Sync files from Rails webpacker manifest.json to S3 asset bucket.

webpacker_sync.rake

# Sync files from webpacker manifest.json to S3 asset bucket.
# Based on asset_sync but much simplified for this case.
#
# Requirements
#
# Add fog to Gemfile.
#
# Environment variables:
# - AWS_S3_ASSETS_BUCKET_NAME
# - AWS_S3_REGION
# 
# Rails credentials yaml must have s3 access key id and secret:
# 
# aws:
#   s3_access_key_id: ...
#   s3_secret_access_key: ...
#
namespace :webpacker do

  desc 'Synchronize files in webpacker manifest.json to S3'
  task :sync => :environment do
    manifest_json = JSON.load(IO.read(Webpacker.config.public_manifest_path))
    # discard leading slash (/)
    assets = manifest_json.map { |_, fn| fn[1..-1] }

    connection = Fog::Storage.new(
      provider: "aws", 
      aws_access_key_id: Rails.application.credentials.dig(:aws, :s3_access_key_id),
      aws_secret_access_key: Rails.application.credentials.dig(:aws, :s3_secret_access_key),
      region: ENV['AWS_S3_REGION'] || raise("Missing S3 Region")
    )
    prefix = public_output_path.relative_path_from(public_path).to_s
    bucket = connection.directories.get(ENV['AWS_S3_ASSETS_BUCKET_NAME'] || raise("Missing bucket name"), :prefix => prefix)
    remote_files = bucket.files.inject([]) { |files, f| files << f.key }

    local_files_to_upload = assets - remote_files
    Rails.logger.info("Syncing #{local_files_to_upload.count} files...")

    # Upload new files
    local_files_to_upload.each do |f|
      next unless public_path.join(f).file?
      upload_file f, bucket
    end
  end

  private

  def wp_config
    Webpacker.config
  end

  def public_path
    wp_config.public_path
  end

  def public_output_path
    wp_config.public_output_path
  end

  def upload_file(f, bucket)
    file_handle = File.open(public_path.join(f))
    file = {
      key: f,
      body: file_handle,
      content_type: ::MIME::Types.type_for(File.extname(f)[1..-1]).first,
      public: true,
      storage_class: 'REDUCED_REDUNDANCY'
    }

    bucket.files.create(file)
    file_handle.close
  end
end