Conflicts Resolved:

	plugins/repository-s3/src/main/java/org/opensearch/repositories/s3/S3BlobContainer.java
	plugins/repository-s3/src/test/java/org/opensearch/repositories/s3/S3BlobStoreContainerTests.java

Author: tqranjan

plugins/repository-s3/src/main/java/org/opensearch/repositories/s3/S3BlobContainer.java

@@ -53,6 +53,8 @@
 import software.amazon.awssdk.services.s3.model.NoSuchKeyException;
 import software.amazon.awssdk.services.s3.model.ObjectAttributes;
 import software.amazon.awssdk.services.s3.model.PutObjectRequest;
+import software.amazon.awssdk.services.s3.model.PutObjectResponse;
+import software.amazon.awssdk.services.s3.model.S3Exception;
 import software.amazon.awssdk.services.s3.model.UploadPartRequest;
 import software.amazon.awssdk.services.s3.model.UploadPartResponse;
 import software.amazon.awssdk.services.s3.paginators.ListObjectsV2Iterable;
@@ -62,6 +64,7 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.message.ParameterizedMessage;
+import org.opensearch.OpenSearchException;
 import org.opensearch.action.support.PlainActionFuture;
 import org.opensearch.common.Nullable;
 import org.opensearch.common.SetOnce;
@@ -72,6 +75,8 @@
 import org.opensearch.common.blobstore.BlobMetadata;
 import org.opensearch.common.blobstore.BlobPath;
 import org.opensearch.common.blobstore.BlobStoreException;
+import org.opensearch.common.blobstore.ConditionalWrite.ConditionalWriteOptions;
+import org.opensearch.common.blobstore.ConditionalWrite.ConditionalWriteResponse;
 import org.opensearch.common.blobstore.DeleteResult;
 import org.opensearch.common.blobstore.InputStreamWithMetadata;
 import org.opensearch.common.blobstore.stream.read.ReadContext;
@@ -96,6 +101,7 @@
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
@@ -117,6 +123,7 @@ class S3BlobContainer extends AbstractBlobContainer implements AsyncMultiStreamB
 
     private final S3BlobStore blobStore;
     private final String keyPath;
+    public static final int HTTP_STATUS_PRECONDITION_FAILED = 412;
 
     S3BlobContainer(BlobPath path, S3BlobStore blobStore) {
         super(path);
@@ -521,6 +528,99 @@ private String buildKey(String blobName) {
         return keyPath + blobName;
     }
 
+    /**
+     * Executes a upload to S3 using conditional write options.
+     * The upload can proceed based on various conditional scenarios like If-Match, If-None-Match, etc.
+     *
+     * @param blobStore     the S3 blob store
+     * @param blobName      the key (name) of the blob
+     * @param input         the input stream containing the blob data
+     * @param blobSize      the size of the blob in bytes
+     * @param metadata      optional metadata to be associated with the blob
+     * @param options       conditional write options for the upload
+     * @param listener      listener to handle the resulting response or error notifications
+     * @throws IOException if an error occurs during upload or if validations fail
+     */
+    void executeSingleUploadConditionally(
+        final S3BlobStore blobStore,
+        final String blobName,
+        final InputStream input,
+        final long blobSize,
+        final Map<String, String> metadata,
+        final ConditionalWriteOptions options,
+        final ActionListener<ConditionalWriteResponse> listener
+    ) throws IOException {
+        // Extra safety checks remain the same
+        if (blobSize > MAX_FILE_SIZE.getBytes()) {
+            throw new IllegalArgumentException("Upload request size [" + blobSize + "] can't be larger than " + MAX_FILE_SIZE);
+        }
+        if (blobSize > blobStore.bufferSizeInBytes()) {
+            throw new IllegalArgumentException("Upload request size [" + blobSize + "] can't be larger than buffer size");
+        }
+
+        PutObjectRequest.Builder putObjectRequestBuilder = PutObjectRequest.builder()
+            .bucket(blobStore.bucket())
+            .key(blobName)
+            .contentLength(blobSize)
+            .storageClass(blobStore.getStorageClass())
+            .acl(blobStore.getCannedACL())
+            .overrideConfiguration(o -> o.addMetricPublisher(blobStore.getStatsMetricPublisher().putObjectMetricPublisher))
+            .expectedBucketOwner(blobStore.expectedBucketOwner());
+
+        // Apply conditional logic based on options
+        if (options.isIfMatch()) {
+            putObjectRequestBuilder.ifMatch(options.getVersionIdentifier());
+        } else if (options.isIfNotExists()) {
+            putObjectRequestBuilder.ifNoneMatch("*");
+        }
+
+        if (CollectionUtils.isNotEmpty(metadata)) {
+            putObjectRequestBuilder = putObjectRequestBuilder.metadata(metadata);
+        }
+
+        // Use extracted encryption configuration helper
+        configureEncryptionSettings(putObjectRequestBuilder, blobStore);
+
+        PutObjectRequest putObjectRequest = putObjectRequestBuilder.build();
+
+        try (AmazonS3Reference clientReference = blobStore.clientReference()) {
+            final InputStream requestInputStream = blobStore.isUploadRetryEnabled()
+                ? new BufferedInputStream(input, (int) (blobSize + 1))
+                : input;
+
+            PutObjectResponse response = SocketAccess.doPrivileged(
+                () -> clientReference.get().putObject(putObjectRequest, RequestBody.fromInputStream(requestInputStream, blobSize))
+            );
+
+            if (response.eTag() != null) {
+                listener.onResponse(ConditionalWriteResponse.success(response.eTag()));
+            } else {
+                IOException exception = new IOException(
+                    "S3 upload for [" + blobName + "] returned null ETag, violating data integrity expectations"
+                );
+                listener.onFailure(exception);
+                throw exception;
+            }
+
+        } catch (S3Exception e) {
+            if (e.statusCode() == HTTP_STATUS_PRECONDITION_FAILED) {
+                listener.onFailure(new OpenSearchException("stale_primary_shard", e, "Precondition Failed : Etag Mismatch", blobName));
+                throw new IOException("Unable to upload object [" + blobName + "] due to ETag mismatch", e);
+            } else {
+                IOException exception = new IOException(
+                    String.format(Locale.ROOT, "S3 error during upload [%s]: %s", blobName, e.getMessage()),
+                    e
+                );
+                listener.onFailure(exception);
+                throw exception;
+            }
+        } catch (SdkException e) {
+            IOException exception = new IOException(String.format(Locale.ROOT, "S3 upload failed for [%s]", blobName), e);
+            listener.onFailure(exception);
+            throw exception;
+        }
+    }
+
     /**
      * Uploads a blob using a single upload request
      */