recharge/node_modules/mysql/lib/PoolConnection.js

var inherits   = require('util').inherits;
var Connection = require('./Connection');
var Events     = require('events');

module.exports = PoolConnection;
inherits(PoolConnection, Connection);

function PoolConnection(pool, options) {
  Connection.call(this, options);
  this._pool  = pool;

  // Bind connection to pool domain
  if (Events.usingDomains) {
    this.domain = pool.domain;
  }

  // When a fatal error occurs the connection's protocol ends, which will cause
  // the connection to end as well, thus we only need to watch for the end event
  // and we will be notified of disconnects.
  this.on('end', this._removeFromPool);
  this.on('error', function (err) {
    if (err.fatal) {
      this._removeFromPool();
    }
  });
}

PoolConnection.prototype.release = function release() {
  var pool = this._pool;

  if (!pool || pool._closed) {
    return undefined;
  }

  return pool.releaseConnection(this);
};

// TODO: Remove this when we are removing PoolConnection#end
PoolConnection.prototype._realEnd = Connection.prototype.end;

PoolConnection.prototype.end = function () {
  console.warn(
    'Calling conn.end() to release a pooled connection is ' +
    'deprecated. In next version calling conn.end() will be ' +
    'restored to default conn.end() behavior. Use ' +
    'conn.release() instead.'
  );
  this.release();
};

PoolConnection.prototype.destroy = function () {
  Connection.prototype.destroy.apply(this, arguments);
  this._removeFromPool(this);
};

PoolConnection.prototype._removeFromPool = function _removeFromPool() {
  if (!this._pool || this._pool._closed) {
    return;
  }

  var pool = this._pool;
  this._pool = null;

  pool._purgeConnection(this);
};