Connect / Express Logger

The connect/express logger was added to log4js by danbell. This allows connect/express servers to log using log4js. See example-connect-logger.js.

var log4js = require("log4js");
var express = require("express");

log4js.configure({
  appenders: {
    console: { type: "console" },
    file: { type: "file", filename: "cheese.log" },
  },
  categories: {
    cheese: { appenders: ["file"], level: "info" },
    default: { appenders: ["console"], level: "info" },
  },
});

var logger = log4js.getLogger("cheese");
var app = express();
app.use(log4js.connectLogger(logger, { level: "info" }));
app.get("/", function (req, res) {
  res.send("hello world");
});
app.listen(5000);

The log4js.connectLogger supports the passing of an options object that can be used to set the following:

log level
log format string or function (the same as the connect/express logger)
nolog expressions (represented as a string, regexp, array, or function(req, res))
status code rulesets

For example:

app.use(
  log4js.connectLogger(logger, {
    level: log4js.levels.INFO,
    format: ":method :url",
  })
);

or:

app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    // include the Express request ID in the logs
    format: (req, res, format) =>
      format(
        `:remote-addr - ${req.id} - ":method :url HTTP/:http-version" :status :content-length ":referrer" ":user-agent"`
      ),
  })
);

When you request of POST, you want to log the request body parameter like JSON. The log format function is very useful. Please use log format function instead “tokens” property for use express’s request or response.

app.use(
  log4js.connectLogger(logger, {
    level: "info",
    format: (req, res, format) =>
      format(`:remote-addr :method :url ${JSON.stringify(req.body)}`),
  })
);

Added automatic level detection to connect-logger, depends on http status response, compatible with express 3.x and 4.x.

http responses 3xx, level = WARN
http responses 4xx & 5xx, level = ERROR
else, level = INFO

app.use(log4js.connectLogger(logger, { level: "auto" }));

The levels of returned status codes can be configured via status code rulesets.

app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    statusRules: [
      { from: 200, to: 299, level: "debug" },
      { codes: [303, 304], level: "info" },
    ],
  })
);

The log4js.connectLogger also supports a nolog option where you can specify a string, regexp, array, or function(req, res) to omit certain log messages. Example of 1.2 below.

app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    format: ":method :url",
    nolog: "\\.gif|\\.jpg$",
  })
);

app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    format: ":method :url",
    nolog: (req, res) => res.statusCode < 400,
  })
);

The log4js.connectLogger can add a response of express to context if context flag is set to true. Application can use it in layouts or appenders.

In application:

app.use(log4js.connectLogger(logger, { context: true }));

In layout:

log4js.addLayout("customLayout", () => {
  return (loggingEvent) => {
    const res = loggingEvent.context.res;
    return util.format(
      ...loggingEvent.data,
      res ? `status: ${res.statusCode}` : ""
    );
  };
});

Example nolog values

nolog value	Will Not Log	Will Log
`"\\.gif"`	http://example.com/hoge.gif http://example.com/hoge.gif?fuga	http://example.com/hoge.agif
`"\\.gif\\|\\.jpg$"`	http://example.com/hoge.gif http://example.com/hoge.gif?fuga http://example.com/hoge.jpg?fuga	http://example.com/hoge.agif http://example.com/hoge.ajpg http://example.com/hoge.jpg?hoge
`"\\.(gif\\|jpe?g\\|png)$"`	http://example.com/hoge.gif http://example.com/hoge.jpeg	http://example.com/hoge.gif?uid=2 http://example.com/hoge.jpg?pid=3
`/\.(gif\\|jpe?g\\|png)$/`	as above	as above
`["\\.jpg$", "\\.png", "\\.gif"]`	same as `"\\.jpg\\|\\.png\\|\\.gif"`	same as `"\\.jpg\\|\\.png\\|\\.gif"`