Docker Registry Client

An API client for the V2 Docker Registry API, for Go applications.

Imports

import (
    "github.com/heroku/docker-registry-client/registry"
    digest "github.com/opencontainers/go-digest"
    "github.com/docker/distribution/manifest"
    "github.com/docker/libtrust"
)

Creating A Client

url      := "https://registry-1.docker.io/"
username := "" // anonymous
password := "" // anonymous
hub, err := registry.New(url, username, password)

Creating a registry will also ping it to verify that it supports the registry API, which may fail. Failures return non-nil err values.

Authentication supports both HTTP Basic authentication and OAuth2 token negotiation.

Listing Repositories

repositories, err := hub.Repositories()

The repositories will be returned as a slice of strings.

Listing Tags

Each Docker repository has a set of tags -- named images that can be downloaded.

tags, err := hub.Tags("heroku/cedar")

The tags will be returned as a slice of strings.

Downloading Manifests

Each tag has a corresponding manifest, which lists the layers and image configuration for that tag.

manifest, err := hub.Manifest("heroku/cedar", "14")

Schema V2

manifest, err := hub.ManifestV2("heroku/cedar", "14")

The returned manifest will be a manifest.SignedManifest pointer. For details, see the github.com/docker/distribution/manifest library.

Retrieving Manifest Digest

A manifest is identified by a digest.

digest, err := hub.ManifestDigest("heroku/cedar", "14")

The returned digest will be a digest.Digest. See github.com/docker/distribution/digest.

Deleting Manifest

To delete a manifest

digest, err := hub.ManifestDigest("heroku/cedar", "14")
err = hub.DeleteManifest("heroku/cedar", digest)

Please notice that, as specified by the Registry v2 API, this call doesn't actually remove the fs layers used by the image.

Downloading Layers

Each manifest contains a list of layers, filesystem images that Docker will compose to create containers.

// or obtain the digest from an existing manifest's FSLayer list
digest := digest.NewDigestFromHex(
    "sha256",
    "a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4",
)
reader, err := hub.DownloadBlob("heroku/cedar", digest)
if reader != nil {
    defer reader.Close()
}
if err != nil {
    return err
}

Uploading Layers

This library can also publish new layers:

digest := digest.NewDigestFromHex(
    "sha256",
    "a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4",
)
exists, err := hub.HasBlob("example/repo", digest)
if err != nil {
    // …
}
if !exists {
    stream := bytes.NewBuffer(...)
    hub.UploadBlob("example/repo", digest, stream, nil)
}

Uploading Manifests

First, create a signed manifest:

manifest := &manifest.Manifest{
    Versioned: manifest.Versioned{
        SchemaVersion: 1,
    },
    Tag: "latest",
    // …
}

key, err := libtrust.GenerateECP256PrivateKey()
if err != nil {
    // …
}

signedManifest := manifest.Sign(manifest, key)
if err != nil {
    // …
}

Production applications should probably reuse keys, rather than generating ephemeral keys. See the libtrust documentation for details.

Then, upload the signed manifest:

err := hub.PutManifest("example/repo", "latest", signedManifest)
if err != nil {
    // …
}

This will also create or update tags, as necessary.