Custom composite cache actions on github actions

action.yaml

name: Cache (v2)
description: >
  Cache files onto S3 bucket. It has 3 steps:
  1. It tries to restore the cache using the given key.
     If the caches hits, exit.
  2. It runs the given script using shell, if the cache missed in step 1.
  3. It saves to the cache after the script.

inputs:
  s3-bucket:
    description: The bucket name.
    required: true
  key:
    description: An explicit key for the cached files.
    required: true
  paths:
    description: >
      List of files/directories to cache. Separated by new line.
      Use relative path to the project root.
    required: true
  run:
    description: Script to run to generate the cached files.
    required: true
outputs:
  hit:
    description: A boolean value to indicate whether there is a cache hit.
    value: ${{ steps.restore-cache.outputs.hit }}
runs:
  using: composite
  steps:
    - name: Restore cache
      id: restore-cache
      run: |
        set +x
        echo "Checking cache: $BUCKET_KEY"
        CACHE_HIT=$(aws --debug s3api head-object --bucket "$BUCKET" --key "$BUCKET_KEY" &> /dev/null; echo $?)
        if [ "$CACHE_HIT" -ne 0 ]; then
          echo "::set-output name=hit::false"
        else
          echo "Restoring cache: $BUCKET_KEY"
          aws s3 cp "s3://$BUCKET/$BUCKET_KEY" - | tar -I zstd -x
          echo "::set-output name=hit::true"
        fi
      shell: bash
      env:
        BUCKET: "${{ inputs.s3-bucket }}"
        BUCKET_KEY: "cache/${{ inputs.key }}.tar.z"
    - name: Run
      run: |
        set +x
        if [ "${{ steps.restore-cache.outputs.hit }}" = "true" ]; then
          exit 0
        fi

        ${{ inputs.run }}
      shell: bash
    - name: Save cache
      run: |
        set +x
        if [ "${{ steps.restore-cache.outputs.hit }}" = "true" ]; then
          exit 0
        fi
        echo "Saving cache: ${{ inputs.paths }} -> $BUCKET_KEY"
        echo "${{ inputs.paths }}" | xargs tar -I zstd -c | aws s3 cp - "s3://$BUCKET/$BUCKET_KEY"
      shell: bash
      env:
        BUCKET: "${{ inputs.s3-bucket }}"
        BUCKET_KEY: "cache/${{ inputs.key }}.tar.z"