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Mobiletto is a JavaScript storage abstraction layer, with optional transparent client-side encryption.


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This document has been translated, via hokeylization, into every language supported by Google Translate!

I'm certain it's not perfect, but I hope it's better than nothing!

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Why Mobiletto?

Goodbye vendor lock-in!

The various cloud storage providers have incompatible APIs. Even those that strive for "S3 compatibility" have idiosyncratic behaviors.

When you choose a particular storage vendor for your app, if you code directly to their API, your app is now dependent on that service. As time goes by and code accumulates, changing vendors becomes increasingly untenable. Welcome to the fun world of vendor lock-in!

Mobiletto was designed to solve this problem. By coding your app to mobiletto's API, you can easily change storage providers and know that your app's storage layer will behave identically.

Extensive testing

All drivers are tested for identical behavior with 60+ tests for each driver. We test all drivers with every combination of:

  • Encryption: both enabled and disabled
  • Redis cache: both enabled and disabled

This approach gives us peace-of-mind that mobiletto will behave the same regardless of which driver you use, and regardless of whether you enable caching and/or encryption.

Driver support

Current Mobiletto storage drivers:

  • s3: Amazon S3
  • b2: Backblaze B2
  • local: local filesystem
  • indexeddb: IndexedDB storage

Contributions to support more cloud storage providers are very welcome!

Quick Start

A short example using the mobiletto s3 driver.

This code would run the same with any other mobiletto storage driver.

const storage = require('mobiletto')
const bucket = await storage.connect('s3', aws_key, aws_secret, {bucket: 'bk'})

// list objects: returns array of metadata objects
const listing = await bucket.list()
const dirList = await bucket.list('some/dir/')
const everything = await bucket.list('', {recursive: true})

// write an entire file
let bytesWritten = await bucket.writeFile('some/path', someBufferOfData)

// write a file from a stream/generator
bytesWritten = await bucket.write('some/path', streamOrGenerator)

// read an entire file
// returns null if an exception would otherwise be thrown
const bufferOrNull = await bucket.safeReadFile('some/path')

// stream-read a file, passing data to callback
const bytesRead = await'some/path', (chunk) => { something with chunk... } )

// remove a file, returns the path removed
let removed = await bucket.remove('some/path')  // removed is a string

// remove a directory, returns array of paths removed
removed = await bucket.remove('some/directory', {recursive: true})  // removed is now an array!


Mobiletto is intended to be used as a library by other JavaScript code.

To work with mobiletto at the command-line, use mobiletto-cli


Support and Funding

I would be very thankful for any contribution via Patreon


Install using npm or yarn. You probably want the lite version that does not include all the translated README files:

npm install mobiletto-lite
yarn add mobiletto-lite

If you really want the README files in every language, install the full version:

npm install mobiletto
yarn add mobiletto

Minimal install

The mobiletto and mobiletto-lite packages include support for all mobiletto storage drivers.

If you know the storage driver(s) that you will need ahead of time, you can lighten your app's footprint by installing the mobiletto-base package, and then one or more of the mobiletto-driver- packages:

Minimal installation with npm

npm install mobiletto-base                # install driver-less mobiletto

npm install mobiletto-driver-s3           # install Amazon S3 driver
npm install mobiletto-driver-b2           # install Backblaze B2 driver
npm install mobiletto-driver-local        # install local filesystem driver
npm install mobiletto-driver-indexeddb    # install IndexedDB driver

Minimal installation with yarn

yarn add mobiletto-base                # install driver-less mobiletto

yarn add mobiletto-driver-s3           # install Amazon S3 driver
yarn add mobiletto-driver-b2           # install Backblaze B2 driver
yarn add mobiletto-driver-local        # install local filesystem driver
yarn add mobiletto-driver-indexeddb    # install IndexedDB driver

Basic usage

A much more extensive example, showing most of the features offered:

// When using mobiletto or mobiletto-lite, all drivers are included
const { mobiletto } = require('mobiletto')

// When using mobiletto-base, use registerDriver to load a storage driver before connecting 
const { registerDriver, mobiletto } = = require('mobiletto-base')
registerDriver('s3', require('mobiletto-driver-s3'))
registerDriver('b2', require('mobiletto-driver-b2'))
registerDriver('local', require('mobiletto-driver-local'))
registerDriver('indexeddb', require('mobiletto-driver-indexeddb'))

// General usage
const api = await mobiletto(driverName, key, secret, opts)

// To use 'local' driver:
//   * key: base directory
//   * secret: ignored, can be null
//   * opts object:
//     * readOnly: optional, never change anything on the filesystem; default is false
//     * fileMode: optional, permissions used when creating new files, default is 0600. can be string or integer
//     * dirMode: optional, permissions used when creating new directories, default is 0700. can be string or integer
const local = await mobiletto('local', '/home/ubuntu/tmp', null, {fileMode: 0o0600, dirMode: '0700'})

// To use 's3' driver:
//   * key: AWS Access Key ID
//   * secret: AWS Secret Key
//   * opts object:
//     * readOnly: optional, never change anything on the bucket; default is false
//     * bucket: required, name of the S3 bucket
//     * region: optional, the AWS region to communicate with, default is us-east-1
//     * prefix: optional, all read/writes within the S3 bucket will be under this prefix
//     * delimiter: optional, directory delimiter, default is '/' (note: always '/' when encryption is enabled)
const s3 = await mobiletto('s3', aws_key, aws_secret, {bucket: 'bk', region: 'us-east-1'})

// To use 'b2' driver:
//   * key: Backblaze Key ID
//   * secret: Backblaze Application Key
//   * opts object:
//     * readOnly: optional, never change anything on the bucket; default is false
//     * bucket: required, the ID (**not the name**) of the B2 bucket
//     * prefix: optional, all read/writes within the B2 bucket will be under this prefix
//     * delimiter: optional, directory delimiter, default is '/' (note: always '/' when encryption is enabled)
//     * partSize: optional, large files will be split into chunks of this size when uploading
const b3 = await mobiletto('b2', b2_key_id, b2_app_key, {bucket: 'bk', partSize: 10000000})

// To use 'indexeddb' driver:
//   * key: IndexedDB database name
//   * secret: ignored, can be null
//   * opts object:
//     * indexedDB: required, the indexedDB object (an instance of IDBFactory)
const idb = await mobiletto('indexeddb', 'my_db', null, { indexedDB })

// List files
api.list()  // --> returns an array of metadata objects

// List files recursively
api.list({ recursive: true })

// List files in a directory
const path = 'some/path'
api.list(path, { recursive: true }) // also supports recursive flag

// Visit files in a directory -- visitor function must be async
api.list(path, { visitor: myAsyncFunc })
api.list(path, { visitor: myAsyncFunc, recursive: true })

// The `list` method throws MobilettoNotFoundError if the path does not exist
// When you call `safeList` on a non-existent path, it returns an empty array
api.safeList('/path/that/does/not/exist') // returns []

// Read metadata for a file
api.metadata(path)    // returns metadata object

// The `metadata` method throws MobilettoNotFoundError if the path does not exist
// When you call `safeMetadata` on a non-existent path, it returns null
api.safeMetadata('/tmp/does_not_exist') // returns null

// Read a file
// Provide a callback that writes the data someplace
const callback = (chunk) => { ... write chunk somewhere ...  }, callback)  // returns count of bytes read

// Read an entire file at once
const data = await api.readFile(path)  // returns a byte Buffer of the file contents

// Read an entire file at once
// returns null if an exception would otherwise be thrown
const bufferOrNull = await bucket.safeReadFile('some/path')

// Write a file
// Provide a generator function that yields chunks of data 
const generator = function* () {
  while ( ... more-data-to-return ... ) {
    data = ... load-data ...
    yield data
local.api(path, generator)  // returns count of bytes written

// Write an entire file at once (convenience method)
await api.writeFile(path, bufferOrString)   // returns count of bytes written

// Delete a file
// Quiet param is optional (default false), when set errors will not be thrown if the path does not exist
// Always returns a value or throws an error.
// Return value may be a single string of the file removed, or an array of all files removed (driver-dependent)
const quiet = true
api.remove(path, {quiet}) // returns single path removed

// Recursively delete a directory and do it quietly (do not report errors)
const recursive = true
const quiet = true
api.remove(path, {recursive, quiet}) // returns array of paths removed


The metadata command returns metadata about a single filesystem entry. Likewise, the return value from the list command is an array of metadata objects.

A metadata object looks like this:

  "name": "fully/qualified/path/to/file",
  "type": "entry-type",
  "size": size-in-bytes,
  "ctime": creation-time-epoch-millis,
  "mtime": modification-time-epoch-millis

The type property can be file, dir, link, or special.

Depending on the type of driver, a list command may not return all fields. The name and type properties should always be present. A subsequent metadata command will return all available properties.

Alternate import style

Import the fully-scoped module and use the connect function:

const storage = require('mobiletto')
const opts = {bucket: 'bk', region: 'us-east-1'}
const s3 = await storage.connect('s3', aws_key, aws_secret, opts)
const objectData = await s3.readFile('some/path')


Mobiletto works best with a redis cache.

Mobiletto will attempt to connect to a redis instance on

You can override either of these:

  • Set the MOBILETTO_REDIS_HOST env var, mobiletto connect here instead of localhost
  • Set the MOBILETTO_REDIS_PORT env var, this port will be used

Mobiletto will store all of its redis keys with the prefix _mobiletto__. You can change this by setting the MOBILETTO_REDIS_PREFIX env var.

You can also set per-connection caching with the opts.redisConfig object:

const redisConfig = {
    enabled: true,     // optional, default is true. if false other props are ignored
    host: '',
    port: 6379,
    prefix: '_mobiletto__'
const opts = { redisConfig, bucket: 'bk', region: 'us-east-1' }
const s3 = await storage.connect('s3', aws_key, aws_secret, opts)

Don't want redis caching?

To disable: pass enabled: false in your opts.redisConfig object when you establish your connection.

As discussed below, disabling caching will have an adverse effect on performance and incur more requests to storage than you really need to.

Caching guidance

Encrypted storage: reading/writing encrypted storage is only a little slower than normal, but navigating around directories (which some things do) is fairly expensive. Using a redis cache will give you a significant performance boost.

The default cache is safe, but doesn't perform well if you have a lot of write/remove operations. Any write or remove operation invalidates the entire cache, ensuring subsequent reads will see the latest changes.

CLI tools

If you're using a CLI tool like mobiletto-cli, you'll definitely want the redis cache enabled, as it lasts across invocations of the mo command.


// Copy a local filesystem mobiletto to S3

// Mirror a local subdirectory from one mobiletto to an S3 mobiletto, with it's own subdirectory
local.mirror(s3, 'some/local-folder', 'some/s3-folder')

The mirror command performs a one-time copy of all files from one mobiletto to another. It does not run any process to maintain the mirror over time. Run the mirror command again to synchronize any missing files.

The return value from mirror is a simple object with counters for how many files were successfully mirrored and how many files had errors:

  success: count-of-files-mirrored,
  errors: count-of-files-with-errors

WARNING: Mirroring large data sets can be very time-consuming and bandwidth-intensive

With the mirror call semantics it can sometimes be confusing to understand who is the reader and who is the writer. Imagine it like an assignment statement: the "left-hand mobiletto" is the thing being assigned to (mirrored data written), and the "right-hand mobiletto" (the argument to the mirror method) is the value being assigned (mirrored data is read).

Transparent encryption

Enable transparent client-side encryption:

// Pass encryption parameters
const encryption = {
  // key is required, must be >= 16 chars
  key: randomstring.generate(128),

  // optional, the default is to derive IV from key
  // when set, IV must be >= 16 chars
  iv: randomstring.generate(128),

  // optional, the default is aes-256-cbc
  algo: 'aes-256-cbc'
const api = await mobiletto(driverName, key, secret, opts, encryption)

// Subsequent write operations will encrypt data (client side) when writing
// Subsequent read operations will decrypt data (client side) when reading

What's happening? A separate "directory entry" (dirent) directory (encrypted) tracks what files are in that directory (aka the dirent directory).

  • The list command reads the directory entry files, decrypts each path listed; then returns metadata for each file
    • list commands are more inefficient, especially for directories with a large number of files
  • The write command writes dirent files in each parent's dirent directory, recursively; then writes the file
    • write commands will incur O(N) writes, with N = depth in the directory hierarchy
  • The remove command removes the corresponding dirent file, and its parent if empty, recursively; then removes the file
    • Non-recursive remove commands will incur O(N) reads and potentially as many deletes, with N = depth in the directory hierarchy
    • Recursive remove commands on large and deep filesystems can be expensive

Note that even with client-side encryption enabled, an adversary with full visibility into your encrypted server-side storage, even without the key, can still see the total number of directories and how many files are in each, and with some effort, discover some or all of the overall structure of the directory hierarchy. Note: Use a relatively flat structure for better security. The adversary would not know the names of the directories/files unless they also knew your encryption key or had otherwise successfully cracked the encryption. All bets are off then!

Performance and caching

Operations on encrypted storage can be slow. Recursive listings and removals can be very slow. Caching via redis helps tremendously, but note that the cache is flushed upon any writes or removes.

Key rotation

Create a mobiletto with your new key, then mirror the old data into it:

const storage = require('mobiletto')

const oldEncryption = { key: .... }
const oldStorage = await storage.connect('s3', aws_key, aws_secret, {bucket: 'bk', region: 'us-east-1'}, oldEncryption)

const newEncryption = { key: .... }
const newStorage = await storage.connect('s3', aws_key, aws_secret, {bucket: 'zz', region: 'us-east-1'}, newEncryption)

newStorage.mirror(oldStorage) // if oldStorage is very large, this may take a looooooong time...

Driver interface

A driver is any JS file that exports a 'storageClient' function with this signature:

function storageClient (key, secret, opts)
  • key: a string, your API key (for the local driver this is the base directory)
  • secret: a string, your API secret (can be omitted for the local driver)
  • opts: an object, the properties are per-driver:
    • For local, the fileMode and dirMode properties determine how new creating files and directories are created
    • For s3, the bucket property is required. Optional properties are:
      • region: the S3 region, default is us-east-1
      • prefix: a prefix to prepend to all S3 paths, default is the empty string
      • delimiter: the directory delimiter, default is '/'

The object that the storageClient function returns must define these functions:

// Test the driver before using, ensure proper configuration
async testConfig ()

// List files in path (or from base-directory)
// If recursive is true, list recursively
// If visitor is defined, it will be an async function. await the visitor function on each file found
// Otherwise, perform the listing and return an array of objects
async list (path, recursive = false, visitor = null)  // path may be omitted

// Read metadata for a path
async metadata (path)

// Read a file, return bytes read
// callback receives a chunk of data. endCallback is called at end-of-stream
async read (path, callback, endCallback = null)

// Write a file, return bytes written
// driver must be able to handle a generator or a stream
async write (path, generatorOrReadableStream)

// Remove a file, or recursively delete a directory
// returns a string of a single path removed, or an array of multiple paths removed
async remove (path, recursive = false, quiet = false)


Mobiletto uses the winston logging library.

Logs will contain file paths and error messages, but will never contain keys, secrets, or any other connection configuration information.

Log level

Use the MOBILETTO_LOG_LEVEL environment variable to set the log level, using one of the npm levels defined in

The default level is error. The most verbose level is silly, although currently mobiletto does not log at levels below debug

MOBILETTO_LOG_LEVEL=silly   # maximum logs!

Log file

By default, the logger writes to the console. To send logs to a file, set the MOBILETTO_LOG_FILE environment variable. When logging to a file, logs will no longer be written to the console.


To turn off logging:



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