action.yml: checkout the source, build a Docker image and push it

Dockerfile

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+FROM debian:buster-slim

action.Dockerfile

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+FROM buildpack-deps:scm as clone
+SHELL ["/bin/bash", "-exo", "pipefail", "-c"]
+
+RUN mkdir actions ;\
+	cd actions ;\
+	git clone --bare https://github.com/actions/checkout.git ;\
+	git -C checkout.git archive --prefix=checkout/ v2 |tar -x ;\
+	git clone --bare https://github.com/actions/upload-artifact.git ;\
+	git -C upload-artifact.git archive --prefix=upload-artifact/ v2 |tar -x ;\
+	rm -rf *.git
+
+
+FROM docker
+
+RUN ["apk", "add", "bash", "grep", "nodejs"]
+COPY --from=clone /actions /actions
+
+COPY action.bash Dockerfile /
+
+CMD ["/action.bash"]

action.bash

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+#!/bin/bash
+set -exo pipefail
+
+TARGET=icinga/icinga2
+
+mkimg () {
+	test -n "$TAG"
+
+	node /actions/checkout/dist/index.js |grep -vFe ::add-matcher::
+	docker build -f /Dockerfile -t "${TARGET}:$TAG" .
+	STATE_isPost=1 node /actions/checkout/dist/index.js
+
+	docker save "${TARGET}:$TAG" |gzip >docker-save.tgz
+	INPUT_NAME=docker-image INPUT_PATH=docker-save.tgz node /actions/upload-artifact/dist/index.js
+	rm docker-save.tgz
+}
+
+push () {
+	test -n "$TAG"
+
+	if [ "$(tr -d '\n' <<<"$DOCKER_HUB_PASSWORD" |wc -c)" -gt 0 ]; then
+		docker login -u icingaadmin --password-stdin <<<"$DOCKER_HUB_PASSWORD"
+		docker push "${TARGET}:$TAG"
+		docker logout
+	fi
+}
+
+case "$GITHUB_EVENT_NAME" in
+	pull_request)
+		grep -qEe '^refs/pull/[0-9]+' <<<"$GITHUB_REF"
+		TAG="pr$(grep -oEe '[0-9]+' <<<"$GITHUB_REF")"
+		mkimg
+		;;
+	push)
+		grep -qEe '^refs/heads/.' <<<"$GITHUB_REF"
+		TAG="$(cut -d / -f 3- <<<"$GITHUB_REF")"
+		mkimg
+		push
+		;;
+	release)
+		grep -qEe '^refs/tags/v[0-9]' <<<"$GITHUB_REF"
+		TAG="$(cut -d v -f 2- <<<"$GITHUB_REF")"
+		mkimg
+		push
+		;;
+	*)
+		echo "Unknown event: $GITHUB_EVENT_NAME" >&2
+		false
+		;;
+esac

action.yml

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+name: Icinga 2 Docker image
+runs:
+  using: docker
+  image: action.Dockerfile