Support manual control of the bulk operation (#42)

src/Elastic.Ingest.Elasticsearch/Indices/IndexChannelOptions.cs

@@ -51,4 +51,9 @@ public IndexChannelOptions(HttpTransport transport) : base(transport) { }
 	/// <para>https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-bulk.html#bulk-api-request-body</para>
 	/// </summary>
 	public Func<TEvent, string, bool>? BulkUpsertLookup { get; set; }
+
+	/// <summary>
+	/// Control the operation header for each bulk operation.
+	/// </summary>
+	public OperationMode OperationMode { get; set; }
 }

src/Elastic.Ingest.Elasticsearch/Indices/OperationMode.cs

@@ -0,0 +1,25 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+namespace Elastic.Ingest.Elasticsearch.Indices;
+
+/// <summary>
+/// Determines the operation header for each bulk operation.
+/// </summary>
+public enum OperationMode
+{
+	/// <summary>
+	/// The mode will be determined automatically based on default rules for the preferred mode.
+	/// </summary>
+	Auto = 0,
+
+	/// <summary>
+	/// Each document will be sent with an 'index' bulk operation header.
+	/// </summary>
+	Index = 1,
+
+	/// <summary>
+	/// Each document will be sent with a 'create' bulk operation header.
+	/// </summary>
+	Create = 2
+}

src/Elastic.Ingest.Elasticsearch/Serialization/BulkRequestDataFactory.cs

@@ -138,6 +138,20 @@ public static BulkOperationHeader CreateBulkOperationHeaderForIndex<TEvent>(TEve
 
 		var id = options.BulkOperationIdLookup?.Invoke(@event);
 
+		if (options.OperationMode == OperationMode.Index)
+		{
+			return skipIndexName
+				? !string.IsNullOrWhiteSpace(id) ? new IndexOperation { Id = id } : new IndexOperation()
+				: !string.IsNullOrWhiteSpace(id) ? new IndexOperation { Index = index, Id = id } : new IndexOperation { Index = index };
+		}
+
+		if (options.OperationMode == OperationMode.Create)
+		{
+			return skipIndexName
+				? !string.IsNullOrWhiteSpace(id) ? new CreateOperation { Id = id } : new CreateOperation()
+				: !string.IsNullOrWhiteSpace(id) ? new CreateOperation { Index = index, Id = id } : new CreateOperation { Index = index };
+		}
+
 		if (!string.IsNullOrWhiteSpace(id) && id != null && (options.BulkUpsertLookup?.Invoke(@event, id) ?? false))
 			return skipIndexName ? new UpdateOperation { Id = id } : new UpdateOperation { Id = id, Index = index };