Add idleConnectionTimeout to pool options

[dicearr]

This option is specially useful when connecting to serverless databases, in which the instances are turned off when there is no connection alive.

Coming from #2195.

This aims to close #1276 and resolve #962.

[gyj1278]

This option is great，and when will it be released to the official edition?@@dougwilson

[dougwilson]

I am working through this module prs and issues this week.

[dougwilson]

This should probably end the connection gracefully, running the QUIT packet to the server instead of just dropping the TCP connection. Various database setups will block a client that keeps dropping TCP connections without properly closing them.

[akleiber]

@dicearr this would be ❤️ by many cloud users. Any plan to continue this PR?

[dicearr]

Hi @akleiber. After the review comment I tried to gracefully close the connection by using conn.end instead of conn.destroy in 6633202, which is a fixup commit. So, I don't think there is too much I can do here. If 6633202 is not what @dougwilson meant, some feedback would be appreciated. If it is, then I just need to squash the commits.

[rolandmarg]

We use this library with aws aurora and idleConnectionTimeout is really needed. I don't really have time to wait for this ticket to be merged. What do you guys think about attaching a timer on connection 'release' event, which will close connection if it's not acquired after 'x' time, can be done on top of library.
update: Seems like you can't call conection.end() on released connection in 'release' event

[Mwni]

This is a temporary solution until this functionality has been merged. Place this right after importing the mysql library.

(() => {
	let createPool = mysql.createPool

	mysql.createPool = function(config){
		let pool = createPool(config)

		if(config.idleConnectionTimeout){
			let getConnection = pool.getConnection

			pool.getConnection = function(callback){
				getConnection.call(pool, (err, connection) => {
					if(err){
						callback(err, connection)
						return
					}

					if(connection.__lastUsed){
						if(Date.now() - connection.__lastUsed > config.idleConnectionTimeout){
							connection.destroy()
							pool.getConnection(callback)
							return
						}
					}

					connection.__lastUsed = Date.now()
					callback(err, connection)
				})
			}
		}

		return pool
	}
})()

This is forward compatible. So what it does is patch the createPool function to check for idleConnectionTimeout, if this setting is present, it patches the pool's getConnection function to destroy any connection, that it was about to serve, that has been been idle for longer than specified.

[qingyang-id]

https://github.com/mysqljs/mysql/pull/2507/files

Hello, everyone, I commit a pr and to solve this issue, any feedback would be appreciated.