AutoDarkMode/Windows-Auto-Night-Mode · error · InvalidOperationException

Failed to deserialize JSON from file: {path}

Error message

Failed to deserialize JSON from file: {path}

What it means

Thrown by FileService.Read<T>() when System.Text.Json cannot parse the contents of a local settings file. The method reads the file with File.ReadAllText, checks for blank content (returns default), then attempts JsonSerializer.Deserialize; any JsonException is caught and re-thrown as InvalidOperationException with the file path as context. It signals that a persisted JSON file exists but is syntactically invalid or does not match the target type T.

Source

Thrown at AutoDarkModeApp/Services/FileService.cs:37

        var path = Path.Combine(folderPath, fileName);
        if (!File.Exists(path))
        {
            return default;
        }

        var json = File.ReadAllText(path);
        if (string.IsNullOrWhiteSpace(json))
        {
            return default;
        }

        try
        {
            return JsonSerializer.Deserialize<T>(json, _jsonOptions);
        }
        catch (JsonException ex)
        {
            throw new InvalidOperationException($"Failed to deserialize JSON from file: {path}", ex);
        }
    }

    public void Save<T>(string folderPath, string fileName, T content)
    {
        if (!Directory.Exists(folderPath))
        {
            Directory.CreateDirectory(folderPath);
        }

        var fileContent = JsonSerializer.Serialize(content, _jsonOptions);
        WriteAllTextWithRetry(Path.Combine(folderPath, fileName), fileContent);
    }

    public void Delete(string folderPath, string fileName)
    {
        if (fileName != null && File.Exists(Path.Combine(folderPath, fileName)))
        {

View on GitHub (pinned to c15b28e921)

Solutions

1. Open the file at the reported {path} and validate its JSON (e.g. with a linter); fix or delete it so the app regenerates defaults.
2. Delete the corrupt file entirely — Read<T> returns default when the file is absent, letting the app rebuild it.
3. Ensure Save() writes atomically (write to a temp file then File.Move/replace) to prevent partial writes from crashes.
4. Verify the file encoding is UTF-8 without BOM issues and that the JSON matches the current type T schema after upgrades.

Example fix

// before (FileService.Save — non-atomic, truncates on crash)
var fileContent = JsonSerializer.Serialize(content, _jsonOptions);
WriteAllTextWithRetry(Path.Combine(folderPath, fileName), fileContent);

// after — write temp then atomic move so a crash cannot leave a truncated file
var temp = Path.Combine(folderPath, fileName + ".tmp");
File.WriteAllText(temp, fileContent, Encoding.UTF8);
if (File.Exists(path)) File.Replace(temp, path, null);
else File.Move(temp, path);

// Pre-validate the file is parseable JSON before deserializing into T
public static bool TryValidateJson(string path)
{
    if (!File.Exists(path)) return true; // absent is fine, Read returns default
    var json = File.ReadAllText(path);
    if (string.IsNullOrWhiteSpace(json)) return true;
    try { using var doc = JsonDocument.Parse(json); return true; }
    catch (JsonException) { return false; }
}

// Type guard for callers of FileService.Read<T>
if (fileService.Read<MySettings>(folder, file) is { } settings)
{
    // settings deserialized successfully
}
else
{
    // file missing, blank, or returned default — apply defaults
}

try
{
    var settings = fileService.Read<MySettings>(folder, file);
}
catch (InvalidOperationException ex) when (ex.InnerException is JsonException)
{
    // corrupt settings file — back it up and let the app regenerate defaults
    File.Move(path, path + ".corrupt");
}

When it happens

Trigger: Calling IFileService.Read<T>(folderPath, fileName) where the file at Path.Combine(folderPath, fileName) contains malformed JSON (truncated, invalid syntax, wrong types). The JsonSerializer.Deserialize<T> call throws JsonException which is wrapped at FileService.cs:37.

Common situations: App crash or power loss during Save() truncates a settings JSON file; antivirus or sync tools (OneDrive) lock and partially rewrite the file; a user manually edits a settings file and introduces a syntax error; an app upgrade changed the type T so an old file no longer deserializes cleanly.

Related errors

• Saving to {path} failed after 10 retries

AI-assisted analysis of AutoDarkMode/Windows-Auto-Night-Mode@c15b28e921 (2026-08-13). Data as JSON: /api/errors/c178f06b386f2f40. Report an issue: GitHub.