[Release/3.1] Address MARS TDS header contained errors

src/System.Data.SqlClient/src/System/Data/SqlClient/TdsParser.cs

@@ -2549,6 +2549,11 @@ private bool TryProcessDone(SqlCommand cmd, SqlDataReader reader, ref RunBehavio
             ushort status;
             int count;
 
+            // This is added back since removing it from here introduces regressions in Managed SNI.
+            // It forces SqlDataReader.ReadAsync() method to run synchronously, 
+            // and will block the calling thread until data is fed from SQL Server.
+            stateObj._syncOverAsync = true;
+
             // status
             // command
             // rowcount (valid only if DONE_COUNT bit is set)
@@ -2639,7 +2644,7 @@ private bool TryProcessDone(SqlCommand cmd, SqlDataReader reader, ref RunBehavio
                     stateObj._pendingData = false;
                 }
             }
-
+            
             // _pendingData set by e.g. 'TdsExecuteSQLBatch'
             // _hasOpenResult always set to true by 'WriteMarsHeader'
             //

src/System.Data.SqlClient/tests/ManualTests/SQL/AsyncTest/AsyncCancelledConnectionsTest.cs

@@ -0,0 +1,263 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace System.Data.SqlClient.ManualTesting.Tests
+{
+    public class AsyncCancelledConnectionsTest
+    {
+        private readonly ITestOutputHelper _output;
+        private const int NumberOfTasks = 100;  // How many attempts to poison the connection pool we will try
+        private const int NumberOfNonPoisoned = 10;  // Number of normal requests for each attempt 
+
+        public AsyncCancelledConnectionsTest(ITestOutputHelper output)
+        {
+            this._output = output;
+        }
+
+        [ActiveIssue(490)] // This test seems to fail regularly in pipelines due to deadlocks. But it's still useful for local testing.
+        [ConditionalFact(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup))]
+        public void CancelAsyncConnections()
+        {
+            string connectionString = DataTestUtility.TcpConnStr;
+            _watch = Stopwatch.StartNew();
+            _random = new Random(4); // chosen via fair dice role.
+            ParallelLoopResult results = new ParallelLoopResult();
+            try
+            {
+                // Setup a timer so that we can see what is going on while our tasks run
+                using (new Timer(TimerCallback, state: null, dueTime: TimeSpan.FromSeconds(5), period: TimeSpan.FromSeconds(5)))
+                {
+                    results = Parallel.For(
+                        fromInclusive: 0,
+                        toExclusive: NumberOfTasks,
+                        (int i) => DoManyAsync(connectionString).GetAwaiter().GetResult());
+                }
+            }
+            catch (Exception ex)
+            {
+                _output.WriteLine(ex.ToString());
+            }
+            while (!results.IsCompleted)
+            {
+                Thread.Sleep(50);
+            }
+            DisplaySummary();
+            foreach (var detail in _exceptionDetails)
+            {
+                _output.WriteLine(detail);
+            }
+            Assert.Empty(_exceptionDetails);
+        }
+
+        // Display one row every 5'ish seconds
+        private void TimerCallback(object state)
+        {
+            lock (_lockObject)
+            {
+                DisplaySummary();
+            }
+        }
+
+        private void DisplaySummary()
+        {
+            int count;
+            lock (_exceptionDetails)
+            {
+                count = _exceptionDetails.Count;
+            }
+
+            _output.WriteLine($"{_watch.Elapsed} {_continue} Started:{_start} Done:{_done} InFlight:{_inFlight} RowsRead:{_rowsRead} ResultRead:{_resultRead} PoisonedEnded:{_poisonedEnded} nonPoisonedExceptions:{_nonPoisonedExceptions} PoisonedCleanupExceptions:{_poisonCleanUpExceptions} Count:{count} Found:{_found}");
+        }
+
+        // This is the the main body that our Tasks run
+        private async Task DoManyAsync(string connectionString)
+        {
+            Interlocked.Increment(ref _start);
+            Interlocked.Increment(ref _inFlight);
+
+            // First poison
+            await DoOneAsync(connectionString, poison: true);
+
+            for (int i = 0; i < NumberOfNonPoisoned && _continue; i++)
+            {
+                // now run some without poisoning
+                await DoOneAsync(connectionString);
+            }
+
+            Interlocked.Decrement(ref _inFlight);
+            Interlocked.Increment(ref _done);
+        }
+
+        // This will do our work, open a connection, and run a query (that returns 4 results sets)
+        // if we are poisoning we will 
+        //   1 - Interject some sleeps in the sql statement so that it will run long enough that we can cancel it
+        //   2 - Setup a time bomb task that will cancel the command a random amount of time later
+        private async Task DoOneAsync(string connectionString, bool poison = false)
+        {
+            try
+            {
+                using (var connection = new SqlConnection(connectionString))
+                {
+                    StringBuilder builder = new StringBuilder();
+                    for (int i = 0; i < 4; i++)
+                    {
+                        builder.AppendLine("SELECT name FROM sys.tables");
+                        if (poison && i < 3)
+                        {
+                            builder.AppendLine("WAITFOR DELAY '00:00:01'");
+                        }
+                    }
+
+                    int rowsRead = 0;
+                    int resultRead = 0;
+
+                    try
+                    {
+                        await connection.OpenAsync();
+                        using (var command = connection.CreateCommand())
+                        {
+                            Task timeBombTask = default;
+                            try
+                            {
+                                // Setup our time bomb
+                                if (poison)
+                                {
+                                    timeBombTask = TimeBombAsync(command);
+                                }
+
+                                command.CommandText = builder.ToString();
+
+                                // Attempt to read all of the data
+                                using (var reader = await command.ExecuteReaderAsync())
+                                {
+                                    try
+                                    {
+                                        do
+                                        {
+                                            resultRead++;
+                                            while (await reader.ReadAsync() && _continue)
+                                            {
+                                                rowsRead++;
+                                            }
+                                        }
+                                        while (await reader.NextResultAsync() && _continue);
+                                    }
+                                    catch when (poison)
+                                    {
+                                        //  This looks a little strange, we failed to read above so this should fail too
+                                        //  But consider the case where this code is elsewhere (in the Dispose method of a class holding this logic)
+                                        try
+                                        {
+                                            while (await reader.NextResultAsync())
+                                            {
+                                            }
+                                        }
+                                        catch
+                                        {
+                                            Interlocked.Increment(ref _poisonCleanUpExceptions);
+                                        }
+
+                                        throw;
+                                    }
+                                }
+                            }
+                            finally
+                            {
+                                // Make sure to clean up our time bomb
+                                // It is unlikely, but the timebomb may get delayed in the Task Queue
+                                // And we don't want it running after we dispose the command
+                                if (timeBombTask != default)
+                                {
+                                    await timeBombTask;
+                                }
+                            }
+                        }
+                    }
+                    finally
+                    {
+                        Interlocked.Add(ref _rowsRead, rowsRead);
+                        Interlocked.Add(ref _resultRead, resultRead);
+                        if (poison)
+                        {
+                            Interlocked.Increment(ref _poisonedEnded);
+                        }
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                if (!poison)
+                {
+                    Interlocked.Increment(ref _nonPoisonedExceptions);
+
+                    string details = ex.ToString();
+                    details = details.Substring(0, Math.Min(200, details.Length));
+                    lock (_exceptionDetails)
+                    {
+                        _exceptionDetails.Add(details);
+                    }
+                }
+
+                if (ex.Message.Contains("The MARS TDS header contained errors."))
+                {
+                    _continue = false;
+                    if (_found == 0) // This check is not really safe we may list more than one.
+                    {
+                        lock (_lockObject)
+                        {
+                            // You will notice that poison will be likely be false here, it is the normal commands that suffer
+                            // Once we have successfully poisoned the connection pool, we may start to see some other request to poison fail just like the normal requests
+                            _output.WriteLine($"{poison} {DateTime.UtcNow.ToString("O")}");
+                            _output.WriteLine(ex.ToString());
+                        }
+                    }
+                    Interlocked.Increment(ref _found);
+                }
+            }
+        }
+
+        private async Task TimeBombAsync(SqlCommand command)
+        {
+            await SleepAsync(100, 3000);
+            command.Cancel();
+        }
+
+        private async Task SleepAsync(int minMs, int maxMs)
+        {
+            int delayMs;
+            lock (_random)
+            {
+                delayMs = _random.Next(minMs, maxMs);
+            }
+            await Task.Delay(delayMs);
+        }
+
+        private Stopwatch _watch;
+
+        private int _inFlight;
+        private int _start;
+        private int _done;
+        private int _rowsRead;
+        private int _resultRead;
+        private int _nonPoisonedExceptions;
+        private int _poisonedEnded;
+        private int _poisonCleanUpExceptions;
+        private bool _continue = true;
+        private int _found;
+        private Random _random;
+        private object _lockObject = new object();
+
+        private HashSet<string> _exceptionDetails = new HashSet<string>();
+    }
+}

src/System.Data.SqlClient/tests/ManualTests/System.Data.SqlClient.ManualTesting.Tests.csproj

@@ -45,6 +45,7 @@
     <Compile Include="ProviderAgnostic\MultipleResultsTest\MultipleResultsTest.cs" />
     <Compile Include="ProviderAgnostic\ReaderTest\ReaderTest.cs" />
     <Compile Include="SQL\AsyncTest\AsyncTest.cs" />
+    <Compile Include="SQL\AsyncTest\AsyncCancelledConnectionsTest.cs" />
     <Compile Include="SQL\CommandCancelTest\CommandCancelTest.cs" />
     <Compile Include="SQL\ConnectionPoolTest\ConnectionPoolTest.cs" />
     <Compile Include="SQL\ConnectivityTests\ConnectivityTest.cs" />