Chances
A Node.js module to mange requesting a uri multiple times. Sometimes requested pages return a bad status code, timeout, or fail for some reason that would be resolved if the page was just requested again. Chances uses request to give a request multiple tries before it returns with errors.
Install
npm install chances
Use
The example below requests sends a request to a uri giving it several chances to return successfully before failing.
var chances = require('chances');
var uri = 'http://www.thing.com';
var limit = 10; // give the uri a max of 10 tries
var tiemout = 5000; // for each try timeout after 5 seconds
var interval = 2000; // then retry in 2 seconds
var maxInterval = 10000; //the max interval
var log = function (mes) { console.log(mes); } // your logger
var gzip = true; // if true, chances will always return gzipped body,
// even if the server doesn't provides one.
var requestOptions = {
headers: {
'User-Agent': 'foo'
}
}; // additional options of request
var randomize = true; //if true, chances will randomize the interval
// the factor is between 1 and 1.5
chances.process({
uri: uri,
limit: limit,
timeout: timeout,
interval: interval,
maxInterval: maxInterval,
requestOptions: requestOptions,
gzip: gzip,
log: log,
randomize: randomize
}, function (err, result) {
// if there is an err it will
// be true. then use result.errs
// to see what went wrong
});
Result
{
uri: 'http://www.domain.com', // given uri
errs: [], // errors collected along the way
body: '<html>stuff</html>' // body html
}
Retry Strategy & Interval
Now, after an request being luanched...
timeoutms later, if there's still no response, it would be regarded as a
failed attempt. The handling of this failed attemp is decided by limit.
When an attempt is failed, limit will decreases, if this limit hit the floor
(limit === 0), chances will stop trying and returning an error. If not,
chances will retry again after a while, the retry interval is decided by
interval, maxInterval and randomize.
The true interval is calculated from interval, maxInterval and randomize.
maxInterval
If maxInterval is set, chances will make sure that current interval
is less than maxInterval, if interval > maxInterval, interval will be set
to maxInterval.
factor & randomize
Each time we meet a failure, the interval will be multipled by a factor to make
it longer. If randomize is true, the factor will be a number between
1.0 and 1.5, otherwise it will be 1.5.