resolved the comments

Signed-off-by: Xiaoxuan Wang <wangxiaoxuan119@gmail.com>

example_copy_test.go

@@ -0,0 +1,356 @@
+/*
+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 oras_test
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/opencontainers/go-digest"
+	specs "github.com/opencontainers/image-spec/specs-go"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"oras.land/oras-go/v2"
+	"oras.land/oras-go/v2/content/memory"
+	"oras.land/oras-go/v2/content/oci"
+	"oras.land/oras-go/v2/internal/spec"
+	"oras.land/oras-go/v2/registry/remote"
+)
+
+var exampleMemoryStore oras.Target
+var remoteHost string
+var (
+	exampleManifest, _ = json.Marshal(spec.Artifact{
+		MediaType:    spec.MediaTypeArtifactManifest,
+		ArtifactType: "example/content"})
+	exampleManifestDescriptor = ocispec.Descriptor{
+		MediaType: spec.MediaTypeArtifactManifest,
+		Digest:    digest.Digest(digest.FromBytes(exampleManifest)),
+		Size:      int64(len(exampleManifest))}
+	exampleSignatureManifest, _ = json.Marshal(spec.Artifact{
+		MediaType:    spec.MediaTypeArtifactManifest,
+		ArtifactType: "example/signature",
+		Subject:      &exampleManifestDescriptor})
+	exampleSignatureManifestDescriptor = ocispec.Descriptor{
+		MediaType: spec.MediaTypeArtifactManifest,
+		Digest:    digest.FromBytes(exampleSignatureManifest),
+		Size:      int64(len(exampleSignatureManifest))}
+)
+
+func pushBlob(ctx context.Context, mediaType string, blob []byte, target oras.Target) (desc ocispec.Descriptor, err error) {
+	desc = ocispec.Descriptor{ // Generate descriptor based on the media type and blob content
+		MediaType: mediaType,
+		Digest:    digest.FromBytes(blob), // Calculate digest
+		Size:      int64(len(blob)),       // Include blob size
+	}
+	return desc, target.Push(ctx, desc, bytes.NewReader(blob)) // Push the blob to the registry target
+}
+
+func generateManifestContent(config ocispec.Descriptor, layers ...ocispec.Descriptor) ([]byte, error) {
+	content := ocispec.Manifest{
+		Config:    config, // Set config blob
+		Layers:    layers, // Set layer blobs
+		Versioned: specs.Versioned{SchemaVersion: 2},
+	}
+	return json.Marshal(content) // Get json content
+}
+
+func TestMain(m *testing.M) {
+	const exampleTag = "latest"
+	const exampleUploadUUid = "0bc84d80-837c-41d9-824e-1907463c53b3"
+
+	// Setup example local target
+	exampleMemoryStore = memory.New()
+	layerBlob := []byte("Hello layer")
+	ctx := context.Background()
+	layerDesc, err := pushBlob(ctx, ocispec.MediaTypeImageLayer, layerBlob, exampleMemoryStore) // push layer blob
+	if err != nil {
+		panic(err)
+	}
+	configBlob := []byte("Hello config")
+	configDesc, err := pushBlob(ctx, ocispec.MediaTypeImageConfig, configBlob, exampleMemoryStore) // push config blob
+	if err != nil {
+		panic(err)
+	}
+	manifestBlob, err := generateManifestContent(configDesc, layerDesc) // generate a image manifest
+	if err != nil {
+		panic(err)
+	}
+	manifestDesc, err := pushBlob(ctx, ocispec.MediaTypeImageManifest, manifestBlob, exampleMemoryStore) // push manifest blob
+	if err != nil {
+		panic(err)
+	}
+	err = exampleMemoryStore.Tag(ctx, manifestDesc, exampleTag)
+	if err != nil {
+		panic(err)
+	}
+
+	// Setup example remote target
+	httpsServer := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		p := r.URL.Path
+		m := r.Method
+		switch {
+		case strings.Contains(p, "/blobs/uploads/") && m == "POST":
+			w.Header().Set("Content-Type", ocispec.MediaTypeImageManifest)
+			w.Header().Set("Location", p+exampleUploadUUid)
+			w.WriteHeader(http.StatusAccepted)
+		case strings.Contains(p, "/blobs/uploads/"+exampleUploadUUid) && m == "GET":
+			w.WriteHeader(http.StatusCreated)
+		case strings.Contains(p, "/manifests/"+string(exampleSignatureManifestDescriptor.Digest)):
+			w.Header().Set("Content-Type", spec.MediaTypeArtifactManifest)
+			w.Header().Set("Docker-Content-Digest", string(exampleSignatureManifestDescriptor.Digest))
+			w.Header().Set("Content-Length", strconv.Itoa(len(exampleSignatureManifest)))
+			w.Write(exampleSignatureManifest)
+		case strings.Contains(p, "/manifests/latest") && m == "PUT":
+			w.WriteHeader(http.StatusCreated)
+		case strings.Contains(p, "/manifests/"+string(exampleManifestDescriptor.Digest)),
+			strings.Contains(p, "/manifests/latest") && m == "HEAD":
+			w.Header().Set("Content-Type", spec.MediaTypeArtifactManifest)
+			w.Header().Set("Docker-Content-Digest", string(exampleManifestDescriptor.Digest))
+			w.Header().Set("Content-Length", strconv.Itoa(len(exampleManifest)))
+			if m == "GET" {
+				w.Write(exampleManifest)
+			}
+		case strings.Contains(p, "/v2/source/referrers/"):
+			var referrers []ocispec.Descriptor
+			if p == "/v2/source/referrers/"+exampleManifestDescriptor.Digest.String() {
+				referrers = []ocispec.Descriptor{exampleSignatureManifestDescriptor}
+			}
+			result := ocispec.Index{
+				Versioned: specs.Versioned{
+					SchemaVersion: 2, // historical value. does not pertain to OCI or docker version
+				},
+				MediaType: ocispec.MediaTypeImageIndex,
+				Manifests: referrers,
+			}
+			if err := json.NewEncoder(w).Encode(result); err != nil {
+				panic(err)
+			}
+		case strings.Contains(p, "/manifests/") && (m == "HEAD" || m == "GET"):
+			w.Header().Set("Content-Type", ocispec.MediaTypeImageManifest)
+			w.Header().Set("Docker-Content-Digest", string(manifestDesc.Digest))
+			w.Header().Set("Content-Length", strconv.Itoa(len([]byte(manifestBlob))))
+			w.Write([]byte(manifestBlob))
+		case strings.Contains(p, "/blobs/") && (m == "GET" || m == "HEAD"):
+			arr := strings.Split(p, "/")
+			digest := arr[len(arr)-1]
+			var desc ocispec.Descriptor
+			var content []byte
+			switch digest {
+			case layerDesc.Digest.String():
+				desc = layerDesc
+				content = layerBlob
+			case configDesc.Digest.String():
+				desc = configDesc
+				content = configBlob
+			case manifestDesc.Digest.String():
+				desc = manifestDesc
+				content = manifestBlob
+			}
+			w.Header().Set("Content-Type", desc.MediaType)
+			w.Header().Set("Docker-Content-Digest", digest)
+			w.Header().Set("Content-Length", strconv.Itoa(len([]byte(content))))
+			w.Write([]byte(content))
+		case strings.Contains(p, "/manifests/") && m == "PUT":
+			w.WriteHeader(http.StatusCreated)
+		}
+
+	}))
+	defer httpsServer.Close()
+	u, err := url.Parse(httpsServer.URL)
+	if err != nil {
+		panic(err)
+	}
+	remoteHost = u.Host
+	http.DefaultTransport = httpsServer.Client().Transport
+
+	os.Exit(m.Run())
+}
+
+func ExampleCopy_remoteToRemote() {
+	reg, err := remote.NewRegistry(remoteHost)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	ctx := context.Background()
+	src, err := reg.Repository(ctx, "source")
+	if err != nil {
+		panic(err) // Handle error
+	}
+	dst, err := reg.Repository(ctx, "target")
+	if err != nil {
+		panic(err) // Handle error
+	}
+
+	tagName := "latest"
+	desc, err := oras.Copy(ctx, src, tagName, dst, tagName, oras.DefaultCopyOptions)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	fmt.Println(desc.Digest)
+
+	// Output:
+	// sha256:7cbb44b44e8ede5a89cf193db3f5f2fd019d89697e6b87e8ed2589e60649b0d1
+}
+
+func ExampleCopy_remoteToLocal() {
+	reg, err := remote.NewRegistry(remoteHost)
+	if err != nil {
+		panic(err) // Handle error
+	}
+
+	ctx := context.Background()
+	src, err := reg.Repository(ctx, "source")
+	if err != nil {
+		panic(err) // Handle error
+	}
+	dst := memory.New()
+
+	tagName := "latest"
+	desc, err := oras.Copy(ctx, src, tagName, dst, tagName, oras.DefaultCopyOptions)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	fmt.Println(desc.Digest)
+
+	// Output:
+	// sha256:7cbb44b44e8ede5a89cf193db3f5f2fd019d89697e6b87e8ed2589e60649b0d1
+}
+
+func ExampleCopy_localToLocal() {
+	src := exampleMemoryStore
+	dst := memory.New()
+
+	tagName := "latest"
+	ctx := context.Background()
+	desc, err := oras.Copy(ctx, src, tagName, dst, tagName, oras.DefaultCopyOptions)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	fmt.Println(desc.Digest)
+
+	// Output:
+	// sha256:7cbb44b44e8ede5a89cf193db3f5f2fd019d89697e6b87e8ed2589e60649b0d1
+}
+
+func ExampleCopy_localToOciFile() {
+	src := exampleMemoryStore
+	tempDir, err := os.MkdirTemp("", "oras_oci_example_*")
+	if err != nil {
+		panic(err) // Handle error
+	}
+	defer os.RemoveAll(tempDir)
+	dst, err := oci.New(tempDir)
+	if err != nil {
+		panic(err) // Handle error
+	}
+
+	tagName := "latest"
+	ctx := context.Background()
+	desc, err := oras.Copy(ctx, src, tagName, dst, tagName, oras.DefaultCopyOptions)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	fmt.Println(desc.Digest)
+
+	// Output:
+	// sha256:7cbb44b44e8ede5a89cf193db3f5f2fd019d89697e6b87e8ed2589e60649b0d1
+}
+
+func ExampleCopy_localToRemote() {
+	src := exampleMemoryStore
+	reg, err := remote.NewRegistry(remoteHost)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	ctx := context.Background()
+	dst, err := reg.Repository(ctx, "target")
+	if err != nil {
+		panic(err) // Handle error
+	}
+
+	tagName := "latest"
+	desc, err := oras.Copy(ctx, src, tagName, dst, tagName, oras.DefaultCopyOptions)
+	if err != nil {
+		panic(err) // Handle error
+	}
+	fmt.Println(desc.Digest)
+
+	// Output:
+	// sha256:7cbb44b44e8ede5a89cf193db3f5f2fd019d89697e6b87e8ed2589e60649b0d1
+}
+
+// Example_copyArtifactManifestRemoteToLocal gives an example of copying
+// an artifact manifest from a remote repository to local.
+func Example_copyArtifactManifestRemoteToLocal() {
+	src, err := remote.NewRepository(fmt.Sprintf("%s/source", remoteHost))
+	if err != nil {
+		panic(err)
+	}
+	dst := memory.New()
+	ctx := context.Background()
+
+	exampleDigest := "sha256:70c29a81e235dda5c2cebb8ec06eafd3cca346cbd91f15ac74cefd98681c5b3d"
+	descriptor, err := src.Resolve(ctx, exampleDigest)
+	if err != nil {
+		panic(err)
+	}
+	err = oras.CopyGraph(ctx, src, dst, descriptor, oras.DefaultCopyGraphOptions)
+	if err != nil {
+		panic(err)
+	}
+
+	// verify that the artifact manifest described by the descriptor exists in dst
+	contentExists, err := dst.Exists(ctx, descriptor)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Println(contentExists)
+
+	// Output:
+	// true
+}
+
+// Example_extendedCopyArtifactAndReferrersRemoteToLocal gives an example of
+// copying an artifact along with its referrers from a remote repository to local.
+func Example_extendedCopyArtifactAndReferrersRemoteToLocal() {
+	src, err := remote.NewRepository(fmt.Sprintf("%s/source", remoteHost))
+	if err != nil {
+		panic(err)
+	}
+	dst := memory.New()
+	ctx := context.Background()
+
+	tagName := "latest"
+	// ExtendedCopy will copy the artifact tagged by "latest" along with all of its
+	// referrers from src to dst.
+	desc, err := oras.ExtendedCopy(ctx, src, tagName, dst, tagName, oras.DefaultExtendedCopyOptions)
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println(desc.Digest)
+	// Output:
+	// sha256:f396bc4d300934a39ca28ab0d5ac8a3573336d7d63c654d783a68cd1e2057662
+}