Loki response status codes 301 and 400 code do not lead to failure workflow

[comradealpha]

winston - 3.3.3
winston-loki - 6.0.3
transport - http

Hello! When Loki returns status code 301 or 400 for POST /loki/api/v1/push transport request does not emit error event and batcher treats this case as successful sending. Looks like this behavior is unexpected, can you please comment on that?

[Linkaynn]

@comradealpha

This PR adds a way to handle your situation: #97

I was not sure if the right way is to add a hook to handle or emit it, feedback is welcome here 😄

[comradealpha]

Unfortunately, this PR seems not to fix my problem, because 301 and 400 codes do not lead to error event emit. Here is some code snippet based on your requests.js code:

const https = require('https')

async function postRequestToFail() {
    return new Promise((resolve, reject) => {
        // Construct the node request options
    const options = {
        hostname: 'loki-transport.free.beeceptor.com',
        path: '/lokibatchpush',
        port:443,
        method: 'POST',
        timeout: 30
    }
  
    console.log("request starts")
    const req = https.request(options, res => {
        res.on('data', _data => {console.log('response status: ' + res.statusCode)})
        res.on('end', () => {console.log('on ended'); resolve();})
    })

    req.on('error', error => {
        console.log('on error' + error)
        reject();
    })
    
    req.end()
    });

}

(async function() {
    await postRequestToFail();
    console.log('awaited');
})();

The output will be:

request starts
response status: 400
on ended
awaited

So, function promise will be never rejected and onConnectionError() from #97 will be never called. I suggest that status code from loki should be checked before resolving.