我在等待 Nodejs 中的多个异步函数时遇到问题

Question

I have a function that uses Axios to download a zip file and extract the file into a temporary directory. The process itself works as intended, but I'm having difficulty awaiting the final result before proceeding. I'll admit that I don't fully understand how to use promises, but that's what I need help learning.

Here is the complete code:

const axios = require('axios');
const StreamZip = require('node-stream-zip');

// Pipedream: steps.trigger.raw_event.body.result_set.download_links.json.all_pages
// Testing: https://api.countdownapi.com/download/results/04_NOVEMBER_2021/1900/Collection_Results_F4C0B671_51_All_Pages.zip
const all_pages = 'https://api.countdownapi.com/download/results/04_NOVEMBER_2021/1900/Collection_Results_F4C0B671_51_All_Pages.zip';
let fileName = 'all_pages.zip';

async function asyncFunc() {
    return await axios.get(all_pages, {responseType: "stream"})
        .then(res => {
            console.log("Waiting ...")

            if (res.status === 200) {
                const path = require("path");
                const SUB_FOLDER = "";
                fileName = fileName || all_pages.split("/").pop();

                const dir = path.resolve(__dirname, SUB_FOLDER, fileName);
                res.data.pipe(fs.createWriteStream(dir));
                res.data.on("end", () => {
                    console.log("Download Completed");

                    const zip = new StreamZip({
                        file: dir,
                        storeEntries: true
                    });
                    zip.on('error', function (err) {
                        console.error('[ERROR]', err);
                    });
                    zip.on('ready', function () {
                        console.log('All entries read: ' + zip.entriesCount);
                        // console.log(zip.entries());
                    });
                    zip.on('entry', function (entry) {
                        const pathname = path.resolve('./tmp', entry.name);
                        if (/\.\./.test(path.relative('./tmp', pathname))) {
                            console.warn("[zip warn]: ignoring maliciously crafted paths in zip file:", entry.name);
                            return;
                        }

                        if ('/' === entry.name[entry.name.length - 1]) {
                            console.log('[DIR]', entry.name);
                            return;
                        }

                        console.log('[FILE]', entry.name);
                        zip.stream(entry.name, function (err, stream) {
                            if (err) {
                                console.error('Error:', err.toString());
                                return;
                            }

                            stream.on('error', function (err) {
                                console.log('[ERROR]', err);
                            });

                            // example: print contents to screen
                            // stream.pipe(process.stdout);

                            // example: save contents to file
                            fs.mkdir(path.dirname(pathname), {recursive: true}, function () {
                                    stream.pipe(fs.createWriteStream(pathname));
                                }
                            );
                        });
                    });
                });
            } else {
                console.log(`ERROR >> ${res.status}`);
            }
        })
        .catch(err => {
            console.log("Error ", err);
        });
}

(async () => {
    try {
        await asyncFunc();
        console.log('Finished')
    } catch (error) {
        console.error(error);
    }
})();

As I said, the code itself works in that it'll download the zip file and extract the contents—however, my test console.log('Finished') fires just after the Axios get. Here are the results of the order of operations:

Waiting ...
Finished
Download Completed
[FILE] Collection_Results_F4C0B671_51_Page_1.json
[FILE] Collection_Results_F4C0B671_51_Page_2.json
[FILE] Collection_Results_F4C0B671_51_Page_3.json
[FILE] Collection_Results_F4C0B671_51_Page_4.json
[FILE] Collection_Results_F4C0B671_51_Page_5.json
[FILE] Collection_Results_F4C0B671_51_Page_6.json
[FILE] Collection_Results_F4C0B671_51_Page_7.json
All entries read: 7

I've tried reading other articles on Promises and similar questions, and I've tried many options without any luck.

Answer 1

A major advantage of using Async/Await is that you can avoid deeply nested, difficult to read code - such as yours. It makes much more sense to break this code into functional units. Rather than thinking about all this code as "must be together", think "works better when apart".

So the entry point can call axios, use .then() to fire off the data file download, use .then() to fire off unzipping, use then() to fire off stream writing function.

You have created a dilemma by using the callback version of StreamZip . It would simplify things a lot if you used the Promise version the API.

Something like the following is easier to rationalize about the order of operation.

  try {
    console.log('Starting')
    axios.get(all_pages, {responseType: "stream"})
      .then(download)
      .then(unzip)
      .then(writeFile)
    console.log('Finished')
  } catch (error) {
    console.error(error);
  }

Answer 2

If you want the Finished statement to show up after all the entries are read, why not just add it to this section of the code?

                    zip.on('ready', function () {
                        console.log('All entries read: ' + zip.entriesCount);
                        // console.log(zip.entries());
                        // ADD THE FINISHED STATEMENT HERE
                    });

Edit

Base on the docs you can do the following after the end of the stream.

const stm = await zip.stream('path/inside/zip.txt');
stm.on('end', () => {
    zip.close();
    // FINISHED AT THIS POINT ?

})

This is another place where you can say you are done streaming (Finished). Depending on the usage you may not have to close the zip here.

Answer 3

You can simply return a new promise instead of the one returned by axios.get and resolve when download is finished like so:

async function asyncFunc() {
  return new Promise(function(resolve, reject){
    axios.get(all_pages, {responseType: "stream"})
      .then(res => {
          console.log("Waiting ...")
          //...
          res.data.on("end", () => {
              console.log("Download Completed");
              // resolve the promise when download is finished
              resolve();