Log4JS - Logstash UDP appender

This is an optional appender for log4js-node.
``bash
npm install @log4js-node/logstashudp
`

The logstashUDP appender supports sending log events to a Logstash server. It uses the node.js core UDP support, and so requires no extra dependencies. Remember to call log4js.shutdown in your application if you want the UDP socket closed cleanly.

Configuration

* type - @log4js-node/logstashudp
* host - string - hostname (or IP-address) of the logstash server
* port - integer - port of the logstash server
* layout - (optional, defaults to dummyLayout) - used for the message field of the logstash data (see layouts)
* extraDataProvider - function (optional, defaults to put the second param of log to fields) - used to enhance the object sent to Logstash via UDP. this will be passed the log event and should return a object.

Example

$3

`javascript
log4js.configure({
appenders: {
logstash: {
type: '@log4js-node/logstashudp',
host: 'log.server',
port: 12345
}
},
categories: {
default: { appenders: ['logstash'], level: 'info' }
}
});
const logger = log4js.getLogger();
logger.info("important log message", { cheese: 'gouda', biscuits: 'hobnob' });
`
This will result in a JSON message being sent to log.server:12345 over UDP, with the following format:
`javascript
{
'@version': '1',
'@timestamp': '2014-04-22T23:03:14.111Z',
'host': 'yourHostname',
'level': 'INFO',
'category': 'default',
'message': 'important log message',
'fields': {
'biscuits': 'hobnob',
'cheese': 'gouda'
}
}
`

$3

`javascript
log4js.configure({
appenders: {
logstash: {
type: '@log4js-node/logstashudp',
host: 'log.server',
port: 12345,
extraDataProvider: loggingEvent => ({
host: 'anotherHostname', // this will replace the default real host
clientIp: '1.2.3.4', // this will be added
fields: {
tag: 'myTag', // this will be added to the fields
pid: loggingEvent.pid, // this will be added to the fields
cheese: 'defaultCheese' // this will be added to the fields but will not be replaced in this example
}
})
}
},
categories: {
default: { appenders: ['logstash'], level: 'info' }
}
});
const logger = log4js.getLogger();
logger.info("important log message", { cheese: 'gouda', biscuits: 'hobnob' });
`
This will result in a JSON message being sent to log.server:12345 over UDP, with the following format:
`javascript
{
'@version': '1',
'@timestamp': '2014-04-22T23:03:14.111Z',
'host': 'anotherHostname',
'level': 'INFO',
'category': 'default',
'message': 'important log message',
'clientIp': '1.2.3.4',
'fields': {
'cheese': 'defaultCheese',
'tag': 'myTag',
'pid': 123
}
}
`
So, if not using the default extraDataProvider`, you have to put the second param of the log to the fields yourself if you want.