dotnet/yarp · error · ArgumentException

Unexpected arg '{remainder[1]}'.

Error message

Unexpected arg '{remainder[1]}'.

What it means

Thrown by CommandLineArgs.ParseRemainder when the trailing positional arguments contain more than one token. The parser only expects a single positional value (the scenario name); any extra positional token is rejected with the offending value interpolated.

Source

Thrown at testassets/TestClient/CommandLineArgs.cs:62

        }

        if (i < args.Length)
        {
            return ParseRemainder(result, args.AsSpan().Slice(i));
        }

        return result;

        static CommandLineArgs ParseRemainder(CommandLineArgs result, Span<string> remainder)
        {
            if (remainder.Length == 0)
            {
                throw new ArgumentException("Expected additional args.");
            }

            if (remainder.Length > 1)
            {
                throw new ArgumentException($"Unexpected arg '{remainder[1]}'.");
            }

            result.Scenario = remainder[0];
            return result;
        }
    }

    public static void ShowHelp()
    {
        Console.WriteLine("ReverseProxy SampleClient.\n");
        Console.WriteLine("--scenario <name>, -s <name>: Runs only the specified scenario.");
        Console.WriteLine(
            "--target <uri>, -t <uri>: Sets the target uri. By default, 'https://localhost:1443/' is used.");
        Console.WriteLine("--help, -h, -?, /?: Shows this help information.");
    }
}

View on GitHub (pinned to bd11867bee)

Solutions

1. Pass exactly one positional scenario name, or use --scenario/-s to name it explicitly.
2. Quote any argument containing spaces.
3. Remove unrecognized flags; only --scenario/-s, --target/-t, and --help/-h/-?//? are recognized.

Example fix

// before
dotnet TestClient ScenarioA ScenarioB

// after
dotnet TestClient --scenario ScenarioA

// Validate argv shape before parsing.
var positional = args.Where(a => !a.StartsWith('-')).ToList();
if (positional.Count > 1)
    throw new ArgumentException($"Only one positional scenario argument is allowed; got {positional.Count}.");

When it happens

Trigger: Running the SampleClient with two or more positional arguments, e.g. `TestClient ScenarioA ScenarioB`, or mixing an unrecognized flag that falls through the switch and becomes positional.

Common situations: Typing two scenario names; passing an unquoted argument containing a space that splits into two tokens; an unrecognized --flag that the switch does not consume so it rolls into the remainder.

Related errors

• Expected additional args.
• Expected status 409 Conflict!
• Expected status 101 Switching Protocols!
• Read {read} bytes, expected 0 after sending Goodbye.
• Read {read} bytes, expected 1.

AI-assisted analysis of dotnet/yarp@bd11867bee (2026-08-13). Data as JSON: /api/errors/5f3522948dc7a42f. Report an issue: GitHub.