Logepi

A tiny, Togepi-sized, logging library for Node.js apps & APIs.

How to install

Using npm

$ npm install --save logepi

Using yarn

$ yarn install logepi

How to use

The library is comprised of two major components:

• A Log static class which creates an instance of a Winston logger, exposing several methods to output messages with different loglevels.
• Middleware functions to add automatic logging of request/response flows for HTTP servers. Currently the library supports Koa and Express.

There's also a TypeScript declaration file available for TS-based apps.

Using the Log API

Importing the library

// commonjs style
const { Log } = require("logepi");
 
// ES modules style
import { Log } from "logepi";

Log an error

Log.error("An error was found", { tags: { process: "foo" } });

Log a warning

Log.warning("Careful!", { tags: { process: "foo" } });

Log at INFO level

Log.info("Hopefully someone will read this.", { tags: { process: "foo" } });

Log at VERBOSE level

Log.verbose("Now I'm all blah-by.", { tags: { process: "foo" } });

Log at DEBUG log

Log.debug("I've said too much!", { tags: { process: "foo" } });

Setting up an output level

In order to filter what messages are printed to the console transport, you can use the Log.setOutputLevel() method:

// Limit messages to "error" level.
Log.setOutputLevel("error");

You can also use the LogLevel enum, with uppercased keys (INFO, WARN, ERROR, VERBOSE, DEBUG).

Using the Koa middleware

Import the library

// commonjs style
const { KoaLoggingMiddleware } = require("logepi");
 
// ES modules style
import { KoaLoggingMiddleware } from "logepi";

Inject it into your app

app
    .use(...)
    // ...make sure it's the *last* middleware...
    .use(KoaLoggingMiddleware());

Using the Express middleware

Import the library

// commonjs style
const { ExpressLoggingMiddleware } = require("logepi");
 
// ES modules style
import { ExpressLoggingMiddleware } from "logepi";

Inject it into your app

app
    .use(...)
    // ...make sure it's the *last* middleware...
    .use(ExpressLoggingMiddleware());

Adding tags to logs

Logepi offers a way to inject tagged data in a logline, with the format [key:value]. When logging, use the tags key on the data argument of any of the Log API methods. There's an example right in the next section.

Configuring logging middlewares

All middlewares expose the same configuration object:

  /**
   * Allows to configure log levels for requests and responses.
   */
  logLevels: {
    /**
     * Sets the log level for all incoming requests.
     */
    request: "info",
 
    /**
     * Sets the log level for all outgoing responses, according to their status code.
     */
    response: {
      status2xx: "info",  // For 200-399 codes
      status4xx: "warn",  // For 400-499 codes
      status5xx: "error"  // For 500-599 codes
    }
  }

How does it look?

Note: Logs are single-lined, but for clarity's sake, they're shown in multiple lines.

Manual logging

Log.info("API is now ready", { tags: { port } });

outputs:

[timestamp:2019-01-11T21:04:41.915Z]
[level:info]
[message:API is now ready]
[port:9000]

Incoming request

[timestamp:2019-01-11T21:00:45.442Z]
[level:info]
[message:IncomingRequest]
[url:/api/apps]
[queryParams:undefined]
[body:{}]
[headers:{"host":"localhost:9000","connection":"keep-alive","upgrade-insecure-requests":"1","user-agent":"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36","accept":"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8","accept-encoding":"gzip, deflate, br","accept-language":"es-ES,es;q=0.9,en;q=0.8,en-US;q=0.7"}]

Outgoing response

[timestamp:2019-01-11T21:00:45.446Z]
[level:info]
[message:OutgoingResponse]
[status:200]
[body:{"ok":true,"data":{"foo":true}}]
[headers:{"host":"localhost:9000","connection":"keep-alive","upgrade-insecure-requests":"1","user-agent":"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36","accept":"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8","accept-encoding":"gzip, deflate, br","accept-language":"es-ES,es;q=0.9,en;q=0.8,en-US;q=0.7"}]

Issues

Feel free to report any issues and we'll figure out a way to make it work.

Want to contribute?

That's great! Open an issue first and let's discuss what you want to add or, by all means, fork this project! :)

License

This project is licensed under the MIT License.