AlekSi / go-githubactions

Go SDK for GitHub Actions - easily author GitHub Actions in Go

GitHub Actions SDK (Go)

This library provides an SDK for authoring GitHub Actions in Go. It has no external dependencies and provides a Go-like interface for interacting with GitHub Actions' build system.

Installation

Download the library:

$ go get -u github.com/sethvargo/go-githubactions/...

Usage

The easiest way to use the library is by importing it and invoking the functions at the root:

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

func main() {
  val := githubactions.GetInput("val")
  if val == "" {
    githubactions.Fatalf("missing 'val'")
  }
}

You can also create an instance with custom fields that will be included in log messages:

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

func main() {
  actions := githubactions.WithFieldsMap(map[string]string{
    "file": "myfile.js",
    "line": "100",
  })

  val := actions.GetInput("val")
  if val == "" {
    actions.Fatalf("missing 'val'")
  }
}

For more examples and API documentation, please see the Go docs.

Publishing

There are multiple ways to publish GitHub Actions written in Go:

• Composite actions
• Pre-compiled binaries with a shim
• Docker containers (see below)

By default, GitHub Actions expects actions to be written in Node.js. For other languages like Go, you need to provide a Dockerfile and entrypoint instructions in an action.yml file:

# your-repo/Dockerfile
FROM golang:1.18
WORKDIR /src
COPY . . 
RUN go build -o /bin/app .
ENTRYPOINT ["/bin/app"]

# your-repo/action.yml
name: My action
author: My name
description: My description

runs:
  using: docker
  image: Dockerfile

And then users can import your action by the repository name:

# their-repo/.github/workflows/thing.yml
steps:
- name: My action
  uses: username/repo@latest

However, this will clone the entire repo and compile the Go code each time the action runs. Worse, it uses the Go base container which is a few hundred MBs and includes a ton of unnecessary things.

Fortunately, GitHub Actions can also source from a Docker container directly from Docker Hub:

steps:
- name: My action
  uses: docker://username/repo:latest

Now we can precompile and publish our Go Action as a Docker container, but we need to make it much, much smaller first. This can be achieved using multi-stage Docker builds:

FROM golang:1.18 AS builder

ENV GO111MODULE=on \
  CGO_ENABLED=0 \
  GOOS=linux \
  GOARCH=amd64

RUN apt-get -qq update && \
  apt-get -yqq install upx

WORKDIR /src
COPY . .

RUN go build \
  -ldflags "-s -w -extldflags '-static'" \
  -o /bin/app \
  . \
  && strip /bin/app \
  && upx -q -9 /bin/app

RUN echo "nobody:x:65534:65534:Nobody:/:" > /etc_passwd



FROM scratch

COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
COPY --from=builder /etc_passwd /etc/passwd
COPY --from=builder --chown=65534:0 /bin/app /app

USER nobody
ENTRYPOINT ["/app"]

The first step, uses a fat container to build, strip, and compress the compiled Go binary. Then, in the second step, the compiled and compressed binary is copied into a scratch (bare) container along with some SSL certificates and a nobody user in which to execute the container.

This will usually produce an image that is less than 10MB in size, making for much faster builds.