zuraffa_minio

A maintained fork of the minio package — the pure Dart client for MinIO and Amazon S3 compatible object storage.

Why a fork?

The upstream minio package has been unmaintained since August 2025. Its issue tracker grew to 36 open issues, most of them unanswered, and its test suite pointed at a public demo server that no longer exists — so the suite was red for everyone, not just for the maintainer.

zuraffa_minio keeps the API of the original package unchanged, so migrating is an import swap:

// before
import 'package:minio/minio.dart';
// after
import 'package:zuraffa_minio/minio.dart';
// or, the default library, which is web safe:
import 'package:zuraffa_minio/zuraffa_minio.dart';

Nothing else in your code has to change: the class is still Minio, the methods keep their names and their parameters, and the models keep their fields.

The models live in their own library, exactly as they did upstream:

import 'package:zuraffa_minio/models.dart';

They are deliberately not exported from the default library: one of them is called Object, and an export would shadow the Object of dart:core in every file that imports the package.

What the fork adds on top:


Dependencies	`xml` 7 (upstream was pinned to 6.4.2), and every other pin moved to its current release
Tests	A hermetic suite that runs against a real MinIO server in CI — the upstream suite could not run at all
Bug fixes	Six reported bugs fixed, plus four more found on the way (see What was fixed)
Features	The feature requests from the issue tracker: cancellation, credential renewal, presigned URL overrides, progress callbacks, parallel transfer, `objectUrl`, `removeObjectsByPrefix`

Usage

Upgrading from 0.2.4

Minio(...) requires accessKey and secretKey again. A 0.2.4 client that omitted them no longer compiles, instead of signing every request with an empty key and staying anonymous without saying so. A client that resolves its own credentials calls Minio.withCredentialsProvider(...), which needs no placeholder keys; once its provider resolves, those credentials take precedence over any static keys the client was built with.

The constructor change shipped in a patch release (0.2.5), so ^0.2.4 resolves it and a dart pub upgrade moves you onto it. Pin 0.2.4 to stay on the old constructor, or depend on ^0.2.5 to adopt the new one. The next breaking change ships as 0.3.0.

Initialize the client

A local MinIO server

final minio = Minio(
  endPoint: '127.0.0.1',
  port: 9000,
  accessKey: 'minioadmin',
  secretKey: 'minioadmin',
  useSSL: false,
);

Amazon S3

final minio = Minio(
  endPoint: 's3.amazonaws.com',
  accessKey: 'YOUR-ACCESSKEYID',
  secretKey: 'YOUR-SECRETACCESSKEY',
  region: 'eu-central-1',
);

Upload and download

import 'dart:typed_data';

import 'package:zuraffa_minio/minio.dart';

Future<void> main() async {
  final minio = Minio(
    endPoint: '127.0.0.1',
    port: 9000,
    accessKey: 'minioadmin',
    secretKey: 'minioadmin',
    useSSL: false,
  );

  final bytes = Uint8List.fromList('hello world'.codeUnits);

  final etag = await minio.putObject(
    'my-bucket',
    'greeting.txt',
    Stream<Uint8List>.value(bytes),
    size: bytes.length,
    onProgress: (written) => print('uploaded $written bytes'),
  );
  print('etag: $etag');

  final data = await minio.getObject('my-bucket', 'greeting.txt');
  final buffer = BytesBuilder();
  await for (final chunk in data) {
    buffer.add(chunk);
  }
  print(String.fromCharCodes(buffer.takeBytes()));

  minio.close();
}

Files

package:zuraffa_minio/io.dart adds the dart:io helpers. It is a separate library on purpose: the default library stays web safe.

import 'package:zuraffa_minio/io.dart';

await minio.fPutObject('my-bucket', 'picture.png', '/tmp/picture.png');
await minio.fGetObject('my-bucket', 'picture.png', '/tmp/picture-copy.png');

Presigned URLs

// expires is a number of seconds
final url = await minio.presignedGetObject(
  'my-bucket',
  'greeting.txt',
  expires: 3600,
);

When the server the client talks to is not the host the browser reaches — a proxy, a CDN, an internal and an external address — the presigned URL can be generated for the public host while the client keeps talking to the internal one:

final url = await minio.presignedUrl(
  'GET',
  'my-bucket',
  'greeting.txt',
  expires: 3600,
  host: 'objects.example.com',
  port: 443,
  useSSL: true,
);

The override is used in the url and in the signature, so the two can never disagree.

Temporary credentials

STS credentials expire. Instead of recreating the client, hand it a provider that returns fresh credentials when they are needed:

final minio = Minio.withCredentialsProvider(
  endPoint: 's3.amazonaws.com',
  region: 'eu-central-1',
  credentialsProvider: () async {
    final session = await assumeRoleWithWebIdentity();
    return MinioCredentials(
      accessKey: session.accessKey,
      secretKey: session.secretKey,
      sessionToken: session.sessionToken,
    );
  },
);

The provider is called before the first request is signed, and again whenever the credentials it returned are older than credentialsTtl (five minutes by default). refreshCredentials() forces a new resolution right away. The accessKey, secretKey and sessionToken getters always report the credentials the next request will be signed with.

Cancelling

final token = MinioCancellationToken();
final minio = Minio(
  endPoint: '127.0.0.1',
  port: 9000,
  accessKey: 'minioadmin',
  secretKey: 'minioadmin',
  useSSL: false,
  cancellationToken: token,
);

final upload = minio.putObject(
  'my-bucket',
  'big.bin',
  Stream<Uint8List>.value(data),
);
token.cancel();     // aborts the request that is in flight
await upload;       // the upload fails

Cancelling closes the underlying HTTP client, so the request that is in flight is aborted. A request that has not been sent yet fails with a MinioRequestCancelledError.

minio.close() aborts everything that is running as well.

Your own HTTP client

The client is injectable, which is the escape hatch for proxies, custom certificates and retry policies:

import 'package:http/io_client.dart';

final minio = Minio(
  endPoint: 'example.com',
  accessKey: '...',
  secretKey: '...',
  httpClient: IOClient(HttpClient()..badCertificateCallback = (_, __, ___) => true),
);

package:zuraffa_minio/io.dart has a shortcut for the certificate case:

final minio = Minio(
  endPoint: 'example.com',
  accessKey: '...',
  secretKey: '...',
  httpClient: createTlsHttpClient(allowInvalidCertificates: true),
);

Parallel transfers

// upload the parts of a multipart upload concurrently
await minio.putObject(
  'my-bucket',
  'big.bin',
  Stream<Uint8List>.value(data),
  size: data.length,
  maxParallelUploads: 4,
);

// download the object as concurrent byte ranges
final stream = await minio.getObject(
  'my-bucket',
  'big.bin',
  parallelism: 8,
  chunkSize: 4 << 20,
);

Regions

The region decides two things: the AWS host the request goes to and the scope the request is signed with. The client keeps both in sync, and it asks the server for the region of a bucket when it does not know it yet.

If the server rejects a request because the region is wrong, it answers with AuthorizationHeaderMalformed and names the region the bucket really lives in. The client then signs and addresses the request again with that region and remembers it for the bucket.

What was fixed

Every fix has a regression test whose name carries the number of the upstream issue it reproduces.

Issue	What was wrong
#6	The notification poller called `json.decode` on the XML payload MinIO sends
#24	A negative object size failed an `assert`, which only exists in debug builds
#38	An unknown region fell back to the global endpoint, which only accepts `us-east-1` signatures
#43	`getRequestUrl` read the region without a null check and threw "Unexpected null value"
#49	`listBuckets` cast the whitespace text nodes between the buckets to `XmlElement`
#108	`statObject` read `content-length` and `last-modified` with a bang operator

Four more bugs were found while writing those tests:

listIncompleteUploads sent the uploads parameter twice, which broke the signature of every request it made.
listParts and listIncompleteUploads read the wrong XML elements and therefore always reported an empty, untruncated page.
listParts cast the document node to XmlElement, which is a TypeError.
listIncompleteUploads failed as a whole when a single upload could not be inspected any more.

Running the tests

The suite needs an S3 compatible server. By default it talks to 127.0.0.1:9000 with the minioadmin credentials:

minio server /tmp/minio-data --address 127.0.0.1:9000
dart test -j 2

Without a server the integration tests are skipped and the offline tests still run. The server can be pointed somewhere else:

Variable	Default	Meaning
`MINIO_ENDPOINT`	`127.0.0.1`	The host of the server
`MINIO_PORT`	`9000`	The port of the server
`MINIO_USE_SSL`	`false`	Whether the server speaks TLS
`MINIO_ACCESS_KEY`	`minioadmin`	The access key
`MINIO_SECRET_KEY`	`minioadmin`	The secret key
`MINIO_REGION`	`us-east-1`	The region to sign for

MinIO's open source server is archived: the docker images are gone and dl.min.io answers 410 Gone. The CI workflow downloads the last release that ships a binary and runs that.

API

Bucket operations	Object operations	Presigned operations	Bucket policy & notification
`makeBucket`	`getObject`	`presignedUrl`	`getBucketNotification`
`listBuckets`	`getPartialObject`	`presignedGetObject`	`setBucketNotification`
`bucketExists`	`putObject`	`presignedPutObject`	`removeAllBucketNotification`
`removeBucket`	`statObject`	`presignedPostPolicy`	`listenBucketNotification`
`listObjects`	`copyObject`		`getBucketPolicy`
`listObjectsV2`	`removeObject`		`setBucketPolicy`
`listIncompleteUploads`	`removeObjects`
`listAllObjects`	`removeObjectsByPrefix`
`listAllObjectsV2`	`objectUrl`
	`initiateNewMultipartUpload`
	`uploadPart`
	`completeMultipartUpload`
	`removeIncompleteUpload`

What was added

Every addition answers an open issue of the upstream package, so the issue tracker and the API stay traceable:

Issue	What was added
#4, #20	`onProgress` on `getObject` and `getPartialObject`
#12	`objectUrl`
#35, #98	`putObject(maxParallelUploads:)`
#45, #85, #93	`MinioCancellationToken` and `MinioRequestCancelledError`
#80	`createTlsHttpClient`
#94	`MinioCredentials`, `credentialsProvider`, `refreshCredentials`
#99	`removeObjectsByPrefix`
#101	`host`, `port` and `useSSL` on the presigned calls
#102	`uploadPart` and the multipart example
#112	`getObject(parallelism:)`

License

MIT — see LICENSE. The original package is MIT licensed as well; the copyright of xuty is kept.