Synchronous request in Node.js with async.retry

Question

nodejs version v10.14.2 OS win7 sp1 64bit

I need the following four lines of code to execute in order

var res2 = await fetchData(url_2, file_path_2);
await console.log('step one.');
var res1 = await fetchData(url_1, file_path_1);
await console.log('step two.');

However, the actual order of their execution is

step one. step two. ........ ........

How can we achieve synchronous execution of these four lines of codes?

var https = require('https');
var fs = require('fs');
var request = require('request');
var async = require("async");

(async() => {

var url_1 = 'https://aaa.bbb.ccc.com';
var url_2 = 'https://library.harvard.edu/';

var file_path_1 = fs.createWriteStream('./intelcenter/aaa.bbb.ccc.txt');
var file_path_2 = fs.createWriteStream('./intelcenter/harvard.txt');

var res2 = await fetchData(url_2, file_path_2);
await console.log('step one.');
var res1 = await fetchData(url_1, file_path_1);
await console.log('step two.');

})();


async function fetchData(url,locpath) {
  return new Promise(function (resolve) {
    async.retry(request(url).pipe(locpath), function(err, result) {
    resolve(result);
    });   
 });
}

Edwin Babu · Accepted Answer · 2018-12-25 04:04:54Z

1

Synchronous Code

I have added callback function for request module and passing the result via next method.

By Default async.retry will make 5 retry.

var fs = require("fs");
var request = require("request");
var async = require("async");

(async () => {
  var url_1 = "https://google.com";
  var url_2 = "https://library.harvard.edu/";

  var file_path_1 = fs.createWriteStream("./intelcenter/aaa.bbb.ccc.txt");
  var file_path_2 = fs.createWriteStream("./intelcenter/harvard.txt");

  var res2 = await fetchData(url_2, file_path_2);
  console.log("step one." + res2);
  var res1 = await fetchData(url_1, file_path_1);
  console.log("step two." + res1);
})();

function fetchData(url, locpath) {
  console.log("inside fetchData");
  return new Promise(function(resolve, reject) {
    async.retry(
      function(next) {
        request(url, function(err, result) {
          if (err) {
            console.log(err);
          }
          console.log("inside request");
          next(result);
        }).pipe(locpath);
      },
      function(result) {
        resolve(result);
      }
    );
  });
}

To know more about async.

Synchronous Code without async.retry

var fs = require("fs");
var request = require("request");

(async () => {
  var url_1 = "https://google.com";
  var url_2 = "https://library.harvard.edu/";

  var file_path_1 = fs.createWriteStream("./intelcenter/aaa.bbb.ccc.txt");
  var file_path_2 = fs.createWriteStream("./intelcenter/harvard.txt");

  var res2 = await fetchData(url_2, file_path_2);
  console.log("step one.");
  var res1 = await fetchData(url_1, file_path_1);
  console.log("step two.");
})();

function fetchData(url, locpath) {
  console.log("inside fetchData");
  return new Promise(function(resolve, reject) {
    request(url, function(err, result) {
      if (err) {
        console.log(err);
      }
      console.log("got result");
      result=JSON.stringify(result);
      locpath.write(result);
      resolve(result);
    });
  });
}

edited Dec 25, 2018 at 4:04

answered Dec 25, 2018 at 2:44

Edwin Babu

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4 Comments

Brad Over a year ago

You should explain what you changed and why.

Edwin Babu Over a year ago

I have removed async.retry, I am writing the result to the file inside the callback function of request module.

Edwin Babu Over a year ago

@Brad I have modified the answer to specifically to this question

pangjiale Over a year ago

The async api , At first, I don't understand the meaning of apiMethod.,now is replaced by function(next) async.retry({ times: 10, interval: function(retryCount) { return 50 * Math.pow(2, retryCount); } }, apiMethod, function(err, result) { // do something with the result });

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