ScpClient: Make -d flag optional or avoid it for better compatibility with Cisco SCP servers

[MicaelLysen]

Hi, and thanks for SSH.NET 👋

I’m using SSH.NET 2025.1.0 (via NuGet) and ran into the same Cisco SCP issue as described in #829 (“Scp on cisco device not working”).

On Cisco devices, the -d option used by ScpClient for uploads is not supported by their SCP implementation. In #829 this shows up as errors like:

-p -d options not supported

When I look at the 2025.1.0 source for ScpClient, I still see scp -t -d ... being used for uploads.

Example usage:

using var scp = new ScpClient(host, username, password);
scp.RemotePathTransformation = RemotePathTransformation.None;
scp.Connect();

using var stream = new MemoryStream(Encoding.UTF8.GetBytes(content));
scp.Upload(stream, "startup-config");

This works fine with OpenSSH servers but fails against Cisco devices due to the -d flag.

Request / proposal

For better interoperability, it would be helpful if ScpClient:

either removed -d for file uploads and just used

scp -t

or exposed a property to disable -d, e.g.:

public bool UseDirectoryFlag { get; set; } = true;

and then:

var target = _remotePathTransformation.Transform(UseDirectoryFlag ? posixPath.Directory : posixPath.File);
var exec = UseDirectoryFlag
    ? $"scp -t -d {target}"
    : $"scp -t {target}";
if (!channel.SendExecRequest(exec))
{
    throw SecureExecutionRequestRejectedException();
}

That would keep current behavior for OpenSSH, but allow users to work with Cisco and other limited SCP implementations without maintaining a custom fork.

Happy to help test any change against Cisco devices if needed.