feat(storage): return file metadata on read (#11212)

* storage: Return file Metadata on file read

* review comments

* review comments

* gofmt

* Access metadata through function, rather than field

Adding a map field to Attrs would have made the object uncomparable

* Store metadata as a pointer

to preserve API compatibility - keeps the Reader struct comparable

---------

Co-authored-by: Chris Cotter <cjcotter@google.com>

Author: jshore1296

storage/client_test.go

@@ -795,6 +795,67 @@ func TestOpenReaderEmulated(t *testing.T) {
 	})
 }
 
+func TestOpenReaderEmulated_Metadata(t *testing.T) {
+	transportClientTest(context.Background(), t, func(t *testing.T, ctx context.Context, project, bucket string, client storageClient) {
+		// Populate test data.
+		_, err := client.CreateBucket(ctx, project, bucket, &BucketAttrs{
+			Name: bucket,
+		}, nil)
+		if err != nil {
+			t.Fatalf("client.CreateBucket: %v", err)
+		}
+		prefix := time.Now().Nanosecond()
+		want := &ObjectAttrs{
+			Bucket: bucket,
+			Name:   fmt.Sprintf("%d-object-%d", prefix, time.Now().Nanosecond()),
+		}
+		w := veneerClient.Bucket(bucket).Object(want.Name).NewWriter(ctx)
+		if _, err := w.Write(randomBytesToWrite); err != nil {
+			t.Fatalf("failed to populate test data: %v", err)
+		}
+		if err := w.Close(); err != nil {
+			t.Fatalf("closing object: %v", err)
+		}
+		if _, err := veneerClient.Bucket(bucket).Object(want.Name).Update(ctx, ObjectAttrsToUpdate{
+			Metadata: map[string]string{
+				"Custom-Key":     "custom-value",
+				"Some-Other-Key": "some-other-value",
+			},
+		}); err != nil {
+			t.Fatalf("failed to update test object: %v", err)
+		}
+
+		params := &newRangeReaderParams{
+			bucket: bucket,
+			object: want.Name,
+			gen:    defaultGen,
+			offset: 0,
+			length: -1,
+		}
+		r, err := client.NewRangeReader(ctx, params)
+		if err != nil {
+			t.Fatalf("opening reading: %v", err)
+		}
+		wantLen := len(randomBytesToWrite)
+		got := make([]byte, wantLen)
+		n, err := r.Read(got)
+		if n != wantLen {
+			t.Fatalf("expected to read %d bytes, but got %d", wantLen, n)
+		}
+		if diff := cmp.Diff(got, randomBytesToWrite); diff != "" {
+			t.Fatalf("Read: got(-),want(+):\n%s", diff)
+		}
+		expectedMetadata := map[string]string{
+			"Custom-Key":     "custom-value",
+			"Some-Other-Key": "some-other-value",
+		}
+		if diff := cmp.Diff(r.Metadata(), expectedMetadata); diff != "" {
+			t.Fatalf("Object Metadata: got(-),want(+):\n%s", diff)
+		}
+
+	})
+}
+
 func TestOpenWriterEmulated(t *testing.T) {
 	transportClientTest(context.Background(), t, func(t *testing.T, ctx context.Context, project, bucket string, client storageClient) {
 		// Populate test data.

storage/grpc_client.go

@@ -1125,6 +1125,7 @@ func (c *grpcStorageClient) NewRangeReader(ctx context.Context, params *newRange
 		wantCRC = checksums.GetCrc32C()
 	}
 
+	metadata := obj.GetMetadata()
 	r = &Reader{
 		Attrs: ReaderObjectAttrs{
 			Size:            size,
@@ -1136,6 +1137,7 @@ func (c *grpcStorageClient) NewRangeReader(ctx context.Context, params *newRange
 			Generation:      obj.GetGeneration(),
 			CRC32C:          wantCRC,
 		},
+		objectMetadata: &metadata,
 		reader: &gRPCReader{
 			stream: res.stream,
 			reopen: reopen,

storage/http_client.go

@@ -1523,6 +1523,14 @@ func parseReadResponse(res *http.Response, params *newRangeReaderParams, reopen
 		}
 	}
 
+	metadata := map[string]string{}
+	for key, values := range res.Header {
+		if len(values) > 0 && strings.HasPrefix(key, "X-Goog-Meta-") {
+			key := key[len("X-Goog-Meta-"):]
+			metadata[key] = values[0]
+		}
+	}
+
 	attrs := ReaderObjectAttrs{
 		Size:            size,
 		ContentType:     res.Header.Get("Content-Type"),
@@ -1536,10 +1544,11 @@ func parseReadResponse(res *http.Response, params *newRangeReaderParams, reopen
 		Decompressed:    res.Uncompressed || uncompressedByServer(res),
 	}
 	return &Reader{
-		Attrs:    attrs,
-		size:     size,
-		remain:   remain,
-		checkCRC: checkCRC,
+		Attrs:          attrs,
+		objectMetadata: &metadata,
+		size:           size,
+		remain:         remain,
+		checkCRC:       checkCRC,
 		reader: &httpReader{
 			reopen:   reopen,
 			body:     body,

storage/integration_test.go

@@ -5044,8 +5044,48 @@ func TestIntegration_ReaderAttrs(t *testing.T) {
 			Metageneration:  attrs.Metageneration,
 			CRC32C:          crc32c(c),
 		}
-		if got != want {
-			t.Fatalf("got\t%v,\nwanted\t%v", got, want)
+		if diff := cmp.Diff(got, want); diff != "" {
+			t.Fatalf("diff got vs want: %v", diff)
+		}
+	})
+}
+
+func TestIntegration_ReaderAttrs_Metadata(t *testing.T) {
+	multiTransportTest(skipJSONReads(context.Background(), "metadata on read not supported on JSON api"), t, func(t *testing.T, ctx context.Context, bucket, _ string, client *Client) {
+		bkt := client.Bucket(bucket)
+
+		const defaultType = "text/plain"
+		o := bkt.Object("reader-attrs-metadata-obj")
+		c := randomContents()
+		if err := writeObject(ctx, o, defaultType, c); err != nil {
+			t.Errorf("Write for %v failed with %v", o.ObjectName(), err)
+		}
+		t.Cleanup(func() {
+			if err := o.Delete(ctx); err != nil {
+				log.Printf("failed to delete test object: %v", err)
+			}
+		})
+
+		oa, err := o.Update(ctx, ObjectAttrsToUpdate{Metadata: map[string]string{"Custom-Key": "custom-value", "Other-Key": "other-value"}})
+		if err != nil {
+			t.Fatal(err)
+		}
+		_ = oa
+
+		o = o.Generation(oa.Generation)
+		rc, err := o.NewReader(ctx)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		got := rc.Metadata()
+		want := map[string]string{
+			"Custom-Key": "custom-value",
+			"Other-Key":  "other-value",
+		}
+
+		if diff := cmp.Diff(got, want); diff != "" {
+			t.Fatalf("diff got vs want: %v", diff)
 		}
 	})
 }

storage/reader.go

@@ -222,7 +222,9 @@ var emptyBody = ioutil.NopCloser(strings.NewReader(""))
 // the stored CRC, returning an error from Read if there is a mismatch. This integrity check
 // is skipped if transcoding occurs. See https://cloud.google.com/storage/docs/transcoding.
 type Reader struct {
-	Attrs              ReaderObjectAttrs
+	Attrs          ReaderObjectAttrs
+	objectMetadata *map[string]string
+
 	seen, remain, size int64
 	checkCRC           bool // Did we check the CRC? This is now only used by tests.
 
@@ -298,3 +300,16 @@ func (r *Reader) CacheControl() string {
 func (r *Reader) LastModified() (time.Time, error) {
 	return r.Attrs.LastModified, nil
 }
+
+// Metadata returns user-provided metadata, in key/value pairs.
+//
+// It can be nil if no metadata is present, or if the client uses the JSON
+// API for downloads. Only the XML and gRPC APIs support getting
+// custom metadata via the Reader; for JSON make a separate call to
+// ObjectHandle.Attrs.
+func (r *Reader) Metadata() map[string]string {
+	if r.objectMetadata != nil {
+		return *r.objectMetadata
+	}
+	return nil
+}

storage/reader_test.go

@@ -29,6 +29,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
 	"google.golang.org/api/option"
 )
 
@@ -380,6 +381,7 @@ func TestContentEncodingGzipWithReader(t *testing.T) {
 			w.Header().Set("Etag", `"c50e3e41c9bc9df34e84c94ce073f928"`)
 			w.Header().Set("X-Goog-Generation", "1587012235914578")
 			w.Header().Set("X-Goog-MetaGeneration", "2")
+			w.Header().Set("X-Goog-Meta-custom-metadata-key", "custom-metadata-value")
 			w.Header().Set("X-Goog-Stored-Content-Encoding", "gzip")
 			w.Header().Set("vary", "Accept-Encoding")
 			w.Header().Set("x-goog-stored-content-length", "43")
@@ -470,6 +472,72 @@ func TestContentEncodingGzipWithReader(t *testing.T) {
 	}, option.WithEndpoint(mockGCS.URL), option.WithoutAuthentication(), option.WithHTTPClient(whc))
 }
 
+func TestMetadataParsingWithReader(t *testing.T) {
+	bucketName := "my-bucket"
+	objectName := "test"
+	downloadObjectXMLurl := fmt.Sprintf("/%s/%s", bucketName, objectName)
+	downloadObjectJSONurl := fmt.Sprintf("/b/%s/o/%s?alt=media&prettyPrint=false&projection=full", bucketName, objectName)
+
+	original := bytes.Repeat([]byte("a"), 4)
+	mockGCS := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.String() {
+		case downloadObjectXMLurl, downloadObjectJSONurl:
+			// Serve back the file.
+			w.Header().Set("Content-Type", "text/plain")
+			w.Header().Set("Etag", `"c50e3e41c9bc9df34e84c94ce073f928"`)
+			w.Header().Set("X-Goog-Generation", "1587012235914578")
+			w.Header().Set("X-Goog-MetaGeneration", "2")
+			w.Header().Set("X-Goog-Meta-custom-metadata-key", "custom-metadata-value")
+			w.Header().Set("vary", "Accept-Encoding")
+			w.Header().Set("x-goog-stored-content-length", "4")
+			w.Header().Set("x-goog-hash", "crc32c=pYIWwQ==")
+			w.Header().Set("x-goog-hash", "md5=xQ4+Qcm8nfNOhMlM4HP5KA==")
+			w.Header().Set("x-goog-storage-class", "STANDARD")
+			w.Write(original)
+		default:
+			fmt.Fprintf(w, "unrecognized URL %s", r.URL)
+		}
+	}))
+	mockGCS.EnableHTTP2 = true
+	mockGCS.StartTLS()
+	defer mockGCS.Close()
+
+	ctx := context.Background()
+	hc := mockGCS.Client()
+	ux, _ := url.Parse(mockGCS.URL)
+	hc.Transport.(*http.Transport).TLSClientConfig.InsecureSkipVerify = true
+	wrt := &alwaysToTargetURLRoundTripper{
+		destURL: ux,
+		hc:      hc,
+	}
+
+	whc := &http.Client{Transport: wrt}
+
+	multiReaderTest(ctx, t, func(t *testing.T, c *Client) {
+		obj := c.Bucket(bucketName).Object(objectName)
+		rd, err := obj.NewReader(ctx)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer rd.Close()
+
+		expectedMetadata := map[string]string{
+			"Custom-Metadata-Key": "custom-metadata-value",
+		}
+		if diff := cmp.Diff(rd.Metadata(), expectedMetadata); diff != "" {
+			t.Fatalf("metadata mismatch diff got vs want: %v", diff)
+		}
+
+		got, err := ioutil.ReadAll(rd)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if g, w := got, original; !bytes.Equal(g, w) {
+			t.Fatalf("Response mismatch\nGot:\n%q\n\nWant:\n%q", g, w)
+		}
+	}, option.WithEndpoint(mockGCS.URL), option.WithoutAuthentication(), option.WithHTTPClient(whc))
+}
+
 // alwaysToTargetURLRoundTripper ensures that every single request
 // is routed to a target destination. Some requests within the storage
 // client by-pass using the provided HTTP client, hence this enforcemenet.