feat: support JSON output for attach and push

Signed-off-by: Billy Zha <[email protected]>

cmd/oras/internal/option/format.go

@@ -0,0 +1,53 @@
+/*
+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 option
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/spf13/pflag"
+	"oras.land/oras/cmd/oras/internal/output/format"
+)
+
+// Format option struct.
+type Format struct {
+	format.Flag
+}
+
+func (opts *Format) ApplyFlags(fs *pflag.FlagSet) {
+	fs.Var(&opts.Flag, "format-stdout", fmt.Sprintf("[Preview] summary output to stdout in the specified format (default %q)", format.Plain))
+}
+
+// Print prints the Output as JSON.
+func (opts *Format) Print(data interface{}, prettify bool) error {
+	var err error
+	switch opts.Flag {
+	case format.Json:
+		var content []byte
+		if prettify {
+			content, err = json.MarshalIndent(data, "", "  ")
+		} else {
+			content, err = json.Marshal(data)
+		}
+		if err != nil {
+			return err
+		}
+		_, err = fmt.Println(string(content))
+		return err
+
+	}
+	return nil
+}

cmd/oras/internal/output/display/print.go

@@ -19,6 +19,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"sync"
 
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -33,10 +34,31 @@ var printLock sync.Mutex
 type PrintFunc func(ocispec.Descriptor) error
 
 // Print objects to display concurrent-safely.
-func Print(a ...any) error {
+var Print func(a ...any) error
+
+func init() {
+	Print = printStdout
+}
+
+// SwitchToStderr switches Print to stderr.
+func SwitchToStderr() {
+	Print = printStderr
+}
+
+// printStdout displays objects concurrent-safely.
+func printStdout(a ...any) error {
+	return printTo(os.Stderr, a...)
+}
+
+// printStderr displays objects concurrent-safely.
+func printStderr(a ...any) error {
+	return printTo(os.Stderr, a...)
+}
+
+func printTo(w io.Writer, a ...any) error {
 	printLock.Lock()
 	defer printLock.Unlock()
-	_, err := fmt.Println(a...)
+	_, err := fmt.Fprintln(w, a...)
 	return err
 }
 

cmd/oras/internal/output/format/format.go

@@ -0,0 +1,58 @@
+/*
+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 format
+
+import (
+	"errors"
+	"strings"
+)
+
+const (
+	Plain = "plain"
+	Json  = "json"
+)
+
+// Printer is the interface that wraps the basic String method.
+type Printer interface {
+	Print(prettify bool) error
+}
+
+// Define a custom value type that implements the pflag.Value interface.
+type Flag string
+
+// Set must have pointer receiver so it doesn't change the value of a copy.
+func (f *Flag) Set(v string) error {
+	switch v {
+	case "":
+		// default
+		*f = Plain
+	case Plain, Json:
+		*f = Json
+	default:
+		return errors.New("invalid format flag, expecting " + f.Type())
+	}
+	return nil
+}
+
+// String is used by pflag to print the default value of a flag.
+func (f *Flag) String() string {
+	return string(*f)
+}
+
+// Type provides optional value used in help text.
+func (c *Flag) Type() string {
+	return strings.Join([]string{Plain, Json}, "|")
+}

cmd/oras/internal/output/format/json.go

@@ -0,0 +1,47 @@
+/*
+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 format
+
+import (
+	"encoding/json"
+	"os"
+)
+
+// JSON is a Output that prints the data as JSON.
+type JSON struct {
+	Data interface{}
+}
+
+// NewJSON creates a new Output with the given data
+func NewJSON(data interface{}) *JSON {
+	return &JSON{Data: data}
+}
+
+// Print prints the Output as JSON.
+func Print(data interface{}, prettify bool) error {
+	var content []byte
+	var err error
+	if prettify {
+		content, err = json.MarshalIndent(data, "", "  ")
+	} else {
+		content, err = json.Marshal(data)
+	}
+	if err != nil {
+		return err
+	}
+	_, err = os.Stdout.Write(content)
+	return err
+}

cmd/oras/root/attach.go

@@ -28,6 +28,7 @@ import (
 	"oras.land/oras-go/v2/content/file"
 	"oras.land/oras-go/v2/registry/remote/auth"
 	"oras.land/oras/cmd/oras/internal/option"
+	"oras.land/oras/cmd/oras/internal/output/display"
 	"oras.land/oras/cmd/oras/internal/output/display/track"
 	"oras.land/oras/internal/graph"
 	"oras.land/oras/internal/registryutil"
@@ -37,6 +38,7 @@ type attachOptions struct {
 	option.Common
 	option.Packer
 	option.Target
+	option.Format
 
 	artifactType string
 	concurrency  int
@@ -83,6 +85,7 @@ Example - Attach file to the manifest tagged 'v1' in an OCI image layout folder
 			return nil
 		},
 		RunE: func(cmd *cobra.Command, args []string) error {
+			display.SwitchToStderr()
 			return runAttach(cmd.Context(), opts)
 		},
 	}
@@ -177,9 +180,13 @@ func runAttach(ctx context.Context, opts attachOptions) error {
 	if !strings.HasSuffix(opts.RawReference, digest) {
 		opts.RawReference = fmt.Sprintf("%s@%s", opts.Path, subject.Digest)
 	}
-	fmt.Println("Attached to", opts.AnnotatedReference())
-	fmt.Println("Digest:", root.Digest)
+	display.Print("Attached to", opts.AnnotatedReference())
+	display.Print("Digest:", root.Digest)
 
 	// Export manifest
-	return opts.ExportManifest(ctx, store, root)
+	if err = opts.ExportManifest(ctx, store, root); err != nil {
+		return err
+	}
+	// TODO: schema, PRD needed
+	return opts.Print(root, opts.TTY != nil)
 }

cmd/oras/root/file.go

@@ -23,6 +23,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"oras.land/oras-go/v2/content/file"
 	"oras.land/oras/cmd/oras/internal/fileref"
+	"oras.land/oras/cmd/oras/internal/output/display"
 )
 
 func loadFiles(ctx context.Context, store *file.Store, annotations map[string]map[string]string, fileRefs []string, verbose bool) ([]ocispec.Descriptor, error) {
@@ -58,7 +59,7 @@ func loadFiles(ctx context.Context, store *file.Store, annotations map[string]ma
 		files = append(files, file)
 	}
 	if len(files) == 0 {
-		fmt.Println("Uploading empty artifact")
+		display.Print("Uploading empty artifact")
 	}
 	return files, nil
 }

cmd/oras/root/push.go

@@ -18,7 +18,6 @@ package root
 import (
 	"context"
 	"errors"
-	"fmt"
 	"os"
 	"strings"
 	"sync"
@@ -43,6 +42,7 @@ type pushOptions struct {
 	option.Packer
 	option.ImageSpec
 	option.Target
+	option.Format
 
 	extraRefs         []string
 	manifestConfigRef string
@@ -122,6 +122,7 @@ Example - Push file "hi.txt" into an OCI image layout folder 'layout-dir' with t
 			return nil
 		},
 		RunE: func(cmd *cobra.Command, args []string) error {
+			display.SwitchToStderr()
 			return runPush(cmd.Context(), opts)
 		},
 	}
@@ -211,7 +212,7 @@ func runPush(ctx context.Context, opts pushOptions) error {
 	if err != nil {
 		return err
 	}
-	fmt.Println("Pushed", opts.AnnotatedReference())
+	display.Print("Pushed", opts.AnnotatedReference())
 
 	if len(opts.extraRefs) != 0 {
 		contentBytes, err := content.FetchAll(ctx, memoryStore, root)
@@ -225,10 +226,13 @@ func runPush(ctx context.Context, opts pushOptions) error {
 		}
 	}
 
-	fmt.Println("Digest:", root.Digest)
+	display.Print("Digest:", root.Digest)
 
 	// Export manifest
-	return opts.ExportManifest(ctx, memoryStore, root)
+	if err = opts.ExportManifest(ctx, memoryStore, root); err != nil {
+		return nil
+	}
+	return opts.Print(root, opts.TTY != nil)
 }
 
 func doPush(dst oras.Target, pack packFunc, copy copyFunc) (ocispec.Descriptor, error) {