Add OCI distribution-spec registry proxying support

This commit implements support for the OCI distribution-spec registry
proxying feature as defined in: https://github.com/opencontainers/distribution-spec/blob/main/spec.md#registry-proxying
When a registry acts as a proxy for multiple upstream registries, it needs
to know which upstream registry to route requests to. The distribution-spec
defines the "ns" query parameter for this purpose. For example, a request
to a proxy for docker.io images would include "?ns=docker.io".

Signed-off-by: Sohan Kunkerkar <sohank2602@gmail.com>

Author: sohankunkerkar

image/docker/docker_client.go

@@ -120,6 +120,9 @@ type dockerClient struct {
 	signatureBase          lookasideStorageBase
 	useSigstoreAttachments bool
 	scope                  authScope
+	// namespaceProxy enables OCI distribution-spec registry proxying.
+	// When set, an "ns" query parameter is appended to all requests.
+	namespaceProxy string
 
 	// The following members are detected registry properties:
 	// They are set after a successful detectProperties(), and never change afterwards.
@@ -491,6 +494,11 @@ func (c *dockerClient) resolveRequestURL(path string) (*url.URL, error) {
 	if err != nil {
 		return nil, err
 	}
+	if c.namespaceProxy != "" {
+		q := res.Query()
+		q.Set("ns", c.namespaceProxy)
+		res.RawQuery = q.Encode()
+	}
 	return res, nil
 }
 

image/docker/docker_client_test.go

@@ -445,3 +445,58 @@ func TestIsManifestUnknownError(t *testing.T) {
 		assert.True(t, res, "%s: %#v", c.name, err)
 	}
 }
+
+func TestResolveRequestURLWithNamespaceProxy(t *testing.T) {
+	for _, c := range []struct {
+		name           string
+		registry       string
+		scheme         string
+		path           string
+		namespaceProxy string
+		expected       string
+	}{
+		{
+			name:           "no namespace proxy",
+			registry:       "registry.example.com",
+			scheme:         "https",
+			path:           "/v2/library/nginx/manifests/latest",
+			namespaceProxy: "",
+			expected:       "https://registry.example.com/v2/library/nginx/manifests/latest",
+		},
+		{
+			name:           "with namespace proxy for docker.io",
+			registry:       "proxy.example.com",
+			scheme:         "https",
+			path:           "/v2/library/nginx/manifests/latest",
+			namespaceProxy: "docker.io",
+			expected:       "https://proxy.example.com/v2/library/nginx/manifests/latest?ns=docker.io",
+		},
+		{
+			name:           "with namespace proxy for quay.io",
+			registry:       "proxy.example.com",
+			scheme:         "https",
+			path:           "/v2/coreos/etcd/blobs/sha256:abc123",
+			namespaceProxy: "quay.io",
+			expected:       "https://proxy.example.com/v2/coreos/etcd/blobs/sha256:abc123?ns=quay.io",
+		},
+		{
+			name:           "with namespace proxy and port",
+			registry:       "proxy.example.com:5000",
+			scheme:         "http",
+			path:           "/v2/myimage/manifests/v1.0",
+			namespaceProxy: "gcr.io",
+			expected:       "http://proxy.example.com:5000/v2/myimage/manifests/v1.0?ns=gcr.io",
+		},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			client := &dockerClient{
+				registry:       c.registry,
+				scheme:         c.scheme,
+				namespaceProxy: c.namespaceProxy,
+			}
+			result, err := client.resolveRequestURL(c.path)
+			require.NoError(t, err)
+			assert.Equal(t, c.expected, result.String())
+		})
+	}
+}

image/docker/docker_image_src.go

@@ -150,6 +150,7 @@ func newImageSourceAttempt(ctx context.Context, sys *types.SystemContext, logica
 		return nil, err
 	}
 	client.tlsClientConfig.InsecureSkipVerify = pullSource.Endpoint.Insecure
+	client.namespaceProxy = pullSource.Endpoint.NamespaceProxy
 
 	s := &dockerImageSource{
 		PropertyMethodsInitialize: impl.PropertyMethods(impl.Properties{

image/pkg/sysregistriesv2/system_registries_v2.go

@@ -71,6 +71,11 @@ type Endpoint struct {
 	// This can only be set in a registry's Mirror field, not in the registry's primary Endpoint.
 	// This per-mirror setting is allowed only when mirror-by-digest-only is not configured for the primary registry.
 	PullFromMirror string `toml:"pull-from-mirror,omitempty"`
+	// NamespaceProxy enables OCI distribution-spec registry proxying.
+	// When set, an "ns" query parameter with this value is appended to all requests,
+	// allowing a single proxy to route to multiple upstream registries.
+	// See https://github.com/opencontainers/distribution-spec/blob/main/spec.md#registry-proxying
+	NamespaceProxy string `toml:"namespace-proxy,omitempty"`
 }
 
 // userRegistriesFile is the path to the per user registry configuration file.