ORAS Java SDK (Java 11 Fork)

Note: This is a fork of oras-project/oras-java maintained with Java 11 compatibility. The upstream project targets Java 17+.

The Java packages remain land.oras.* — you can switch between this fork and upstream by changing only the Maven/Gradle coordinates.

OCI Registry as Storage enables libraries to push OCI Artifacts to OCI Conformant registries. This is a Java SDK for Java developers to empower them to do this in their applications.

Consuming SDK

Maven

<dependency>
    <groupId>io.roastedroot</groupId>
    <artifactId>oras-java</artifactId>
    <version>VERSION_HERE</version>
</dependency>

Gradle

implementation 'io.roastedroot:oras-java:VERSION_HERE'

Examples

Authentication

Using existing credentials from ~/.docker/config.json or $XDG_RUNTIME_DIR/containers/auth.json:

Registry registry = Registry.builder().defaults().build();

Using a username and password:

Registry registry = Registry.builder().defaults("username", "password").build();

Push a single file

Registry registry = Registry.builder().insecure().build();
LocalPath artifact = LocalPath.of(Path.of("my-file.txt"));
Manifest manifest = registry.pushArtifact(ContainerRef.parse("localhost:5000/hello:v1"), artifact);

Push multiple files with a custom artifact type

Push several files at once with a custom artifact type, per-file media types, and manifest-level annotations:

Registry registry = Registry.builder().insecure().build();

Annotations annotations = Annotations.ofManifest(Map.of("build-tool", "maven"))
        .withFileAnnotations("pom.xml", Map.of("format", "xml"));

Manifest manifest = registry.pushArtifact(
        ContainerRef.parse("localhost:5000/my-app:v1"),
        ArtifactType.from("application/vnd.maven+type"),
        annotations,
        LocalPath.of(Path.of("pom.xml"), "application/xml"),
        LocalPath.of(Path.of("target/app.jar"), "application/java-archive"));

The resulting manifest will contain one layer per file, each annotated with its filename via org.opencontainers.image.title.

Push a directory

Directories are automatically compressed as a tar+gzip archive and tagged with org.opencontainers.image.title set to the directory name. The io.deis.oras.content.unpack annotation is set to true so the SDK automatically extracts the archive on pull.

Registry registry = Registry.builder().insecure().build();
Manifest manifest = registry.pushArtifact(
        ContainerRef.parse("localhost:5000/my-configs:v1"),
        LocalPath.of(Path.of("config-dir")));

To push a directory as a plain zip instead:

Manifest manifest = registry.pushArtifact(
        ContainerRef.parse("localhost:5000/my-configs:v1"),
        LocalPath.of(Path.of("config-dir"), "application/zip"));

Pull an artifact

Files are automatically written using the org.opencontainers.image.title layer annotation as the filename. The third argument controls whether existing files are overwritten:

Registry registry = Registry.builder().insecure().build();
registry.pullArtifact(ContainerRef.parse("localhost:5000/hello:v1"), Path.of("output-dir"), true);

Attach an artifact (referrers)

Attach a signature or attestation to an already-pushed artifact. The attached manifest references the original via its subject field and is discoverable through the Referrers API:

Registry registry = Registry.builder().insecure().build();
ContainerRef ref = ContainerRef.parse("localhost:5000/my-app:v1");

// Push the main artifact first
Manifest manifest = registry.pushArtifact(ref,
        ArtifactType.from("application/vnd.maven+type"),
        LocalPath.of(Path.of("pom.xml"), "application/xml"));

// Attach a signature as a referrer
Manifest signatureManifest = registry.attachArtifact(
        ref,
        ArtifactType.from("application/vnd.example.signature"),
        LocalPath.of(Path.of("pom.xml.asc")));

// List all referrers for the artifact
Referrers referrers = registry.getReferrers(
        ref.withDigest(manifest.getDescriptor().getDigest()), null);

Assemble a manifest from individual blobs

For fine-grained control, push blobs and configs individually before assembling and pushing the manifest:

Registry registry = Registry.builder().insecure().build();
ContainerRef ref = ContainerRef.parse("localhost:5000/my-app:v1");

// Push individual layers
Layer layer1 = registry.pushBlob(ref, Files.readAllBytes(Path.of("schema.json")))
        .withAnnotations(Map.of(Const.ANNOTATION_TITLE, "schema.json"));
Layer layer2 = registry.pushBlob(ref, Files.readAllBytes(Path.of("data.csv")))
        .withAnnotations(Map.of(Const.ANNOTATION_TITLE, "data.csv"));

// Push a custom config
Config config = registry.pushConfig(ref, Config.empty().withMediaType("application/vnd.example.config+json"));

// Assemble and push the manifest
Manifest manifest = Manifest.empty()
        .withConfig(config)
        .withLayers(List.of(layer1, layer2));
registry.pushManifest(ref, manifest);

Copy between registries

Copy a tagged artifact — including all its blobs — from one registry to another:

Registry source = Registry.builder().defaults("user", "pass").insecure().build();
Registry target = Registry.builder().defaults("user", "pass").build();

ContainerRef from = ContainerRef.parse("localhost:5000/my-app:v1");
ContainerRef to   = ContainerRef.parse("registry.example.com/my-app:v1");

CopyUtils.copy(source, from, target, to, CopyUtils.CopyOptions.shallow());

OCI Layout

OCI Layout lets you work with artifacts stored on disk in the OCI Image Layout format.

Push to an OCI Layout directory:

LayoutRef ref = LayoutRef.parse("/tmp/my-layout:latest");
OCILayout ociLayout = OCILayout.Builder.builder().defaults(Path.of("/tmp/my-layout")).build();

Manifest manifest = ociLayout.pushArtifact(
        ref,
        ArtifactType.from("application/vnd.example.type"),
        Annotations.empty(),
        LocalPath.of(Path.of("my-file.txt"), "text/plain"));

Pull from an OCI Layout directory:

LayoutRef ref = LayoutRef.parse("/tmp/my-layout:latest");
OCILayout ociLayout = OCILayout.Builder.builder().defaults(Path.of("/tmp/my-layout")).build();
ociLayout.pullArtifact(ref, Path.of("output-dir"), false);

Tar-backed OCI Layout (single-file, portable archive):

LayoutRef ref = LayoutRef.parse("/tmp/my-layout.tar:latest");
OCILayout ociLayout = OCILayout.Builder.builder().defaults(Path.of("/tmp/my-layout.tar")).build();

ociLayout.pushArtifact(ref, ArtifactType.from("application/vnd.example.type"),
        Annotations.empty(), LocalPath.of(Path.of("my-file.txt"), "text/plain"));

// Pull from the same tar
ociLayout.pullArtifact(ref, Path.of("output-dir"), false);

Copy from OCI Layout to a registry:

LayoutRef layoutRef = LayoutRef.parse("/tmp/my-layout:latest");
OCILayout ociLayout = OCILayout.Builder.builder().defaults(Path.of("/tmp/my-layout")).build();

Registry registry = Registry.builder().defaults("user", "pass").build();
ContainerRef target = ContainerRef.parse("registry.example.com/my-app:v1");

CopyUtils.copy(ociLayout, layoutRef, registry, target, CopyUtils.CopyOptions.shallow());

Registries configuration

Since version 0.7.0 the ORAS Java SDK supports the registries.conf format (see the containers/image documentation).

The SDK reads configuration from the following locations, in order (later entries override earlier ones):

1. /etc/containers/registries.conf
2. /etc/containers/registries.conf.d/*.conf (alphabetical)
3. $HOME/.config/containers/registries.conf
4. $HOME/.config/containers/registries.conf.d/*.conf (alphabetical)

Supported features

# Short-name resolution mode (enforcing is the default)
short-name-mode = "enforcing"
unqualified-search-registries = ["docker.io"]

# Rewrite a location via a prefix
[[registry]]
prefix = "docker.io/bitnami"
location = "docker.io/bitnamilegacy"

# Block a registry
[[registry]]
prefix = "gcr.io"
blocked = true

# Mark a registry as insecure
[[registry]]
location = "localhost:5000"
insecure = true

# Mirrors — tried in order before falling back to the upstream registry
[[registry]]
prefix = "registry.example.com"
location = "registry.example.com"
mirror-by-digest-only = false   # set to true to restrict all mirrors to digest-only pulls

  [[registry.mirror]]
  location = "mirror1.example.com"
  insecure = false
  pull-from-mirror = "all"       # "all" (default) | "tag-only" | "digest-only"

  [[registry.mirror]]
  location = "mirror2.example.com"
  insecure = true
  pull-from-mirror = "digest-only"

Resolution and evaluation order

Reference resolution always happens before any security decision, and every security decision is evaluated against the effective (resolved) reference — not the reference originally supplied. For each operation the SDK:

1. Resolves the reference: short-name / unqualified-search expansion (e.g. nginx -> docker.io/library/nginx), prefix -> location rewrites, and mirror selection.
2. Evaluates blocked, insecure (HTTP vs HTTPS) and the trust policy against that resolved reference.
3. Connects and transfers bytes.

This ordering is intentional: block-list and plaintext decisions must bind to the host the request actually reaches. Evaluating them on the pre-rewrite reference would let a mirror or alias redirect traffic to a blocked or plaintext host while the check passed on the original name. registries.conf and policy.json are trusted operator-controlled configuration; a threat model in which an attacker can edit those files is out of scope (that host is already compromised).

Two consequences worth noting:

• Policy scope is repository-level. The policy.json format scopes rules to registry[/namespace/repository] only — tags and digests are stripped before matching. A policy rule cannot protect (or single out) a specific tag or digest.
• The trust policy is a pull-time gate. Manifest/index pulls are verified against the policy; deletes are only checked against blocked/insecure, never content-verified. Protecting a specific digest from deletion must be enforced by registry-side RBAC / tag immutability, not by the client trust policy.

Trust policy

The ORAS Java SDK can enforce a containers trust policy when pulling, using the policy.json format used by Podman, Skopeo and Buildah.

The policy is loaded from the following locations, in order (the first that exists wins):

1. $HOME/.config/containers/policy.json
2. /etc/containers/policy.json

If no policy file is found, an accept-all policy is used. You can also set it explicitly:

// Load from a specific file
Registry registry = Registry.builder()
        .defaults()
        .withPolicy(Path.of("/etc/containers/policy.json"))
        .build();

// Or build one programmatically
Registry registry = Registry.builder()
        .defaults()
        .withPolicy(ContainersPolicy.rejectAll())
        .build();

When a policy is set, every manifest/index pull is evaluated against it and rejected (OrasException) if it does not pass.

Supported requirement types

Type	Supported	Behaviour
insecureAcceptAnything	Yes	Accept the image without any verification (trust all).
reject	Yes	Reject the image unconditionally.
sigstoreSigned	Yes	Accept only images with a valid keyed Sigstore (cosign) signature.
signedBy (GPG)	No	Not implemented. Legacy

sigstoreSigned

Only keyed verification is supported for now. If keyPath or keyData is present it contains a single Sigstore public key (the cosign.pub produced by cosign generate-key-pair), and only signatures made by that key are accepted:

• keyPath — path to a PEM public key file.
• keyData — the same key, base64-encoded inline.

Multiple keys (keyPaths/keyDatas) and keyless (Fulcio/Rekor) verification are not supported. Signatures are discovered through the OCI referrers API (the Sigstore bundle, application/vnd.dev.sigstore.bundle.v0.3+json, attached to the image); no local signature store is consulted. Verification binds the signature to the pulled image by its digest. The signedIdentity field is not supported and is ignored if present, because the cosign bundle payload carries only the image digest and no claimed Docker reference to match against.

{
    "default": [{"type": "insecureAcceptAnything"}],
    "transports": {
        "docker": {
            "example.com/my-image": [
                {"type": "sigstoreSigned", "keyPath": "/home/me/my-key.pub"}
            ]
        }
    }
}

Attribution

This project is a fork of oras-project/oras-java, originally created by Valentin Delaye and the ORAS Authors. We are grateful to the original contributors for their work on the ORAS Java SDK.

License

This code is licensed under the Apache 2.0 LICENSE.