metadata/label diffing logic can fail to update sometimes

[BenWhitehead]

When attempting to update object metadata or bucket labels without first fetching the current state, the update can fail to yield the desired state.

Effects all versions >= 2.17.0

Current workaround is to fetch the current BucketInfo or BlobInfo before updating.

[BenWhitehead]

The following tests illustrate reproduce the failure reliably:

Index: google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITNestedUpdateMaskTest.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITNestedUpdateMaskTest.java b/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITNestedUpdateMaskTest.java
--- a/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITNestedUpdateMaskTest.java	(revision d6f494407bc64e3918a0ea2fbc10626c8b45b960)
+++ b/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITNestedUpdateMaskTest.java	(date 1758137155360)
@@ -136,6 +136,15 @@
     assertThat(gen2.getMetadata()).isEqualTo(param.expected);
   }
 
+  @Test
+  public void testBlobMetadata_updateBaseOnNewInfoInsteadOfResolvedInfo() {
+    BlobInfo blob = newBlobInfo(param.initial);
+    Blob gen1 = storage.create(blob, BlobTargetOption.doesNotExist());
+    BlobInfo updated = BlobInfo.newBuilder(bucket, gen1.getName()).setMetadata(param.update).build();
+    Blob gen2 = storage.update(updated, BlobTargetOption.metagenerationMatch(gen1.getMetageneration()));
+    assertThat(gen2.getMetadata()).isEqualTo(param.expected);
+  }
+
   @Test
   public void testBlobContexts() {
     ObjectContexts initial = contextsFromMap(param.initial);
@@ -155,6 +164,25 @@
     assertContextsWithEqualValues(gen2.getContexts(), expected);
   }
 
+  @Test
+  public void testBlobContexts_updateBaseOnNewInfoInsteadOfResolvedInfo() {
+    ObjectContexts initial = contextsFromMap(param.initial);
+    ObjectContexts update = contextsFromMap(param.update);
+    ObjectContexts expected = contextsFromMap(param.expected);
+
+    String blobName = generator.randomObjectName();
+    BlobInfo.Builder builder = BlobInfo.newBuilder(bucket, blobName);
+    if (initial != null) {
+      builder.setContexts(initial);
+    }
+    BlobInfo info = builder.build();
+    Blob gen1 = storage.create(info, BlobTargetOption.doesNotExist());
+
+    BlobInfo modified = BlobInfo.newBuilder(bucket, gen1.getName()).setContexts(update).build();
+    Blob gen2 = storage.update(modified, BlobTargetOption.metagenerationMatch(gen1.getMetageneration()));
+    assertContextsWithEqualValues(gen2.getContexts(), expected);
+  }
+
   @Test
   public void testBlob_metadataAndContext() {
     ObjectContexts initial = contextsFromMap(param.initial);
@@ -178,6 +206,30 @@
     assertContextsWithEqualValues(gen2.getContexts(), expected);
     assertThat(gen2.getMetadata()).isEqualTo(param.expected);
   }
+
+  @Test
+  public void testBlob_metadataAndContext_updateBaseOnNewInfoInsteadOfResolvedInfo() {
+    ObjectContexts initial = contextsFromMap(param.initial);
+    ObjectContexts update = contextsFromMap(param.update);
+    ObjectContexts expected = contextsFromMap(param.expected);
+
+    String blobName = generator.randomObjectName();
+    BlobInfo.Builder builder = BlobInfo.newBuilder(bucket, blobName);
+    if (initial != null) {
+      builder.setContexts(initial);
+    }
+    if (param.initial != null) {
+      builder.setMetadata(param.initial);
+    }
+
+    BlobInfo info = builder.build();
+    Blob gen1 = storage.create(info, BlobTargetOption.doesNotExist());
+
+    BlobInfo modified = BlobInfo.newBuilder(bucket, gen1.getName()).setContexts(update).setMetadata(param.update).build();
+    Blob gen2 = storage.update(modified, BlobTargetOption.metagenerationMatch(gen1.getMetageneration()));
+    assertContextsWithEqualValues(gen2.getContexts(), expected);
+    assertThat(gen2.getMetadata()).isEqualTo(param.expected);
+  }
 
   private static void assertContextsWithEqualValues(
       @Nullable ObjectContexts actual, @Nullable ObjectContexts expected) {