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I'm using one SftpClient object, simultaneously on two different threads. While the primary thread is doing a large upload (UploadFile()), I have a background task making sure we're still connected by doing ListDirectory("/") every few seconds. When I do that, the SftpClient disconnects.
I tested this using two different SSH servers: My primary target is a small embedded device, running Dropbear SSH server. On that server, the disconnect usually happens on the very first call to ListDirectory. For testing, I also tried a server running OpenSSH on Rocky Linux 8. Using that, the call to ListDirectory generally succeeds several times, but it eventually fails as well.
I am using SSH.NET version 2024.2.0 on .Net 9.
Here is a self-contained demonstration program.
using Renci.SshNet;
namespace SshMultiUseTest;
internal class Program
{
#if false
// This is my small embedded device. Low power. Running PetaLinux on a Xilinx SoC.
// SSH Server is Dropbear v2020.80. (No, I can't change that.)
// (Why 127.0.0.1? I'm on a work computer, with a strict VPN. I have to use an SSH tunnel
// to make connections to machines on the local network.)
const string host = "127.0.0.1";
const int port = 2122;
const string user = "root";
const string privKey = "DeviceKey.id_rsa";
#else
// This is my Linux server. It's a normal desktop PC, maybe 10 years old. Intel i7 of some sort.
// Running Rocky Linux 8. SSH Server is OpenSSH 8.0p1.
const string host = "127.0.0.1";
const int port = 2200;
const string user = "dyaw";
const string privKey = "id_rsa";
#endif
const string largeFile = "C:\\Data\\deviceUpgrade.mfuf";
static void Main(string[] args)
{
SftpClient sftpClient = new(
host, port, user,
new PrivateKeyFile(typeof(Program).Assembly.GetManifestResourceStream(typeof(Program), privKey)!));
sftpClient.Connect();
// Verify connectivity
foreach (var item in sftpClient.ListDirectory("/")) { }
using FileStream fs = new(largeFile, FileMode.Open, FileAccess.Read);
int count = 0;
void callback(ulong uploaded)
{
int newCount = Interlocked.Increment(ref count);
if (newCount < 20 || newCount % 100 == 0)
Console.WriteLine("Uploaded: {0:N0}", uploaded);
}
Task largeUploadTask = Task.Run(() => sftpClient.UploadFile(fs, "/home/" + user + "/uploadTest", callback));
int exceptionCount = 0;
while (!largeUploadTask.IsCompleted)
{
Thread.Sleep(1000);
try
{
foreach (var item in sftpClient.ListDirectory("/")) { }
Console.WriteLine("Small Task: Directory Listing complete");
exceptionCount = 0;
}
catch (Exception e)
{
if (++exceptionCount < 5)
{
// These get repetitive after the first couple. Be quiet.
Console.WriteLine("From small task: {0}: {1}", e.GetType().FullName, e.Message);
}
}
}
try
{
largeUploadTask.Wait();
}
catch (Exception e)
{
if (e is AggregateException && e.InnerException != null)
e = e.InnerException;
Console.WriteLine("From large task: {0}: {1}", e.GetType().FullName, e.Message);
}
}
}
Result, connecting to the embedded device:
Uploaded: 65,460
Uploaded: 32,730
Uploaded: 98,190
Uploaded: 130,920
Uploaded: 163,650
Uploaded: 196,380
Uploaded: 229,110
Uploaded: 261,840
Uploaded: 294,570
Uploaded: 327,300
Uploaded: 360,030
Uploaded: 392,760
Uploaded: 425,490
Uploaded: 458,220
Uploaded: 490,950
Uploaded: 523,680
Uploaded: 556,410
Uploaded: 589,140
Uploaded: 621,870
Uploaded: 3,273,000
Uploaded: 6,546,000
From small task: Renci.SshNet.Common.SshException: Channel was closed.
From small task: System.InvalidOperationException: The session is not open.
From small task: System.InvalidOperationException: The session is not open.
From small task: System.InvalidOperationException: The session is not open.
(long pause here)
From large task: Renci.SshNet.Common.SshOperationTimeoutException: Session operation has timed out
I'm using one SftpClient object, simultaneously on two different threads. While the primary thread is doing a large upload (
UploadFile()), I have a background task making sure we're still connected by doingListDirectory("/")every few seconds. When I do that, the SftpClient disconnects.I tested this using two different SSH servers: My primary target is a small embedded device, running Dropbear SSH server. On that server, the disconnect usually happens on the very first call to ListDirectory. For testing, I also tried a server running OpenSSH on Rocky Linux 8. Using that, the call to ListDirectory generally succeeds several times, but it eventually fails as well.
I am using SSH.NET version 2024.2.0 on .Net 9.
Here is a self-contained demonstration program.
Result, connecting to the embedded device:
Result, connecting to my regular server:
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