fs2-blobstore / fs2-blobstore Edit

Minimal, idiomatic, stream-based Scala interface for key/value store implementations

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Minimal, idiomatic, Scala interface based on fs2 for blob- and file store implementations. This library provides sources as sinks for a variety of stores (S3, GCS, Azure, SFTP, Box) that you can compose with fs2 programs.


fs2-blobstore is published to maven central, add to build.sbt:

libraryDependencies ++= Seq(
  "com.github.fs2-blobstore" %% "core"  % "0.7.3",
  "com.github.fs2-blobstore" %% "sftp"  % "0.7.3",
  "com.github.fs2-blobstore" %% "s3"    % "0.7.3",
  "com.github.fs2-blobstore" %% "gcs"   % "0.7.3",
  "com.github.fs2-blobstore" %% "azure" % "0.7.3",
  "com.github.fs2-blobstore" %% "box"   % "0.7.3"


Upload all files under a S3 prefix to a SFTP server, filter blank lines and run 20 uploads in parallel.

import blobstore.Path
import blobstore.s3.S3Store
import blobstore.sftp.SftpStore
import cats.effect.{Blocker, ExitCode, IO, IOApp}
import com.jcraft.jsch.{JSch, Session}
import software.amazon.awssdk.services.s3.S3AsyncClient
import fs2.Stream

object Example extends IOApp {

  val connectSftp: IO[Session] = IO {
    val jsch = new JSch()

  val s3Client: S3AsyncClient = S3AsyncClient.builder().build()

    * Transfer 20 files in parallel and filter blank lines
  def logic(s3: S3Store[IO], sftp: SftpStore[IO]): Stream[IO, Unit] =
      .map { path: Path =>
        s3.get(path, chunkSize = 32 * 1024)
      .parJoin(maxOpen = 20)

  override def run(args: List[String]): IO[ExitCode] = {
    Blocker[IO].use { blocker =>
      val program = for {
        s3   <- Stream.eval(S3Store[IO](s3Client))
        sftp <- SftpStore(absRoot = "", connectSftp, blocker)
        _    <- logic(s3, sftp)
      } yield ExitCode.Success



Store Abstraction

The goal of the Store interface is to have a common representation of key/value functionality (get, put, list, etc) as streams that can be composed, transformed and piped just like any other fs2.Stream or fs2.Pipe regardless of the underlying storage mechanism.

This is especially useful for unit testing if you are building a S3, GCS or SFTP backed system as you can provide a filesystem based implementation for tests that is guaranteed to work the same way as you production environment.

The three main activities in a key/value store are modeled like:

def list(path: Path): fs2.Stream[F, Path]
def get(path: Path, chunkSize: Int): fs2.Stream[F, Byte]
def put(path: Path): Pipe[F, Byte, Unit] 

Note that list and get are modeled as streams since they are reading (potentially) very large amounts of data from storage, while put is represented as a sink of byte so that any stream of bytes can be piped into it to upload data to storage.

Path Abstraction

Path is an abstraction for referencing files and folders in Stores:

trait Path {
  def root: Option[String]
  def pathFromRoot: cats.data.Chain[String]
  def fileName: Option[String]
  def size: Option[Long]
  def isDir: Option[Boolean]
  def lastModified: Option[java.time.Instant]

Usually concrete store would have specific implementation of this trait exposing some store-specific metadata, but all stores should accept any implementation of Path. Store might apply some optimizations given its specific Path, although it's not a requirement. There is a default most generic implementation of PathBasePath, it's used for instance when path is constructed from string.

By importing implicit PathOps into the scope you can make use of path composition / and filename function that returns the substring of the path's key after the last path separator.

NOTE: a good improvement to the path abstraction would be to handle OS specific separators when referring to filesystem paths.

Implicit Ops

import blobstore.implicits._

StoreOps and PathOps provide functionality on both Store and Path for commonly performed tasks (i.e. upload/download a file from/to local filesystem, collect all returned paths when listing, composing paths or extracting filename of the path).

Most of these common tasks encapsulate stream manipulation and provide a simpler interface that return the corresponding effect monad. These are also very good examples of how to use blobstore streams and sink in different scenarios.


All store implementations must support and pass the suite of tests in AbstractStoreTest. It is expected that each store implementation (like s3, sftp, file) should contain the Store implementation and at least one test suite that inherits from AbstractStoreTest and overrides store and root attributes:

import cats.effect.IO
import blobstore.Store
import blobstore.AbstractStoreTest

class MyStoreImplTest extends AbstractStoreTest {
  override val store: Store[IO] = MyStoreImpl( ... )
  override val root: String = "my_store_impl_tests"

This test suite will guarantee that basic operations are supported properly and consistent with all other Store implementations.

Running Tests:

Tests are set up to run via docker-compose:

docker-compose run --rm sbt "testOnly * -- -l blobstore.IntegrationTest"

This will start a minio (Amazon S3 compatible object storage server), Azurite (A lightweight server clone of Azure Storage) and SFTP containers and run all tests not annotated as @IntegrationTest. GCS is tested against the in-memory local Storage

Yes, we understand SftpStoreTest, AzureStoreTest and S3StoreTest are also integration tests because they connect to external services, but we don't mark them as such because we found these containers that allow to run them along unit tests, and we want to exercise as much of the store code as possible.

Currently, tests for BoxStore are annotated with @IntegrationTest because we have not found a box docker image. To run BoxStore integration tests locally you need to provide BOX_TEST_BOX_DEV_TOKEN.

Run box tests with:

sbt box/test

Note: this will exercise AbstractStoreTest tests against your box.com account.

Store Implementations


FileStore backed by local FileSystem. FileStore is provided as part of core module because it doesn't include any additional dependencies and it is used as the default source store in TransferOps tests. It only requires root path in the local file system:

import blobstore.{Path, Store}
import blobstore.fs.FileStore
import java.nio.file.Paths
import cats.effect.{Blocker, ExitCode, IO, IOApp}

object FileStoreExample extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = Blocker[IO].use { blocker =>
    val store: Store[IO] = FileStore[IO](Paths.get("tmp/"), blocker)


S3Store backed by AWS SDK V2. It requires a configured instance of S3AsyncClient:

import software.amazon.awssdk.services.s3.S3AsyncClient
import blobstore.s3.S3Store

object S3Example extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
    val s3 = {
        val builder = S3AsyncClient.builder()
        // Configure client
        // ...
    S3Store[IO](s3).flatMap{store =>
        // ...
    }.attempt.map(_.fold(_ => ExitCode.Error, _ => ExitCode.Success))


GcsStore backed by Google Cloud Storage. It requires a configured Storage:

import blobstore.gcs.GcsStore
import com.google.cloud.storage.{Storage, StorageOptions}

object GcsExample extends IOApp {
   def run(args: List[String]): IO[ExitCode] = Blocker[IO].use { blocker =>
     val storage: Storage = StorageOptions.getDefaultInstance.getService
     val store: Store[IO] = GcsStore(storage, blocker, List.empty)


SftpStore backed by SFTP server with Jsch client. It requires a computation resulting in a Session:

import blobstore.sftp.SftpStore
import com.jcraft.jsch.{JSch, Session}

object SftpExample extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = Blocker[IO].use { blocker =>
    val session: IO[Session] = IO {
      val jsch = new JSch()

    val store: fs2.Stream[IO, SftpStore[IO]] = SftpStore("", session, blocker)



AzureStore backed by Azure Storage Blob client library for Java. It requires a configured instance of BlobServiceAsyncClient:

import com.azure.storage.blob.BlobServiceClientBuilder
import blobstore.azure.AzureStore

object AzureExample extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
    val azure = {
        val builder = new BlobServiceClientBuilder()
        // Configure client
        // ...
    AzureStore[IO](azure).flatMap{store =>
        // ...
    }.attempt.map(_.fold(_ => ExitCode.Error, _ => ExitCode.Success))


BoxStore backed by a BoxAPIConnection, which has multiple options for authentication. This requires that you have a Box app set up already. See Box SDK documentation for more details:

import blobstore.box.BoxStore
import com.box.sdk.BoxAPIConnection

object BoxExample extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = Blocker[IO].use { blocker =>
    val api = new BoxAPIConnection("myDeveloperToken")
    val store: Store[IO] = BoxStore[IO](api, blocker)