support artifact discovery for oras cli

Signed-off-by: Shiwei Zhang <shizh@microsoft.com>

cmd/oras/discover.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	ctxo "github.com/deislabs/oras/pkg/context"
+	"github.com/deislabs/oras/pkg/oras"
+
+	"github.com/containerd/containerd/reference"
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+)
+
+type discoverOptions struct {
+	targetRef    string
+	artifactType string
+	verbose      bool
+
+	debug     bool
+	configs   []string
+	username  string
+	password  string
+	insecure  bool
+	plainHTTP bool
+}
+
+func discoverCmd() *cobra.Command {
+	var opts discoverOptions
+	cmd := &cobra.Command{
+		Use:   "discover [options] <name:tag|name@digest>",
+		Short: "discover artifacts from remote registry",
+		Long: `discover artifacts from remote registry
+
+Example - Discover artifacts of type "" linked with the specified reference:
+  oras discover --artifact-type application/vnd.cncf.notary.v2 localhost:5000/hello:latest
+`,
+		Args: cobra.ExactArgs(1),
+		PreRunE: func(cmd *cobra.Command, args []string) error {
+			if opts.artifactType == "" {
+				return errors.New("artifact type not specified")
+			}
+			return nil
+		},
+		RunE: func(cmd *cobra.Command, args []string) error {
+			opts.targetRef = args[0]
+			return runDiscover(opts)
+		},
+	}
+
+	cmd.Flags().StringVarP(&opts.artifactType, "artifact-type", "", "", "artifact type")
+	cmd.Flags().BoolVarP(&opts.verbose, "verbose", "v", false, "verbose output")
+
+	cmd.Flags().BoolVarP(&opts.debug, "debug", "d", false, "debug mode")
+	cmd.Flags().StringArrayVarP(&opts.configs, "config", "c", nil, "auth config path")
+	cmd.Flags().StringVarP(&opts.username, "username", "u", "", "registry username")
+	cmd.Flags().StringVarP(&opts.password, "password", "p", "", "registry password")
+	cmd.Flags().BoolVarP(&opts.insecure, "insecure", "", false, "allow connections to SSL registry without certs")
+	cmd.Flags().BoolVarP(&opts.plainHTTP, "plain-http", "", false, "use plain http and not https")
+	return cmd
+}
+
+func runDiscover(opts discoverOptions) error {
+	ctx := context.Background()
+	if opts.debug {
+		logrus.SetLevel(logrus.DebugLevel)
+	} else if !opts.verbose {
+		ctx = ctxo.WithLoggerDiscarded(ctx)
+	}
+
+	resolver := newResolver(opts.username, opts.password, opts.insecure, opts.plainHTTP, opts.configs...)
+
+	desc, artifacts, err := oras.Discover(ctx, resolver, opts.targetRef, opts.artifactType)
+	if err != nil {
+		if err == reference.ErrObjectRequired {
+			return fmt.Errorf("image reference format is invalid. Please specify <name:tag|name@digest>")
+		}
+		return err
+	}
+
+	fmt.Println("Discovered", len(artifacts), "artifacts referencing", opts.targetRef)
+	fmt.Println("Digest:", desc.Digest)
+	for _, artifact := range artifacts {
+		fmt.Println("Reference:", artifact.ArtifactType)
+		for _, blob := range artifact.Blobs {
+			fmt.Println("-", blob.Digest)
+		}
+	}
+
+	return nil
+}

cmd/oras/main.go

@@ -11,7 +11,14 @@ func main() {
 		Use:          "oras [command]",
 		SilenceUsage: true,
 	}
-	cmd.AddCommand(pullCmd(), pushCmd(), loginCmd(), logoutCmd(), versionCmd())
+	cmd.AddCommand(
+		pullCmd(),
+		pushCmd(),
+		discoverCmd(),
+		loginCmd(),
+		logoutCmd(),
+		versionCmd(),
+	)
 	if err := cmd.Execute(); err != nil {
 		os.Exit(1)
 	}

pkg/oras/discover.go

@@ -1,29 +1,29 @@
-package oras
-
-import (
-	"context"
-
-	"github.com/containerd/containerd/remotes"
-	artifactspec "github.com/notaryproject/artifacts/specs-go/v2"
-	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
-)
-
-// Discover discovers artifacts referencing the specified artifact
-func Discover(ctx context.Context, resolver remotes.Resolver, ref, artifactType string) (ocispec.Descriptor, []artifactspec.Artifact, error) {
-	_, desc, err := resolver.Resolve(ctx, ref)
-	if err != nil {
-		return ocispec.Descriptor{}, nil, err
-	}
-
-	discoverer, err := resolver.Discoverer(ctx, ref)
-	if err != nil {
-		return ocispec.Descriptor{}, nil, err
-	}
-
-	artifacts, err := discoverer.Discover(ctx, desc, artifactType)
-	if err != nil {
-		return ocispec.Descriptor{}, nil, err
-	}
-
-	return desc, artifacts, err
-}
+package oras
+
+import (
+	"context"
+
+	"github.com/containerd/containerd/remotes"
+	artifactspec "github.com/notaryproject/artifacts/specs-go/v2"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// Discover discovers artifacts referencing the specified artifact
+func Discover(ctx context.Context, resolver remotes.Resolver, ref, artifactType string) (ocispec.Descriptor, []artifactspec.Artifact, error) {
+	_, desc, err := resolver.Resolve(ctx, ref)
+	if err != nil {
+		return ocispec.Descriptor{}, nil, err
+	}
+
+	discoverer, err := resolver.Discoverer(ctx, ref)
+	if err != nil {
+		return ocispec.Descriptor{}, nil, err
+	}
+
+	artifacts, err := discoverer.Discover(ctx, desc, artifactType)
+	if err != nil {
+		return ocispec.Descriptor{}, nil, err
+	}
+
+	return desc, artifacts, err
+}