Add MySqlConnection.ResetConnectionAsync. Fixes #831

Author: bgrainger

azure-pipelines.yml

@@ -197,7 +197,7 @@ jobs:
     matrix:
       'MySQL 5.6':
         image: 'mysql:5.6'
-        unsupportedFeatures: 'Ed25519,Json,Sha256Password,LargePackets,CachingSha2Password,SessionTrack,Tls13,UuidToBin'
+        unsupportedFeatures: 'Ed25519,Json,Sha256Password,LargePackets,CachingSha2Password,ResetConnection,SessionTrack,Tls13,UuidToBin'
       'MySQL 5.7':
         image: 'mysql:5.7'
         unsupportedFeatures: 'Ed25519,CachingSha2Password,Tls13,UuidToBin'

src/MySqlConnector/MySql.Data.MySqlClient/MySqlConnection.cs

@@ -415,6 +415,24 @@ private async Task OpenAsync(IOBehavior? ioBehavior, CancellationToken cancellat
 #endif
 		}
 
+		/// <summary>
+		/// Resets the session state of the current open connection; this clears temporary tables and user-defined variables.
+		/// </summary>
+		/// <param name="cancellationToken">A token to cancel the asynchronous operation.</param>
+		/// <returns>A <c>ValueTask</c> representing the asynchronous operation.</returns>
+#if NET45 || NET461 || NET471 || NETSTANDARD1_3 || NETSTANDARD2_0
+		public async Task ResetConnectionAsync(CancellationToken cancellationToken = default)
+#else
+		public async ValueTask ResetConnectionAsync(CancellationToken cancellationToken = default)
+#endif
+		{
+			var session = Session;
+			Log.Debug("Session{0} resetting connection", session.Id);
+			await session.SendAsync(ResetConnectionPayload.Instance, AsyncIOBehavior, cancellationToken).ConfigureAwait(false);
+			var payload = await session.ReceiveReplyAsync(AsyncIOBehavior, cancellationToken).ConfigureAwait(false);
+			OkPayload.Create(payload.Span, session.SupportsDeprecateEof, session.SupportsSessionTrack);
+		}
+
 		[AllowNull]
 		public override string ConnectionString
 		{

tests/SideBySide/ConnectionTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Data;
+using System.Threading.Tasks;
 using Dapper;
 using MySql.Data.MySqlClient;
 using Xunit;
@@ -241,6 +242,31 @@ public void CloneWithCopiesExistingPassword()
 			connection2.Open();
 			Assert.Equal(ConnectionState.Open, connection2.State);
 		}
+
+		[Fact]
+		public async Task ResetConnectionThrowsIfNotOpen()
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			await Assert.ThrowsAsync<InvalidOperationException>(async () => await connection.ResetConnectionAsync());
+		}
+
+		[SkippableFact(ServerFeatures.ResetConnection)]
+		public async Task ResetConnectionClearsUserVariables()
+		{
+			var csb = AppConfig.CreateConnectionStringBuilder();
+			csb.AllowUserVariables = true;
+			using var connection = new MySqlConnection(csb.ConnectionString);
+			await connection.OpenAsync();
+
+			connection.Execute("set @temp_var = 1;");
+			var tempVar = connection.ExecuteScalar<int?>("select @temp_var;");
+			Assert.Equal(1, tempVar);
+
+			await connection.ResetConnectionAsync();
+
+			tempVar = connection.ExecuteScalar<int?>("select @temp_var;");
+			Assert.Null(tempVar);
+		}
 #endif
 	}
 }

tests/SideBySide/ServerFeatures.cs

@@ -23,5 +23,6 @@ public enum ServerFeatures
 		Ed25519 = 0x4000,
 		UnixDomainSocket = 0x8000,
 		Tls13 = 0x1_0000,
+		ResetConnection = 0x2_0000,
 	}
 }