Implement CloneWith. Fixes #736

Author: bgrainger

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

@@ -21,7 +21,7 @@ public sealed class MySqlConnection : DbConnection
 #endif
 	{
 		public MySqlConnection()
-			: this("")
+			: this(default)
 		{
 		}
 
@@ -447,12 +447,31 @@ public override async ValueTask DisposeAsync()
 			}
 		}
 
-		public MySqlConnection Clone() => new MySqlConnection(this);
+		public MySqlConnection Clone() => new MySqlConnection(m_connectionString, m_hasBeenOpened);
 
 #if !NETSTANDARD1_3
 		object ICloneable.Clone() => Clone();
 #endif
 
+		/// <summary>
+		/// Returns an unopened copy of this connection with a new connection string. If the <c>Password</c>
+		/// in <paramref name="connectionString"/> is not set, the password from this connection will be used.
+		/// This allows creating a new connection with the same security information while changing other options,
+		/// such as database or pooling.
+		/// </summary>
+		/// <param name="connectionString">The new connection string to be used.</param>
+		/// <returns>A new <see cref="MySqlConnection"/> with different connection string options but
+		/// the same password as this connection (unless overridden by <paramref name="connectionString"/>).</returns>
+		public MySqlConnection CloneWith(string connectionString)
+		{
+			var newBuilder = new MySqlConnectionStringBuilder(connectionString ?? throw new ArgumentNullException(nameof(connectionString)));
+			var currentBuilder = new MySqlConnectionStringBuilder(m_connectionString);
+			var shouldCopyPassword = newBuilder.Password.Length == 0 && (!newBuilder.PersistSecurityInfo || currentBuilder.PersistSecurityInfo);
+			if (shouldCopyPassword)
+				newBuilder.Password = currentBuilder.Password;
+			return new MySqlConnection(newBuilder.ConnectionString, m_hasBeenOpened && shouldCopyPassword && !currentBuilder.PersistSecurityInfo);
+		}
+
 		internal ServerSession Session
 		{
 			get
@@ -675,10 +694,10 @@ internal void SetState(ConnectionState newState)
 			}
 		}
 
-		private MySqlConnection(MySqlConnection other)
-			: this(other.m_connectionString)
+		private MySqlConnection(string connectionString, bool hasBeenOpened)
+			: this(connectionString)
 		{
-			m_hasBeenOpened = other.m_hasBeenOpened;
+			m_hasBeenOpened = hasBeenOpened;
 		}
 
 		private void VerifyNotDisposed()

tests/SideBySide/ConnectionTests.cs

@@ -172,5 +172,75 @@ public void CloneDoesNotDisclosePassword()
 			Assert.Equal(connection.ConnectionString, connection2.ConnectionString);
 			Assert.DoesNotContain("password", connection2.ConnectionString, StringComparison.OrdinalIgnoreCase);
 		}
+
+#if !BASELINE
+		[Theory]
+		[InlineData(false)]
+		[InlineData(true)]
+		public void CloneWithUsesNewConnectionString(bool openConnection)
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			if (openConnection)
+				connection.Open();
+			using var connection2 = connection.CloneWith("user=root;password=pass;server=example.com;database=test");
+			Assert.Equal("User Id=root;Password=pass;Server=example.com;Database=test", connection2.ConnectionString);
+		}
+
+		[Fact]
+		public void CloneWithUsesExistingPassword()
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			var newConnectionString = "user=root;server=example.com;database=test";
+			using var connection2 = connection.CloneWith(newConnectionString);
+
+			var builder = new MySqlConnectionStringBuilder(newConnectionString);
+			builder.Password = AppConfig.CreateConnectionStringBuilder().Password;
+			Assert.Equal(builder.ConnectionString, connection2.ConnectionString);
+		}
+
+		[Theory]
+		[InlineData(false)]
+		[InlineData(true)]
+		public void CloneWithDoesNotDiscloseExistingPassword(bool persistSecurityInfo)
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			connection.Open();
+
+			var newConnectionString = "user=root;server=example.com;database=test;Persist Security Info=" + persistSecurityInfo;
+			using var connection2 = connection.CloneWith(newConnectionString);
+
+			var builder = new MySqlConnectionStringBuilder(newConnectionString);
+			Assert.Equal(builder.ConnectionString, connection2.ConnectionString);
+		}
+
+		[Theory]
+		[InlineData(false)]
+		[InlineData(true)]
+		public void CloneWithDoesDiscloseExistingPasswordIfPersistSecurityInfo(bool persistSecurityInfo)
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString + ";Persist Security Info=true");
+			connection.Open();
+
+			var newConnectionString = "user=root;server=example.com;database=test;Persist Security Info=" + persistSecurityInfo;
+			using var connection2 = connection.CloneWith(newConnectionString);
+
+			var builder = new MySqlConnectionStringBuilder(newConnectionString);
+			builder.Password = AppConfig.CreateConnectionStringBuilder().Password;
+			Assert.Equal(builder.ConnectionString, connection2.ConnectionString);
+		}
+
+		[Fact]
+		public void CloneWithCopiesExistingPassword()
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			connection.Open();
+
+			var builder = AppConfig.CreateConnectionStringBuilder();
+			builder.Password = "";
+			using var connection2 = connection.CloneWith(builder.ConnectionString);
+			connection2.Open();
+			Assert.Equal(ConnectionState.Open, connection2.State);
+		}
+#endif
 	}
 }