mq-mqi-nodejs

This repository demonstrates a way to call IBM MQ from applications running in a Node.js environment.

The initial release of this code is being done to encourage feedback, to see if it is useful to continue with further development and how it might be improved.

MQI Description

The package exposes the IBM MQ programming interface via a wrapper layer implemented in JavaScript. This should make it easy for a Node.js developer to send and receive messages via MQ, and interact with other MQ-enabled applications in the organisation.

The package is based on the full MQI. It uses essentially the same verbs and structures as the C or COBOL interface, but with a more appropriate style for this environment. It removes the need for a developer to worry about how to map elements to the underlying C libraries and instead enables a focus on the business application code. For example, JavaScript strings are used instead of fixed-length, spaced-padded fields.

Most MQI verbs and parameters are implemented here. Where there are missing details within the verbs, these are shown by TODO markers in the source files.

It is assumed that someone using this package does have a basic understanding of the procedural MQI, as that is needed to decide which options and fields may need to be set for each verb.

The implemented verbs follow the JavaScript style, invoking user-supplied callback functions on completion. In all cases, the callbacks are presented with an MQError object as the first parameter when an error or warning occurs (null otherwise), followed by other relevant objects and data. If the callback is not provided by the application, then either an exception is thrown, or the verb returns.

Synchrony

All the verbs are essentially synchronous, even though they invoke callbacks for any returned errors and information. The exception to this is for getting messages from a queue.

Note that MQ also has a concept of Asynchronous Put (an MQPMO option) usable from client applications. That can be used in conjunction with a later call to the Stat() function to determine the success of the Put calls, but it is not related to asynchronous notification of the operation completion in JavaScript terms.

This implementation includes two mechanisms for retrieving messages from a queue:

• GetSync() is the call that does an MQGET(wait) synchronously. In a Node environment, it blocks the execution thread until it completes. That may be OK for an immediate retrieval where the wait time is set to zero, but it is not recommended for any times where you want to wait a while for a message to arrive. Some of the samples use this function for simplicity, where the Get() is not the interesting aspect being demonstrated.
• Get() is the call that works asynchronously. The callback given as a parameter to this function is invoked asynchronously. To stop the callback being called for further messages, use the GetDone() function.

The asynchronous retrieval is now implemented using a polling MQGET(immediate) operation. Originally, this package used the MQCB and MQCTL functions to work fully asynchronously, but the threading model used within the MQ libraries does not work well with the Node model, and more detailed testing was demonstrating deadlocks that could not be solved without changes to the underlying MQ products. The polling is done by default every 10 seconds; applications can override that by calling the setPollTime function.

Sample programs amqsget and amqsgeta demonstrate the two different techniques.

Alternative JavaScript routes into MQ

There are already some other ways to access MQ from Node.js:

• Take a look at the MQ Light client available from NPM. MQ supports connections from MQ Light clients via AMQP channels.
• The MQTT protocol has an implementation here. MQ supports connections from MQTT clients via the XR service and Telemetry channels.
• MQ V9.0.4 includes a simple REST API for messaging that is accessible from any environment. See here for more information.

These interfaces may be suitable for many messaging applications, even though they do not give access to the full services available from MQ such as transactions.

Unimplemented capabilities

All the application-level MQI verbs are now implemented.

There are no structure definitions for elements in message contents such as the MQRFH2 or MQDLH headers. When putting messages, JavaScript Buffers and strings can be used; when getting messages, data is always returned in a Buffer. The amqsget samples show one way to convert that Buffer to a string for printing.

The default behaviour assumes use of a local queue manager. Client connections should work if defined via CCDT or MQSERVER environment variable and the program sets the MQCNO_CLIENT_BINDING flag in the MQCNO options during Connx() or sets the MQ_CONNECT_TYPE environment variable to "CLIENT". The package also includes an implementation of the MQCD and MQSCO structures to permit programmatic creation of client connection details.

Extra operations

The package includes a couple of verbs that are not standard in the MQI.

• GetDone() is used to complete asynchronous retrieval of messages.
• GetSync() is equivalent of the traditional MQGET operation.
• Lookup() extracts strings corresponding to MQI numbers, similar to the MQConstants.lookup() method in Java.

Requirements

This package was developed using

• MQ V9 on Linux x64
• node version 6.11
• npm 3.10.10

I have run it on Windows, where the NPM 'windows-build-tools' package also needed to be installed first.

Installation:

To install this package, you can pull it straight from the NPM repository.

mkdir <something>
cd <something>
npm install ibmmq

Installation of the package will automatically install any prerequisite packages downloadable from the npm repository.

It also requires the MQ C client libraries to be installed.

For Windows and Linux x64, the npm installation process now tries to access the Redistributable Client packages and unpack them automatically. The installation of this library succeeds even if the download and unpack of the MQ runtime libraries fails in some way.

If you do not want this automatic installation of the MQ runtime, then set the environment variable "MQIJS_NOREDIST" to any value before running npm install. The MQ libraries will then be found at runtime using mechanisms such as searching LD_LIBRARY_PATH.

For other MQ-supported platforms and environments, the C runtime can be installed from your MQ installation media, or from the full Client downloads at this site. The Redistributable Client packages for Windows and Linux x64 are also available directly from this site.

Sample applications

Samples are provided to demonstrate most MQI uses, including ways put and get messages, and to subscribe to topics. The source code of these samples should be reviewed for an fuller idea of how this package can be used.

The sample applications use, by default, a local queue manager QM1 and ability to use SYSTEM.DEFAULT.LOCAL.QUEUE or the topic SYSTEM.DEFAULT.TOPIC. These values can be overridden on the command line.

The amqsput sample shows how to fill in authentication options with userid and password values.

The two amqsget samples show use of synchronous and asynchronous APIs for retrieving messages.

Samples amqsinq and amqsset show how to inquire on, and set, attributes of an object.

Run like:

cd <something>/node_modules/ibmmq/samples
. setmqenv -s  -k     # to make sure MQ libraries can be found

node amqsput.js
node amqsget.js

There are various forms of the setmqenv command parameters, depending on your environment and platform. This is just one example; read the KnowledgeCenter for more options if you need them.

Containers

The samples directory includes a Dockerfile that can be used as the basis of generating an independent container to run MQ programs. The run.docker script builds and executes the container. Environment variables are used in the Dockerfile and the script to control connection to the queue manager.

Documentation

The package contains JSDoc comments that can be formatted using the makedoc script in the root directory. The generated documentation is then accessible via a web browser.

History

See CHANGES.

Health Warning

This package is provided as-is with no guarantees of support or updates. There are also no guarantees of compatibility with any future versions of the package. The API is subject to change based on any feedback.

Issues and Contributions

For feedback and issues relating specifically to this package, please use the GitHub issue tracker.

Contributions to this package can be accepted under the terms of the IBM Contributor License Agreement, found in the file CLA.md of this repository. When submitting a pull request, you must include a statement stating you accept the terms in the CLA.