microsoft/semantic-kernel · error · ArgumentException

Unknown type {type}

Error message

Unknown type {type}

What it means

Thrown by GetNetType's switch expression when a protobuf field type enum value is not one of the recognized TYPE_* cases (DOUBLE, FLOAT, INT64, ... BYTES, etc.). The default arm raises ArgumentException naming the unrecognized type token.

Source

Thrown at dotnet/src/Functions/Functions.Grpc/GrpcOperationRunner.cs:351

    private static Type GetNetType(string type) =>
        type switch
        {
            "TYPE_DOUBLE" => typeof(double),
            "TYPE_FLOAT" => typeof(float),
            "TYPE_INT64" => typeof(long),
            "TYPE_UINT64" => typeof(ulong),
            "TYPE_INT32" => typeof(int),
            "TYPE_FIXED64" => typeof(ulong),
            "TYPE_FIXED32" => typeof(uint),
            "TYPE_BOOL" => typeof(bool),
            "TYPE_STRING" => typeof(string),
            "TYPE_BYTES" => typeof(byte[]),
            "TYPE_UINT32" => typeof(uint),
            "TYPE_SFIXED32" => typeof(int),
            "TYPE_SFIXED64" => typeof(long),
            "TYPE_SINT32" => typeof(int),
            "TYPE_SINT64" => typeof(long),
            _ => throw new ArgumentException($"Unknown type {type}", nameof(type)),
        };
}

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Restrict the .proto operation payload to primitive scalar types the switch handles.
2. Avoid enum-typed, message-typed, or map fields in the gRPC operation contract used by this runner.
3. If you need an unsupported type, pass it as a string and handle conversion yourself.

Example fix

// before
// .proto field: repeated Item items = 1; (message type)
// after
// .proto field: string items_json = 1; (primitive)

// Inspect your .proto: only use scalar types this runner maps (TYPE_STRING, TYPE_INT32, ...).

try { /* invoke */ }
catch (ArgumentException ex) when (ex.Message.Contains("Unknown type")) {
    // a field type is unsupported; simplify the .proto
}

When it happens

Trigger: A FieldDescriptorProto.Type value outside the handled set — typically a newer protobuf type (e.g. enum-typed or message-typed fields that arrive as a Type enum the switch doesn't map) or a corrupt descriptor.

Common situations: Using complex message/enum/map fields in the .proto that the runner does not yet support; protobuf-schema features ahead of the supported set.

Related errors

• Impossible to create type for '{dataContractMetadata.Name}'
• Parsing of '{protoFileName}' .proto document has failed. Det
• No '{fullTypeName}' message type is found while resolving da
• Impossible to find protobuf type name corresponding to '{typ
• Unsupported parameter type: {typeString}

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/160f8d9ce28f19d5. Report an issue: GitHub.