BornToBeRoot/NETworkManager · error · InvalidOperationException

Hosts file name is invalid.

Error message

Hosts file name is invalid.

What it means

In the HostsFileEditor constructor, Path.GetFileName(HostsFilePath) is assigned to the FileSystemWatcher Filter; if it returns null/empty the ??-fallback throws InvalidOperationException('Hosts file name is invalid.'). This happens when the path ends in a directory separator or is empty, leaving no file-name component.

Solutions

1. Pass the complete file path including the file name (e.g. ...\etc\hosts).
2. Normalize with Path.GetFullPath and verify !string.IsNullOrEmpty(Path.GetFileName(path)) before constructing.
3. Validate in settings UI that the configured value is a file, not a directory.
4. Catch the InvalidOperationException and revert to the default hosts path.

Example fix

// before
var editor = new HostsFileEditor(@"C:\Windows\System32\drivers\etc\");
// after
var p = Path.GetFullPath(path);
if (string.IsNullOrEmpty(Path.GetFileName(p)))
    p = Path.Combine(p, "hosts");
var editor = new HostsFileEditor(p);

// ensure the path has a file-name component
if (string.IsNullOrWhiteSpace(Path.GetFileName(path)))
    path = Path.Combine(path, "hosts");

null

try
{
    var editor = new HostsFileEditor(path);
}
catch (InvalidOperationException ex) when (ex.Message.Contains("file name"))
{
    Log.Warn("Hosts path has no file name; using default", ex);
    var editor = new HostsFileEditor(Path.Combine(DirPart, "hosts"));
}

When it happens

Trigger: Constructing HostsFileEditor with a HostsFilePath that is a directory path (trailing backslash), an empty string, or otherwise lacks a file-name segment so Path.GetFileName yields null.

Common situations: Configuration storing a directory instead of the full hosts file path; string truncation when persisting the setting; tests passing directory paths.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Hosts file path is invalid.

AI-assisted analysis of BornToBeRoot/NETworkManager@2780d65469 (2026-09-12). Data as JSON: /api/errors/dbaae5211e5ece22. Report an issue: GitHub.

Appendix: source

Thrown at Source/NETworkManager.Models/HostsFileEditor/HostsFileEditor.cs:87

    private static readonly Regex HostsFileEntryRegex = new(RegexHelper.HostsEntryRegex);

    #endregion

    #region Constructor

    static HostsFileEditor()
    {
        // Create a file system watcher to monitor changes to the hosts file
        try
        {
            Log.Debug("HostsFileEditor - Creating file system watcher for hosts file...");

            // Create the file system watcher
            HostsFileWatcher = new FileSystemWatcher();
            HostsFileWatcher.Path = Path.GetDirectoryName(HostsFilePath) ??
                                    throw new InvalidOperationException("Hosts file path is invalid.");
            HostsFileWatcher.Filter = Path.GetFileName(HostsFilePath) ??
                                      throw new InvalidOperationException("Hosts file name is invalid.");
            HostsFileWatcher.NotifyFilter = NotifyFilters.LastWrite;

            // Maybe fired twice. This is a known bug/feature.
            // See: https://stackoverflow.com/questions/1764809/filesystemwatcher-changed-event-is-raised-twice
            HostsFileWatcher.Changed += (_, _) => OnHostsFileChanged();

            // Enable the file system watcher
            HostsFileWatcher.EnableRaisingEvents = true;

            Log.Debug("HostsFileEditor - File system watcher for hosts file created.");
        }
        catch (Exception ex)
        {
            Log.Error("Failed to create file system watcher for hosts file.", ex);
        }
    }

    #endregion

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