main.js

"use strict";

var crypto = require("crypto");
var zlib = require("zlib");
var Promise = require("bluebird");
var AWS = require("aws-sdk");
var createError = require("custom-error-generator");
var _ = require("lodash");

var MessageError = createError('MessageError');
var InvalidArgumentError = createError('InvalidArgumentError');

/**
 * Service Bus factory
 * @param {String} queueUrl
 * @param {Object} options
 * @returns {Object}
 */
function serviceBusFactory(queueUrl, options) {

    validate(queueUrl, options);

    var _delegate;
    var _isPolling = false;
    var _queueUrl = queueUrl;

    var _sqs = new AWS.SQS({
        accessKeyId: options.accessKeyId,
        secretAccessKey: options.secretAccessKey,
        region: options.region
    });

    var receiveMessagesAsync = Promise.promisify(_sqs.receiveMessage, _sqs);
    var deleteMessageAsync = Promise.promisify(_sqs.deleteMessage, _sqs);
    var sendMessageAsync = Promise.promisify(_sqs.sendMessage, _sqs);

    function acknowledge(message, callback) {

        return deleteMessageAsync({
            QueueUrl: _queueUrl,
            ReceiptHandle: message.receiptHandle
        }).nodeify(callback);
    }

    function publish(data, callback) {

        var bufferHashHex;

        return toBuffer(data)
            .then(function(buffer) {

                bufferHashHex = md5(buffer);
                return buffer;
            })
            .then(zipBuffer)
            .then(function (zippedBuffer) {

                return sendMessageAsync({
                    QueueUrl: _queueUrl,
                    MessageBody: bufferHashHex,
                    DelaySeconds: 0,
                    MessageAttributes: {
                        data: {
                            DataType: "Binary",
                            BinaryValue: zippedBuffer
                        }
                    }
                });
            })
            .then(function (message) {

                if (md5(bufferHashHex) !== message.MD5OfMessageBody) {
                    throw MessageError("Message body MD5 mismatch")
                }

                return bufferHashHex;
            })
            .nodeify(callback);
    }

    function subscribe(delegate, callback) {

        return new Promise(function (resolve, reject) {

            if (!delegate || typeof delegate !== "function") {
                return reject(new Error("No delegate function provided"));
            }

            _delegate = delegate;
            next();

            return resolve();

        }).nodeify(callback);
    }

    function poll() {

        _isPolling = true;

        var params = {
            QueueUrl: _queueUrl,
            MaxNumberOfMessages: 10,
            VisibilityTimeout: 60,
            WaitTimeSeconds: 10,
            MessageAttributeNames: ["data"]
        };

        receiveMessagesAsync(params)
            .then(function (data) {

                _isPolling = false;

                if (data && data.Messages) {

                    return parseMessages(data.Messages)
                        .then(function(messages) {
                           _delegate(messages, next);
                        });
                }
                else {
                    next();
                }
            })
            .catch(function (err) {

                _isPolling = false;
                throw err;
            });
    }

    function next() {

        if (_isPolling) return;
        poll();
    }

    function parseMessages(messages, callback) {

        return Promise.resolve(messages)
            .map(function(message) {

                return Promise.resolve(message)
                    .then(function(message) {

                        if (!message.MessageAttributes ||
                            !message.MessageAttributes.data ||
                            !message.MessageAttributes.data.BinaryValue) {

                            throw MessageError("Message has invalid payload");
                        }

                        if (message.MD5OfBody !== md5(message.Body)) {
                            throw MessageError("Message body MD5 mismatch")
                        }

                        return unzipBuffer(message.MessageAttributes.data.BinaryValue)
                            .then(function(buffer) {

                                var bufferHashHex = md5(buffer);

                                if (bufferHashHex !== message.Body) {
                                   throw MessageError("Message body MD5 mismatch")
                                }

                                return buffer;
                            })
                            .then(toObject);
                    })
                    .then(function(body) {

                        return {
                            messageId: message.MessageId,
                            receiptHandle: message.ReceiptHandle,
                            body: body
                        }
                    });

            }).nodeify(callback);
    }

    function toBuffer(data, callback) {

        return new Promise(function (resolve, reject) {

            if (!_.isPlainObject(data)) {
                return reject(new InvalidArgumentError("Input data has to be plain object"));
            }

            try {
                var dataString = JSON.stringify(data);
                var dataBuffer = new Buffer(dataString);

                return resolve(dataBuffer);
            }
            catch (err) {
                return reject(err);
            }
        }).nodeify(callback);
    }

    function toObject(buffer, callback) {

        return new Promise(function (resolve, reject) {

            try {
                var data = JSON.parse(buffer);
                return resolve(data);
            }
            catch (err) {
                return reject(err);
            }
        }).nodeify(callback);
    }

    function zipBuffer(buffer, callback) {

        return new Promise(function (resolve, reject) {

            try {
                zlib.gzip(buffer, function (err, res) {

                    if (err) {
                        return reject(err);
                    }

                    return resolve(res);
                });
            }
            catch (err) {
                return reject(err);
            }
        }).nodeify(callback);
    }

    function unzipBuffer(zippedBuffer, callback) {

        return new Promise(function (resolve, reject) {

            zlib.gunzip(zippedBuffer, function (err, res) {

                if (err) {
                    return reject(err);
                }

                return resolve(res);
            });
        }).nodeify(callback);
    }

    function md5(data) {

        var hash = crypto.createHash('md5');
        hash.update(data);
        return hash.digest('hex');
    }

    function hash(data, callback) {

        return toBuffer(data)
            .then(md5)
            .nodeify(callback);
    }

    function validate(queueUrl, options) {

        if (!_.isString(queueUrl)) {
            throw InvalidArgumentError("No AWS SQS queue URL provided");
        }

        if (!options) {
            throw InvalidArgumentError("No options provided");
        }

        if (!options.accessKeyId) {
            throw InvalidArgumentError("No AWS 'accessKeyId' provided");
        }

        if (!options.secretAccessKey) {
            throw InvalidArgumentError("No AWS 'secretAccessKey' provided");
        }

        if (!options.region) {
            throw InvalidArgumentError("No AWS 'region' provided");
        }
    }

    return {
        hash: hash,
        publish: publish,
        subscribe: subscribe,
        acknowledge: acknowledge,
        InvalidArgumentError: InvalidArgumentError,
        MessageError: MessageError
    };
}

module.exports = serviceBusFactory;