Winston Middleware for Express

Winston log wrappers and middleware for Express.

Usage

You can install express-winston-middleware using NPM:

$ npm install express-winston-middleware

From there, you can create a Log instance or use the request Express middleware.

Examples

See the examples directory for some basic use cases.

Logger

The Log logger class internally creates and wraps a Winston logger. You can create one with:

var winston = require("winston");
var Log = require("express-winston-middleware").Log;

// Create logger with Console transport and "foo" metadata item.
var log = new Log({
  transports: [
    new (winston.transports.Console)({ json: true })
  ]
}, {
  // Metadata to add to each log response.
  foo: "bar"
});

// Log something.
log.info("Hello World!");

which produces the following output:

{
  "date": "2013-12-01T23:29:48.035Z",
  "env": "development",
  "server": {
    "id": "m",
    "pid": 24638,
    "hostName": "titan.local"
  },
  "foo": "bar",
  "level": "info",
  "message": "Hello World!"
}

Express Middleware

The request middleware is added to your Express setup like:

var express = require("express");
var app = express(),
var winMid = require("express-winston-middleware");

/* ... */

// Same options and meta as for the `Log` class.
app.use(new winMid.request({
  transports: [
    new (winston.transports.Console)({ json: true })
  ]
}, {
  // Metadata to add to each log response.
  foo: "bar"
})));

and produces output for requests like:

{
  "date": "2013-12-01T23:32:54.759Z",
  "server": {
    "id": "m",
    "pid": 24653,
    "hostName": "titan.local"
  },
  "req": {
    "method": "GET",
    "host": "localhost:2000",
    "path": "/",
    "query": ""
  },
  "res": {
    "statusCode": 304
  },
  "foo": "bar",
  "level": "info",
  "message": "request"
}

The middleware attaches a logger to the response locals, available as res.locals._log, so that in addition to automatic request logging messages you can log extra messages with all of the current request metadata. E.g.:

app.get("/foo", function (req, res) {
  res.locals._log.info("This is an extra manual log message!", {
    extra: "metadata"
  });
  // Rest of your code here...
});

API

• request(opts, baseMeta) - Express request middleware
• error(opts, baseMeta) - Express error middleware
• uncaught(opts, baseMeta) - Global uncaught exception handler
• Log(opts, baseMeta) - Logger class.
• Log.addMeta(meta)
• Log.addReq(req)
• Log.transformMeta(fn)
• Log.addRes(res)
• Log.addError(err)

request(opts, baseMeta) - Express request middleware

Creates a middleware function using base metadata. Integration:

app.use(winMid.request({
  transports: [ new (winston.transports.Console)({ json: true }) ]
}, { foo: "bar" }));

Once integrated, a logger will be attached to the response locals, and available as res.locals._log. The logger will then be removed at the end of the request.

error(opts, baseMeta) - Express error middleware

Creates a middleware function for Express. Integration:

app.use(winMid.error({
  transports: [ new (winston.transports.Console)({ json: true }) ]
}, { foo: "bar" }));

uncaught(opts, baseMeta) - Global uncaught exception handler

Creates a handler function for any uncaught exception. Integration:

process.on("uncaughtException", winMid.uncaught({
  transports: [ new (winston.transports.Console)({ json: true }) ]
}, { foo: "bar" }));

Note: Terminates process at end.

Log(opts, baseMeta) - Logger class.

Wraps Winston logger with additional functionality.

var log = new winMid.Log({
  transports: [ new (winston.transports.Console)({ json: true }) ]
}, { foo: "bar" }));

Log.addMeta(meta)

Add arbitrary meta to all subsequent log statements.

Log.addReq(req)

Add request to meta.

Log.transformMeta(fn)

Set a delayed single transform function to mutate a copy of the metadata right before a logging event. You can only presently have one such function. And it is delayed so that for things like request end, you can effectively access all the metadata.

The transform is applied on each log call and passes a copy of the mutated metadata to the actual log call.

The function signature should be fn(existingMeta) and return mutated metadata.

Log.addRes(res)

Add response to meta.

Log.addError(err)

Add error to meta.

Contributions

Please see the Contributions Guide for how to help out with the plugin.

We test all changes with Travis CI. Here's our current build status:

Licenses

All code is 2013-2016 Formidable Labs. Released under the MIT License.