SFTP downloads hang in 2025.1.0+ but work in 2025.0.0 #1843

Summary

An SFTP download that completes successfully with SSH.NET 2025.0.0 hangs after upgrading to 2025.1.0 or 2026.0.0.

Versions tested

• Works: SSH.NET 2025.0.0
• Hangs: SSH.NET 2025.1.0
• Hangs: SSH.NET 2026.0.0

Environment

• .NET version: [insert]
• OS: [insert]
• SFTP server product and version: [insert]

Reproduction

The original implementation opens the remote file as an SftpFileStream and copies it to a local destination stream:

await using var fileStream = File.Create("file path");
await using var sftpFileStream = await client.OpenAsync(
    "file name",
    FileMode.Open,
    FileAccess.Read,
    CancellationToken.None);

await sftpFileStream.CopyToAsync(fileStream);

This completes with SSH.NET 2025.0.0. With 2025.1.0 and 2026.0.0, the operation does not complete.

I also tested the dedicated download API:

await using var fileStream = File.Create("file path");
await client.DownloadFileAsync(
    "file name",
    fileStream,
    CancellationToken.None);

It hangs as well in 2025.1.0 and 2026.0.0.

Expected behavior

The file download should complete, as it does with SSH.NET 2025.0.0.

Actual behavior

The download hangs indefinitely with 2025.1.0 and 2026.0.0, without completing or throwing an exception.