Mark Taylor's Blog

How to remove MQ authorities for deleted ids

A userid or group deleted from the operating system still shows up in a queue manager’s authority lists. Ideally you would have removed those authorisations before deleting the id, but if you have not, then MQ will not usually let you delete the authorisations later. This post explains the procedure that I use to remove MQ authorities for deleted ids or to cold-start the authorisations when testing. I’ll also describe a second procedure that you might prefer.

There are both use-at-own-risk methods, but I’ve given an outline a few times in posts and replies elsewhere. After a bit of encouragement, I finally decided it might be better to give fuller details so you can make a proper evaluation of whether to use the technique.

C switch statement efficiency

MQ V8 introduced a header file, cmqstrc.h, that maps constants in the MQI to string values. I’ve mentioned it a few times recently, both here and in some other forums. One question came in, asking about how well that code worked. So I’ve recreated some tests I wrote back in 2015, to demonstrate what compilers do with that pattern. This shows the efficiency of writing large switch statements in C.

MQ and Node.js: an update to the TypeScript interface

I recently wrote an article about new TypeScript bindings for the MQ and Node.js interface. Version 0.9.21 of the MQ Node.js interface includes an update to the TypeScript definitions that can assist further in writing correct programs by describing how MQI flags or bitfield parameters are set. Showing how this new capability works was a bit too long to simply add to the original article. So I’ve written this piece.

MQ and Node.js: working with TypeScript

MQ application programs for the Node.js environment can now use TypeScript definitions. This brings the opportunity to compile and check your JavaScript programs for correctness before running them. This post will talk more about what TypeScript is and how it can help your MQ Node.js development activity.

Substantial credit for the API definitions and translations of the example programs needs to be given to Andre, who submitted a Pull Request to our github repository.

Resolving subscription authorisation failures

It never fails to amaze me how often the same question gets asked by different people from different projects at around the same time. This time, I was asked by two people about resolving subscription authorisation failures. I could find lots of information about IBM MQ publish/subscribe, and general descriptions of what security checks are made. But there was not so much on how to use information from the queue manager that can help to deal with the inevitable failures.

Decoding MQI constants

On Twitter, Michael asked: “any logic or hints on how to interpret the PCF parameter names returned as multiples from the com.ibm.mq.headers.pcf?” Which is a very good question but a proper answer is far too long to type there. There are several different ways that you can approach the problem, depending on what you are trying to do. So this post talks about decoding MQI constants.

Event formatter changes with MQ 9.2.4

IBM has just announced MQ 9.2.4. No matter how hard you search the announcement letters you will still not be able to find anything about the event formatter changes that I was able to slip into the release. That’s because changes to samples don’t normally deserve highlighting in formal marketing documents. But I hope this change still turns out to be useful.

Warning: is it an error

Something I dealt with recently in independent exchanges with several different people was about programming with IBM MQ, and dealing with MQI errors that might not be errors. This post is a short discussion about the not-quite-failed status of a warning. Is it an error? What is the difference between MQI errors and warnings?

Memories are made of NIS

I was reading this article about the potential removal of the NIS (Network Information System) component from Fedora systems. It reminded me of an old experience managing our department’s systems.

Skeleton of a site attack

Last week I went to edit a draft post, and found that I couldn’t access the blogging system. The web server returned errors – usually 504 (Gateway Timeout) but there were sometimes 4xx errors. This all runs on a local NAS device just a few metres away from where I was typing. The rest of my network seemed fine. So it seemed unlikely to be a network or service provider problem. I started to investigate. As there is no high-value or personal information stored here, I didn’t initially suspect an attacker. But that’s what it turned out to be. I decided to write up my experience, written to show the skeleton of how a site attack might appear, along with some thoughts on what helped diagnose and repel it.