CoplayDev/unity-mcp · error · ArgumentOutOfRangeException

Port must be positive.

Error message

Port must be positive.

What it means

SetPreferredPort rejects non-positive ports immediately with ArgumentOutOfRangeException ('port <= 0') before any availability probe. This is an argument guard ensuring a valid port number is supplied.

Source

Thrown at MCPForUnity/Editor/Helpers/PortManager.cs:94

        /// <summary>
        /// Decide whether a configured port that keeps reporting AddressAlreadyInUse should be
        /// abandoned for a freshly discovered port. Returns false (keep retrying the same port)
        /// until it has been continuously busy for <see cref="BusyPortFallbackWindowSeconds"/>,
        /// which distinguishes a domain-reload socket-release race from a foreign occupant (#1173).
        /// </summary>
        public static bool ShouldAbandonBusyPort(double busyForSeconds)
            => busyForSeconds >= BusyPortFallbackWindowSeconds;

        /// <summary>
        /// Persist a user-selected port and return the value actually stored.
        /// If <paramref name="port"/> is unavailable, the next available port is chosen instead.
        /// </summary>
        public static int SetPreferredPort(int port)
        {
            if (port <= 0)
            {
                throw new ArgumentOutOfRangeException(nameof(port), "Port must be positive.");
            }

            if (!IsPortAvailable(port))
            {
                throw new InvalidOperationException($"Port {port} is already in use.");
            }

            SavePort(port);
            return port;
        }

        /// <summary>
        /// Find an available port starting from the default port
        /// </summary>
        /// <returns>Available port number</returns>
        private static int FindAvailablePort()
        {
            // Always try default port first

View on GitHub (pinned to c21bf496bc)

Solutions

1. Pass a positive port in the valid range, typically 1024-65535.
2. Validate and normalize the configured port (defaulting to the project default) before calling SetPreferredPort.
3. Distinguish 'unset' (use auto-find) from 'explicit invalid' (surface a config error).

Example fix

// before
SetPreferredPort(parsedPort); // parsedPort may be 0 when config missing

// after
int port = parsedPort > 0 ? parsedPort : PortManager.DefaultPort;
SetPreferredPort(port);

int NormalizePort(int candidate, int fallback)
{
    if (candidate <= 0 || candidate > 65535) return fallback;
    return candidate;
}

int port = NormalizePort(configPort, PortManager.DefaultPort);
if (port <= 0) throw new InvalidOperationException("No valid port configured.");
PortManager.SetPreferredPort(port);

static bool IsValidPort(int port) => port > 0 && port <= 65535;

try { PortManager.SetPreferredPort(port); }
catch (ArgumentOutOfRangeException)
{
    // Config supplied an invalid port; fall back to the default and retry.
    PortManager.SetPreferredPort(PortManager.DefaultPort);
}

When it happens

Trigger: Calling SetPreferredPort with 0, a negative number, or an uninitialized int (default 0) from missing config. The check is 'if (port <= 0)'.

Common situations: Port config unset and defaulting to 0; a parse error producing 0; off-by-one in a port-range computation; a null/empty config value coerced to 0.

Related errors

• Port {port} is already in use.
• No available ports found in range {DefaultPort}-{DefaultPort
• uid required
• zipPath required
• No Unity instance found on port {value}. Available: {availab

AI-assisted analysis of CoplayDev/unity-mcp@c21bf496bc (2026-08-13). Data as JSON: /api/errors/3124007f2e4ecf41. Report an issue: GitHub.