Add MySqlHelper.EscapeString. Fixes #277.

Author: bgrainger

src/MySqlConnector/MySqlClient/MySqlHelper.cs

@@ -1,10 +1,40 @@
 using System;
+using System.Text;
 
 namespace MySql.Data.MySqlClient
 {
 	public sealed class MySqlHelper
 	{
 		[Obsolete("Use MySqlConnection.ClearAllPools or MySqlConnection.ClearAllPoolsAsync")]
 		public static void ClearConnectionPools() => MySqlConnection.ClearAllPools();
+
+		/// <summary>
+		/// Escapes single and double quotes, and backslashes in <paramref name="input"/>.
+		/// </summary>
+		public static string EscapeString(string value)
+		{
+			if (value == null)
+				throw new ArgumentNullException(nameof(value));
+
+			StringBuilder sb = null;
+			int last = -1;
+			for (int i = 0; i < value.Length; i++)
+			{
+				if (value[i] == '\'' || value[i] == '\"' || value[i] == '\\')
+				{
+					if (sb == null)
+						sb = new StringBuilder();
+					if (i > last - 1)
+						sb.Append(value, last + 1, i - last - 1);
+					sb.Append('\\');
+					sb.Append(value[i]);
+					last = i;
+				}
+			}
+			if (sb != null && last < value.Length - 1)
+				sb.Append(value, last + 1, value.Length - last - 1);
+
+			return sb?.ToString() ?? value;
+		}
 	}
 }

tests/MySqlConnector.Tests/MySqlHelperTests.cs

@@ -0,0 +1,26 @@
+using MySql.Data.MySqlClient;
+using Xunit;
+
+namespace MySql.Data.Tests
+{
+	public class MySqlHelperTests
+	{
+		[Theory]
+		[InlineData("", "")]
+		[InlineData("test", "test")]
+		[InlineData("\"", "\\\"")]
+		[InlineData("'", "\\'")]
+		[InlineData("\\", "\\\\")]
+		[InlineData(@"'begin", @"\'begin")]
+		[InlineData(@"end'", @"end\'")]
+		[InlineData(@"mid'dle", @"mid\'dle")]
+		[InlineData(@"'a'b'", @"\'a\'b\'")]
+		public void EscapeString(string input, string expected)
+		{
+			var actual = MySqlHelper.EscapeString(input);
+			Assert.Equal(expected, actual);
+			if (expected == input)
+				Assert.Same(input, actual);
+		}
+	}
+}