This year I’m taking part in the awesome Advent of Code, and because I haven’t done a lot of Ruby over the past couple of years I thought this would be an excellent opportunity to refresh my skills. In case you’re unfamiliar, AoC is a series of twenty-five coding challenges. Each day leading up to Christmas a new challenge is posted on the site, and there’s a global leaderboard. You can also have local leaderboards (We have one at BJSS for example).
I did originally consider using the opportunity to learn a new language, but the desire to get back to Ruby proved too strong. In truth, I’m glad it did – every time I come back to Ruby after a break, I’m pleasantly surprised by both the bits I’d forgotten and the bits that have been added.
This post is a little rough, and is intended both as a memory aid for myself and as an example for anyone else who needs to know this stuff. I’ve recently decided to push toward x86_64 support in my toy/research OS project, and needed to build a GCC cross compiler for that target. In my case I already had an x86 cross compiler built, but I’ve tried to make the steps general for those that don’t.
These steps are tested with binutils 2.26.1 and GCC 6.1.0. I’m using those versions as they match the version of my x86 cross compiler – These steps might work with the more recent versions, but I can’t guarantee it. I will at some point update my cross compilers, at which point I’ll update these steps.
1. Go to your $HOME/src. Create first if needed.
# mkdir ~/src
# cd ~/src
2. Set up prefixes. PATH is only needed if not already set (e.g. this is your first cross compiler on this system).
Java’s default methods (introduced back in Java 8) are one of those features that solve the intended problem reasonably well, while at the same time allowing all kinds of nasty code and weird inheritance stuff when used in a general-purpose kind of way. Indeed, they’ve been the subject of a tonofposts and the way they (fail to) work still surprises people. They’ve been around for a while now, and there’s a lot of good advice out there on how they should and shouldn’t be used, so that’s not what I’m going to talk about in this post.
What I am going to talk about, however, is the way I’m using them in Moxy, as a way to do a lot less work in runtime-generated bytecode.
A bit of background
Moxy is a mock framework, and it does it’s job by generating mock classes at runtime. These mock classes naturally use a fair bit of bytecode generation, replacing real method implementations with new methods that implement the mock behaviour.
These mock methods do the standard mock thing of recording their invocation, and then they implement behaviour that has been set-up on the mock beforehand.
In order to implement this behaviour, mock objects need access to all kinds of state that’s specific to the instance – stubbed return values, exceptions they should throw, and more. They also need to have easy access to the mock engine that created them (so they can record invocations, for example).
This is often implemented via static methods on some class somewhere whose job it is to store state. The generated code will typically be peppered with a ton of invokestatic instructions that calls out to methods on those classes in order to get things done.
This works, but it has a few problems:
Some kind of mapping between instances and their state must be maintained.
It can make it difficult to swap out mock strategies in a clean fashion.
It can make testing (of the framework) difficult.
The Moxy approach
Instead of storing state statically, Moxy stores it right there in the mock, and all interaction with the state is done with instance methods. These methods can’t be inherited from a superclass (since mocks usually subclass the mocked class), and I really don’t want to generate them (I like to keep generated code to a minimum, as it’s harder to maintain and test that regular Java), so instead Moxy abuses default methods.
It works like this:
All mocks implement an interface, ASMMockSupport.
This interface defines one abstract method, __moxy_asm_ivars(). This method is implemented in generated code (since interfaces don’t have instance variables, the mocks hold the variables and expose them via this method)*.
The support interfaces defines a ton of default methods that do various kinds of work based on those instance variables.
The actual generated code for mocked methods uses invokeinterface calls on this to get stuff done as needed.
Other parts of the framework that interact with the mocks (e.g. stubbers) simple cast the mock instance to ASMMockSupport and call the methods they need.
* Yes, that’s a strange name for a method. Moxy does this to lessen the chances of its built-in methods clashing with methods being mocked.
The default methods on the support interface handle things like finding the engine that created the mock, adding stubbing, finding appropriate stubbing for a given invocation, running delegate methods and actions, and determining whether the current thread is currently in what Moxy calls a monitored invocation (used for recording purposes only, when mock behaviour is disabled).
This has the benefit that a whole lot of fairly-complex code that would otherwise be either generated, or stuffed into static methods, is now implemented, in Java, as instance methods. They’re easy to unit-test, and they’re easy to maintain. The added bonus is the generated bytecode is also easier to maintain, since it’s as short as possible.
Is this the intended use of default methods? Not at all. Is it correct, or appropriate? I’ll leave that to you to decide. I firmly believe, however, that in this very limited use-case it’s a good solution to a tricky problem, all things considered.
If you’re interested in looking at the code, you’ll find it here.
We all love to use mocks in our Java tests, right? Add the usual mock framework to your test dependencies, sprinkle a few mock, when and thenWhatever calls in to your code, and happy days. You’re able to test things in isolation, and as an added bonus ensure your code is actually calling the stuff it’s supposed to be calling by verifying the mock afterwards. The sun is shining, life is good, and your code is tested to perfection.
But then the clouds roll in, and you have to test a final class. Or you need to mock out a static method in some legacy code. Or, horror, some code that directly calls new on a class you want to mock.
You could hit up StackOverflow, where you’ll find that all these things are possible with existing frameworks, assuming you’re prepared to add in another dependency, use a ton of boilerplate, and refactor your (production) code a bit. Depending on which framework you’re currently using there are a ton of different ways you can kind of achieve what you need.
By now you’ve sunk another hour or two, and it’s still not quite working.
What if there was another way?
The other way
What if I told you there was a framework out there that let you take a final class, and just do this?
I believe I mentioned that I’m back at work on the Curb project. In case you missed that, Curb is a ruby extension that provides bindings to the libcurl library. I started it way back, left to concentrate on other things (having kids, making money, etc) and now I’m involved again, working with Todd Fisher who took over maintaining the project when I bowed out. I’ll be fixing bugs, answering questions and generally helping out.
In the meantime, I’ve also started work on porting (if that’s the right word) Curb to FFI, with a view to moving away from the existing C code. The motivations are manifold:
As it stands, Curb is pretty much tied to MRI. In the modern Ruby world, where you’ve got JRuby and Rubinius and who-knows-what-next, this is recognised as a bad thing.
It’s a nightmare to get it working on Windows. This is because, and I can speak with some authority here as someone who develops on Windows every day, Windows sucks for development. Unless you’re using all-Microsoft tooling, in which case it’s pretty awesome. But for interoperability with portable code, and libraries targeted primarily at other platforms, it sucks.
FFI is probably the right way to do these things these days. 10+ years ago, when Curb was first hacked together in about six hours, C extensions were the shizz. Now, not so much. Unless you really need the level of hardware hackery and performance you can get with C, things are better off in Ruby code.
So to sum up, this port is about future-proofing Curb, making it easier to develop, easier to use cross-platform, and (in the long run) safer, probably more performant, and ensuring it can run on all Rubies, including whatever whizz-bang next-gen thing comes out next week (my bet is it’ll be written in Rust. Or Go. Or something…).
As I mentioned in my previous post, I’m now working on Curb again, and currently on Windows. Back in 2006 when I wrote the original Curb, I wouldn’t go near a Windows box for religious reasons, and the project has never officially supported the platform. There are plenty of bugs and posts around about people having mixed success with getting it to work.
Since then, my views have mellowed, partly I think because I’ve come to appreciate that there’s no room for religion in software engineering – you use the right tool for the job. Partly that, and partly by my desire to, you know, get paid and own stuff and whatnot. These days I do as much work on Windows as I do on *nix, and my bank balance is all the better for it. So anyway, back to the point of this post.
Building Curb on Windows is a bit of a nightmare. It took me a fair while to figure it out, and I wrote the damn thing. If it got me feeling like the guy in the picture above, then how must the everyday user trying to get the gem going feel? If they’re just trying to install it and write some code, I’m guessing they immediately give up and go with another library. But what if they are trying to use something else that depends on the Curb gem? I’m guessing that’s when they get so frustrated they file shouty bug reports with the project. And I don’t blame them. It would have been nice to have someone to shout at while I was trying to get it working.
In the end, I did get it going, but it required me to build libcurl from source. I posted an answer to the bug report I mentioned above with the how-to of it, and the poor person who filed it reported back that it worked. You could click through, but I’ll reproduce the steps below to save your finger.
Most likely, your compiled libcurl is incompatible with the ruby devkit compiler. You can verify this by running (this is on my machine, obviously change your paths):
> c:\Ruby200Devkit\mingw\bin\gcc.exe -L. -lcurl
# c:/[...]/ld.exe: skipping incompatible ./libcurl.dll when searching for -lcurl
# c:/[...]/ld.exe: skipping incompatible ./libcurl.dll when searching for -lcurl
# c:/[...]/bin/ld.exe: cannot find -lcurl
# collect2.exe: error: ld returned 1 exit status
Notice the lines about “Skipping incompatible” before the final “cannot find lcurl”. Try grabbing the curl source from https://curl.haxx.se/download/curl-7.54.0.tar.gz , extract it somewhere, and then open up a terminal and try the following:
> which gcc
# important - verify here that the gcc is the one from your ruby devkit!
> sh configure --with-winssl # and whatever other options you require
> make install
It’s very important that you don’t have any other mingw/msys/cygwin compilers in your path, and that you do this in a windows terminal, not msys/cygwin sh. Otherwise, you’ll probably just build another incompatible library.
You should now have libcurl-4.dll in c:\path-to-your-ruby-devkit\local\bin. Now it gets a bit messy, so hang in there. This part is probably a bug in the build, but easy to work around.
> cd c:\path-to-your-ruby-devkit\local\bin
> copy libcurl-4.dll libcurl.dll
The build needs libcurl.dll (it won’t compile with libcurl-4.dll, but the extension won’t run without the -4 suffix, so we’ll have to manually copy the dll later on).
Way back in 2006, after reading on ruby-talk about people’s problems using libcurl with Ruby, I put together a basic C extension to replace the (by-then-unmaintained) bindings that already existed. Little did I know then that it would end up being some of the most popular open-source code I’ve written.
In time, pressures of family, work, and life in general meant I didn’t have a lot of time to devote to my open-source works, and so Todd Fisher took over as maintainer of the project, and did some awesome work improving it, building the multi interface code, and generally making Curb more and more useful. The project is still going strong over ten years later.
I came back to Curb via some work I was doing on a Windows-based system, and after a few hiccups building the library I found myself patching things up a bit to make them work on Windows (which isn’t officially a supported platform for Curb), and a couple of pull requests later Todd got in touch and asked if I’d like to be added to the project on Github. I thought this over for, oh, about ten seconds, and then said yes. I have more time these days for Open Source work, and I don’t have anything currently on the front-burner, so I’m now back on Curb. Todd’s still the boss (after all, he has more code in there than I do!) but I’ll be happily working away, fixing bugs where I can, and trying to make life easier for people out there wanting to use Curb on Windows.
Here’s the original announcement of Curb, from November of 2006.
From: Ross Bamford
Date: November 17, 2006 1:25:05 PM CST
To: ruby-talk_at_ruby-lang.org (ruby-talk ML)
Subject: [ANN] Curb 0.0.1 – New ruby libcurl bindings
Curb 0.0.1 is now available from http://curb.rubyforge.org. Curb
provides nice, easy to use bindings to the libcurl URL transfer
This is the first release, and Curb is still a work-in-progress.
Currently, it supports the curl_easy interface, and can handle the
most common usages for libcurl.
The project is now seeking user feedback, testers on various
platforms, and requests for the features you need the most.
Just a quick note to say that the blog is now back online, but sadly missing quite a few posts that were lost by my old webhost.
The last post I’ve been able to restore is from almost two years ago, when I was just starting out on the drone project. Here’s a quick summary of what’s been happening since then:
The drone project is still unfinished, and has fallen by the wayside a bit if I’m honest. I still plan to get it going, someday.
I’ve recently found time to resume work on my minimal experimental kernel, Mink. (Find it on github if you’re interested).
I have a new day-job – I’m now working for a small non-IT company, putting together a brand new bespoke MRP system for them using Java EE, with a Vaadin front end. In between times, I’m also the entire IT department, which is kinda stressful but also fun.
So all in all you’ve not missed a great deal, and now the blog has a new home, I’ll be regularly updating here with new posts.
Because I like experimenting with things, and because I love cool toys, I’ve decided the time is right to build myself a drone quadcopter.
I’ve played around with RC ‘copters before, and my electronics knowledge is fair (if a little rusty), so I’m not too worried about the actual build (he said, naively). The bit I’m really looking forward to is the software.
I’m still very much in the planning stages (so far I’ve bought one bit of hardware – see pic right). The main goal for this drone is that it will not be radio controlled. I want it to be totally autonomous, without any onboard RC gear at all. That’s right – I even want it to handle take-off and landing all by itself. A tad over-ambitious? I guess only time will tell!
That’s all for now on the drone front, but stay tuned for updates as the build progresses. I’ll be posting here as things move on, and hopefully some day soon I’ll post a video of the maiden flight!
The sharp-eyed amongst you might already have realised how I’m planning to control my drone, but if not, then consider this: Where might I find a device that runs code, and has accelerometers/gyros, a compass, GPS, a camera and wireless network capability, all built in as standard?