Add support for Cloud Native Buildpacks pack CLI

Signed-off-by: David Gageot <[email protected]>

pack/Dockerfile

@@ -0,0 +1,7 @@
+FROM busybox
+ENV PACK_VERSION=v0.4.1
+RUN wget -O- https://github.com/buildpack/pack/releases/download/${PACK_VERSION}/pack-${PACK_VERSION}-linux.tgz | tar zx
+
+FROM gcr.io/distroless/base
+ENTRYPOINT ["/pack"]
+COPY --from=0 /pack /

pack/README.md

@@ -0,0 +1,19 @@
+# Pack
+
+[pack](https://github.com/buildpack/pack) is the CLI for building apps using [Cloud Native Buildpacks](https://buildpacks.io).
+
+This build step invokes `pack` commands in [Google Cloud Build](cloud.google.com/cloud-build/).
+
+Arguments passed to this builder will be passed to `pack` directly, allowing
+callers to run [any pack
+command](https://buildpacks.io/docs/using-pack/).
+
+## Usage:
+
+To build a Docker image from sources:
+
+```
+steps:
+- name: gcr.io/$PROJECT_ID/pack
+  args: ["build", "--builder", "heroku/buildpacks:18", "gcr.io/$PROJECT_ID/sample:tag"]
+```

pack/cloudbuild.yaml

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+# In this directory, run the following command to build this builder.
+# $ gcloud builds submit . --config=cloudbuild.yaml
+
+steps:
+- name: 'gcr.io/cloud-builders/docker'
+  args: ['build', '--tag=gcr.io/${PROJECT_ID}/pack', '.']
+- name: 'gcr.io/${PROJECT_ID}/pack'
+  args: ['--help']
+
+images: ['gcr.io/${PROJECT_ID}/pack']
+tags: ['cloud-builders-community']

pack/example/cloudbuild.yaml

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+steps:
+- name: 'gcr.io/$PROJECT_ID/pack'
+  args:
+    - build
+    - --builder
+    - heroku/buildpacks:18
+    - gcr.io/$PROJECT_ID/pack-sample
+
+images:
+  - gcr.io/$PROJECT_ID/pack-sample

pack/example/go.mod

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+module github.com/GoogleCloudPlatform/cloud-builders-community/pack/sample
+
+go 1.13

pack/example/main.go

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+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+)
+
+func main() {
+	http.HandleFunc("/", hello)
+
+	log.Println("Listening on port 8080")
+	http.ListenAndServe(":8080", nil)
+}
+
+func hello(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello, World!")
+}