feat: support --format in oras discover

cmd/oras/internal/display/handler.go

@@ -19,12 +19,16 @@ import (
 	"io"
 	"os"
 
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+
 	"oras.land/oras/cmd/oras/internal/display/content"
 	"oras.land/oras/cmd/oras/internal/display/metadata"
 	"oras.land/oras/cmd/oras/internal/display/metadata/descriptor"
 	"oras.land/oras/cmd/oras/internal/display/metadata/json"
+	"oras.land/oras/cmd/oras/internal/display/metadata/table"
 	"oras.land/oras/cmd/oras/internal/display/metadata/template"
 	"oras.land/oras/cmd/oras/internal/display/metadata/text"
+	"oras.land/oras/cmd/oras/internal/display/metadata/tree"
 	"oras.land/oras/cmd/oras/internal/display/status"
 )
 
@@ -97,6 +101,20 @@ func NewPullHandler(format string, path string, tty *os.File, out io.Writer, ver
 	return statusHandler, metadataHandler
 }
 
+// NewDiscoverHandler returns status and metadata handlers for discover command.
+func NewDiscoverHandler(out io.Writer, outputType string, path string, rawReference string, desc ocispec.Descriptor, verbose bool) metadata.DiscoverHandler {
+	switch outputType {
+	case "tree", "":
+		return tree.NewDiscoverHandler(out, path, desc, verbose)
+	case "table":
+		return table.NewDiscoverHandler(out, rawReference, desc, verbose)
+	case "json":
+		return json.NewDiscoverHandler(out, desc, path)
+	default:
+		return template.NewDiscoverHandler(out, desc, path, outputType)
+	}
+}
+
 // NewManifestFetchHandler returns a manifest fetch handler.
 func NewManifestFetchHandler(out io.Writer, format string, outputDescriptor, pretty bool, outputPath string) (metadata.ManifestFetchHandler, content.ManifestFetchHandler) {
 	var metadataHandler metadata.ManifestFetchHandler

cmd/oras/internal/display/metadata/interface.go

@@ -31,6 +31,17 @@ type AttachHandler interface {
 	OnCompleted(opts *option.Target, root, subject ocispec.Descriptor) error
 }
 
+// DiscoverHandler handles metadata output for discover events.
+type DiscoverHandler interface {
+	// MultiLevelSupported returns true if the handler supports multi-level
+	// discovery.
+	MultiLevelSupported() bool
+	// OnDiscovered is called after a referrer is discovered.
+	OnDiscovered(referrer, subject ocispec.Descriptor) error
+	// OnCompleted is called when referrer discovery is completed.
+	OnCompleted() error
+}
+
 // ManifestFetchHandler handles metadata output for manifest fetch events.
 type ManifestFetchHandler interface {
 	// OnFetched is called after the manifest content is fetched.

cmd/oras/internal/display/metadata/json/attach.go

@@ -21,6 +21,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"oras.land/oras/cmd/oras/internal/display/metadata"
 	"oras.land/oras/cmd/oras/internal/display/metadata/model"
+	"oras.land/oras/cmd/oras/internal/display/utils"
 	"oras.land/oras/cmd/oras/internal/option"
 )
 
@@ -38,5 +39,5 @@ func NewAttachHandler(out io.Writer) metadata.AttachHandler {
 
 // OnCompleted is called when the attach command is completed.
 func (ah *AttachHandler) OnCompleted(opts *option.Target, root, subject ocispec.Descriptor) error {
-	return printJSON(ah.out, model.NewPush(root, opts.Path))
+	return utils.PrintPrettyJSON(ah.out, model.NewPush(root, opts.Path))
 }

cmd/oras/internal/display/metadata/json/discover.go

@@ -0,0 +1,63 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package json
+
+import (
+	"fmt"
+	"io"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"oras.land/oras-go/v2/content"
+	"oras.land/oras/cmd/oras/internal/display/metadata"
+	"oras.land/oras/cmd/oras/internal/display/metadata/model"
+	"oras.land/oras/cmd/oras/internal/display/utils"
+)
+
+// discoverHandler handles json metadata output for discover events.
+type discoverHandler struct {
+	out       io.Writer
+	root      ocispec.Descriptor
+	path      string
+	referrers []ocispec.Descriptor
+}
+
+// NewDiscoverHandler creates a new handler for discover events.
+func NewDiscoverHandler(out io.Writer, root ocispec.Descriptor, path string) metadata.DiscoverHandler {
+	return &discoverHandler{
+		out:  out,
+		root: root,
+		path: path,
+	}
+}
+
+// MultiLevelSupported implements metadata.DiscoverHandler.
+func (h *discoverHandler) MultiLevelSupported() bool {
+	return false
+}
+
+// OnDiscovered implements metadata.DiscoverHandler.
+func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) error {
+	if !content.Equal(subject, h.root) {
+		return fmt.Errorf("unexpected subject descriptor: %v", subject)
+	}
+	h.referrers = append(h.referrers, referrer)
+	return nil
+}
+
+// OnCompleted implements metadata.DiscoverHandler.
+func (h *discoverHandler) OnCompleted() error {
+	return utils.PrintPrettyJSON(h.out, model.NewDiscover(h.path, h.referrers))
+}

cmd/oras/internal/display/metadata/json/manifest_fetch.go

@@ -22,6 +22,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"oras.land/oras/cmd/oras/internal/display/metadata"
 	"oras.land/oras/cmd/oras/internal/display/metadata/model"
+	"oras.land/oras/cmd/oras/internal/display/utils"
 )
 
 // manifestFetchHandler handles JSON metadata output for manifest fetch events.
@@ -42,5 +43,5 @@ func (h *manifestFetchHandler) OnFetched(path string, desc ocispec.Descriptor, c
 	if err := json.Unmarshal(content, &manifest); err != nil {
 		manifest = nil
 	}
-	return printJSON(h.out, model.NewFetched(path, desc, manifest))
+	return utils.PrintPrettyJSON(h.out, model.NewFetched(path, desc, manifest))
 }

cmd/oras/internal/display/metadata/json/pull.go

@@ -21,6 +21,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"oras.land/oras/cmd/oras/internal/display/metadata"
 	"oras.land/oras/cmd/oras/internal/display/metadata/model"
+	"oras.land/oras/cmd/oras/internal/display/utils"
 	"oras.land/oras/cmd/oras/internal/option"
 )
 
@@ -51,5 +52,5 @@ func (ph *PullHandler) OnFilePulled(name string, outputDir string, desc ocispec.
 
 // OnCompleted implements metadata.PullHandler.
 func (ph *PullHandler) OnCompleted(opts *option.Target, desc ocispec.Descriptor) error {
-	return printJSON(ph.out, model.NewPull(ph.path+"@"+desc.Digest.String(), ph.pulled.Files()))
+	return utils.PrintPrettyJSON(ph.out, model.NewPull(ph.path+"@"+desc.Digest.String(), ph.pulled.Files()))
 }

cmd/oras/internal/display/metadata/json/push.go

@@ -21,6 +21,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"oras.land/oras/cmd/oras/internal/display/metadata"
 	"oras.land/oras/cmd/oras/internal/display/metadata/model"
+	"oras.land/oras/cmd/oras/internal/display/utils"
 	"oras.land/oras/cmd/oras/internal/option"
 )
 
@@ -45,5 +46,5 @@ func (ph *PushHandler) OnCopied(opts *option.Target) error {
 
 // OnCompleted is called after the push is completed.
 func (ph *PushHandler) OnCompleted(root ocispec.Descriptor) error {
-	return printJSON(ph.out, model.NewPush(root, ph.path))
+	return utils.PrintPrettyJSON(ph.out, model.NewPush(root, ph.path))
 }

cmd/oras/internal/display/metadata/json/json.go → cmd/oras/internal/display/metadata/model/discover.go

@@ -13,15 +13,21 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package json
+package model
 
-import (
-	"encoding/json"
-	"io"
-)
+import ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 
-func printJSON(out io.Writer, object any) error {
-	encoder := json.NewEncoder(out)
-	encoder.SetIndent("", "  ")
-	return encoder.Encode(object)
+type discover struct {
+	Manifests []Descriptor
+}
+
+// NewDiscover creates a new discover model.
+func NewDiscover(name string, descs []ocispec.Descriptor) discover {
+	discover := discover{
+		Manifests: make([]Descriptor, 0, len(descs)),
+	}
+	for _, desc := range descs {
+		discover.Manifests = append(discover.Manifests, FromDescriptor(name, desc))
+	}
+	return discover
 }

cmd/oras/internal/display/metadata/table/discover.go

@@ -0,0 +1,100 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package table
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"oras.land/oras-go/v2/content"
+	"oras.land/oras/cmd/oras/internal/display/metadata"
+	"oras.land/oras/cmd/oras/internal/display/utils"
+)
+
+// discoverHandler handles json metadata output for discover events.
+type discoverHandler struct {
+	out          io.Writer
+	rawReference string
+	root         ocispec.Descriptor
+	verbose      bool
+	referrers    []ocispec.Descriptor
+}
+
+// NewDiscoverHandler creates a new handler for discover events.
+func NewDiscoverHandler(out io.Writer, rawReference string, root ocispec.Descriptor, verbose bool) metadata.DiscoverHandler {
+	return &discoverHandler{
+		out:          out,
+		rawReference: rawReference,
+		root:         root,
+		verbose:      verbose,
+	}
+}
+
+// MultiLevelSupported implements metadata.DiscoverHandler.
+func (h *discoverHandler) MultiLevelSupported() bool {
+	return false
+}
+
+// OnDiscovered implements metadata.DiscoverHandler.
+func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) error {
+	if !content.Equal(subject, h.root) {
+		return fmt.Errorf("unexpected subject descriptor: %v", subject)
+	}
+	h.referrers = append(h.referrers, referrer)
+	return nil
+}
+
+// OnCompleted implements metadata.DiscoverHandler.
+func (h *discoverHandler) OnCompleted() error {
+	if n := len(h.referrers); n > 1 {
+		fmt.Fprintln(h.out, "Discovered", n, "artifacts referencing", h.rawReference)
+	} else {
+		fmt.Fprintln(h.out, "Discovered", n, "artifact referencing", h.rawReference)
+	}
+	fmt.Fprintln(h.out, "Digest:", h.root.Digest)
+	if len(h.referrers) == 0 {
+		return nil
+	}
+	fmt.Fprintln(h.out)
+	return h.printDiscoveredReferrersTable()
+}
+
+func (h *discoverHandler) printDiscoveredReferrersTable() error {
+	typeNameTitle := "Artifact Type"
+	typeNameLength := len(typeNameTitle)
+	for _, ref := range h.referrers {
+		if length := len(ref.ArtifactType); length > typeNameLength {
+			typeNameLength = length
+		}
+	}
+
+	print := func(key string, value interface{}) {
+		fmt.Fprintln(h.out, key, strings.Repeat(" ", typeNameLength-len(key)+1), value)
+	}
+
+	print(typeNameTitle, "Digest")
+	for _, ref := range h.referrers {
+		print(ref.ArtifactType, ref.Digest)
+		if h.verbose {
+			if err := utils.PrintPrettyJSON(h.out, ref); err != nil {
+				return fmt.Errorf("error printing JSON: %w", err)
+			}
+		}
+	}
+	return nil
+}

cmd/oras/internal/display/metadata/template/discover.go

@@ -0,0 +1,64 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package template
+
+import (
+	"fmt"
+	"io"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"oras.land/oras-go/v2/content"
+	"oras.land/oras/cmd/oras/internal/display/metadata"
+	"oras.land/oras/cmd/oras/internal/display/metadata/model"
+)
+
+// discoverHandler handles json metadata output for discover events.
+type discoverHandler struct {
+	referrers []ocispec.Descriptor
+	template  string
+	path      string
+	root      ocispec.Descriptor
+	out       io.Writer
+}
+
+// NewDiscoverHandler creates a new handler for discover events.
+func NewDiscoverHandler(out io.Writer, root ocispec.Descriptor, path string, template string) metadata.DiscoverHandler {
+	return &discoverHandler{
+		out:      out,
+		root:     root,
+		path:     path,
+		template: template,
+	}
+}
+
+// MultiLevelSupported implements metadata.DiscoverHandler.
+func (h *discoverHandler) MultiLevelSupported() bool {
+	return false
+}
+
+// OnDiscovered implements metadata.DiscoverHandler.
+func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) error {
+	if !content.Equal(subject, h.root) {
+		return fmt.Errorf("unexpected subject descriptor: %v", subject)
+	}
+	h.referrers = append(h.referrers, referrer)
+	return nil
+}
+
+// OnCompleted implements metadata.DiscoverHandler.
+func (h *discoverHandler) OnCompleted() error {
+	return parseAndWrite(h.out, model.NewDiscover(h.path, h.referrers), h.template)
+}