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Development on GitHub Action: Require Conditional Status Checks

Unit Testing and Code Structure

  • The cmd/requireconditional/main.go script is intended to be as short as possible so we can maximize the amount of code that can be tested: 
    package main

import (
	githubactions "github.com/sethvargo/go-githubactions"

	"github.com/blend/require-conditional-status-checks/pkg/requireconditional"
)

func main() {
	action := githubactions.New()
	err := requireconditional.Run(action)
	if err != nil {
		action.Fatalf("%v", err)
	}
}
  • Any code that deals with GitHub Actions inputs, outputs or log messages will need to import github.com/sethvargo/go-githubactions.
  • When writing (testable) code that uses the githubactions package, a pointer action *githubactions.Action should be used rather than the global wrappers around the package defaultAction. For example use action.GetInput("role") instead of githubactions.GetInput("role").
  • In order to test code involving GitHub Actions, it's critical to be able to both control environment variables (these are inputs) and to monitor writes to STDOUT. In order to do this in tests, both the STDOUT writer and the Getenv() provider can be replaced: 
    actionLog := bytes.NewBuffer(nil)
envMap := map[string]string{
	"INPUT_ROLE":  "user",
	"INPUT_LEASE": "3600",
}
action := githubactions.New(
	githubactions.WithWriter(actionLog),
	githubactions.WithGetenv(func(key string) string {
		return envMap[key]
	}),
)
// ...
it.Equal("...", actionLog.String())

Testing: Invoking Actions Locally

In order to sanity check an implementation, it can be quite useful to run an action locally instead of doing a pre-release and waiting on a fully triggered GitHub Actions workflow. To run an action locally, it's enough to run the cmd/requireconditional/main.go binary with the correct environment variables.

There are two types of environment variables needed; the GITHUB_* environment variables that come with the workflow. See the dhermes/actions-playground repository for a collection of captured GITHUB_* environment variables from real GitHub Actions workflows, organized by event type (e.g. pull_request or push event). The other type of inputs are provided in inputs: to the action (i.e. the inputs from action.yml). These get transformed into INPUT_* environment variables by GitHub.

For example:

env \
  'GITHUB_API_URL=https://api.github.com' \
  'GITHUB_REPOSITORY=dhermes/actions-playground' \
  'GITHUB_EVENT_NAME=pull_request' \
  'GITHUB_EVENT_PATH=./tmp/event.json' \
  "INPUT_GITHUB-TOKEN=$(cat ./tmp/token.txt)" \
  'INPUT_TIMEOUT=30m' \
  'INPUT_INTERVAL=30s' \
  'INPUT_CHECKS-FILENAME=./tmp/checks.yml' \
  go run ./cmd/requireconditional/main.go

To locally run an existing release of this action, the command would be similar

git clone git@github.com:blend/require-conditional-status-checks.git
cd ./require-conditional-status-checks
env \
  'GITHUB_API_URL=https://api.github.com' \
  'GITHUB_REPOSITORY=dhermes/actions-playground' \
  'GITHUB_EVENT_NAME=pull_request' \
  'GITHUB_EVENT_PATH=./tmp/event.json' \
  "INPUT_GITHUB-TOKEN=$(cat ./tmp/token.txt)" \
  'INPUT_TIMEOUT=30m' \
  'INPUT_INTERVAL=30s' \
  'INPUT_CHECKS-FILENAME=./tmp/checks.yml' \
  node index.js  # Or `./main-darwin-amd64-5786bbfeff4524101e761a8cd8a7d1d05de82d01` directly

Release

  • The action can be "released" by building static binaries and checking them in to the main branch.
  • The convention is to build binaries (via make release) of the form main-${GOOS}-${GOARCH}-${VERSION} (where ${VERSION} can be a human-readable string or a git SHA).
  • Additionally, an index.js file should be updated to reflect the ${VERSION} the binaries were built with (more on why we use index.js to dispatch our binaries). This can be generated via make generate-index.
  • The action.yml file describing the inputs and outputs and the entrypoint binary will need to be copied over to the main branch. This file should always stay in sync with the code in pkg/requireconditional/config.go.
  • The content in the main branch can remain minimal and the README.md can just point back to the development branch. By keeping the content minimal, running a new workflow via GitHub Actions will be able to download the action more quickly.

Release Helper: Makefile

$ make  # OR: make help
Makefile for Require Conditional Status Checks GitHub Action

Usage:
   make generate-index        Generate `index.js` file for current VERSION
   make main-darwin-amd64     Build static binary for darwin/amd64
   make main-darwin-arm64     Build static binary for darwin/arm64
   make main-linux-amd64      Build static binary for linux/amd64
   make main-linux-arm64      Build static binary for linux/arm64
   make main-windows-amd64    Build static binary for windows/amd64
   make main-windows-arm64    Build static binary for windows/arm64
   make release               Build all static binaries and `index.js`

FAQ

Why Not using: docker?

By running a static binary directly on the host, we don't need to eat extra costs of docker pull or docker build.

Why Not using: composite?

We are not able to use using: composite. Instead we use using: node16 and introduce an index.js shim to exec out to the correct static Go binary for the current GOOS and GOARCH.

This is due to a limitation of GitHub Actions encountered when using actions-runner-controller in GitHub Enterprise (GHE) 3.1 and earlier. The processes spawned with using: composite and using: node16 had nearly identical environment variables, but they differed slightly in critical ways. Environment variables only present for using: node16 were:

ACTIONS_RUNTIME_TOKEN=***
ACTIONS_RUNTIME_URL=https://acme.github.enterprise.invalid/_services/pipelines/...
INPUT_WIDGET=testing
# acme.github.enterprise.invalid is a stand in for the GHE hostname

and those only present for using: composite were:

GITHUB_ACTION_PATH=/runner/_work/_actions/actions/proof-of-concept/main

Are the Release Binaries Optimized?

The main-${GOOS}-${GOARCH}-${VERSION} make targets build Go binaries with custom -ldflags to reduce binary size and then use the upx tool to reduce even further. (See related blog post.)