Greg Hall
Greggermeister thoughts

Greggermeister thoughts

Dependency management for C++ using Maven and Nexus

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Greg Hall
·Jan 31, 2022·

4 min read

See https://github.com/bantling/tools/tree/master/depmgmt

Choice of Maven

I tried using Conan, and found it overall good, but a bit disappointing. I used Conan on a project that needed development for a relatively short time, then it would sit for years with very little development. At some point after the development sprint was done, the Jenkins builds started to fail because IT upgraded the server, part of which was upgrading Python applications that are installed via pip, which includes Conan. Turns out the upgraded Conan no longer worked with the build files we had.

Part of the problem was I had originally set it up so that Conan was only for dependencies - while it had the ability to generate CMake recipes, I felt it would more than likely not work out for some unforseeable reason. Somebody else on the team was the kind of guy who liked to go full bore all poker chips in on a tool, and thought it was better to have a one button solution that can pull deps, generate CMake files, use CMake to generate Makefiles and run them, producing an artifact in one command.

It worked for awhile, then didn't (after he was gone, of course!). He is a good developer, and a smart guy, but I guess did not at the time fully appreciate how such decisions can fail in the long run. In the end, it would have been better if he had left it as is. Nobody was clamouring for a better solution as far as I was aware.

So I decided on a future round with C++ on another project to give Maven a try, because:

  • I know Maven has native archives
  • I really only need Maven for dependency management, I don't need to tie it into the compile process (let Make do that)
  • I figured Maven should really be capable of being a general build tool that can build anything (like Ant or Make)

With some research (and the requisite swearing), I found I could use the following facilities of Maven to create a very simple system for managing dependencies for any arbitrary purpose (in this case C++ libraries and executables):

  • pom packaging type, which essentially can build anything, but you have to explicitly describe most steps
  • a minimal ~/.m2/settings.xml file that just provides the id, username, and password of a repo to deploy to
  • declare dependencies in pom as usual with type and scope added (don't usually need these)
  • declare a profile in pom to specify value of ${project.build.directory} var for usage elsewhere
  • declare in pom where to unpack dependencies
  • declare in pom how to compile code (use make)
  • declare in pom how to package files (use assembly.xml to declare what gets zipped up)
  • declare in pom that we want to be able to deploy
  • declare in pom the server id and url to deploy to (the url could probably be moved to settings.xml)

Obviously, the pom.xml contains stuff you don't normally have to provide, but is actually still smaller than your average over bloated Java project pom.xml with 150 transitive dependencies, and quite straight forward to understand.

I really only found one small minor gotcha: although the assembly plugin is capable of using better compression formats like bzip and gzip, the dependency plugin only allows you to say it is a zip format. Since it is just a tiny amount of code that is being zipped, it wouldn't matter anyway. Yes, the jar packaging type loads dependencies via jar files, but in terms of compression, a jar file is literally a zip file with a different extension - you could use Windows Explorer to compress a folder of java compiled code into a zip, rename it .jar, and execute it with java -jar.

Conclusion

I'm quite happy with the result, the usual maven commands can be used to grab dependencies, compile, clean, and deploy. I would definitely use Maven for dependency management for C and C++ projects, or really any other situation where you need it, and it isn't already provided for whatever reason.

Maven is a really good general dependency manager, packager and deployment tool for pretty much anything you want to apply a version to, and shove into an artifact repository.

It's also extremely simple to test the small app that depends on a library that in turn depends on another library. Just run a single short loop in bash:

for i in cpp3 cpp2 cpp1;do ( cd $i && mvn deploy ); done

That's it - each project pulls in any needed deps, gets compiled, packaged, and deployed to nexus in one command. The README.adoc at the url provided at the beginning of this article also provides a few simple commands to get Nexus 3 running in docker, and ready to deploy to.

 
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