Add custom vector data converters for high performance ingest scenarios

docs/reference/source-serialization.md

@@ -16,6 +16,9 @@ Source serialization refers to the process of (de)serializing POCO types in cons
   - [Registering custom `System.Text.Json` converters](#registering-custom-converters)
   - [Creating a custom `Serializer`](#creating-custom-serializers)
 - [Native AOT](#native-aot)
+- [Vector data serialization](#vector-data-serialization)
+  - [Opt‑in on document properties](#optin-on-document-properties)
+  - [Configure encodings globally](#configure-encodings-globally)
 
 ## Modeling documents with types [modeling-documents-with-types]
 
@@ -451,3 +454,58 @@ static void ConfigureOptions(JsonSerializerOptions o)
     o.TypeInfoResolver = UserTypeSerializerContext.Default;
 }
 ```
+
+## Vector data serialization [vector-data-serialization]
+
+Efficient ingestion of high-dimensional vectors often benefits from compact encodings rather than verbose JSON arrays. The client provides opt‑in converters for vector properties in your source documents that serialize to either hexadecimal or `base64` strings, depending on the vector type and the Elasticsearch version you target.
+
+- Float vectors can use `base64` starting from Elasticsearch 9.3.0.
+- Byte/bit vectors can use hexadecimal strings starting from Elasticsearch 8.14.0 and `base64` starting from Elasticsearch 9.3.0.
+- The legacy representation (JSON arrays) remains available for backwards compatibility.
+
+Base64 is the preferred format for high‑throughput indexing because it minimizes payload size and reduces JSON parsing overhead.
+
+### Opt‑in on document properties [optin-on-document-properties]
+
+Vector encodings are opt‑in. Apply a `System.Text.Json` `JsonConverter` attribute on the vector property of your POCO. For best performance, model the properties as `ReadOnlyMemory<T>`.
+
+```csharp
+using System;
+using System.Text.Json.Serialization;
+using Elastic.Clients.Elasticsearch.Serialization;
+
+public class ImageEmbedding
+{
+    [JsonConverter(typeof(FloatVectorDataConverter))] <1>
+    public ReadOnlyMemory<float> Vector { get; set; }
+}
+
+public class ByteSignature
+{
+    [JsonConverter(typeof(ByteVectorDataConverter))] <2>
+    public ReadOnlyMemory<byte> Signature { get; set; }
+}
+```
+
+1. `FloatVectorDataConverter` enables `base64` encoding for float vectors.
+2. `ByteVectorDataConverter` enables `base64` encoding for byte vectors.
+
+Without these attributes, vectors are serialized using the default source serializer behavior.
+
+### Configure encodings globally [configure-encodings-globally]
+
+When the opt‑in attributes are present, you can control the actual wire encoding globally via `ElasticsearchClient` settings on a per‑type basis:
+
+- `FloatVectorDataEncoding`: controls float vector encoding (legacy arrays or `base64`).
+- `ByteVectorDataEncoding`: controls byte/bit vector encoding (legacy arrays, hexadecimal, or `base64`).
+
+These settings allow a single set of document types to work against mixed clusters. For example, a library using the 8.19.x client can talk to both 8.x and 9.x servers and dynamically opt out of `base64` on older servers without maintaining duplicate POCOs (with/without converter attributes).
+
+::::{note}
+
+Set the encoding based on your effective server version:
+
+- Float vectors: use `base64` for 9.3.0+; otherwise use legacy arrays.
+- Byte/bit vectors: prefer `base64` for 9.3.0+; use hexadecimal for 8.14.0–9.2.x; otherwise use legacy arrays.
+
+::::

src/Elastic.Clients.Elasticsearch/_Shared/Core/Configuration/ElasticsearchClientSettings.cs

@@ -115,6 +115,8 @@ public abstract class ElasticsearchClientSettingsBase<TConnectionSettings> :
 	private readonly Serializer _sourceSerializer;
 	private BeforeRequestEvent? _onBeforeRequest;
 	private bool _experimentalEnableSerializeNullInferredValues;
+	private FloatVectorDataEncoding _floatVectorDataEncoding = Serialization.FloatVectorDataEncoding.Base64;
+	private ByteVectorDataEncoding _byteVectorDataEncoding = Serialization.ByteVectorDataEncoding.Base64;
 	private ExperimentalSettings _experimentalSettings = new();
 
 	private bool _defaultDisableAllInference;
@@ -165,6 +167,8 @@ protected ElasticsearchClientSettingsBase(
 	FluentDictionary<Type, string> IElasticsearchClientSettings.RouteProperties => _routeProperties;
 	Serializer IElasticsearchClientSettings.SourceSerializer => _sourceSerializer;
 	BeforeRequestEvent? IElasticsearchClientSettings.OnBeforeRequest => _onBeforeRequest;
+	FloatVectorDataEncoding IElasticsearchClientSettings.FloatVectorDataEncoding => _floatVectorDataEncoding;
+	ByteVectorDataEncoding IElasticsearchClientSettings.ByteVectorDataEncoding => _byteVectorDataEncoding;
 	ExperimentalSettings IElasticsearchClientSettings.Experimental => _experimentalSettings;
 
 	bool IElasticsearchClientSettings.ExperimentalEnableSerializeNullInferredValues => _experimentalEnableSerializeNullInferredValues;
@@ -198,6 +202,18 @@ public TConnectionSettings DefaultFieldNameInferrer(Func<string, string> fieldNa
 	public TConnectionSettings ExperimentalEnableSerializeNullInferredValues(bool enabled = true) =>
 		Assign(enabled, (a, v) => a._experimentalEnableSerializeNullInferredValues = v);
 
+	/// <inheritdoc cref="IElasticsearchClientSettings.FloatVectorDataEncoding"/>
+	/// <param name="encoding">The default vector data encoding to use.</param>
+	/// <returns>This settings instance for chaining.</returns>
+	public TConnectionSettings FloatVectorDataEncoding(FloatVectorDataEncoding encoding) =>
+		Assign(encoding, (a, v) => a._floatVectorDataEncoding = v);
+
+	/// <inheritdoc cref="IElasticsearchClientSettings.ByteVectorDataEncoding"/>
+	/// <param name="encoding">The default vector data encoding to use.</param>
+	/// <returns>This settings instance for chaining.</returns>
+	public TConnectionSettings ByteVectorDataEncoding(ByteVectorDataEncoding encoding) =>
+		Assign(encoding, (a, v) => a._byteVectorDataEncoding = v);
+
 	public TConnectionSettings Experimental(ExperimentalSettings settings) =>
 		Assign(settings, (a, v) => a._experimentalSettings = v);
 

src/Elastic.Clients.Elasticsearch/_Shared/Core/Configuration/IElasticsearchClientSettings.cs

@@ -5,7 +5,10 @@
 using System;
 using System.Collections.Generic;
 using System.Reflection;
+
 using Elastic.Clients.Elasticsearch.Requests;
+using Elastic.Clients.Elasticsearch.Serialization;
+
 using Elastic.Transport;
 
 namespace Elastic.Clients.Elasticsearch;
@@ -116,14 +119,37 @@ public interface IElasticsearchClientSettings : ITransportConfiguration
 	BeforeRequestEvent? OnBeforeRequest { get; }
 
 	/// <summary>
-	/// This is an advanced setting which controls serialization behaviour for inferred properies such as ID, routing and index name.
-	/// <para>When enabled, it may reduce allocations on serialisation paths where the cost can be more significant, such as in bulk operations.</para>
+	/// This is an advanced setting which controls serialization behaviour for inferred properties such as ID, routing and index name.
+	/// <para>When enabled, it may reduce allocations on serialization paths where the cost can be more significant, such as in bulk operations.</para>
 	/// <para>As a by-product it may cause null values to be included in the serialized data and impact payload size. This will only be a concern should some
-	/// typed not have inferrence mappings defined for the required properties.</para>
+	/// typed not have inference mappings defined for the required properties.</para>
 	/// </summary>
-	/// <remarks>This is marked as experiemental and may be removed or renamed in the future once its impact is evaluated.</remarks>
+	/// <remarks>This is marked as experimental and may be removed or renamed in the future once its impact is evaluated.</remarks>
 	bool ExperimentalEnableSerializeNullInferredValues { get; }
 
+	/// <summary>
+	/// Controls the vector data encoding to use for <see cref="ReadOnlyMemory{T}"/> properties
+	/// in documents during ingestion when the <see cref="FloatVectorDataConverter"/> is used.
+	/// </summary>
+	/// <remarks>
+	///	Setting this value to <see cref="FloatVectorDataEncoding.Legacy"/> provides backwards
+	/// compatibility when talking to Elasticsearch servers with a version older than 9.3.0
+	/// (required for <see cref="ByteVectorDataEncoding.Base64"/>).
+	/// </remarks>
+	FloatVectorDataEncoding FloatVectorDataEncoding { get; }
+
+	/// <summary>
+	/// Controls the vector data encoding to use for <see cref="ReadOnlyMemory{T}"/> properties
+	/// in documents during ingestion when the <see cref="ByteVectorDataConverter"/> is used.
+	/// </summary>
+	/// <remarks>
+	///	Setting this value to <see cref="ByteVectorDataEncoding.Legacy"/> provides backwards
+	/// compatibility when talking to Elasticsearch servers with a version older than 8.14.0
+	/// (required for <see cref="ByteVectorDataEncoding.Hex"/>) or older than 9.3.0 (required
+	/// for <see cref="ByteVectorDataEncoding.Base64"/>).
+	/// </remarks>
+	ByteVectorDataEncoding ByteVectorDataEncoding { get; }
+
 	/// <summary>
 	/// Experimental settings.
 	/// </summary>

src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonWriterExtensions.cs

@@ -250,6 +250,21 @@ public static void WriteUnionValue<T1, T2>(this Utf8JsonWriter writer, JsonSeria
 		);
 	}
 
+	public static void WriteSpanValue<T>(this Utf8JsonWriter writer, JsonSerializerOptions options, ReadOnlySpan<T> span,
+		JsonWriteFunc<T>? writeElement)
+	{
+		writeElement ??= static (w, o, v) => WriteValue(w, o, v);
+
+		writer.WriteStartArray();
+
+		foreach (var element in span)
+		{
+			writeElement(writer, options, element);
+		}
+
+		writer.WriteEndArray();
+	}
+
 	#endregion Delegate Based Write Methods
 
 	#region Specialized Write Methods