Edward Thomson

libgit2 v0.99 Released

February 19, 2020  •  12:04 PM

Today we've released libgit2 v0.99. 🎉🎉🎉

libgit2 v0.99

libgit2 is a linkable library for working with git repositories in any application. It's used by IDEs, GUI clients for Git, hosting providers, scientific computing tools, and even scuba diving log software.

Whether you keep your code on GitHub, GitLab, Bitbucket, or nearly anywhere else, it's libgit2 that does the work every time you click the "merge pull request" button. So if you write software, you've probably used libgit2, even if you don't know it.

And – finally – we're getting close to releasing version 1.0.

When I started working on libgit2, eight years ago, I joined a group of developers from all over the world who were working on the project. And shortly after I did, we started planning for all the things that we'd need to do to get to libgit2 version 1.0.

I honestly don't remember a single one of those things.

But I do remember that the biggest thing that we needed to provide to users wasn't features or functionality, it was API consistency.

See, back in ye olde days, we had this idea that we could build the perfect Git library. It would have the perfect API. And once we got there, then we would never need to change it, and that would be our 1.0. And until that happened, we could just keep changing the API until it was perfect. It was, after all, just a prerelease. (Look, it's still version zero-point-something!) And once we got there, all the developers that use libgit2 would be super happy about our great API!

Well, reader, I probably don't have to tell you that people were not, in fact, super happy. It turns out that changing the API on people all the time is not really a recipe for satisfaction.

Hell, even I hated it. I used to be that guy who would bring in new versions of libgit2 into Visual Studio. And then I'd suffer through finding all the places that called git_checkout and needed to be updated whenever we made some API change to "make things better". And then I'd curse myself and my friends who did that.

And as time went on, git became more popular. And more people wanted to build apps that talked to git repositories. And we had more users and more applications building on top of libgit2. And then breaking the API just became cruel.

So after the last release – v0.28 – we made a (long overdue) decision: we needed to release a v1.0, finally. And then we'd need to stop breaking the API in minor releases.

So we challenged ourselves to do the refactorings that we wanted to do to improve the API consistency while still keeping the API backward compatible. Sometimes this meant #defines. Sometimes this meant making the old functions proxy to the new functions. And sometimes this just meant realizing that perfection is unattainable. (It got real deep, y'all.)

But we succeeded in our mission: we believe that v0.99 is completely API-compatible with v0.28. This is the first release that we can say that about. Which means that this is the pre-release for v1.0.

So, please, if you're a libgit2 user, give v0.99 a shot. We'll do a period of stabilization to ensure that there are no significant bugs, and then we'll release v1.0 🔜.

And once we do that, we'll start looking forward to v2.0, because that's when semver says that we can make breaking API changes again.

Just Kidding!

This is day 31 of my GitHub Actions Advent Calendar. If you want to see the whole list of tips as they're published, see the index.

Advent calendars usually run through Christmas, but I'm going to keep posting about GitHub Actions through the end of December. Consider it bonus content!

Yesterday we built an action that let you send a tweet from a GitHub Actions workflow. Once we built it, you can use it by referencing it in my repository, as ethomson/send-tweet-action@v1. But… how do people find it?

Well, there's always your favorite search engine – which, perhaps surprisingly, does a good job of crawling GitHub.1


But we can do better than relying on a search engine. If we publish this action to the GitHub Marketplace, then people who want to build a workflow have a focused place to look for actions that they can use to extend GitHub. The marketplace will even show up in the workflow editor, so that people can find actions easily.

Marketplace Editor

Thankfully, publishing to the marketplace is easy. Once I've created an action and my repository has an action.yml in it, then GitHub will prompt you to create a release, which will let you publish an action to the marketplace.

Publish Prompt

When you create a new release for an action, GitHub will give you the option to publish that release to the marketplace. This will help users find your action with the marketplace search.


Once I've published this release, it will now exist in the marketplace. Now whenever somebody searches for "send tweet" or "twitter", they'll find the send tweet action.

Marketplace Search

Now people can easily find an action – whether it's from a search engine, or from the marketplace.

That's the end of my GitHub Actions Advent Calendar! I've had a blast writing it, and I hope that you've learned some things about GitHub Actions along the way. I can't wait to see what you build to automate your GitHub workflows!

  1. This was in private browsing mode, and on a different wireless network than the one that I was working on yesterday when I was searching for Twitter APIs and GitHub Actions documentation. This hardly suggests that this will be the general results, though. 

This is day 30 of my GitHub Actions Advent Calendar. If you want to see the whole list of tips as they're published, see the index.

Advent calendars usually run through Christmas, but I'm going to keep posting about GitHub Actions through the end of December. Consider it bonus content!

Yesterday we built an action that posted to a GitHub issue. It showed how easy it is to work with GitHub APIs from within an action. But actions are generally written in JavaScript, so they can easily integrate with APIs from other services. This lets you create actions that can create an issue in Jira, send a text message, or upload security information about your project.

One of the things that I want to automate is sending a tweet – this is something I do whenever I release a new version of something, to announce its availability.

And I'd love an action that I can use in a workflow to automate this. If you look in the GitHub Actions Marketplace, you can see that there is actually an action already that can tweet. Unfortunately, it's built as a docker container.

You can create actions as either a Docker container or a JavaScript application. It might seem easier to get started with a container-based action, but there are limitations: only Linux based workflows (those that run on ubuntu-latest) can use them. Using a JavaScript action ensures that your action can be used in any workflow.

So if I want to send a tweet whenever any of my projects are released – including the ones that run on macOS or Windows – then I'll need to create a JavaScript action that can send a tweet.

To do this, I'll start with the sample TypeScript action and add in the twitter npm package so that I can communicate with the Twitter API. This is quite straightforward – I'll need to take the authentication as inputs to the action and use those to create a Twitter API instance.

const twitter = new Twitter({
  consumer_key: core.getInput('consumer-key'),
  consumer_secret: core.getInput('consumer-secret'),
  access_token_key: core.getInput('access-token'),
  access_token_secret: core.getInput('access-token-secret')

Then I can send a tweet by calling the /statuses/update API. I'll take another input to the action that will be the status to tweet.

  {status: core.getInput('status')},
  (error, data, response) => { if (error) throw error }

Once I've got that written, all I need to do is package it up – creating a distribution branch, pushing that up to GitHub, and then creating a release.

You can find the finished product at github.com/ethomson/send-tweet-action, so you can use ethomson/send-tweet-action@v1 as part of a workflow.

Now any time I push to this repository, it will send a tweet.

You can use this action to send a tweet whenever a release is created, a wiki is updated, or a deployment occurs. Or, just for fun, like what I've done.

It's easy to integrate other APIs into an action to let you automate other tools based on activities in your repository. I can't wait to see what you build!

GitHub Actions Day 29: Creating an Action

December 29, 2019  •  2:47 PM

This is day 29 of my GitHub Actions Advent Calendar. If you want to see the whole list of tips as they're published, see the index.

Advent calendars usually run through Christmas, but I'm going to keep posting about GitHub Actions through the end of December. Consider it bonus content!

So far this month we've looked at a lot of workflows for GitHub Actions. Almost all of them will run commands as part of the workflow. Some of them will also make use of actions to help set up the environment or expand the workflow.

An action is a piece of code – either a runnably docker container or a JavaScript application – that you can re-use within several workflows.

There are several actions that GitHub provides to use within your workflows. For example, the checkout action will clone your repository so that you can build and test it. The setup-node action will set up the requested version of Node.js in the PATH. And the clever github-script action lets you run JavaScript within the GitHub context.

But it's straightforward to create your own action that you can use in your workflows or share with others. GitHub provides a toolkit to help you get starting building a workflow in JavaScript or TypeScript.

I'm going to take the TypeScript sample as a start and create an action that listens for comments on an issue. And when it sees a particular comment – /octocat – then it will reply by posting a random Octocat from the Octodex.

First, we'll get some data out of the github.context, which contains information out of the workflow execution. From there, we can get the repository that we're running in, the issue that was commented on, and the body of the comment that was posted.

const context = (github as any).context
const repository = context.payload.repository
const issue = context.payload.issue
const comment = context.payload.comment.body

We also want to establish an outbound connection to GitHub – we can create an instance of OctoKit (the GitHub API), connecting back to our repository with the GITHUB_TOKEN. (Users will need to pass their GITHUB_TOKEN when they invoke the action.)

const token = process.env.GITHUB_TOKEN || ''
const octokit = new github.GitHub(token)

Now that we've got all this plumbing in place, we can add our business logic. We want to do some work when we see a comment that is /octocat (or /mona).

if (command == '/octocat' || command == '/mona') {
  // display an octocat

When we see that comment, we'll grab a random octocat image from a list of octocats.

const rand = Math.floor(Math.random() * octocats.length)
const octocat = octocats[rand]

Now that we have the Octocat that we want to post, we can use the Octokit API to post it, by calling issues.createComment(...). We'll post Markdown with an inline image to the Octocat that we chose at random.

  owner: repository.owner.login,
  repo: repository.name,
  issue_number: issue.number,
  body: '![' + octocat + '](' + octodex_url + '/' + octocat + ')'

I've put this all together and packaged it up as mona-action. When you add it to your workflow:

on: issue_comment

    runs-on: ubuntu-latest
    - uses: ethomson/mona-action@master
        GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"

And you add a comment on an issue that is /octocat, you'll get a nice image as a result:


Certainly this is a simplistic example, but this gives you an idea of how you can take advantage of the GitHub Actions API to retrieve data about the action execution within your workflow, and how to use the Octokit API to communicate back with GitHub. From there you can create an action that suits your workflow.

Want to see this action in full? It's at https://github.com/ethomson/mona-action

GitHub Actions Day 28: Repository Automation

December 28, 2019  •  2:47 PM

This is day 28 of my GitHub Actions Advent Calendar. If you want to see the whole list of tips as they're published, see the index.

Advent calendars usually run through Christmas, but I'm going to keep posting about GitHub Actions through the end of December. Consider it bonus content!

This month we've looked at a lot of different ways to build and test your code when a pull request is opened, or when a pull request is merged into the master branch. And we've looked at different ways to deploy your code to a package registry or to a cloud provider.

But GitHub Actions provides triggers for any operation that happens in your repository, not just the ones start CI/CD workflows. Here's some simple examples that display information about the event and are a good basis to build on.

Issue Comment

The issue_comment event is triggered whenever someone adds a comment on an issue or a pull request. The payload provides information about the issue and the comment that was added.

Here's a workflow that uses jq to get the issue comment out of the payload.

When this workflow runs it will print the comment.

Issue Comment

Wiki Changed

The gollum event is triggered whenever someone changes the repository's wiki. The payload provides information about the wiki pages that were changed.

Here's a workflow that uses jq to get the wiki information out of the payload.

When this workflow runs it will print the URL to the first wiki page that was changed.

Issue Comment


You don't have to run a workflow based on any activity in your repository at all; you can also run workflows on a schedule. When you use the schedule trigger, you can specify when the workflow should run using crontab(5) syntax.

  - cron: 0 2 1 * *

In this case, the workflow will run at 2:00 AM every morning on the first day of every month (UTC). cron syntax is tricky, so be sure to consult the documentation if you haven't worked with it before.


Although GitHub Actions provides great functionality for CI/CD workflows, there are triggers for almost every operation in your repository that you can use to automate functionality. With the last few days of the month, we'll look at a more concrete example.