Unable to connect to SqlServer instance with managed SNI and Timeout=0 on SqlClient 5.0

[vonzshik]

Describe the bug

While attempting to establish the connection to SqlServer instance while having Timeout=0 in the connection string the app becomes unresponsive. I'm able to reproduce this problem on linux and windows with AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.UseManagedNetworkingOnWindows", true). It works fine on SqlClient 4.1.0.

To reproduce

AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.UseManagedNetworkingOnWindows", true);

var sw = Stopwatch.StartNew();
using var connection = new SqlConnection("Server=.;Database=master;Integrated Security=false;User ID=sa;Password=SomePassword;Pooling=true;Max Pool Size=1024;TrustServerCertificate=true;Timeout=0");
await connection.OpenAsync();

using var cmd = connection.CreateCommand();
cmd.CommandText = "SELECT 1";
await cmd.ExecuteNonQueryAsync();
Console.WriteLine($"Connection established successfully in {sw.ElapsedMilliseconds}ms. Press any key to continue...");
Console.ReadKey();

Expected behavior

SqlClient should be able to establish a connection with Timeout=0, just like in previous verions

Further technical details

Microsoft.Data.SqlClient 5.0
.NET target: .NET 6.0
SQL Server version: SQL Server 2017
Operating system: CentOS 7, Windows 10

Additional context

The problem is because while waiting for the dns, the timeout passed there is the default TimeSpan, which is 0, and that's why it fails immediately (it should have been -1):

SqlClient/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNITcpHandle.cs

Lines 150 to 159 in bd21d76

	TimeSpan ts = default(TimeSpan);
	// In case the Timeout is Infinite, we will receive the max value of Int64 as the tick count
	// The infinite Timeout is a function of ConnectionString Timeout=0
	bool isInfiniteTimeOut = long.MaxValue == timerExpire;
	if (!isInfiniteTimeOut)
	{
	ts = DateTime.FromFileTime(timerExpire) - DateTime.Now;
	ts = ts.Ticks < 0 ? TimeSpan.FromTicks(0) : ts;
	}

SqlClient/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNITcpHandle.cs

Line 362 in bd21d76

bool complete = serverAddrTask.Wait(timeout);

This was introduced in #1578.

[vonzshik]

Just tested, changing that part of code like this makes it work:

Task<IPAddress[]> serverAddrTask = Dns.GetHostAddressesAsync(serverName);
if (isInfiniteTimeout)
{
	serverAddrTask.Wait();
}
else
{
	bool complete = serverAddrTask.Wait(timeout);

	// DNS timed out - don't block
	if (!complete)
		return null;
}

[lcheunglci]

Thanks @vonzshik for bringing this to our attention. We'll have to discuss with the team and see if this is the desired behaviour or a regression and get back to you soon.