🚀 Enable building multiarch images

Dockerfile

@@ -6,7 +6,7 @@ RUN apt-get update \
   && echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
   $(lsb_release -cs) stable" | tee /etc/apt/sources.list.d/docker.list > /dev/null \
   && apt-get update \
-  && apt-get install -y docker-ce docker-ce-cli containerd.io
+  && apt-get install -y docker-ce docker-ce-cli containerd.io jq
 ADD entrypoint.sh /entrypoint.sh
 ENTRYPOINT ["/entrypoint.sh"]
 

action.yml

@@ -53,6 +53,9 @@ inputs:
   no_push:
     description: 'Set no_push to true if you want to prevent the action from pushing to a registry (default: false)'
     required: false
+  platforms:
+    description: 'Use platforms for building multi-arch images'
+    required: false
 outputs:
   tag:
     description: 'Is the tag, which was pushed'
@@ -85,4 +88,5 @@ runs:
         INPUT_TAGS: ${{ inputs.tags }}
         INPUT_TAG_NAMES: ${{ inputs.tag_names }}
         INPUT_TAG_SEMVER: ${{ inputs.tag_semver }}
-        INPUT_NO_PUSH: ${{ inputs.no_push }}
+        INPUT_NO_PUSH: ${{ inputs.no_push }}
+        INPUT_PLATFORMS: ${{ inputs.platforms }}

entrypoint.sh

@@ -62,10 +62,16 @@ main() {
     exit 0
   fi
 
-  push
+  if ! uses "${INPUT_PLATFORMS}"; then
+    push
+  fi
 
   echo "::set-output name=tag::${FIRST_TAG}"
-  DIGEST=$(docker inspect --format='{{index .RepoDigests 0}}' ${DOCKERNAME})
+  if uses "${INPUT_PLATFORMS}"; then
+    DIGEST=$(jq -r '."containerimage.digest"' metadata.json)
+  else 
+    DIGEST=$(docker inspect --format='{{index .RepoDigests 0}}' ${DOCKERNAME})
+  fi
   echo "::set-output name=digest::${DIGEST}"
 
   docker logout
@@ -184,7 +190,12 @@ build() {
   for TAG in ${TAGS}; do
     BUILD_TAGS="${BUILD_TAGS}-t ${INPUT_NAME}:${TAG} "
   done
-  docker build ${INPUT_BUILDOPTIONS} ${BUILDPARAMS} ${BUILD_TAGS} ${CONTEXT}
+  if uses "${INPUT_PLATFORMS}"; then
+    local PLATFORMS="--platform ${INPUT_PLATFORMS}"
+    docker buildx build --push --metadata-file metadata.json ${PLATFORMS} ${INPUT_BUILDOPTIONS} ${BUILDPARAMS} ${BUILD_TAGS} ${CONTEXT}
+  else
+    docker build ${INPUT_BUILDOPTIONS} ${BUILDPARAMS} ${BUILD_TAGS} ${CONTEXT}
+  fi
 }
 
 push() {

test.bats

@@ -647,6 +647,58 @@ teardown() {
 /usr/local/mock/docker logout"
 }
 
+@test "it supports building multiple platforms" {
+  export GITHUB_REF='refs/heads/main'
+  export INPUT_PLATFORMS='linux/amd64,linux/arm64'
+
+  cat <<EOT >> metadata.json
+{
+  "containerimage.buildinfo/linux/amd64": {
+    "frontend": "dockerfile.v0",
+    "attrs": {
+      "filename": "Dockerfile"
+    },
+    "sources": [
+      {
+        "type": "docker-image",
+        "ref": "docker.io/library/alpine:latest",
+        "pin": "sha256:7580ece7963bfa863801466c0a488f11c86f85d9988051a9f9c68cb27f6b7872"
+      }
+    ]
+  },
+  "containerimage.buildinfo/linux/arm64": {
+    "frontend": "dockerfile.v0",
+    "attrs": {
+      "filename": "Dockerfile"
+    },
+    "sources": [
+      {
+        "type": "docker-image",
+        "ref": "docker.io/library/alpine:latest",
+        "pin": "sha256:7580ece7963bfa863801466c0a488f11c86f85d9988051a9f9c68cb27f6b7872"
+      }
+    ]
+  },
+  "containerimage.descriptor": {
+    "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
+    "digest": "sha256:aa2c7631cc1bbf588192ec7e55b428ad92fe63834200303f28e93444d7fc114a",
+    "size": 741
+  },
+  "containerimage.digest": "sha256:aa2c7631cc1bbf588192ec7e55b428ad92fe63834200303f28e93444d7fc114a",
+  "image.name": "my/repository:latest"
+}
+EOT
+
+  run /entrypoint.sh
+
+  expectStdOutContains "::set-output name=tag::latest::set-output name=digest::sha256:aa2c7631cc1bbf588192ec7e55b428ad92fe63834200303f28e93444d7fc114a"
+
+  expectMockCalledContains "/usr/local/mock/docker login -u USERNAME --password-stdin
+/usr/local/mock/docker buildx build --push --metadata-file metadata.json --platform linux/amd64,linux/arm64 -t my/repository:latest .
+/usr/local/mock/docker logout"
+  expectMockArgs ""
+}
+
 expectStdOutIs() {
   local expected=$(echo "${1}" | tr -d '\n')
   local got=$(echo "${output}" | tr -d '\n')