Concurrency-logger NPM

concurrency-logger

HTTP logging middleware especially useful to unwind concurrent operations without losing the request context

Install

$ npm install concurrency-logger

Usage

With koa

Basic usage

import Koa from 'koa';
import createLogger from 'concurrency-logger';

const app = new Koa;

// Logger is stateful as it contains information about concurrent requests
// Same instance needs to be reused across requests
const logger = createLogger(/* options */);

app.use(logger);

Log from middleware

// Log something in context to a specific request to trace it back easily -
// also when there are multiple concurrent requests
app.use(async (context, next) => {
    context.log('Log!');
    context.log.info('Info!');
    context.log.error('Error!');

    await next();
});

Attach more context to the log

const logger = createLogger({
    req: context => (
        context.originalUrl + '\n' +
        context.get('User-Agent')
    )
});

Include localized timestamps

const logger = createLogger({
    timestamp: true
});

Write log to file

import { createWriteStream } from 'fs';

// To read log use program that interprets ANSI escape codes,
// e.g. cat or less -r
const log = createWriteStream('logs/requests.log');

const logger = createLogger({
    reporter: log
});

Adjust alert levels per method and response time

const logger = createLogger({
    getLevel: (responseTime, context) => {
        /*
            GET
              0 -  99ms: 0
            100 - 149ms: 1
            150 - 199ms: 2
            200 - 249ms: 3
            250 - 299ms: 4
            300 - 349ms: 5
            > 350ms    : 6

            POST
              0 - 149ms: 0
            150 - 225ms: 1
                   ... : ...
        */

        let threshold = 50; // ms

        if (['POST', 'PUT'].includes(context.method)) {
            threshold *= 1.5;
        }

        return Math.floor(responseTime / threshold) - 1;
    }
});

Standalone

import createLogger from 'concurrency-logger';

const logger = createLogger(/* options */);

(async () => {
    const context = {
        method: 'GET',
        originalUrl: '/'
    };

    const next = async () => {
        await new Promise(resolve => setTimeout(resolve, 100));

        context.status = 200;
    };

    try {
        await logger(context, next);
    } catch (error) {
        // Errors are passed through
    }
})();

API

Option	Type	Default	Description	Example
minSlots	integer	`1`	Amount of space that is provisioned to display concurrent request lanes. Number of lanes will automatically scale up as the number of concurrent requests grow.	`3`
getLevel	integer: function(responseTime: integer)	`responseTime => Math.floor(responseTime / 50) - 1`	Map response time to alert level. Alert levels go from 0 (default color) to 6 (dark red). By default that means `<100ms: 0`, `<150ms: 1` `<200ms: 2`, ..., `>=350ms: 6`.	`responseTime => Math.floor(responseTime / 100)`
width	integer, boolean(`false`)	`undefined`	If no width is provided, it will be dynamically read from `process.stdout.columns`. Pass in an integer to break all lines according to the specified fixed (terminal character) width. Pass in `false` if you want the lines not to break at all.	`80`, `132`, `false`
timestamp	boolean	`false`	Print localized timestamp for every requests.	`true`, `false`
slim	boolean	`false`	"Slim mode": don't use an extra character between request lanes to shrink width, but make them harder to separate visually.	`true`, `false`
reporter	writable stream	`process.stdout`	Specify a stream that handles the output lines. Write to terminal or stream to a log file, for example. Note that the lines contain ANSI color codes, so when streaming to a file you might need a program that can read those. E.g. `less -r requests.log`	`require('fs').createWriteStream('logs/requests.log')`
req	any: function(context: object)	`context => context.originalUrl`	Attach additional information to the request log line.	`context => context.originalUrl + '\n' + context.get('User-Agent')`
res	any: function(context: object)	`context => context.originalUrl`	Attach additional information to the response log line.	`context => context.originalUrl + '\n' + context.get('User-Agent')`

Developing

Install development dependencies

$ npm install

Create new fixtures to test against

$ npm run create-fixtures

Manually review fixtures (you need a program that renders ANSI escape codes)

$ less -r test/fixtures/*

Run tests

$ npm test

Run code linter

$ npm run lint

Compile to ES5 from /src to /lib

$ npm run compile

Initialize demo project

$ git clone git@github.com:PabloSichert/concurrency-logger demo
$ cd demo
demo $ git checkout gh-pages
demo $ npm install

Build demo

demo $ npm run compile

http request log logger concurrent concurrency koa middleware

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