storage: always send destination in compose request

The Compose call returns an error if the destination field
of the JSON body is empty. So we set it unconditionally.

The previous code set both the bucket and name fields, but
that isn't necessary. Setting just the bucket is sufficient.

Change-Id: Ib4f83da0c71df73516be39401053b6ea739c6d31
Reviewed-on: https://code-review.googlesource.com/8992
Reviewed-by: Jonathan Amsterdam <jba@google.com>

storage/copy.go

@@ -148,11 +148,9 @@ func (c *Composer) Run(ctx context.Context) (*ObjectAttrs, error) {
 	}
 
 	req := &raw.ComposeRequest{}
-	if !reflect.DeepEqual(c.ObjectAttrs, ObjectAttrs{}) {
-		req.Destination = c.ObjectAttrs.toRawObject(c.dst.bucket)
-		req.Destination.Name = c.dst.object
-	}
-
+	// Compose requires a non-empty Destination, so we always set it,
+	// even if the caller-provided ObjectAttrs is the zero value.
+	req.Destination = c.ObjectAttrs.toRawObject(c.dst.bucket)
 	for _, src := range c.srcs {
 		if err := src.validate(); err != nil {
 			return nil, err

storage/integration_test.go

@@ -550,33 +550,46 @@ func TestObjects(t *testing.T) {
 	}
 
 	// Test object composition.
-	compDst := bkt.Object("composed")
 	var compSrcs []*ObjectHandle
 	var wantContents []byte
 	for _, obj := range objects {
 		compSrcs = append(compSrcs, bkt.Object(obj))
 		wantContents = append(wantContents, contents[obj]...)
 	}
+	checkCompose := func(obj *ObjectHandle, wantContentType string) {
+		rc, err := obj.NewReader(ctx)
+		if err != nil {
+			t.Fatalf("NewReader: %v", err)
+		}
+		slurp, err = ioutil.ReadAll(rc)
+		if err != nil {
+			t.Fatalf("ioutil.ReadAll: %v", err)
+		}
+		defer rc.Close()
+		if !bytes.Equal(slurp, wantContents) {
+			t.Errorf("Composed object contents\ngot:  %q\nwant: %q", slurp, wantContents)
+		}
+		if got := rc.ContentType(); got != wantContentType {
+			t.Errorf("Composed object content-type = %q, want %q", got, wantContentType)
+		}
+	}
+
+	// Compose should work even if the user sets no destination attributes.
+	compDst := bkt.Object("composed1")
 	c := compDst.ComposerFrom(compSrcs...)
-	c.ContentType = "text/json"
 	if _, err := c.Run(ctx); err != nil {
 		t.Fatalf("ComposeFrom error: %v", err)
 	}
-	rc, err := compDst.NewReader(ctx)
-	if err != nil {
-		t.Fatalf("compDst.NewReader: %v", err)
-	}
-	slurp, err = ioutil.ReadAll(rc)
-	if err != nil {
-		t.Fatalf("compDst ioutil.ReadAll: %v", err)
-	}
-	defer rc.Close()
-	if !bytes.Equal(slurp, wantContents) {
-		t.Errorf("Composed object contents\ngot:  %q\nwant: %q", slurp, wantContents)
-	}
-	if got, want := rc.ContentType(), "text/json"; got != want {
-		t.Errorf("Composed object content-type = %q, want %q", got, want)
+	checkCompose(compDst, "application/octet-stream")
+
+	// It should also work if we do.
+	compDst = bkt.Object("composed2")
+	c = compDst.ComposerFrom(compSrcs...)
+	c.ContentType = "text/json"
+	if _, err := c.Run(ctx); err != nil {
+		t.Fatalf("ComposeFrom error: %v", err)
 	}
+	checkCompose(compDst, "text/json")
 }
 
 func namesEqual(obj *ObjectAttrs, bucketName, objectName string) bool {

storage/storage_test.go

@@ -467,6 +467,7 @@ func TestObjectCompose(t *testing.T) {
 			},
 			wantURL: "/storage/v1/b/foo/o/bar/compose?alt=json",
 			wantReq: raw.ComposeRequest{
+				Destination: &raw.Object{Bucket: "foo"},
 				SourceObjects: []*raw.ComposeRequestSourceObjects{
 					{Name: "baz"},
 					{Name: "quux"},
@@ -488,7 +489,7 @@ func TestObjectCompose(t *testing.T) {
 			wantReq: raw.ComposeRequest{
 				Destination: &raw.Object{
 					Bucket:      "foo",
-					Name:        "bar",
+					Name:        "not-bar",
 					ContentType: "application/json",
 				},
 				SourceObjects: []*raw.ComposeRequestSourceObjects{
@@ -509,6 +510,7 @@ func TestObjectCompose(t *testing.T) {
 			},
 			wantURL: "/storage/v1/b/foo/o/bar/compose?alt=json&ifGenerationMatch=12&ifMetagenerationMatch=34",
 			wantReq: raw.ComposeRequest{
+				Destination: &raw.Object{Bucket: "foo"},
 				SourceObjects: []*raw.ComposeRequestSourceObjects{
 					{
 						Name:       "baz",