Escape the escape char when writing.

src/CsvHelper/CsvWriter.cs

@@ -52,9 +52,11 @@ public class CsvWriter : IWriter
 		private readonly char injectionEscapeCharacter;
 		private readonly InjectionOptions injectionOptions;
 		private readonly CsvMode mode;
+		private readonly string escapeString;
 		private readonly string escapeQuoteString;
 		private readonly string escapeDelimiterString;
 		private readonly string escapeNewlineString;
+		private readonly string escapeEscapeString;
 
 		private bool disposed;
 		private bool hasHeaderBeenWritten;
@@ -112,6 +114,7 @@ public CsvWriter(TextWriter writer, IWriterConfiguration configuration, bool lea
 			escapeDelimiterString = new string(configuration.Delimiter.SelectMany(c => new[] { configuration.Escape, c }).ToArray());
 			escapeNewlineString = new string(configuration.NewLine.SelectMany(c => new[] { configuration.Escape, c }).ToArray());
 			escapeQuoteString = new string(new[] { configuration.Escape, configuration.Quote });
+			escapeEscapeString = new string(new[] { configuration.Escape, configuration.Escape });
 			hasHeaderRecord = configuration.HasHeaderRecord;
 			includePrivateMembers = configuration.IncludePrivateMembers;
 			injectionCharacters = configuration.InjectionCharacters;
@@ -121,6 +124,7 @@ public CsvWriter(TextWriter writer, IWriterConfiguration configuration, bool lea
 			newLine = configuration.NewLine;
 			quote = configuration.Quote;
 			quoteString = configuration.Quote.ToString();
+			escapeString = configuration.Escape.ToString();
 			injectionOptions = configuration.InjectionOptions;
 			shouldQuote = configuration.ShouldQuote;
 			trimOptions = configuration.TrimOptions;
@@ -165,13 +169,19 @@ public virtual void WriteField(string field, bool shouldQuote)
 				// All quotes must be escaped.
 				if (shouldQuote)
 				{
+					if (escapeString != quoteString)
+					{
+						field = field?.Replace(escapeString, escapeEscapeString);
+					}
+
 					field = field?.Replace(quoteString, escapeQuoteString);
 					field = quote + field + quote;
 				}
 			}
 			else if (mode == CsvMode.Escape)
 			{
 				field = field?
+					.Replace(escapeString, escapeEscapeString)
 					.Replace(quoteString, escapeQuoteString)
 					.Replace(delimiter, escapeDelimiterString)
 					.Replace(newLine, escapeNewlineString);

tests/CsvHelper.Tests/Writing/WriteCustomEscapeTests.cs

@@ -0,0 +1,63 @@
+using CsvHelper.Configuration;
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using System.Threading.Tasks;
+using System.Xml.Linq;
+using Xunit;
+
+namespace CsvHelper.Tests.Writing
+{
+	public class WriteCustomEscapeTests
+	{
+		[Fact]
+		public void WriteField_CustomEscapeChar_ModeRFC4180_EscapesQuotesAndEscapeCharacter()
+		{
+			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
+			{
+				HasHeaderRecord = false,
+				Escape = '\\',
+			};
+			using (var writer = new StringWriter())
+			using (var csv = new CsvWriter(writer, config))
+			{
+				// {"json":"{\"name\":\"foo\"}"}
+				// json string -> csv field
+				// "{\"json\":\"{\\\"name\\\":\\\"foo\\\"}\"}"
+				csv.WriteField(@"{""json"":""{\""name\"":\""foo\""}""}");
+				csv.Flush();
+
+				var expected = @"""{\""json\"":\""{\\\""name\\\"":\\\""foo\\\""}\""}""";
+				Assert.Equal(expected, writer.ToString());
+			}
+		}
+
+		[Fact]
+		public void WriteField_CustomEscapeChar_ModeEscape_EscapesQuotesAndEscapeCharacter()
+		{
+			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
+			{
+				HasHeaderRecord = false,
+				Escape = '\\',
+				Mode = CsvMode.Escape,
+			};
+			using (var writer = new StringWriter())
+			using (var csv = new CsvWriter(writer, config))
+			{
+				// {"json":"{\"name\":\"foo\"}"}
+				// json string -> csv field
+				// {\"json\":\"{\\\"name\\\":\\\"foo\\\"}\"}
+				csv.WriteField(@"{""json"":""{\""name\"":\""foo\""}""}");
+				csv.Flush();
+
+				var expected = @"{\""json\"":\""{\\\""name\\\"":\\\""foo\\\""}\""}";
+				Assert.Equal(expected, writer.ToString());
+			}
+		}
+	}
+}