

run() {
    this.dispatch();
    return this.finish();
}

answered Sep 25 '18 at 06:30

Shubham Gupta

2,596
1
8
19

Thanks! I tried: testUpload.run().then(...). But didn't work. Am I missing something? – abhisek Sep 25 '18 at 06:46
did your then get invoked ? – Shubham Gupta Sep 25 '18 at 06:52
No it didnt. I tried console.log with some hardcoded string. But it didnt show up – abhisek Sep 25 '18 at 06:56

score 0 · Answer 2 · answered Sep 25 '18 at 06:35

I have modified your code, please check if it works for you:

const config = require('../config.json');

const stream = require('stream');
const axios = require('axios');
const AWS = require('aws-sdk');

class S3RemoteUploader {
    constructor(remoteAddr){
        this.remoteAddr = remoteAddr;
        this.stream = stream;
        this.axios = axios;
        this.config = config;
        this.AWS = AWS;
        this.AWS.config.update({
            accessKeyId: this.config.api_key,
            secretAccessKey: this.config.api_secret
        });
        this.spacesEndpoint = new this.AWS.Endpoint(this.config.endpoint);
        this.s3 = new this.AWS.S3({endpoint: this.spacesEndpoint});

        this.file_name = this.remoteAddr.substring(this.remoteAddr.lastIndexOf('/')+1);
        this.obj_key = this.config.subfolder+'/'+this.file_name;
        this.content_type = 'application/octet-stream';

        this.uploadStream();
    }

    uploadStream(){
        const pass = new this.stream.PassThrough();
        this.promise = this.s3.upload({
            Bucket: this.config.bucket,
            Key: this.obj_key,
            ACL: this.config.acl,
            Body: pass,
            ContentType: this.content_type
        }).promise();
        return pass;
    }

    initiateAxiosCall() {
       return axios({
            method: 'get',
            url: this.remoteAddr,
            responseType: 'stream'
        });
    }

    dispatch() {
        this.initiateAxiosCall().then( (response) => {
            if(response.status===200){
                this.content_type = response.headers['content-type'];
                response.data.pipe(this.uploadStream());
                 this.finish();
            }
        });
    }

    async finish(){
        //console.log(this.promise); /* return Promise { Pending } */
        return this.promise.then( (r) => {
            console.log(r.Location);
            return r.Location;
        }).catch( (e)=>{
            console.log(e);
        });
    }

    run() {
        this.dispatch();
    }
}

Could you please guide me how to call the method to get r.Location? — abhisek, Sep 25 '18 at 06:45
which method you are referring here? Can you tell me if the code inside dispatch executes and the call to finish() is done? — Ritesh Waghela, Sep 25 '18 at 06:55
I created an instance (using your class) and then instance.promise.then(..) but didnt work — abhisek, Sep 25 '18 at 06:58
You need to first call instance.run() and then in the next line you can have your code. — Ritesh Waghela, Sep 25 '18 at 07:05

Promise.then not being invoked

2 Answers2