User proper write-once semantics for GCS repository

plugins/repository-gcs/src/main/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageBlobContainer.java

@@ -66,9 +66,6 @@ public InputStream readBlob(String blobName) throws IOException {
 
     @Override
     public void writeBlob(String blobName, InputStream inputStream, long blobSize) throws IOException {
-        if (blobExists(blobName)) {
-            throw new FileAlreadyExistsException("blob [" + blobName + "] already exists, cannot overwrite");
-        }
         blobStore.writeBlob(buildKey(blobName), inputStream, blobSize);
     }
 

plugins/repository-gcs/src/main/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageBlobStore.java

@@ -42,6 +42,7 @@
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.NoSuchFileException;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -56,6 +57,7 @@
 import java.util.stream.StreamSupport;
 
 import static java.net.HttpURLConnection.HTTP_NOT_FOUND;
+import static java.net.HttpURLConnection.HTTP_PRECON_FAILED;
 
 class GoogleCloudStorageBlobStore extends AbstractComponent implements BlobStore {
 
@@ -191,7 +193,7 @@ InputStream readBlob(String blobName) throws IOException {
         } catch (GoogleJsonResponseException e) {
             GoogleJsonError error = e.getDetails();
             if ((e.getStatusCode() == HTTP_NOT_FOUND) || ((error != null) && (error.getCode() == HTTP_NOT_FOUND))) {
-                throw new NoSuchFileException(e.getMessage());
+                throw new NoSuchFileException(blobName, null, e.getMessage());
             }
             throw e;
         }
@@ -209,8 +211,16 @@ void writeBlob(String blobName, InputStream inputStream, long blobSize) throws I
             stream.setLength(blobSize);
 
             Storage.Objects.Insert insert = client.objects().insert(bucket, null, stream);
+            insert.setIfGenerationMatch(0L); // ensures that the file does not already exist
             insert.setName(blobName);
-            insert.execute();
+            try {
+                insert.execute();
+            } catch (GoogleJsonResponseException e) {
+                GoogleJsonError error = e.getDetails();
+                if ((e.getStatusCode() == HTTP_PRECON_FAILED) || ((error != null) && (error.getCode() == HTTP_PRECON_FAILED))) {
+                    throw new FileAlreadyExistsException(blobName, null, e.getMessage());
+                }
+            }
         });
     }
 

plugins/repository-gcs/src/test/java/org/elasticsearch/repositories/gcs/MockStorage.java

@@ -138,6 +138,16 @@ public StorageObject execute() throws IOException {
                         throw newBucketNotFoundException(getBucket());
                     }
 
+                    if (getIfGenerationMatch() != null) {
+                        if (getIfGenerationMatch() == 0L) {
+                            if (blobs.containsKey(getName())) {
+                                throw newPreconditionFailedException(getName());
+                            }
+                        } else {
+                            throw new AssertionError("not implemented");
+                        }
+                    }
+
                     ByteArrayOutputStream out = new ByteArrayOutputStream();
                     Streams.copy(insertStream.getInputStream(), out);
                     blobs.put(getName(), out.toByteArray());
@@ -236,6 +246,11 @@ private static GoogleJsonResponseException newObjectNotFoundException(final Stri
         return new GoogleJsonResponseException(builder, new GoogleJsonError());
     }
 
+    private static GoogleJsonResponseException newPreconditionFailedException(final String object) {
+        HttpResponseException.Builder builder = new HttpResponseException.Builder(412, "Precondition Failed: " + object, new HttpHeaders());
+        return new GoogleJsonResponseException(builder, new GoogleJsonError());
+    }
+
     /**
      * {@link MockedHttpTransport} extends the existing testing transport to analyze the content
      * of {@link com.google.api.client.googleapis.batch.BatchRequest} and delete the appropriates

test/framework/src/main/java/org/elasticsearch/repositories/ESBlobStoreContainerTestCase.java

@@ -29,6 +29,7 @@
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.NoSuchFileException;
 import java.util.Arrays;
 import java.util.HashMap;
@@ -149,7 +150,7 @@ public void testVerifyOverwriteFails() throws IOException {
             final BytesArray bytesArray = new BytesArray(data);
             writeBlob(container, blobName, bytesArray);
             // should not be able to overwrite existing blob
-            expectThrows(IOException.class, () -> writeBlob(container, blobName, bytesArray));
+            expectThrows(FileAlreadyExistsException.class, () -> writeBlob(container, blobName, bytesArray));
             container.deleteBlob(blobName);
             writeBlob(container, blobName, bytesArray); // after deleting the previous blob, we should be able to write to it again
         }