dotnet/yarp · error · ArgumentException

Expected additional args.

Error message

Expected additional args.

What it means

Thrown by the SampleClient's CommandLineArgs.ParseRemainder when it is asked to parse a remainder that contains zero tokens. In the shipped parser this branch is effectively unreachable because ParseRemainder is only called when i < args.Length, so the slice always has length >= 1; it exists as a defensive guard for the 'a scenario name is required' intent.

Source

Thrown at testassets/TestClient/CommandLineArgs.cs:57

                case "--target":
                case "-t":
                    result.Target = args[++i];
                    break;
            }
        }

        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.");

View on GitHub (pinned to bd11867bee)

Solutions

1. Pass a scenario name, e.g. `--scenario Http2PostExpectContinueScenario` or as a single positional argument.
2. If you modified CommandLineArgs, ensure ParseRemainder is only invoked with a non-empty remainder, or remove the now-dead branch.

// Guard the CLI entry point: require a scenario before running.
var args2 = CommandLineArgs.Parse(args);
if (string.IsNullOrEmpty(args2.Scenario)) {
    CommandLineArgs.ShowHelp();
    return 1;
}

When it happens

Trigger: Conceptually: invoking the SampleClient in a way that reaches ParseRemainder with an empty remainder. In practice this requires an internal caller change; the normal CLI path cannot trigger it because the loop only delegates when there is at least one remaining token.

Common situations: Editing the parser and removing the guard that ensures remainder.Length > 0 before calling ParseRemainder; calling ParseRemainder directly from a test with an empty span.

Related errors

• Unexpected arg '{remainder[1]}'.
• 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/d5012aa6aaf54752. Report an issue: GitHub.