slay-contextlog

Creates a context configurable logger for use with asynchronous workflows.

Usage

This module can be used by doing:

app.preboot(require('slay-contextlog');
// ...
  app.contextLog.info('hiya!');
// ...

Description

Sometimes when writing code you need to create asynchronous workflows.

It can be hard to manage object references to your logger, this module will attach an app.contextLog property to track your async workflows.

var buildId = 1;
app.contextLog.info('about to do things');
app.withBreadcrumb({
  buildId: buildId
}, () => {
  // app.contextLog includes build id in any metadata
  app.contextLog.info('something happened');
  fs.readFile('thing.txt', (err. body) => {
    // app.contextLog still has build id
    app.withBreadcrumb({
      fileCRC: crc(body)
    }, () => {
      app.contextLog.info('something else happened');
    });
  });
});

outputs:

about to do things
something happened {breadcrumbs=[buildId=1]}
something else happened {breadcrumbs=[buildId=1,fileCRC=DEADBEEF]}

API

app.contextLog

This is a winston logger that can be used to log info based upon your current context. It is the preferred approach to logging vs app.log.

app.runWithLoggerBreadcrumb(value, fn);

A bit of a mouthful! This function runs fn with a app.contextLog that contains value in the metadata array breadcrumbs. Any callbacks queued during execution of fn.

NOTE: It does not ensure Promise callbacks are set to the proper context for now due to technical limitations of Promise.

Workflows

Retries

Some operations need to track retries of operations like unsafe operations. If we add breadcrumbs to an existing operation, it will produce 2 breadcrumbs with retries_left:n and retries_left:n-1. This is undesirable. The solution is to ensure attempt is always given the logger it originally gave a breadcrumb.

function attempt(fn, retriesLeft, done) {
  // cache original logger
  const logger = app.contextLog;
  function next(err) {
    if (err) {
      perform(retriesLeft--);
      return;
    }

    done();
  }

  function perform(retriesLeft) {
    if (retriesLeft === 0) {
      return void done(Error('No success'));
    }

    app.contextLog = logger;
    app.withBreadcrumb({retriesLeft}, () => fn(next));
  }

  perform(retriesLeft);
}

There are various ways to cache the original logger besides this, but it is something to note.

Test

npm test

License

MIT