Error: connect ETIMEDOUT when scraping

问题

I have a function that:
1. gets an array of 3000 'id' properties from mongoDB documents from collection foo.
2. Creates a GET request for each ID to get 'resp' obj for id, and stores it in another database.

router.get('/', (req, res) => {

    var collection = db.get().collection('foo');
    var collection2 = db.get().collection('test');
    collection.distinct('id',  (err, idArr) => { // count: 3000+
    idArr.forEach(id => {
    let url = 'https://externalapi.io/id=' + id
    request(url, (error, response, body) => {
           if (error) { 
             console.log(error) 
           } else {
             resp = JSON.parse(resp);
             collection2.insert(resp);
           }
    });
});

Node Error Log:

[0] events.js:163
[0]       throw er; // Unhandled 'error' event
[0]       ^
[0]
[0] Error: connect ETIMEDOUT [EXT URL REDACTED]
[0]     at Object.exports._errnoException (util.js:1050:11)
[0]     at exports._exceptionWithHostPort (util.js:1073:20)
[0]     at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1093:14)

I am using simple-rate-limiter not to cause rate limits (25cps):

const limit = require("simple-rate-limiter");
const request = limit(require("request")).to(20).per(1000);

But anywhere between 300-1700 requests I receive this error which crashes node on the command line. How can I handle this error to prevent my app from crashing?

I have tried a lot of error handling, but none of them were able to handle connect ETIMEDOUT

回答1:

As discussed in comments, if you want to control the max number of requests that are in-flight at the same time, you can use Bluebird to do that fairly easily like this:

const Promise = require('bluebird');
const rp = require('request-promise');

router.get('/', (req, res) => {

    let collection = db.get().collection('foo');
    let collection2 = db.get().collection('test');
    collection.distinct('id', (err, idArr) => { // count: 3000+
        if (err) {
            // handle error here, send some error response
            res.status(501).send(...);
        } else {
            Promise.map(idArr, id => {
                let url = 'https://externalapi.io/id=' + id
                return rp(url).then(body => {
                    if (error) {
                        console.log(error)
                    } else {
                        let resp = JSON.parse(body);
                        // probably want to return a promise here too, but I'm unsure what DB you're using
                        collection2.insert(resp);
                    }
                }).catch(err => {
                    // decide what you want to do when a single request fails here
                    // by providing a catch handler that does not rethrow, other requests will continue
                });
                   // pick some concurrency value here that does not cause errors
            }, {concurrency: 10}).then(() => {
                // all requests are done, send final response
                res.send(...);
            }).catch(err => {
                // your code may never get here (depends upon earlier .catch() handler)
            });
        }
    });
});

来源：https://stackoverflow.com/questions/44167484/error-connect-etimedout-when-scraping