Download objects from Google Cloud Storage using Google API Client Libraries for Ruby

download_from_gcs.rb

client = Google::APIClient.new(
  application_name: "hoge"
)
storage = client.discovered_api("storage", "v1")
scopes = ["https://www.googleapis.com/auth/devstorage.read_write"]
auth = Google::Auth::ServiceAccountCredentials.new(
  json_key_io: StringIO.new(json_keyfile),
  scope: scopes
)
auth.fetch_access_token!
client.authorization = auth

gcs_bucket = "my-bucket"
page_token = nil
result = client.execute(
  api_method: storage.objects.list,
  parameters: {bucket: gcs_bucket, prefix: prefix, pageToken: page_token}
)
result.data.items.each do |item|
  response = client.execute(
    api_method: storage.objects.get,
    # get metadata of item
    # parameters: {bucket: gcs_bucket, object: item.name}
    # get item itself
    parameters: {bucket: gcs_bucket, object: item.name, alt: "media"}
  )
end