Managing Dependencies

Packages, dependencies, versions.

This post will explore two tools and how I’ve been using them. Godep as the consumer of third-party packages, and gopkg.in as a library author.

go get

Before using these tools, get comfortable with the fundamentals of GOPATH and go get .

At first I found GitHub’s forking mechanism at odds with the go tool. It took a shift in perspective – a slightly different approach to how I was using git. Katrina Owen clearly demonstrates the steps in Contributing to Open Source Git Repositories in Go.

For many projects go get is enough. Before adopting another tool, consider the reasons for doing so. The Case Against Third Party Libraries by Ben Johnson is good food for thought.

Godep

“If you’re using an externally supplied package and worry that it might change in unexpected ways, the simplest solution is to copy it to your local repository.” - Go FAQ

Godep is a tool by Keith Rarick that does this copying for you.

If you are worried about unexpected changes, Godep can provide a safety net, but then so can backing up your /src folder. Personally, this isn’t the most compelling reason to use Godep.

Some time ago I put Godep through its paces for Go Package Management and Packages & Dependencies (slides). Still, I had little reason to use it – not until recently.

While working with a library for Apple Push Notifications, I made a few small pull requests. Benny Wong, who maintains the library, was away on his honeymoon at the time. Congrats Benny!

If my project was a solo effort, I wouldn’t feel the need for Godep, but I was working on a team. Suddenly I needed to ensure my team had my changes. I wanted something easy to explain while continuing to contribute changes upstream. So I ran:

1 godep save

It copied my current branch from src/github.com/timehop/apns into a Godeps folder which I checked in with the project. Then I added instructions in the README to use:

1 godep go build

Doing so will manipulate the GOPATH to use the code copied into myproject/Godeps .

As I made more changes, I found myself working in src/github.com/timehop/apns and using go build as usual. Before pushing to GitHub, I’d just update the Godeps folder with:

1 godep update github.com/timehop/apns

Godep worked out quite well. With just a few commands, you can snapshot (and restore) your project’s dependencies and continue to work as usual.

One downside is that everyone using your project needs Godep. That’s fine for a private project, but ideally open source can be installed with just go get . Keith Rarick added an -r option for this purpose, which the CoreOS team has had success with.

Now that -r is available, there wouldn’t be any harm in using Godep for a command-line tool like Looper. I just haven’t felt the need. Even if a dependency were to disappear, I have the code in /src , so I could recover.

Godep isn’t something I use for libraries either – for that, let’s take a look at gopkg.in.

gopkg.in

Versioning is a crutch. If I could design the perfect API from the beginning, would I bother with version numbers? Nope.

Versions can be a signal too. Often 1.0 means stability and 2.0 means shiny, but there are more precise ways to signal changes. For my code, a new major version just means “Sorry everyone, I broke things.”

“If a complete break is required, create a new package with a new import path.” - Go FAQ

Gustavo Niemeyer provides the Go community with a simple stateless website called gopkg.in. It turns branches and tags on GitHub into new import paths.

For those who rather host their own, Stephen Gutekanst wrote a variation that you can run on your project’s own domain.

In either case, people use a library just like any other, with go get and an import path.

1 2 3 4 5 import "gopkg.in/fsnotify.v1" // ... watcher , err := fsnotify . NewWatcher () // note : fsnotify , not fsnotify . v1

When I adopted fsnotify from Chris Howey, my express purpose was to break the API.

Having discussed the API with members of the Go team, I had a number of changes to make. At the same time, I knew I didn’t have it all figured out. The error handling needs a good long look, and integrating new watchers will inevitably result in more changes.

With version 2 and even version 3 in sight, I turned to gopkg.in. It was a relatively straightforward process. Just tag each release with semantic versions.

fsnotify has some things going for it that make this simple:

It has one dependency – the standard library.

The entire library is in one package. There are no absolute import paths to internal packages.

So far gopkg.in has worked out quite well. One day I hope to not need it. ;-)

I Saw Three Ships Come Sailing In

Godep and gopkg.in aren’t the only options, but they are two community provided tools that can be used alongside go get . Both gopkg.in and godep -r allow other developers to install a project or library with go get . No special tools required.

When using Godep for a project, an import proxy like gopkg.in doesn’t seem all that necessary. Yet they work just fine together.

It has been 1.5 years since I first wrote about Go Package Management. In that time I’ve learned a lot, and some things have changed. The next few years should prove interesting, but I’m really happy with what we have today.

I would like to say thank you to the people who wrote the tools that make my life better. Thanks!

P.S. Remember good things come in small packages.