'use strict';
var EventEmitter = require('events'),
inherits = require('util').inherits,
MongoNetworkError = require('mongodb-core').MongoNetworkError;
var cursorOptionNames = ['maxAwaitTimeMS', 'collation', 'readPreference'];
/**
* Creates a new Change Stream instance. Normally created using {@link Collection#watch|Collection.watch()}.
* @class ChangeStream
* @since 3.0.0
* @param {(Db|Collection)} changeDomain The collection against which to create the change stream
* @param {Array} pipeline An array of {@link https://www.mongodb.com/docs/manual/reference/operator/aggregation-pipeline/|aggregation pipeline stages} through which to pass change stream documents
* @param {object} [options=null] Optional settings
* @param {string} [options.fullDocument='default'] Allowed values: ‘default’, ‘updateLookup’. When set to ‘updateLookup’, the change stream will include both a delta describing the changes to the document, as well as a copy of the entire document that was changed from some time after the change occurred.
* @param {number} [options.maxAwaitTimeMS] The maximum amount of time for the server to wait on new documents to satisfy a change stream query
* @param {object} [options.resumeAfter=null] Specifies the logical starting point for the new change stream. This should be the _id field from a previously returned change stream document.
* @param {number} [options.batchSize=null] The number of documents to return per batch. See {@link https://www.mongodb.com/docs/manual/reference/command/aggregate|aggregation documentation}.
* @param {object} [options.collation=null] Specify collation settings for operation. See {@link https://www.mongodb.com/docs/manual/reference/command/aggregate|aggregation documentation}.
* @param {ReadPreference} [options.readPreference=null] The read preference. Defaults to the read preference of the database or collection. See {@link https://www.mongodb.com/docs/manual/reference/read-preference|read preference documentation}.
* @fires ChangeStream#close
* @fires ChangeStream#change
* @fires ChangeStream#end
* @fires ChangeStream#error
* @return {ChangeStream} a ChangeStream instance.
*/
var ChangeStream = function(collection, pipeline, options) {
var Collection = require('./collection');
// Ensure the provided collection is actually a collection
if (!(collection instanceof Collection)) {
throw new Error(
'collection provided to ChangeStream constructor is not an instance of Collection'
);
}
var self = this;
self.pipeline = pipeline || [];
self.options = options || {};
self.promiseLibrary = collection.s.promiseLibrary;
// Extract namespace and serverConfig from the collection
self.namespace = {
collection: collection.collectionName,
database: collection.s.db.databaseName
};
self.serverConfig = collection.s.db.serverConfig;
// Determine correct read preference
self.options.readPreference = self.options.readPreference || collection.s.readPreference;
// Create contained Change Stream cursor
self.cursor = createChangeStreamCursor(self);
// Listen for any `change` listeners being added to ChangeStream
self.on('newListener', function(eventName) {
if (eventName === 'change' && self.cursor && self.cursor.listenerCount('change') === 0) {
self.cursor.on('data', function(change) {
processNewChange(self, null, change);
});
}
});
// Listen for all `change` listeners being removed from ChangeStream
self.on('removeListener', function(eventName) {
if (eventName === 'change' && self.listenerCount('change') === 0 && self.cursor) {
self.cursor.removeAllListeners('data');
}
});
};
inherits(ChangeStream, EventEmitter);
// Create a new change stream cursor based on self's configuration
var createChangeStreamCursor = function(self) {
if (self.resumeToken) {
self.options.resumeAfter = self.resumeToken;
}
var changeStreamCursor = buildChangeStreamAggregationCommand(
self.serverConfig,
self.namespace,
self.pipeline,
self.resumeToken,
self.options
);
/**
* Fired for each new matching change in the specified namespace. Attaching a `change` event listener to a Change Stream will switch the stream into flowing mode. Data will then be passed as soon as it is available.
*
* @event ChangeStream#change
* @type {object}
*/
if (self.listenerCount('change') > 0) {
changeStreamCursor.on('data', function(change) {
processNewChange(self, null, change);
});
}
/**
* Change stream close event
*
* @event ChangeStream#close
* @type {null}
*/
changeStreamCursor.on('close', function() {
self.emit('close');
});
/**
* Change stream end event
*
* @event ChangeStream#end
* @type {null}
*/
changeStreamCursor.on('end', function() {
self.emit('end');
});
/**
* Fired when the stream encounters an error.
*
* @event ChangeStream#error
* @type {Error}
*/
changeStreamCursor.on('error', function(error) {
self.emit('error', error);
});
if (self.pipeDestinations) {
const cursorStream = changeStreamCursor.stream(self.streamOptions);
for (let pipeDestination in self.pipeDestinations) {
cursorStream.pipe(pipeDestination);
}
}
return changeStreamCursor;
};
var buildChangeStreamAggregationCommand = function(
serverConfig,
namespace,
pipeline,
resumeToken,
options
) {
var changeStreamStageOptions = {};
if (options.fullDocument) {
changeStreamStageOptions.fullDocument = options.fullDocument;
}
if (resumeToken || options.resumeAfter) {
changeStreamStageOptions.resumeAfter = resumeToken || options.resumeAfter;
}
// Map cursor options
var cursorOptions = {};
cursorOptionNames.forEach(function(optionName) {
if (options[optionName]) {
cursorOptions[optionName] = options[optionName];
}
});
var changeStreamPipeline = [{ $changeStream: changeStreamStageOptions }];
changeStreamPipeline = changeStreamPipeline.concat(pipeline);
var command = {
aggregate: namespace.collection,
pipeline: changeStreamPipeline,
readConcern: { level: 'majority' },
cursor: {
batchSize: options.batchSize || 1
}
};
// Create and return the cursor
return serverConfig.cursor(
namespace.database + '.' + namespace.collection,
command,
cursorOptions
);
};
/**
* Check if there is any document still available in the Change Stream
* @function ChangeStream.prototype.hasNext
* @param {ChangeStream~resultCallback} [callback] The result callback.
* @throws {MongoError}
* @return {Promise} returns Promise if no callback passed
*/
ChangeStream.prototype.hasNext = function(callback) {
return this.cursor.hasNext(callback);
};
/**
* Get the next available document from the Change Stream, returns null if no more documents are available.
* @function ChangeStream.prototype.next
* @param {ChangeStream~resultCallback} [callback] The result callback.
* @throws {MongoError}
* @return {Promise} returns Promise if no callback passed
*/
ChangeStream.prototype.next = function(callback) {
var self = this;
if (this.isClosed()) {
if (callback) return callback(new Error('Change Stream is not open.'), null);
return self.promiseLibrary.reject(new Error('Change Stream is not open.'));
}
return this.cursor
.next()
.then(function(change) {
return processNewChange(self, null, change, callback);
})
.catch(function(err) {
return processNewChange(self, err, null, callback);
});
};
/**
* Is the cursor closed
* @method ChangeStream.prototype.isClosed
* @return {boolean}
*/
ChangeStream.prototype.isClosed = function() {
if (this.cursor) {
return this.cursor.isClosed();
}
return true;
};
/**
* Close the Change Stream
* @method ChangeStream.prototype.close
* @param {ChangeStream~resultCallback} [callback] The result callback.
* @return {Promise} returns Promise if no callback passed
*/
ChangeStream.prototype.close = function(callback) {
if (!this.cursor) {
if (callback) return callback();
return this.promiseLibrary.resolve();
}
// Tidy up the existing cursor
var cursor = this.cursor;
delete this.cursor;
return cursor.close(callback);
};
/**
* This method pulls all the data out of a readable stream, and writes it to the supplied destination, automatically managing the flow so that the destination is not overwhelmed by a fast readable stream.
* @method
* @param {Writable} destination The destination for writing data
* @param {object} [options] {@link https://nodejs.org/api/stream.html#stream_readable_pipe_destination_options|Pipe options}
* @return {null}
*/
ChangeStream.prototype.pipe = function(destination, options) {
if (!this.pipeDestinations) {
this.pipeDestinations = [];
}
this.pipeDestinations.push(destination);
return this.cursor.pipe(destination, options);
};
/**
* This method will remove the hooks set up for a previous pipe() call.
* @param {Writable} [destination] The destination for writing data
* @return {null}
*/
ChangeStream.prototype.unpipe = function(destination) {
if (this.pipeDestinations && this.pipeDestinations.indexOf(destination) > -1) {
this.pipeDestinations.splice(this.pipeDestinations.indexOf(destination), 1);
}
return this.cursor.unpipe(destination);
};
/**
* This method will cause a stream in flowing mode to stop emitting data events. Any data that becomes available will remain in the internal buffer.
* @return {null}
*/
ChangeStream.prototype.pause = function() {
return this.cursor.pause();
};
/**
* This method will cause the readable stream to resume emitting data events.
* @return {null}
*/
ChangeStream.prototype.resume = function() {
return this.cursor.resume();
};
/**
* Return a modified Readable stream including a possible transform method.
* @method
* @param {object} [options=null] Optional settings.
* @param {function} [options.transform=null] A transformation method applied to each document emitted by the stream.
* @return {Cursor}
*/
ChangeStream.prototype.stream = function(options) {
this.streamOptions = options;
return this.cursor.stream(options);
};
// Handle new change events. This method brings together the routes from the callback, event emitter, and promise ways of using ChangeStream.
var processNewChange = function(self, err, change, callback) {
// Handle errors
if (err) {
// Handle resumable MongoNetworkErrors
if (err instanceof MongoNetworkError && !self.attemptingResume) {
self.attemptingResume = true;
if (callback) {
return self.cursor.close(function(closeErr) {
if (closeErr) {
return callback(err, null);
}
self.cursor = createChangeStreamCursor(self);
return self.next(callback);
});
}
return self.cursor
.close()
.then(() => (self.cursor = createChangeStreamCursor(self)))
.then(() => self.next());
}
if (typeof callback === 'function') return callback(err, null);
if (self.listenerCount('error')) return self.emit('error', err);
return self.promiseLibrary.reject(err);
}
self.attemptingResume = false;
// Cache the resume token if it is present. If it is not present return an error.
if (!change || !change._id) {
var noResumeTokenError = new Error(
'A change stream document has been received that lacks a resume token (_id).'
);
if (typeof callback === 'function') return callback(noResumeTokenError, null);
if (self.listenerCount('error')) return self.emit('error', noResumeTokenError);
return self.promiseLibrary.reject(noResumeTokenError);
}
self.resumeToken = change._id;
// Return the change
if (typeof callback === 'function') return callback(err, change);
if (self.listenerCount('change')) return self.emit('change', change);
return self.promiseLibrary.resolve(change);
};
/**
* The callback format for results
* @callback ChangeStream~resultCallback
* @param {MongoError} error An error instance representing the error during the execution.
* @param {(object|null)} result The result object if the command was executed successfully.
*/
module.exports = ChangeStream;