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A library for connecting to Google Cloud Storage through Lua.


You can learn more about authenticating with Google Cloud Storage here:

Here's a quick guide to get you started:

The easiest way use this library is to create a service account for your project. You'll need to generate a private key and store it alongside your configuration.

Go to the cloud console: Enable Cloud Storage if you haven't done so already. You may also need to enter billing information.

Navigate to IAM & admin » Service accounts, located on the sidebar. Click Create service account.

Create service account

Select Furnish a new private key and select JSON as the type. After creating the service account your browser will download a .json file. Store that securely, since it grants access to your project.

The .json is used to create a new API client with this library:

local google = require ""
local storage = google.CloudStorage:from_json_key_file("path/to/my-key.json")

-- you can now use any of the methods on the storage object
local files = assert(storage:get_bucket("my_bucket"))

Using a p12/pem secret key

Use these directions only if you have a key created with the P12 type.

The private key downloaded from the Cloud Console is a .p12 file. The key uses a hard coded password notasecret.

In order to use it, it must be converted to a .pem file. Run the following command (replacing key.p12 and key.pem with the input filename and desired output filename). Enter notasecret for the password.

openssl pkcs12 -in key.p12 -out key.pem -nodes -clcerts

One more piece of information is needed: the service account email address. You'll find it labeled Service account ID on the service account list. It might look something like

You can now connect to the API. Create a new client like this:

local oauth = require "cloud_storage.oauth"
local google = require ""

-- replace with your service account ID
local o = oauth.OAuth("", "path/to/key.pem")

-- use your id as the second argument, everything before the @ in your service account ID
local storage = google.CloudStorage(o, "cloud-storage")

local files = assert(storage:get_bucket("my_bucket"))



This module contains the OAuth implementation used by the storage API.

local oauth = require "cloud_storage.oauth"

ouath_instance = oauth.OAuth(service_email, path_to_pem_file=nil)

Create a new OAuth object. Handles OAuth authenticated requests.

It's not necessary to use this module directly if loading private key from a .json file.

Communicates with the Google cloud storage API.

local google = require ""

Error handling

Any methods that fail to execute will return nil, an error message, and an object that represents the error. Successful responses will return a Lua table containing the details of the operation.

storage = oauth.CloudStorage(ouath_instance, project_id)

Create a new instance of a storage object from an OAuth instance.

local storage = google.CloudStorage(o, "111111111111")

storage = oauth.CloudStorage:from_json_key_file(json_key_file_name)

Create a new instance of a storage object from a .json private key file generated by the Google Cloud Console.



storage:get_file(bucket, key)

storage:delete_file(bucket, key)

storage:head_file(bucket, key)

storage:copy_file(source_bucket, source_key, dest_bucket, dest_key, options={})


  • acl: value to use for x-goog-acl, defaults to public-read
  • headers: table of additional headers to include in request

storage:compose(bucket, key, source_keys, options={})

Composes a new file from multiple source files in the same bucket by concatenating them.

source_keys is an array of keys as strings or an array of key declarations as tables.

The table format for a source key is structured like this:

  name = "file.png",
  -- optional fields:
  generation = "1361471441094000",
  if_generation_match = "1361471441094000",


  • acl: value to use for x-goog-acl, defaults to public-read
  • mimetype: sets Content-type header for the composed file
  • headers: table of additional headers to include in request

storage:put_file_string(bucket, key, data, opts={})

Note: this API previously had key as an option but it was moved to second argument

Uploads the string data to the bucket at the specified key.

Options include:

  • mimetype: sets Content-type header for the file, defaults to not being set
  • acl: sets the x-goog-acl header for file, defaults to public-read
  • headers: an optional array table of any additional headers to send
storage:put_file_string("my_bucket", "message.txt", "hello world!", {
  mimetype = "text/plain",
  acl = "private"

storage:put_file(bucket, fname, opts={})

Reads fname from disk and uploads it. The key of the file will be the name of the file unless opts.key is provided. The mimetype of the file is guessed based on the extension unless opts.mimetype is provided.

storage:put_file("my_bucket", "source.lua", {
  mimetype = "text/lua"

All the same options from put_file_string are available for this method.

Note: This method is currently inefficient . The whole file is loaded into memory and sent at once in the request. An alternative implementation will be added in the future. Open a ticket if you need it.

storage:start_resumable_upload(bucket, key, options={})


  • acl: value to use for x-goog-acl, defaults to public-read
  • mimetype: sets Content-type header for the composed file
  • headers: table of additional headers to include in request

storage:signed_url(bucket, key, expiration)

Creates a temporarily URL for downloading an object regardless of it's ACL. expiration is a Unix timestamp in the future, like one generated from os.time().

print(storage:signed_url("my_bucket", "message.txt", os.time() + 100))

storage:put_file_acl(bucket, key, acl)


1.0.0 Mar 31, 2018

  • Changed put_file_string now takes key as second argument, instead of within options table
  • Replace luacrypto with luaossl
  • Add support for json private keys
  • Better error handling for all API calls. (Failures return nil, error message, and error object)
  • Add copy_file and compose methods
  • Add upload_url method to create upload URLs
  • Add start_resumable_upload method for creating resumable uploads
  • Headers are canonicalized and sorted to make them consistent between calls
  • Fix bug where special characters in key were not being URL encoded
  • Fix bug where some special characters were not being encoded for signed URLs
  • Rewrite documentation tutorial

0.1.0 Sep 29, 2013

  • Initial release


A Lua library for communicating with Google Cloud Storage



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