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SafeMongoConnection.js
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SafeMongoConnection.js
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var MongoClient = require('mongodb').MongoClient;
var Q = require('q');
Q.longStackSupport = true;
// Created to handle the frequent disconnects of our mongo replica set
// (necessary regardless b/c every database is bound to have issues once
// in a while, though ours seems to have more than most)
var SafeMongoConnection = function(connectionURL, connectionOptions) {
this.db = undefined;
this.connectionURL = connectionURL;
this.connectionOptions = connectionOptions;
this.maxRetries = 50;
this.msBetweenRetries = 400;
// A promise:
// Resolves when we are connected (or re-connected) to the DB
// Rejects if database connection failed
// Gets overwritten as new connection attempts are made
this.connectionPromise = Q.fapply(function() {
throw err('Connection never established!');
});
// A flag indicating whether we are in the process of (re-) connecting
// to the DB
this.connecting = false;
};
// Used for the inital connection
SafeMongoConnection.prototype.connect = function() {
this.connecting = true;
this.connectionPromise = this._reconnect();
return this.connectionPromise;
};
// Attempts to connect to the database (with certain # of retries)
SafeMongoConnection.prototype._reconnect = function() {
var attemptToConnect = function(attemptsRemaining) {
return Q.ninvoke(MongoClient, 'connect', this.connectionURL, this.connectionOptions)
.then(function(db) {
console.log('Database connected!', new Date());
this.connecting = false;
this.db = db;
return db;
}.bind(this))
.fail(function(err) {
console.log('*****');
console.log('Error connecting to database:', new Date());
console.log(err);
console.log('*****');
if (attemptsRemaining > 1) {
attemptsRemaining--;
console.log('Will attempt to reconnect in ' + this.msBetweenRetries +
' milliseconds (' + attemptsRemaining +
' attempt(s) remaining)...', new Date());
return Q.delay(this.msBetweenRetries)
.then(function() {
return attemptToConnect(attemptsRemaining);
});
} else {
console.log('Unable to connect to database.', new Date());
this.connecting = false;
throw(err);
}
}.bind(this));
}.bind(this);
return attemptToConnect(this.maxRetries);
};
// Disconnects from the database (if applicable)
// Always returns a promise
SafeMongoConnection.prototype.disconnect = function() {
if (this.db) {
return Q.ninvoke(this.db, 'close')
.then(function() {
this.db = undefined;
return true;
});
} else {
console.log('DB was never connected, no need to disconnect.', new Date());
// Written this way b/c we always want to return a promise here
return Q.fapply(function() { return true; });
}
};
// Make sure database is still connected
// If it is not connected, attempt to reconnect
// Always returns a promise
SafeMongoConnection.prototype._confirmConnection = function() {
var handleDownedConnection = function() {
if (this.connecting) {
console.log('Connection is down, already in the process of reconnecting...', new Date());
// After connection attempt finishes, this will either have the new (working) DB connection,
// or it will have been rejected (leading to an eventual error on a .fail or .done statement)
return this.connectionPromise;
} else {
console.log('Connection went down! Attempting to reconnect...', new Date());
// Update the connection status and connection promise:
this.connecting = true;
// Disconnect first
this.connectionPromise = this.disconnect()
// Then try to reconnect
.then(function() {
return this._reconnect();
}.bind(this));
return this.connectionPromise;
}
}.bind(this);
// Make sure the connection is defined
if (this.db) {
// Ping the mongo server to make sure connection is up
return Q.ninvoke(this.db, 'command', { ping: 1 })
.timeout(5000).then(function(pingResult) {
// If the connection is up, return the database
if (pingResult) {
return this.db;
// If not, attempt to reconnect
} else {
return handleDownedConnection();
}
}.bind(this))
// If not, attempt to reconnect
.fail(function(err) {
return handleDownedConnection();
});
} else {
console.log('No connection found! Attempting to reconnect...', new Date());
// Update the connection status and connection promise:
this.connecting = true;
this.connectionPromise = this.disconnect().then(function() {
return this._reconnect();
}.bind(this));
return this.connectionPromise;
}
};
// Used to safely run arbitrary mongo commands on the database
// Accepts the name of the collection, the name of the method,
// and then an arbitrary number of arguments to pass to the method
SafeMongoConnection.prototype.safeInvoke = function(collectionName, methodName) {
var args = Array.prototype.slice.call(arguments, 2);
// Confirms connection beforehand
return this._confirmConnection()
// Once database connection is confirmed, runs the function
.then(function() {
return Q.npost(this.db.collection(collectionName), methodName, args);
}.bind(this));
};
module.exports = SafeMongoConnection;