Tyrrrz/YoutubeDownloader · error · InvalidOperationException

Invalid JSON for type '{typeToConvert.FullName}'.

Error message

Invalid JSON for type '{typeToConvert.FullName}'.

What it means

Thrown by the custom ContainerJsonConverter.Read while deserializing the LastContainer setting. The converter expects a JSON object of exactly {"Name":"<non-empty>"} and treats anything else - null, a bare string, an object without a Name property, an empty name, or a Name in a different case - as invalid, because Container (YoutubeExplode) has no implicit default.

Source

Thrown at YoutubeDownloader/Services/SettingsService.cs:111

            {
                while (reader.Read() && reader.TokenType != JsonTokenType.EndObject)
                {
                    if (
                        reader.TokenType == JsonTokenType.PropertyName
                        && reader.GetString() == "Name"
                        && reader.Read()
                        && reader.TokenType == JsonTokenType.String
                    )
                    {
                        var name = reader.GetString();
                        if (!string.IsNullOrWhiteSpace(name))
                            result = new Container(name);
                    }
                }
            }

            return result
                ?? throw new InvalidOperationException(
                    $"Invalid JSON for type '{typeToConvert.FullName}'."
                );
        }

        public override void Write(
            Utf8JsonWriter writer,
            Container value,
            JsonSerializerOptions options
        )
        {
            writer.WriteStartObject();
            writer.WriteString("Name", value.Name);
            writer.WriteEndObject();
        }
    }
}

public partial class SettingsService

View on GitHub (pinned to bbcff03951)

Solutions

1. Delete or reset the settings file so it regenerates with the default (Container.Mp4).
2. Correct the offending JSON to the canonical shape {"Name":"mp4"} (or webm/mp3/etc.).
3. Make the converter tolerant: return a default on null/empty, accept a bare string for backward compat, and use case-insensitive property matching so legacy/corrupt values don't crash settings load.

Example fix

// before: any deviation from {"Name":"..."} throws and blocks settings load
return result
    ?? throw new InvalidOperationException($"Invalid JSON for type '{typeToConvert.FullName}'.");

// after: fall back to a sensible default instead of throwing
return result ?? Container.Mp4;

using var doc = JsonDocument.Parse(File.ReadAllText(settingsPath));

if (doc.RootElement.TryGetProperty(nameof(SettingsService.LastContainer), out var c)
    && (c.ValueKind != JsonValueKind.Object
        || !c.TryGetProperty("Name", out var n)
        || n.ValueKind != JsonValueKind.String
        || string.IsNullOrWhiteSpace(n.GetString())))
{
    // reset LastContainer to the default before deserializing
}

try
{
    settings.Load();
}
catch (InvalidOperationException ex) when (ex.Message.StartsWith("Invalid JSON for type"))
{
    File.Move(settingsPath, settingsPath + ".bak", overwrite: true);
    settings.Load(); // regenerates with defaults
}

When it happens

Trigger: The settings file (StartOptions.Current.SettingsPath) holds a LastContainer value that isn't {"Name":"mp4"} - e.g. null, "mp4", {}, {"Container":"mp4"}, or {"name":"mp4"}. The property comparison reader.GetString() == "Name" at line 98 is case-sensitive, so camelCase/lowercase keys fail. Reached whenever settings are loaded/deserialized.

Common situations: Upgrading from an older app version that serialized Container differently (e.g. as a plain string or under a different key); hand-editing the settings file; partial-write corruption; a casing change in the serialized form; schema drift after a YoutubeExplode version bump.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of Tyrrrz/YoutubeDownloader@bbcff03951 (2026-08-13). Data as JSON: /api/errors/4fcd34045c2f9ee3. Report an issue: GitHub.