fix: update FakeStorageRpc to better handle resumable sessions that o…

…verwrite existing objects (#1296)

google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/testing/FakeStorageRpc.java

@@ -356,7 +356,7 @@ public String open(StorageObject object, Map<Option, ?> options) throws StorageE
     checkGeneration(key, generationMatch);
     metadata.put(key, object);
 
-    return fullname(object);
+    return key;
   }
 
   @Override
@@ -613,11 +613,12 @@ public MockLowLevelHttpResponse getResponse() {
         try {
           ByteArrayOutputStream baos = new ByteArrayOutputStream();
           this.getStreamingContent().writeTo(baos);
+          bytes = futureContents.get(key);
           byte[] byteArray = baos.toByteArray();
           if (storageObject.getGeneration() != null) {
-            contents.put(key, concat(bytes, byteArray));
+            futureContents.put(key, concat(bytes, byteArray));
           } else {
-            contents.put(key, byteArray);
+            futureContents.put(key, byteArray);
           }
 
           List<String> contentRanges = getHeaders().get("content-range");
@@ -637,6 +638,8 @@ public MockLowLevelHttpResponse getResponse() {
               resp.addHeader("Content-Type", "application/json;charset=utf-8");
               resp.addHeader("Content-Length", String.valueOf(string.length()));
               resp.setContent(string);
+              contents.put(key, byteArray);
+              futureContents.remove(key);
             } else {
               resp.setStatusCode(NOT_FOUND);
             }

google-cloud-nio/src/test/java/com/google/cloud/storage/contrib/nio/testing/FakeStorageRpcTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * 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 com.google.cloud.storage.contrib.nio.testing;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.cloud.WriteChannel;
+import com.google.cloud.storage.Blob;
+import com.google.cloud.storage.BlobId;
+import com.google.cloud.storage.BlobInfo;
+import com.google.cloud.storage.Storage;
+import com.google.cloud.storage.Storage.BlobWriteOption;
+import com.google.cloud.storage.StorageOptions;
+import com.google.cloud.storage.contrib.nio.testing.LocalStorageHelper.FakeStorageRpcFactory;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import org.junit.Test;
+
+public final class FakeStorageRpcTest {
+
+  @Test
+  public void overwritingAnObjectOverwritesItsContent() throws IOException {
+    Storage storage =
+        StorageOptions.http()
+            .setServiceRpcFactory(new FakeStorageRpcFactory())
+            .build()
+            .getService();
+
+    try (WriteChannel writer =
+        storage.writer(
+            BlobInfo.newBuilder(BlobId.of("bucket", "obj", 0L)).build(),
+            BlobWriteOption.generationMatch())) {
+      writer.write(ByteBuffer.wrap("abc".getBytes(StandardCharsets.UTF_8)));
+    }
+    Blob gen1 = storage.get(BlobId.of("bucket", "obj"));
+    // get existing generation
+    String gen1read1 = new String(gen1.getContent(), StandardCharsets.UTF_8);
+    assertThat(gen1read1).isEqualTo("abc");
+    System.out.println("gen1read1 = " + gen1read1);
+
+    // start an upload that will overwrite the existing generation
+    WriteChannel writer = storage.writer(gen1, BlobWriteOption.generationMatch());
+    writer.write(ByteBuffer.wrap("def".getBytes(StandardCharsets.UTF_8)));
+    // make sure we can still read the existing generations value after starting but before closing
+    String gen1read2 = new String(gen1.getContent(), StandardCharsets.UTF_8);
+    assertThat(gen1read2).isEqualTo("abc");
+    writer.close();
+
+    Blob gen2 = storage.get(BlobId.of("bucket", "obj"));
+    String gen2read1 = new String(gen2.getContent(), StandardCharsets.UTF_8);
+    System.out.println("gen2read1 = " + gen2read1);
+    assertThat(gen2read1).isEqualTo("def");
+  }
+}