I am facing a situation similar to the one discussed in this blog post: Polling with promises. The author explains using promises for polling until a JobID is returned. I intend to implement this using Q.
I want to chain promises together but my attempts with Q.delay() have not been successful. Here is an example of what I'm trying to achieve:
var promise = uploadFile();
promise.then(startImageProcessingJob)
.then(saveConvertedImage);
I need help creating a promise that can poll until the data is retrieved or the maximum number of tries is reached.
The author's code uses bluebird. Here is the relevant snippet:
var getJobStatusAsync = Promise.promisifyAll(api);
function poll(jobId, retry) {
if(!retry) retry = 5;
if(!retry--) throw new Error('Too many retries');
return getJobStatusAsync(jobId)
.then(function(data) {
if(data.state === 'error') throw new Error(data.error);
if(data.state === 'finished') return data;
return Promise.delay(jobId, 10000).then(poll);
});
Edit:
In response to Traktor53's comment, I am sharing the logic I have developed so far. My goal is to utilize ZamZar as a third-party service for image conversion within my Angular application. Here is how I plan to use promises:
(1) Upload the file from the client to the server (Node);
(2) Initiate image conversion using the ZamZar API and obtain the JobID;
(3) Poll the ZamZar API for status updates based on the JobID until the image is ready for download. Once the image is ready, retrieve the fileId and download it back to the Node server;
(4) Display the PNG image on the client browser by integrating it into an HTML canvas using three.js and fabric.js.
/* Dependencies */
var express = require('express');
var request = require('request');
var formidable = require('formidable');
var randomstring = require("randomstring");
var fs = require('fs');
var Q = require('q');
/*
* Node Helper functions
*/
convertFileUtil = function() {
/**
* Step 1: Upload file from client to node server.
* Parses the uploaded file using formidable and moves it to a custom temp directory.
* Returns a promise with the directory path of the uploaded file for subsequent methods.
*/
var uploadFileFromClientToNodeServer = function(req) {
var q = Q.defer();
var form = new formidable.IncomingForm();
var tmpFolder = 'upload/' + randomstring.generate() + '/';
form.parse(req, function(err, fields, files) {
// File upload handling logic
});
return q.promise;
};
/**
* Step 2: Post the temp file to ZamZar for conversion.
* This method returns a promise containing the JobID of the conversion job.
*/
var postTempFileToZamZar = function(filePath) {
// Post file to ZamZar logic
};
/*
* Step 3: Poll for PNG.
*/
var pollZamZarForOurPngFile = function(dataObj) {
// Polling logic
}
// API
return {
uploadFileFromClientToNodeServer: uploadFileFromClientToNodeServer,
postTempFileToZamZar: postTempFileToZamZar,
pollZamZarForOurPngFile: pollZamZarForOurPngFile,
};
};
// Call to convert file.
app.post('/convertFile', function (req, res) {
var util = convertFileUtil();
var promise = util.uploadFileFromClientToNodeServer(req);
promise
.then(util.postTempFileToZamZar)
.then(util.pollZamZarForOurPngFile);
.then(function(data) {
console.log('Done processing');
});
});