[Remote Cluster State] Remote state interfaces

server/src/main/java/org/opensearch/gateway/remote/AbstractRemoteBlobStoreObject.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.gateway.remote;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.Base64;
+import java.util.concurrent.ExecutorService;
+import org.opensearch.common.CheckedRunnable;
+import org.opensearch.common.blobstore.BlobPath;
+import org.opensearch.core.action.ActionListener;
+import org.opensearch.core.compress.Compressor;
+import org.opensearch.gateway.remote.ClusterMetadataManifest.UploadedMetadata;
+import org.opensearch.index.translog.transfer.BlobStoreTransferService;
+import org.opensearch.repositories.blobstore.BlobStoreRepository;
+import org.opensearch.threadpool.ThreadPool;
+
+/**
+ * An extension of {@link RemoteObject} class which caters to the use case of writing to and reading from a blob storage
+ *
+ * @param <T> The class type which can be uploaded to or downloaded from a blob storage.
+ */
+public abstract class AbstractRemoteBlobStoreObject<T> implements RemoteObject<T> {
+
+    public static final String PATH_DELIMITER = "/";
+
+    private final BlobStoreTransferService transferService;
+    private final BlobStoreRepository blobStoreRepository;
+    private final String clusterName;
+    private final ExecutorService executorService;
+
+    public AbstractRemoteBlobStoreObject(BlobStoreTransferService blobStoreTransferService, BlobStoreRepository blobStoreRepository, String clusterName,
+        ThreadPool threadPool) {
+        this.transferService = blobStoreTransferService;
+        this.blobStoreRepository = blobStoreRepository;
+        this.clusterName = clusterName;
+        this.executorService = threadPool.executor(ThreadPool.Names.GENERIC);
+    }
+
+    public abstract BlobPathParameters getBlobPathParameters();
+
+    public abstract String getFullBlobName();
+
+    public String getBlobFileName() {
+        if (getFullBlobName() == null) {
+            generateBlobFileName();
+        }
+        String[] pathTokens = getFullBlobName().split(PATH_DELIMITER);
+        return getFullBlobName().split(PATH_DELIMITER)[pathTokens.length - 1];
+    }
+
+    public abstract String generateBlobFileName();
+
+    public abstract UploadedMetadata getUploadedMetadata();
+
+    @Override
+    public CheckedRunnable<IOException> writeAsync(ActionListener<Void> listener) {
+        return () -> {
+            assert get() != null;
+            // TODO add implementation
+        };
+    }
+
+    @Override
+    public T read() throws IOException {
+        assert getFullBlobName() != null;
+        return deserialize(
+            transferService.downloadBlob(getBlobPathForDownload(), getBlobFileName()));
+    }
+
+    @Override
+    public void readAsync(ActionListener<T> listener) {
+        executorService.execute(() -> {
+            try {
+                listener.onResponse(read());
+            } catch (Exception e) {
+                listener.onFailure(e);
+            }
+        });
+    }
+
+    public BlobPath getBlobPathForUpload() {
+        BlobPath blobPath = blobStoreRepository.basePath().add(encodeString(clusterName)).add("cluster-state").add(clusterUUID());
+        for (String token : getBlobPathParameters().getPathTokens()) {
+            blobPath = blobPath.add(token);
+        }
+        return blobPath;
+    }
+
+    public BlobPath getBlobPathForDownload() {
+        String[] pathTokens = extractBlobPathTokens(getFullBlobName());
+        BlobPath blobPath = blobStoreRepository.basePath();
+        for (String token : pathTokens) {
+            blobPath = blobPath.add(token);
+        }
+        return blobPath;
+    }
+
+    protected Compressor getCompressor() {
+        return blobStoreRepository.getCompressor();
+    }
+
+    protected BlobStoreRepository getBlobStoreRepository() {
+        return this.blobStoreRepository;
+    }
+
+    private static String[] extractBlobPathTokens(String blobName) {
+        String[] blobNameTokens = blobName.split(PATH_DELIMITER);
+        return Arrays.copyOfRange(blobNameTokens, 0, blobNameTokens.length - 1);
+    }
+
+    private static String encodeString(String content) {
+        return Base64.getUrlEncoder().withoutPadding().encodeToString(content.getBytes(StandardCharsets.UTF_8));
+    }
+}

server/src/main/java/org/opensearch/gateway/remote/BlobPathParameters.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.gateway.remote;
+
+import java.util.List;
+
+public class BlobPathParameters {
+
+    private List<String> pathTokens;
+    private String filePrefix;
+
+    public BlobPathParameters(List<String> pathTokens, String filePrefix) {
+        this.pathTokens = pathTokens;
+        this.filePrefix = filePrefix;
+    }
+
+    public List<String> getPathTokens() {
+        return pathTokens;
+    }
+
+    public String getFilePrefix() {
+        return filePrefix;
+    }
+}

server/src/main/java/org/opensearch/gateway/remote/RemoteObject.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.gateway.remote;
+
+import java.io.IOException;
+import java.io.InputStream;
+import org.opensearch.common.CheckedRunnable;
+import org.opensearch.core.action.ActionListener;
+
+/**
+ * An interface to read/write and object from/to a remote storage. This interface is agnostic of the remote storage type.
+ * @param <T> The object type which can be upload to or download from remote storage.
+ */
+public interface RemoteObject <T> {
+    public T get();
+    public String clusterUUID();
+    public InputStream serialize() throws IOException;
+    public T deserialize(InputStream inputStream) throws IOException;
+
+    public CheckedRunnable<IOException> writeAsync(ActionListener<Void> listener);
+    public T read() throws IOException;
+    public void readAsync(ActionListener<T> listener);
+
+}