test(storage): Add buffer reuse test. (#12555)

cjc25 · web-flow · commit 3f14ec87b4a3 · 2025-07-14T14:43:18.000-04:00
This confirms that implementations don't retain the user-provided buffer
after the return from Write() in any important way.
diff --git a/storage/client_test.go b/storage/client_test.go
@@ -2529,6 +2529,47 @@ func TestWriterChunkTransferTimeoutEmulated(t *testing.T) {
 	})
 }
 
+func TestWriterChunkBufferReuseEmulated(t *testing.T) {
+	transportClientTest(context.Background(), t, func(t *testing.T, ctx context.Context, project, bucket string, client storageClient) {
+		c := &Client{tc: client}
+		if err := c.Bucket(bucket).Create(ctx, project, &BucketAttrs{}); err != nil {
+			t.Fatalf("creating bucket: %v", err)
+		}
+		objName := fmt.Sprintf("object-%d", time.Now().Nanosecond())
+		w := c.Bucket(bucket).Object(objName).NewWriter(ctx)
+		const chunkSize = 32 * 1024 * 1024
+		w.ChunkSize = chunkSize
+
+		// Write twice using the same buffer, then clear it.
+		buf := bytes.Repeat([]byte("A"), chunkSize)
+		if n, err := w.Write(buf); err != nil || n != chunkSize {
+			t.Errorf("failed first write: wrote %v, want %v, err %v", n, chunkSize, err)
+		}
+		copy(buf, bytes.Repeat([]byte("B"), chunkSize))
+		if n, err := w.Write(buf); err != nil || n != chunkSize {
+			t.Errorf("failed second write: wrote %v, want %v, err %v", n, chunkSize, err)
+		}
+		clear(buf)
+		if err := w.Close(); err != nil {
+			t.Errorf("failed close: %v", err)
+		}
+
+		r, err := c.Bucket(bucket).Object(objName).NewReader(ctx)
+		if err != nil {
+			t.Fatalf("opening reading: %v", err)
+		}
+		defer r.Close()
+		want := append(bytes.Repeat([]byte("A"), chunkSize), bytes.Repeat([]byte("B"), chunkSize)...)
+		got, err := io.ReadAll(r)
+		if err != nil {
+			t.Fatalf("reading object: %v", err)
+		}
+		if !bytes.Equal(got, want) {
+			t.Errorf("content does not match, got len %v, want len %v", len(got), len(want))
+		}
+	})
+}
+
 func TestWriterChunkRetryDeadlineEmulated(t *testing.T) {
 	transportClientTest(context.Background(), t, func(t *testing.T, ctx context.Context, project, bucket string, client storageClient) {
 		const (
