You must rewind your incoming buffer when you fail to encode a character in a CharsetEncoder or you’ll get an IllegalArgumentException

Andy Balaam from Andy Balaam's Blog

I am writing a CharsetEncoder in Java, which is my kind of fun.

I was getting a mysterious error when I identified that I could not encode certain characters:

Exception in thread "main" java.lang.IllegalArgumentException
	at java.nio.Buffer.position(
	at java.nio.charset.CharsetEncoder.encode(
	at java.nio.charset.CharsetEncoder.encode(
	at java.nio.charset.Charset.encode(
	at java.nio.charset.Charset.encode(

After some investigation I realised the library code in Charset.encode was expecting me not to have consumed any characters of my incoming CharBuffer if I rejected the input by returning something like CoderResult.unmappableForLength.

Of course, in order to discover the input was unmappable, I did have to read it, but I made this problem go away by stepping back one char when I found an error like this:

public CoderResult encodeLoop(CharBuffer in, ByteBuffer out) {
    char ch = in.get();
    if(isUnmappable(ch)) {
        in.position(in.position() - 1);
        return CoderResult.unmappableForLength(2);
    // ... rest of method ...

I hope this helps someone.

Practical psychology books for software engineers

Derek Jones from The Shape of Code

So you have read my (draft) book on evidence-based software engineering and want to learn more about human psychology. What books do I suggest?

I wrote a book about C that attempted to use results from cognitive psychology to understand developer characteristics. This work dates from around 2000, and some of my book choices may have been different, had I studied the subject 10 years later. Another consequence is that this list is very weak on social psychology.

I own all the following books, but it may have been a few years since I last took them off the shelf.

There are two very good books providing a broad introduction: “Cognitive psychology and its implications” by Anderson, and “Cognitive psychology: A student’s handbook” by Eysenck and Keane. They have both been through many editions, and buying a copy that is a few editions earlier than current, saves money for little loss of content.

“Engineering psychology and human performance” by Wickens and Hollands, is a general introduction oriented towards stuff that engineering requires people to do.

Brain functioning: “Reading in the brain” by Dehaene (a bit harder going than “The number sense”). For those who want to get down among the neurons “Biological psychology” by Kalat.

Consciouness: This issue always comes up, so let’s kill it here and now: “The illusion of conscious will” by Wegner, and “The mind is flat” by Chater.

Decision making: What is the difference between decision making and reasoning? In psychology those with a practical orientation study decision making, while those into mathematical logic study reasoning. “Rational choice in an uncertain world” by Hastie and Dawes, is a general introduction; “The adaptive decision maker” by Payne, Bettman and Johnson, is a readable discussion of decision making models. “Judgment under Uncertainty: Heuristics and Biases” by Kahneman, Slovic and Tversky, is a famous collection of papers that kick started the field at the start of the 1980s.

Evolutionary psychology: “Human evolutionary psychology” by Barrett, Dunbar and Lycett. How did we get to be the way we are? Watch out for the hand waving (bones can be dug up for study, but not the software of our mind), but it weaves a coherent’ish story. If you want to go deeper, “The Adapted Mind: Evolutionary Psychology and the Generation of Culture” by Barkow, Tooby and Cosmides, is a collection of papers that took the world by storm at the start of the 1990s.

Language: “The psychology of language” by Harley, is the book to read on psycholinguistics; it is engrossing (although I have not read the latest edition).

Memory: I have almost a dozen books discussing memory. What these say is that there are a collection of memory systems having various characteristics; which is what the chapters in the general coverage books say.

Modeling: So you want to model the human brain. ACT-R is the market leader in general cognitive modeling. “Bayesian cognitive modeling” by Lee and Wagenmakers, is a good introduction for those who prefer a more abstract approach (“Computational modeling of cognition” by Farrell and Lewandowsky, is a big disappointment {they have written some great papers} and best avoided).

Reasoning: The study of reasoning is something of a backwater in psychology. Early experiments showed that people did not reason according to the rules of mathematical logic, and this was treated as a serious fault (whose fault it was, shifted around). Eventually most researchers realised that the purpose of reasoning was to aid survival and reproduction, not following the recently (100 years or so) invented rules of mathematical logic (a few die-hards continue to cling to the belief that human reasoning has a strong connection to mathematical logic, e.g., Evans and Johnson-Laird; I have nearly all their books, but have not inflicted them on the local charity shop yet). Gigerenzer has written several good books: “Adaptive thinking: Rationality in the real world” is a readable introduction, also “Simple heuristics that make us smart”.

Social psychology: “Social learning” by Hoppitt and Laland, analyzes the advantages and disadvantages of social learning; “The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter” by Henrich, is a more populist book (by a leader in the field).

Vision: “Visual intelligence” by Hoffman is a readable introduction to how we go about interpreting the photons entering our eyes, while “Graph design for the eye and mind” by Kosslyn is a rule based guide to visual presentation. “Vision science: Photons to phenomenology” by Palmer, for those who are really keen.

Several good books have probably been omitted, because I failed to spot them sitting on the shelf. Suggestions for books covering topics I have missed welcome, or your own preferences.

Proxy Weirdness – Socket Closed on 404

Chris Oldwood from The OldWood Thing

While investigating the issue that led to the discovery of the strange default behaviour of the .Net HttpClient class which I wrote up in “Surprising Defaults – HttpClient ExpectContinue” we also unearthed some other weirdness in a web proxy that sat between our on-premise adapter and our cloud hosted service.

Web proxies are something I’ve had cause to complain about before (see “The Curse of NTLM Based HTTP Proxies”) as they seem to interfere in unobvious ways and the people you need to consult with to resolve them are almost always out of reach [1]. In this particular instance nobody we spoke to in the company’s networks team knew anything about it and trying to identify if it’s your on-premise proxy and not something broken with any of the other intermediaries that sit between you and the endpoint is often hard to establish.

The Symptoms

Whilst trying to track down where the “Expect: 100-Continue” header was coming from, as we didn’t initially believe it was from our code, we ran a WireShark trace to see if we could capture the traffic from, and to, our box. What was weird in the short trace that we captured was that the socket looked like it kept closing after every request. Effectively we sent a PUT request, the response would come back, and immediately afterwards the socket would be closed (RST).

Naturally we put this on the yak stack. Sometime later when checking the number of connections to the TIBCO server I used the Sysinternals’ TCPView tool to see what the service was doing and again I noticed that sockets were being opened and closed repeatedly. As we had 8 threads concurrently processing the message queue it was easy to see 8 sockets open and close again as in TCPView they go green on creation and red briefly on termination.

At least, that appeared to be true for the HTTP requests which went out to the cloud, but not for the HTTP requests that went sideways to the internal authentication service. However they also had an endpoint hosted in the cloud which our cloud service used and we didn’t see that behaviour with them (i.e. cloud-to-cloud), or when we re-configured our on-premise service to use it either (i.e. on-premise-to-cloud). This suggested it was somehow related to our service, but how?

The HttpClient we were using for both sets of requests were the same [2] and so we were pretty sure that it wasn’t our fault, this time, although as the old saying goes “once bitten, twice shy”.

Naturally when it comes to working with HTTP one of the main diagnostic tools you reach for is CURL and so we replayed our requests via that to see if we could reproduce it with a different (i.e. non-.Net based) technology.

Phased Switchover

While the service we were writing was new, it was intended to replace an existing one and so part of the rollout plan was to phase it in slowly. This meant that all reads and writes would go to both versions of the service but only the one where any particular customer’s data resided would succeed. The consumers of the service would therefore get a 404 from us if the data hadn’t been migrated, which in the early stages of development applied to virtually every request.

A few experiments later to compare the behaviour for requests of migrated data versus unmigrated data and we had an answer. For some reason a proxy between our on-premise adapter and our web hosted service endpoint was injecting a “Connection: Close” header when a PUT or DELETE [3] request returned a 404. The HttpClient naturally honoured the response and duly closed the underlying socket.

However it did not have this behaviour for a GET or HEAD request that returned a 404 (I can’t remember about POST). Hence the reason we didn’t see this behaviour with the authentication service was because we only sent GETs, and anyway, they returned a 200 with a JSON error body instead of a 404 for invalid tokens [4].


I wish I could say that we tracked down the source of the behaviour and provide some closure but I can’t. The need for the on-premise adapter flip-flopped between being essential and merely a performance test aid, and then back again. The issue remained as a product backlog item so we wouldn’t forget it, but nothing more happened while I was there.

We informed the network team that we were opening and closing sockets like crazy, which these days with TLS is somewhat more expensive and therefore would generate extra load, but had to leave that with them along with an offer of help if they wanted to investigate it further, as much for our own sanity.

It’s problems like these which cause teams to deviate from established conventions because ultimately one is within their control while the other is outside it and the path of least resistance is nearly always seen as a winner from the business perspective.


[1] I’m sure they’re not hidden on purpose but unless you have a P1 incident it’s hard to get their attention as they’re too busy dealing with actual fires to worry about a bit of smoke elsewhere.

[2] The HttpClient should be treated as a Singleton and not disposed per request, which is a common mistake.

[3] See “PUT vs POST and Idempotency” for more about that particular choice.

[4] The effects of this style of API response on monitoring and how you need to refactor to make the true outcome visible are covered in my recent Overload article “Monitoring: Turning Noise into Signal”.

Agile won the war but lost the peace

Allan Kelly from Allan Kelly Associates


“I’ve spoken of the shining city all my political life, … in my mind it was a tall, proud city built on rocks stronger than oceans, wind-swept, God-blessed, and teeming with people of all kinds living in harmony and peace; a city with free ports that hummed with commerce and creativity. And if there had to be city walls, the walls had doors and the doors were open to anyone with the will and the heart to get here. That’s how I saw it, and see it still” President Ronald Reagan, Farewell to the Nation, January 11, 1989

Back in 2001 when the word agile appeared it was a manifesto – a set of ideas, the term “agile” also served to group a bunch of tools and techniques which could make software development “better.” More importantly to my mind, it painted a picture of a shining city on a hill we all wanted to live in.

Agile was a place you wanted to go, it was a journey you wanted to make, it offered hope. More important as the tools – sprints, stand-ups, etc. – and approaches – just in time, last responsible moment, test first – were the stories agile people – including myself – told. These were stories of a better world, of that shining city on the hill.

And not unimportantly, in a world of search engines “agile” gave you something to search for. Before agile you could search “make my software development team better” or “software development process improvement” but what you got was a very mixed offering. AltaVista (and the young Google) would suggest links for CMMI, or ISO-9000, or vendor tools to “fix it”, or proper design, or… there was no coherent message. Most of these ideas resolved around senior people making big decisions and then imposing them.

Then along came agile: it offered to involve everyone, everyone made decisions, everyone was happy and we could all go to that shining city on a hill – more than that, we all had an important part to play in building that city.

Today everyone is agile. Nobody is promoting traditional (“waterfall”) working, CMMI, PMI and everyone else has incorporated agile (to some degree). Not being agile is about as popular as leprosy.

But very few of us have reached the shining city on the hill.

Along the way agile has been watered down, in becoming compatible with everything else it is less different, it is less attractive, fewer workers are motivated to take the journey. And as “the powers that be” have found ways to bring control-and-command back to teams (maybe in the name of scaling) fewer people are invited to help build the city.

Ironically, as we (the agile community) has made agile management friendly we have made it less worker friendly. Today senior managers “get agile” and want their organisations to be agile. But those at the code face seem to have less and less motivation. And those in the middle… sometimes they seem to want to change just enough to declare success but no so much that things really change.

For some people agile has become completely discredited – I wrote Why do Dev’s hate agile? last year and I’m presenting it in London next week. Agile isn’t a shining city on a hill, agile is trench warfare.

And Googling “agile” presents a long long list of links with less and less coherence.

Agile won the war. Agile is respectable and everyone is agile now. Big business rush to be agile, Governments want to be agile, blue-chip consultancies will sell you agile.

But agile lost the peace.

While many say they are agile few software developers live in a shiny city. The place they live in might be better than the place they came from but it doesn’t live up to the dream many of us shared 15 years ago. Agile has become an excuse for failure and a thing to be imposed.

The thing that passes for “agile” today is too often a watered down version of the original dream. Worse still, we don’t have a word to describe that shining city we all want to get to. Russians have an expression for this:

“We wanted the best, it turned out like always.” Viktor Stepanovich Chernomyrdin, Prime Minister Russia, 1998-1999

Me? – I still dream of that shining city on the hill, I still believe agile is the right way to get their, I still wave the flag for agile but more and more I feel the need to explain myself and tell people that the agile I dream of is not the agile they may experience.

The post Agile won the war but lost the peace appeared first on Allan Kelly Associates.

Practical statistics books for software engineers

Derek Jones from The Shape of Code

So you have read my (draft) book on evidence-based software engineering and want to learn more about the statistical techniques used, but are not interested lots of detailed mathematics. What books do I suggest?

All the following books are sitting on the shelf next to where I write (not that they get read that much these days).

Before I took the training wheels off my R usage, my general go to book was (I still look at it from time to time): “The R Book” by Crawley, second edition; “R in Action” by Kabacoff is a good general read.

In alphabetical subject order:

Categorical data: “Categorical Data Analysis” by Agresti, the third edition is a weighty tomb (in content and heaviness). Plenty of maths+example; more of a reference.

Compositional data: “Analyzing compositional data with R” by van den Boogaart and Tolosana-Delgado, is more or less the only book of its kind. Thankfully, it is quite good.

Count data: “Modeling count data” by Hilbe, may be more than you want to know about count data. Readable.

Circular data: “Circular statistics in R” by Pewsey, Neuhauser and Ruxton, is the only non-pure theory book available. The material seems to be there, but is brief.

Experiments: “Design and analysis of experiments” by Montgomery.

General: “Applied linear statistical models” by Kutner, Nachtsheim, Neter and Li, covers a wide range of topics (including experiments) using a basic level of mathematics.

Mixed-effects models: “Mixed-effects models in S and S-plus” by Pinheiro and Bates, is probably the book I prefer; “Mixed effects models and extensions in ecology with R” by Zuur, Ieno, Walker, Saveliev and Smith, is another view on an involved topic (plus lots of ecological examples).

Modeling: “Statistical rethinking” by McElreath, is full of interesting modeling ideas, using R and Stan. I wish I had some data to try out some of these ideas.

Regression analysis: “Applied Regression Analysis and Generalized Linear Models” by Fox, now in its third edition (I also have the second edition). I found this the most useful book, of those available, for a more detailed discussion of regression analysis. Some people like “Regression modeling strategies” by Harrell, but this does not appeal to me.

Survival analysis: “Introducing survival and event history analysis” by Mills, is a readable introduction covering everything; “Survival analysis” by Kleinbaum and Klein, is full of insights but more of a book to dip into.

Time series: The two ok books are: “Time series analysis and its application: with R examples” by Shumway and Stoffler, contains more theory, while “Time series analysis: with applications in R” by Cryer and Chan, contains more R code.

There are lots of other R/statistics books on my shelves (just found out I have 31 of Springer’s R books), some ok, some not so. I have a few ‘programming in R’ style books; if you are a software developer, R the language is trivial to learn (its library is another matter).

Suggestions for books covering topics I have missed welcome, or your own preferences (as a software developer).

Godot: Dragging and dropping physics objects video

Andy Balaam from Andy Balaam's Blog

Series: 2D Shapes, drag and drop

Continuing to explore the Godot 3 game engine. I want to make a game where you drag blocks around and balance them on each other, but I couldn’t find much documentation on how to drag-and-drop objects (except menu UI elements), and especially I found quite a few wrinkles when doing this with objects that are normally controlled by the physics engine.

This time we actually write some code in Godot’s programming language, GDScript.

Someone installed a Scheme development environment on their phone

Timo Geusch from The Lone C++ Coder's Blog

Ben Simon has a post up on his blog describing how he set up a scheme development environment on his Galaxy S9 Android phone. It was also an especially timely post as I had been eyeing a Mac Quadra with a Symbolics Lisp Machine extension card on eBay. As if we needed another reminder just […]

The post Someone installed a Scheme development environment on their phone appeared first on The Lone C++ Coder's Blog.

Archimedean Skew – a.k.

a.k. from thus spake a.k.

About a year and a half ago we saw how we could use Gaussian copulas to define dependencies between the elements of a vector valued multivariate random variable whose elements, when considered in isolation, were governed by arbitrary cumulative distribution functions, known as marginals. Whilst Gaussian copulas are quite flexible, they can't represent every possible dependency between those elements and in this post we shall take a look at some others defined by the Archimedean family of copulas.