Add Csv processor (#4374)

Relates: #4341

This commit adds the Csv processor to the collection of ingest
processors.

(cherry picked from commit f91ccda)

src/Nest/Ingest/ProcessorFormatter.cs

@@ -41,6 +41,7 @@ internal class ProcessorFormatter : IJsonFormatter<IProcessor>
 			{ "drop", 29 },
 			{ "circle", 30 },
 			{ "enrich", 31 },
+			{ "csv", 32 },
 		};
 
 		public IProcessor Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)
@@ -157,6 +158,9 @@ public IProcessor Deserialize(ref JsonReader reader, IJsonFormatterResolver form
 					case 31:
 						processor = Deserialize<EnrichProcessor>(ref reader, formatterResolver);
 						break;
+					case 32:
+						processor = Deserialize<CsvProcessor>(ref reader, formatterResolver);
+						break;
 				}
 			}
 			else
@@ -185,6 +189,9 @@ public void Serialize(ref JsonWriter writer, IProcessor value, IJsonFormatterRes
 				case "append":
 					Serialize<IAppendProcessor>(ref writer, value, formatterResolver);
 					break;
+				case "csv":
+					Serialize<ICsvProcessor>(ref writer, value, formatterResolver);
+					break;
 				case "convert":
 					Serialize<IConvertProcessor>(ref writer, value, formatterResolver);
 					break;

src/Nest/Ingest/Processors/CsvProcessor.cs

@@ -0,0 +1,114 @@
+using System;
+using System.Linq.Expressions;
+using System.Runtime.Serialization;
+using Elasticsearch.Net;
+using Elasticsearch.Net.Utf8Json;
+
+
+namespace Nest
+{
+	/// <summary>
+	/// Extracts fields from CSV line out of a single text field within a document.
+	/// Any empty field in CSV will be skipped.
+	/// <para></para>
+	/// Available in Elasticsearch 7.6.0+
+	/// </summary>
+	[InterfaceDataContract]
+	public interface ICsvProcessor : IProcessor
+	{
+		/// <summary>
+		/// The field to extract data from
+		/// </summary>
+		[DataMember(Name ="field")]
+		Field Field { get; set; }
+
+		/// <summary>
+		/// The array of fields to assign extracted values to.
+		/// </summary>
+		[DataMember(Name ="target_fields")]
+		Fields TargetFields { get; set; }
+
+		/// <summary>
+		/// Separator used in CSV, has to be single character string. Defaults to <c>,</c>
+		/// </summary>
+		[DataMember(Name = "separator")]
+		string Separator { get; set; }
+
+		/// <summary>
+		/// Quote used in CSV, has to be single character string. Defaults to <c>"</c>
+		/// </summary>
+		[DataMember(Name = "quote")]
+		string Quote { get; set; }
+
+		/// <summary>
+		/// If <c>true</c> and <see cref="Field" /> does not exist or is null,
+		/// the processor quietly exits without modifying the document. Default is <c>false</c>
+		/// </summary>
+		[DataMember(Name = "ignore_missing")]
+		bool? IgnoreMissing { get; set; }
+
+		/// <summary>
+		/// Trim whitespaces in unquoted fields. Default is <c>false</c>;
+		/// </summary>
+		[DataMember(Name = "trim")]
+		bool? Trim { get; set; }
+	}
+
+	/// <inheritdoc cref="ICsvProcessor"/>
+	public class CsvProcessor : ProcessorBase, ICsvProcessor
+	{
+		/// <inheritdoc />
+		public Field Field { get; set; }
+		/// <inheritdoc />
+		public Fields TargetFields { get; set; }
+		/// <inheritdoc />
+		public string Separator { get; set; }
+		/// <inheritdoc />
+		public string Quote { get; set; }
+		/// <inheritdoc />
+		public bool? IgnoreMissing { get; set; }
+		/// <inheritdoc />
+		public bool? Trim { get; set; }
+		/// <inheritdoc />
+		protected override string Name => "csv";
+	}
+
+	/// <inheritdoc cref="ICsvProcessor"/>
+	public class CsvProcessorDescriptor<T> : ProcessorDescriptorBase<CsvProcessorDescriptor<T>, ICsvProcessor>, ICsvProcessor
+		where T : class
+	{
+		protected override string Name => "csv";
+		Field ICsvProcessor.Field { get; set; }
+		Fields ICsvProcessor.TargetFields { get; set; }
+		bool? ICsvProcessor.IgnoreMissing { get; set; }
+		string ICsvProcessor.Quote { get; set; }
+		string ICsvProcessor.Separator { get; set; }
+		bool? ICsvProcessor.Trim { get; set; }
+
+		/// <inheritdoc cref="ICsvProcessor.Field" />
+		public CsvProcessorDescriptor<T> Field(Field field) => Assign(field, (a, v) => a.Field = v);
+
+		/// <inheritdoc cref="ICsvProcessor.Field" />
+		public CsvProcessorDescriptor<T> Field<TValue>(Expression<Func<T, TValue>> objectPath) =>
+			Assign(objectPath, (a, v) => a.Field = v);
+
+		/// <inheritdoc cref="ICsvProcessor.TargetFields" />
+		public CsvProcessorDescriptor<T> TargetFields(Func<FieldsDescriptor<T>, IPromise<Fields>> targetFields) =>
+			Assign(targetFields, (a, v) => a.TargetFields = v?.Invoke(new FieldsDescriptor<T>())?.Value);
+
+		/// <inheritdoc cref="ICsvProcessor.TargetFields" />
+		public CsvProcessorDescriptor<T> TargetFields(Fields targetFields) => Assign(targetFields, (a, v) => a.TargetFields = v);
+
+		/// <inheritdoc cref="ICsvProcessor.IgnoreMissing" />
+		public CsvProcessorDescriptor<T> IgnoreMissing(bool? ignoreMissing = true) => Assign(ignoreMissing, (a, v) => a.IgnoreMissing = v);
+
+		/// <inheritdoc cref="ICsvProcessor.Trim" />
+		public CsvProcessorDescriptor<T> Trim(bool? trim = true) => Assign(trim, (a, v) => a.Trim = v);
+
+		/// <inheritdoc cref="ICsvProcessor.Quote" />
+		public CsvProcessorDescriptor<T> Quote(string quote) => Assign(quote, (a, v) => a.Quote = v);
+
+		/// <inheritdoc cref="ICsvProcessor.Separator" />
+		public CsvProcessorDescriptor<T> Separator(string separator) => Assign(separator, (a, v) => a.Separator = v);
+	}
+}

src/Nest/Ingest/ProcessorsDescriptor.cs

@@ -22,6 +22,11 @@ public class ProcessorsDescriptor : DescriptorPromiseBase<ProcessorsDescriptor,
 		public ProcessorsDescriptor Append<T>(Func<AppendProcessorDescriptor<T>, IAppendProcessor> selector) where T : class =>
 			Assign(selector, (a, v) => a.AddIfNotNull(v?.Invoke(new AppendProcessorDescriptor<T>())));
 
+		/// <inheritdoc cref="ICsvProcessor"/>
+		public ProcessorsDescriptor Csv<T>(Func<CsvProcessorDescriptor<T>, ICsvProcessor> selector) where T : class =>
+			Assign(selector, (a, v) => a.AddIfNotNull(v?.Invoke(new CsvProcessorDescriptor<T>())));
+
+
 		/// <inheritdoc cref="IConvertProcessor"/>
 		public ProcessorsDescriptor Convert<T>(Func<ConvertProcessorDescriptor<T>, IConvertProcessor> selector) where T : class =>
 			Assign(selector, (a, v) => a.AddIfNotNull(v?.Invoke(new ConvertProcessorDescriptor<T>())));

tests/Tests/Ingest/ProcessorAssertions.cs

@@ -70,6 +70,30 @@ public class Append : ProcessorAssertion
 			public override string Key => "append";
 		}
 
+		[SkipVersion("<7.6.0", "Introduced in Elasticsearch 7.6.0+")]
+		public class Csv : ProcessorAssertion
+		{
+			public override Func<ProcessorsDescriptor, IPromise<IList<IProcessor>>> Fluent => d => d
+				.Csv<Project>(c => c
+					.Field(p => p.Name)
+					.TargetFields(new[] { "targetField1", "targetField2" })
+				);
+
+			public override IProcessor Initializer => new CsvProcessor
+			{
+				Field = "name",
+				TargetFields = new[] { "targetField1", "targetField2" },
+			};
+
+			public override object Json => new
+			{
+				field = "name",
+				target_fields = new[] { "targetField1", "targetField2" },
+			};
+
+			public override string Key => "csv";
+		}
+
 		public class Convert : ProcessorAssertion
 		{
 			public override Func<ProcessorsDescriptor, IPromise<IList<IProcessor>>> Fluent => d => d