Throw exception when a large packet is detected. Fixes #40

Author: bgrainger

src/MySqlConnector/MySqlClient/CommandExecutors/TextCommandExecutor.cs

@@ -1,5 +1,8 @@
-using System.Data;
+using System;
+using System.Data;
 using System.Data.Common;
+using System.IO;
+using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
 using MySql.Data.Protocol.Serialization;
@@ -55,8 +58,18 @@ public virtual async Task<DbDataReader> ExecuteReaderAsync(string commandText, M
 				statementPreparerOptions |= StatementPreparerOptions.OldGuids;
 			var preparer = new MySqlStatementPreparer(commandText, parameterCollection, statementPreparerOptions);
 			var payload = new PayloadData(preparer.ParseAndBindParameters());
-			await m_command.Connection.Session.SendAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
-			return await MySqlDataReader.CreateAsync(m_command, behavior, ioBehavior, cancellationToken).ConfigureAwait(false);
+			try
+			{
+				await m_command.Connection.Session.SendAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
+				return await MySqlDataReader.CreateAsync(m_command, behavior, ioBehavior, cancellationToken).ConfigureAwait(false);
+			}
+			catch (Exception ex) when (payload.ArraySegment.Count > 4194304 && (ex is SocketException || ex is IOException))
+			{
+				// the default MySQL Server value for max_allowed_packet (in MySQL 5.7) is 4MiB: https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_allowed_packet
+				// use "decimal megabytes" (to round up) when creating the exception message
+				int megabytes = payload.ArraySegment.Count / 1000000;
+				throw new MySqlException("Error submitting {0}MB packet; ensure 'max_allowed_packet' is greater than {0}MB.".FormatInvariant(megabytes), ex);
+			}
 		}
 
 		readonly MySqlCommand m_command;

tests/SideBySide/DataTypes.cs

@@ -510,30 +510,50 @@ public void QueryBlob(string column, int padLength)
 		[InlineData("TinyBlob", 255)]
 		[InlineData("Blob", 65535)]
 		[InlineData("MediumBlob", 16777215)]
+		[InlineData("LongBlob", 33554432)]
 		[InlineData("LongBlob", 67108864)]
+		[InlineData("LongBlob", 134217728)]
 		public async Task InsertLargeBlobAsync(string column, int size)
 		{
-			// verify that this amount of data can be sent to MySQL successfully
-			var maxAllowedPacket = (await m_database.Connection.QueryAsync<int>("select @@max_allowed_packet").ConfigureAwait(false)).Single();
-			if (maxAllowedPacket < size)
-				return; // TODO: Use [SkippableFact]
+			// NOTE: MySQL Server will reset the connection when it receives an oversize packet, so we need to create a test-specific connection here
+			using (var connection = new MySqlConnection(AppConfig.CreateConnectionStringBuilder().ConnectionString))
+			{
+				await connection.OpenAsync();
 
-			var data = CreateByteArray(size);
+				// verify that this amount of data can be sent to MySQL successfully
+				var maxAllowedPacket = (await connection.QueryAsync<int>("select @@max_allowed_packet").ConfigureAwait(false)).Single();
+				var shouldFail = maxAllowedPacket < size + 100;
 
-			long lastInsertId;
-			using (var cmd = new MySqlCommand(Invariant($"insert into datatypes_blobs(`{column}`) values(?)"), m_database.Connection)
-			{
-				Parameters = { new MySqlParameter { Value = data } }
-			})
-			{
-				await cmd.ExecuteNonQueryAsync().ConfigureAwait(false);
-				lastInsertId = cmd.LastInsertedId;
-			}
+				var data = CreateByteArray(size);
+
+				long lastInsertId;
+				using (var cmd = new MySqlCommand(Invariant($"insert into datatypes_blobs(`{column}`) values(?)"), connection)
+				{
+					Parameters = { new MySqlParameter { Value = data } }
+				})
+				{
+					try
+					{
+						await cmd.ExecuteNonQueryAsync().ConfigureAwait(false);
+						lastInsertId = cmd.LastInsertedId;
+						Assert.False(shouldFail);
+					}
+					catch (MySqlException ex)
+					{
+						lastInsertId = -1;
+						Assert.True(shouldFail);
+						Assert.Contains("packet", ex.Message);
+					}
+				}
 
-			var queryResult = (await m_database.Connection.QueryAsync<byte[]>(Invariant($"select `{column}` from datatypes_blobs where rowid = {lastInsertId}")).ConfigureAwait(false)).Single();
-			TestUtilities.AssertEqual(data, queryResult);
+				if (!shouldFail)
+				{
+					var queryResult = (await connection.QueryAsync<byte[]>(Invariant($"select `{column}` from datatypes_blobs where rowid = {lastInsertId}")).ConfigureAwait(false)).Single();
+					TestUtilities.AssertEqual(data, queryResult);
 
-			await m_database.Connection.ExecuteAsync(Invariant($"delete from datatypes_blobs where rowid = {lastInsertId}")).ConfigureAwait(false);
+					await connection.ExecuteAsync(Invariant($"delete from datatypes_blobs where rowid = {lastInsertId}")).ConfigureAwait(false);
+				}
+			}
 		}
 
 		[Theory]
@@ -543,27 +563,44 @@ public async Task InsertLargeBlobAsync(string column, int size)
 		[InlineData("LongBlob", 67108864)]
 		public void InsertLargeBlobSync(string column, int size)
 		{
-			// verify that this amount of data can be sent to MySQL successfully
-			var maxAllowedPacket = m_database.Connection.Query<int>("select @@max_allowed_packet").Single();
-			if (maxAllowedPacket < size)
-				return; // TODO: Use [SkippableFact]
+			// NOTE: MySQL Server will reset the connection when it receives an oversize packet, so we need to create a test-specific connection here
+			using (var connection = new MySqlConnection(AppConfig.CreateConnectionStringBuilder().ConnectionString))
+			{
+				connection.Open();
 
-			var data = CreateByteArray(size);
+				// verify that this amount of data can be sent to MySQL successfully
+				var maxAllowedPacket = m_database.Connection.Query<int>("select @@max_allowed_packet").Single();
+				var shouldFail = maxAllowedPacket < size + 100;
 
-			long lastInsertId;
-			using (var cmd = new MySqlCommand(Invariant($"insert into datatypes_blobs(`{column}`) values(?)"), m_database.Connection)
-			{
-				Parameters = { new MySqlParameter { Value = data } }
-			})
-			{
-				cmd.ExecuteNonQuery();
-				lastInsertId = cmd.LastInsertedId;
-			}
+				var data = CreateByteArray(size);
 
-			var queryResult = m_database.Connection.Query<byte[]>(Invariant($"select `{column}` from datatypes_blobs where rowid = {lastInsertId}")).Single();
-			TestUtilities.AssertEqual(data, queryResult);
+				long lastInsertId;
+				using (var cmd = new MySqlCommand(Invariant($"insert into datatypes_blobs(`{column}`) values(?)"), connection)
+				{
+					Parameters = { new MySqlParameter { Value = data } }
+				})
+				{
+					try
+					{
+						cmd.ExecuteNonQuery();
+						lastInsertId = cmd.LastInsertedId;
+					}
+					catch (MySqlException ex)
+					{
+						lastInsertId = -1;
+						Assert.True(shouldFail);
+						Assert.Contains("packet", ex.Message);
+					}
+				}
 
-			m_database.Connection.Execute(Invariant($"delete from datatypes_blobs where rowid = {lastInsertId}"));
+				if (!shouldFail)
+				{
+					var queryResult = connection.Query<byte[]>(Invariant($"select `{column}` from datatypes_blobs where rowid = {lastInsertId}")).Single();
+					TestUtilities.AssertEqual(data, queryResult);
+
+					connection.Execute(Invariant($"delete from datatypes_blobs where rowid = {lastInsertId}"));
+				}
+			}
 		}
 
 		private static byte[] CreateByteArray(int size)