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    Storage Abstraction

    Provides an abstraction layer for interacting with a storage; this storage can be a local file system or a cloud storage. Currently local disk storage, Backblaze B2, Google Cloud and Amazon S3 and compliant cloud services are supported.

    Because the API only provides basic storage operations (see below) the API is cloud agnostic. This means for instance that you can develop your application using storage on local disk and then use Google Cloud or Amazon S3 in your production environment without changing any code.

    Table of contents

    Instantiate a storage

    const s = new Storage(config);

    When instantiating a new Storage the argument config is used to create an adapter that translates the generic API calls to storage specific calls. You can provide the config argument in 2 forms:

    1. using a configuration object (js: typeof === "object" ts: AdapterConfig)
    2. using a configuration URL (typeof === "string")

    Internally configuration URL will be converted to a configuration object so any rule that applies to a configuration object also applies to configuration URLs.

    The configuration must specify a type; the type is used to create the appropriate adapter. The value of the type is one of the enum members of StorageType:

    enum StorageType {
      LOCAL = "local",
      GCS = "gcs",
      S3 = "s3",
      B2 = "b2",

    Configuration object

    A configuration object extends IAdapterConfig:

    interface IAdapterConfig {
      type: string;
      slug?: boolean;
      bucketName?: string;

    Besides the mandatory key type one or more keys may be mandatory or optional dependent on the type of storage; for instance keys for passing credentials such as keyFilename for Google Storage or accessKeyId and secretAccessKey for Amazon S3, and keys for further configuring the storage service such as sslEnabled for Amazon S3.

    The optional key slug determines if bucket names and paths to files in buckets are slugified automatically.

    Another optional key is bucketName; for most cloud storage services it is required to select a bucket after a connection to the service has been made. If you don't want or can't provide a bucket name on initialization you can use selectBucket to do so afterwards.

    Configuration URL

    Configuration urls always start with a protocol that defines the type of storage:

    • local:// → local storage
    • gcs:// → Google Cloud
    • s3:// → Amazon S3
    • b2:// → Backblaze B2

    These values match the values in the enum StorageType shown above. What follows after the protocol is the part that contains the configuration of the storage. The format of the URL differs per storage type, see the documentation per adapter below for details.

    // local storage
    const url = "local://path/to/bucket";
    // Amazon S3
    const url =
    // Google Cloud Storage
    const url =
    // Backblaze B2
    const url =


    The adapters are the key part of this library; where the Storage is merely a thin wrapper (see How it works), adapters perform the actual actions on the storage by translating generic API methods calls to storage specific calls.

    Below follows a description of the available adapters; what the configuration objects and URLs look like and what the default values are. Also per adapter the peer dependencies are listed as a handy copy-pasteble npm command. The peer dependencies are usually wrapper libraries such as aws-sdk but can also be specific modules with a specific functionality such as rimraf for local storage.

    If you want to use one or more of the adapters in your project make sure you install the required peer dependencies. By installing only the dependencies that you will actually use, your project codebase will stay as slim and maintainable as possible.

    You can also add more adapters yourself very easily, see below

    Local storage

    peer dependencies:
    > npm i glob rimraf

    Configuration object:

    type ConfigLocal = {
      type: StorageType;
      directory: string;
      slug?: boolean;
      mode?: string | number;

    Configuration url:

    const url = "local://path/to/your/bucket?mode=750";

    The key mode is used to set the access rights when creating new buckets. The default value is 0o777. You can pass this value both as a string and as a number.

    If you use a configuration URL you can only pass values as strings; string values without radix prefix will be interpreted as octal numbers, so "750" is the same as "0o750" and both yield the same numeric value 0o750 or 488 decimal.

    When using a configuration object you can also pass mode as a number, please don't forget the radix prefix if you don't use decimal numbers, e.g. 750 is probably not what you want, pass 0o750 or 488 instead. Best is to use strings to avoid confusion.


    const config = {
      type: StorageType.LOCAL,
      directory: "path/to/folder/bucket",
      mode: "750",
    const s = new Storage(config);
    // or
    const url = "local://path/to/folder/bucket?mode=750";
    const s = new Storage(url);

    Files will be stored in path/to/folder/bucket, folders will be created if necessary. As you can see the last folder of the directory will be used as bucket; if you call getSelectedBucket() the name of this folder will be returned.

    Note the use of double and triple slashes:

    // example #2
    const s = new Storage {
      type: StorageType.LOCAL,
      directory: "files",
    const s = new Storage("local://files") // note: 2 slashes
    s.getConfiguration().directory;  // folder where the process runs, process.cwd()
    s.getConfiguration().bucketName; // 'files'
    // example #3
    const s = new Storage {
      type: StorageType.LOCAL,
      directory: "/files",
    const s = new Storage("local:///files") // note: 3 slashes
    s.getConfiguration().directory;  // '/' root folder (may require extra permissions)
    s.getConfiguration().bucketName; // 'files'

    Google Cloud

    peer dependencies:
    > npm i @google-cloud/storage ramda

    Configuration object:

    type ConfigGoogleCloud = {
      type: StorageType;
      keyFilename: string; // path to keyFile.json
      projectId?: string;
      bucketName?: string;
      slug?: boolean;

    Configuration url:

    const url = "gcs://path/to/keyFile.json:projectId@bucketName?slug=false";

    The project id is optional; if you omit the value for project id, the id will be read from the key file:

    const s = new Storage({
      type: StorageType.GCS,
      keyFilename: "path/to/keyFile.json",
    const s = new Storage("gcs://path/to/keyFile.json");

    Another example:

    // example #1
    const s = new Storage({
      type: StorageType.GCS,
      keyFilename: "path/to/keyFile.json",
      bucketName: "bucket",
    const s = new Storage("gcs://path/to/keyFile.json@bucket");

    Amazon S3

    peer dependencies:
    > npm i aws-sdk

    Config object:

    type ConfigAmazonS3 = {
      type: StorageType;
      accessKeyId: string;
      secretAccessKey: string;
      slug?: boolean;
      region?: string;
      bucketName?: string;
      endpoint?: string;
      useDualstack?: boolean;
      maxRetries?: number;
      maxRedirects?: number;
      sslEnabled?: boolean;
      [id: string]: boolean | string | number; // configuration is extensible

    Configuration url:

    const url =


    const s = new Storage({
      type: StorageType.S3,
      accessKeyId: "key",
      secretAccessKey: "secret",
      region: "eu-west-2"
      useDualStack: true,
      sslEnabled: true,
    const s = new Storage("s3://key:secret@eu-west-2/bucket?useDualStack=true&sslEnabled=true");

    You can omit a value for region but because secretAccessKey can contain slashes you must include the @ in your URL:

    const s = new Storage("s3://key:secret@bucket?useDualStack=true&sslEnabled=true");

    If you want to specify a bucket name but not a region, put a slash behind the region, and right before the question mark in case your URL has a query string:

    const s = new Storage("s3://key:secret@eu-west-2/");
    const s = new Storage("s3://key:secret@eu-west-2/?useDualStack=true&sslEnabled=true");

    Backblaze B2

    peer dependencies:
    > npm i backblaze-b2 @gideo-llc/backblaze-b2-upload-any

    Config object:

    type ConfigBackBlazeB2 = {
      type: StorageType;
      applicationKeyId: string;
      applicationKey: string;
      bucketName?: string;

    Configuration url:

    const url =


    const s = new Storage({
      type: StorageType.B2,
      applicationKeyId: "keyId",
      applicationKey: "key",
      bucketName: "bucket",
    const s = new Storage("b2://keyId:key@bucket");

    API methods



    Some cloud storage services need some initial setup that can't be handled in the constructor before they can be used, for instance an async authorization. Also if your storage is set to use a previously non-existing bucket, this bucket will be created in this method.

    If initial setup is required it is handled in this method, if no setup is required this method simply returns true. Note that you need to call this method even it the storage type doesn't need any setup; this is done to abstract away the differences between all types of storage.



    Runs a simple test to test the storage configuration. The test is a call to listFiles and if it fails it throws an error.



    Creates a new bucket, does not fail if the bucket already exists. If the bucket was created successfully it returns "bucket created" or if already existed "bucket exists", else it will reject with an error message.

    Note: dependent on the type of storage and the credentials used, you may need extra access rights for this action. E.g.: sometimes a user may only access the contents of one single bucket.


    selectBucket(namestring | null)Promise<void>;

    Selects a or another bucket for storing files, the bucket will be created automatically if it doesn't exist. If you pass null an empty string or nothing at all the currently selected bucket will be deselected.

    Returns "bucket selected" or "bucket deselected".

    Note: dependent on the type of storage and the credentials used, you may need extra access rights for this action. E.g.: sometimes a user may only access the contents of one single bucket.


    clearBucket(name?: string)Promise<void>;

    Removes all files in the bucket. If you omit the name parameter all files in the currently selected bucket will be removed. If no bucket is selected an error will be thrown.

    Returns "bucket cleared".

    Note: dependent on the type of storage and the credentials used, you may need extra access rights for this action.


    deleteBucket(name?: string)Promise<void>;

    Deletes the bucket and all files in it. If you omit the name parameter the currently selected bucket will be deleted. If no bucket is selected an error will be thrown.

    Returns "bucket deleted"

    Note: dependent on the type of storage and the credentials used, you may need extra access rights for this action.



    Returns a list with the names of all buckets in the storage.

    Note: dependent on the type of storage and the credentials used, you may need extra access rights for this action. E.g.: sometimes a user may only access the contents of one single bucket.



    Returns the name of the currently selected bucket or an empty string ("") if no bucket has been selected.


    addFileFromPath(filePathstring, targetPathstring)Promise<void>;

    Copies a file from a local path to the provided path in the storage. The value for targetPath needs to include at least a file name; the value will be slugified automatically if slug is to true, see default options.


    addFileFromBuffer(bufferBuffer, targetPathstring)Promise<void>;

    Copies a buffer to a file in the storage. The value for targetPath needs to include at least a file name; the value will be slugified automatically if slug is to true, see default options. This method is particularly handy when you want to move uploaded files to the storage, for instance when you use Express.Multer with MemoryStorage.


    addFileFromReadable(streamReadable, targetPathstring)Promise<void>;

    Allows you to stream a file directly to the storage. The value for targetPath needs to include at least a file name; the value will be slugified automatically if slug is to true, see default options. This method is particularly handy when you want to store files while they are being processed; for instance if a user has uploaded a full-size image and you want to store resized versions of this image in the storage; you can pipe the output stream of the resizing process directly to the storage.


    getFileAsReadable(namestring, options?: {start?: number, end?: number})Promise<Readable>;

    Returns a file in the storage as a readable stream. You can specify a byte range by using the extra range argument, see these examples:

    getFileAsReadable("image.png"); // &rarr; reads whole file
    getFileAsReadable("image.png", {}); // &rarr; reads whole file
    getFileAsReadable("image.png", { start: 0 }); // &rarr; reads whole file
    getFileAsReadable("image.png", { start: 0, end: 1999 }); // &rarr; reads first 2000 bytes
    getFileAsReadable("image.png", { end: 1999 }); // &rarr; reads first 2000 bytes
    getFileAsReadable("image.png", { start: 2000 }); // &rarr; reads file from byte 2000



    Removes a file from the bucket. Does not fail if the file doesn't exist.

    Returns "file removed" or "file not found".



    Returns the size of a file in the currently selected bucket and throws an error if no bucket has been selected.



    Returns whether a file exists or not.


    listFiles()Promise<[string, number][]>;

    Returns a list of all files in the currently selected bucket; for each file a tuple is returned containing the path and the size of the file. If no bucket is selected an error will be thrown.



    Returns the type of storage, value is one of the enum StorageType.



    Retrieves the configuration as provided during instantiation. If you have provided the configuration in url form, the function will return it as an configuration object.

    Note that in this configuration object the value of the key bucketName will not change if you have selected a different bucket after initialization, the key bucketName will still hold the value of the initially set bucket. Use getSelectedBucket() to retrieve the actual value of bucketName.


    switchAdapter(configstring | AdapterConfig)void;

    Switch to another adapter in an existing Storage instance at runtime. The config parameter is the same type of object or URL that you use to instantiate a storage. This method can be handy if your application needs a view on multiple storages. If your application needs to copy over files from one storage to another, say for instance from Google Cloud to Amazon S3, then it is more convenient to create 2 separate Storage instances. This method is also called by the constructor to instantiate the initial storage type.

    How it works

    A Storage instance is actually a thin wrapper around one of the available adapters; it creates an instance of an adapter based on the configuration object or URL that you provide. Then all API calls to the Storage are forwarded to this adapter instance, below a code snippet of the Storage class that shows how createBucket is forwarded:

    // member function of class Storage
    async createBucket(name?: string)Promise<string> {
      return this.adapter.createBucket(name);

    The class Storage implements the interface IStorage and this interface declares the complete API. Because all adapters have to implement this interface as well, either by extending AbstractAdapter or otherwise, all API calls on Storage can be directly forwarded to the adapters.

    The adapter subsequently takes care of translating the generic API to storage specific functions. Therefor, dependent on what definitions you use, this library could be seen as a wrapper or a shim.

    The method switchAdapter is not declared in IStorage but in the Storage class itself; this method parses the configuration and creates the appropriate adapter instance. This is done by a lookup table that maps a storage type to a path to an adapter module; the module will be loaded in runtime using require().

    More adapter classes can be added for different storage types, note however that there are many cloud storage providers that keep their API compliant with Amazon S3, for instance Wasabi.

    Adding more adapters

    If you want to add an adapter you can choose to make your adapter a class or a function; so if you don't like OOP you can implement your adapter using FP or any other coding style or programming paradigm you like.

    Your adapter might use a wrapper library for the storage type that you create the adapter for, like for instance aws-sdk is used in the Amazon S3 adapter. Add these dependencies to the peer dependencies in the package.json file in the ./publish folder

    This way your extra dependencies will not be installed automatically but have to be installed manually if the user actually uses your adapter in their code.

    Please add an npm command to your documentation that users can copy paste to their terminal, e.g. npm i storage-wrapper additional-module.

    And for library developers you can add your dependencies to the dependencies in the package.json file in the root directory as well because only the files in the publish folder are published to npm.

    Define your configuration

    Your configuration object should at least contain a key type and its value should be one of the values of the enum StorageType. You could accomplish this by extending the interface IConfig:

    interface IConfig {
      type: StorageType;

    Your configuration URL should also at least contain the type; the name of the type is used for the protocol part of the URL. This name should be added to the enum StorageType.

    // add your type to the enum
    enum StorageType {
      LOCAL = "local",
      GCS = "gcs", // Google Cloud Storage
      S3 = "s3", // Amazon S3
      B2 = "b2", // BackBlaze B2
      YOUR_TYPE = "yourtype",
    // your configuration URL
    const u = "yourtype://and/the:rest@anything/goes?option1=value1&option2=value2...";
    // your configuration object
    const o = {
      type: "yourtype", // mandatory

    You can format the configuration URL completely as you like as long as your adapter has an appropriate parsing function. If your url fit in the template type://part1:part2@part3/bucketName?option1=value1&option2=value2... you can use the parseURL function in ./util.ts.

    Adapter class

    You could choose to let your adapter class extend the class AbstractStorage. If you look at the code you can see that it only implements small parts of the API such as the test method. Also it performs some sanity checking of parameters of a few API functions; this way you don't have to implement these checks in all derived classes.

    One thing to note is the way addFileFromPath, addFileFromBuffer and addFileFromReadable are implemented; these are all forwarded to the non-API function store. This function stores files in the storage using 3 different types of origin; a path, a buffer and a stream. Because these ways of storing have a lot in common they are grouped together in a single overloaded method.

    For the rest it contains stub methods that need to be overruled or extended by the adapter subclasses.

    You don't necessarily have to extend AbstractAdapter but if you choose not to your class should implement the IStorage interface. Most handy utility functions that are used in AbstractAdapter are defined in the file ./src/util.ts so you can easily import them in your own class as well.

    You can use this template as a starting point for your adapter. The template contains a lot of additional documentation per method.

    Adapter function

    The only requirement for this type of adapter is that your module exports a function createAdapter that takes a configuration object or URL as parameter and returns an object that has the shape of the interface IStorage.

    If you like, you can use the utility functions defined in ./src/util.js. Also there is a template file that you can use as a starting point for your module.

    Register your adapter

    After you've finished your adapter module you need to register it, this requires 3 simple steps:

    1] As mentioned earlier the adapters are loaded at runtime, therefor you have to add your type and the path to your module to the lookup table at the top of the file ./src/Storage.ts.

    2] Add your type to the enum StorageTypes in ./src/types.ts.

    3] Also in the file ./src/types.ts add your configuration type that extends IAdapterConfig and add it to the union type AdapterConfig as well.


    If you want to run the tests you have to checkout the repository from github and install all dependencies with npm install or yarn install. There are tests for all storage types; note that you may need to add your credentials to a .env file, see the file .env.default for more explanation, or provide credentials in another way. Also it should be noted that these tests require that the credentials allow to create, delete and list buckets.

    You can run tests per storage type using one of these commands, see also the file package.json:

    # test local disk 
    npm run test-local
    # test Google Cloud Storage 
    npm run test-gcs
    # test Amazon S3 
    npm run test-s3
    # test Backblaze B2 
    npm run test-b2

    To run a generic Jasmine test that uses local storage and does not require any credentials use this command:

    npm run test-jasmine

    There are also Jamine tests that test a set of configuration objects and URLs per storage type:

    # test config local disk 
    npm run test-config-local
    # test config Google Cloud Storage 
    npm run test-config-gcs
    # test config Amazon S3 
    npm run test-config-s3
    # test config Backblaze B2 
    npm run test-config-b2

    To run all tests:

    npm run test-all

    You can find some additional non-Jasmine tests in the file tests/test.ts. You can test a single type of storage or run all tests, just open the file and uncomment you want to run and:

    npm test

    Example application

    A simple application that shows how you can use the storage abstraction package can be found in this repository. It uses and Ts.ED and TypeORM and it consists of both a backend and a frontend.

    Questions and requests

    Please let us know if you have any questions and/or request by creating an issue.


    npm i @tweedegolf/storage-abstraction

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    • daniel2g
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