# Connect / Express Logger

The connect/express logger was added to log4js by [danbell](https://github.com/danbell). This allows connect/express servers to log using log4js. See `example-connect-logger.js`.

```javascript
var log4js = require('./lib/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, or array)
- status code rulesets

For example:

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

or:

```javascript
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"`)
}));
```

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

```javascript
app.use(log4js.connectLogger(logger, { level: 'auto' }));
```

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

```javascript
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, or array to omit certain log messages. Example of 1.2 below.

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

## 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"` |