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Download files with Cloud Storage on Flutter

Cloud Storage for Firebase allows you to quickly and easily download files from a Cloud Storage bucket provided and managed by Firebase.

Note: By default, a Cloud Storage bucket requires Firebase Authentication to perform any action on the bucket's data or files. You can change your Firebase Security Rules for Cloud Storage to allow unauthenticated access. Since Firebase and your project's default App Engine app share this bucket, configuring public access may make newly uploaded App Engine files publicly accessible, as well. Be sure to restrict access to your Cloud Storage bucket again when you set up Authentication.

Create a Reference​

To download a file, first create a Cloud Storage reference to the file you want to download.

You can create a reference by appending child paths to the root of your Cloud Storage bucket, or you can create a reference from an existing gs:// or https:// URL referencing an object in Cloud Storage.

// Create a storage reference from our app
final storageRef = FirebaseStorage.instance.ref();

// Create a reference with an initial file path and name
final pathReference = storageRef.child("images/stars.jpg");

// Create a reference to a file from a Google Cloud Storage URI
final gsReference =
    FirebaseStorage.instance.refFromURL("gs://YOUR_BUCKET/images/stars.jpg");

// Create a reference from an HTTPS URL
// Note that in the URL, characters are URL escaped!
final httpsReference = FirebaseStorage.instance.refFromURL(
    "https://firebasestorage.googleapis.com/b/YOUR_BUCKET/o/images%20stars.jpg");

Download Files​

Once you have a reference, you can download files from Cloud Storage by calling the getData() or getStream(). If you prefer to download the file with another library, you can get a download URL with getDownloadUrl().

Download in memory​

Download the file to a UInt8List with the getData() method. This is the easiest way to download a file, but it must load the entire contents of your file into memory. If you request a file larger than your app's available memory, your app will crash. To protect against memory issues, getData() takes a maximum amount of bytes to download. Set the maximum size to something you know your app can handle, or use another download method.

final islandRef = storageRef.child("images/island.jpg");

try {
  const oneMegabyte = 1024 * 1024;
  final Uint8List? data = await islandRef.getData(oneMegabyte);
  // Data for "images/island.jpg" is returned, use this as needed.
} on FirebaseException catch (e) {
  // Handle any errors.
}

Download to a local file​

The writeToFile() method downloads a file directly to a local device. Use this if your users want to have access to the file while offline or to share the file in a different app. writeToFile() returns a DownloadTask which you can use to manage your download and monitor the status of the download.

final islandRef = storageRef.child("images/island.jpg");

final appDocDir = await getApplicationDocumentsDirectory();
final filePath = "${appDocDir.absolute}/images/island.jpg";
final file = File(filePath);

final downloadTask = islandRef.writeToFile(file);
downloadTask.snapshotEvents.listen((taskSnapshot) {
  switch (taskSnapshot.state) {
    case TaskState.running:
      // TODO: Handle this case.
      break;
    case TaskState.paused:
      // TODO: Handle this case.
      break;
    case TaskState.success:
      // TODO: Handle this case.
      break;
    case TaskState.canceled:
      // TODO: Handle this case.
      break;
    case TaskState.error:
      // TODO: Handle this case.
      break;
  }
});

Download Data via URL​

If you already have download infrastructure based around URLs, or just want a URL to share, you can get the download URL for a file by calling the getDownloadURL() method on a Cloud Storage reference.

final imageUrl =
    await storageRef.child("users/me/profile.png").getDownloadURL();

Handle Errors​

There are a number of reasons why errors may occur on download, including the file not existing, or the user not having permission to access the desired file. More information on errors can be found in the Handle Errors section of the docs.

Full Example​

A full example of a download with error handling is shown below:

final islandRef = storageRef.child("images/island.jpg");

final appDocDir = await getApplicationDocumentsDirectory();
final filePath = "${appDocDir.absolute}/images/island.jpg";
final file = File(filePath);

final downloadTask = islandRef.writeToFile(file);
downloadTask.snapshotEvents.listen((taskSnapshot) {
  switch (taskSnapshot.state) {
    case TaskState.running:
      // TODO: Handle this case.
      break;
    case TaskState.paused:
      // TODO: Handle this case.
      break;
    case TaskState.success:
      // TODO: Handle this case.
      break;
    case TaskState.canceled:
      // TODO: Handle this case.
      break;
    case TaskState.error:
      // TODO: Handle this case.
      break;
  }
});

You can also get and update metadata for files that are stored in Cloud Storage.