ppy/osu · error · IOException

Deserialization of arbitrary type is not supported.

Error message

Deserialization of arbitrary type is not supported.

What it means

Thrown by SerializationReader when the type discriminator byte equals ObjType.OtherType during generic object deserialisation. The reader only supports primitive types, byte/char arrays, DateTime, and ILegacySerializable; an 'OtherType' marker indicates an arbitrary serialised object that this reader deliberately refuses to instantiate.

Source

Thrown at osu.Game/IO/Legacy/SerializationReader.cs:178

                    return ReadSingle();

                case ObjType.DoubleType:
                    return ReadDouble();

                case ObjType.DecimalType:
                    return ReadDecimal();

                case ObjType.DateTimeType:
                    return ReadDateTime();

                case ObjType.ByteArrayType:
                    return ReadByteArray();

                case ObjType.CharArrayType:
                    return ReadCharArray();

                case ObjType.OtherType:
                    throw new IOException("Deserialization of arbitrary type is not supported.");

                default:
                    return null;
            }
        }
    }

    public enum ObjType : byte
    {
        NullType,
        BoolType,
        ByteType,
        UInt16Type,
        UInt32Type,
        UInt64Type,
        SByteType,
        Int16Type,
        Int32Type,

View on GitHub (pinned to d9c73e12ad)

Solutions

1. Confirm the stream section is meant to be read with the generic object reader; if it's a known ILegacySerializable, use ReadBList<T>/the typed path instead.
2. Verify the data source and format version match the reader's expectations; reject incompatible files.
3. Catch IOException around deserialisation and treat the payload as unsupported rather than crashing the import.

Example fix

// before
object value = reader.ReadObject(); // throws on OtherType

// after
try
{
    object value = reader.ReadObject();
}
catch (IOException ex) when (ex.Message.Contains("not supported"))
{
    Logger.Log("Unsupported serialised type encountered; payload skipped.", LoggingTarget.Database);
}

// Before generic read, confirm the expected type byte for this field.
ObjType t = (ObjType)reader.PeekByte();
if (t == ObjType.OtherType) throw new InvalidDataException("Unsupported object type in stream.");

try { object value = reader.ReadObject(); }
catch (IOException ex) when (ex.Message.Contains("not supported"))
{ /* skip unsupported payload */ }

When it happens

Trigger: Calling the generic ReadObject/deserialise path on a stream whose type byte is OtherType — i.e. the data was written by a serialiser that embedded a complex type the osu! reader can't reconstruct. A security/integrity guard against unexpected types.

Common situations: Replay or legacy data produced by a different/newer serialiser, a truncated stream where the type byte is garbage, or an attempt to read a section with the wrong reader method.

Related errors

• Bad ticks count read!
• input .lzma is too short
• Can't Read 1
• Unknown hit object type.
• Unknown file format (no content)

AI-assisted analysis of ppy/osu@d9c73e12ad (2026-08-13). Data as JSON: /api/errors/0b623288a26835b9. Report an issue: GitHub.