dotnet/aspnetcore · error · Error

Invalid payload for Invocation message.

Error message

Invalid payload for Invocation message.

What it means

Thrown by _createInvocationMessage when the decoded properties array has fewer than 5 elements. The Invocation message layout is [MessageType.Invocation, headers, invocationId, target, arguments, streamIds?]. Fewer than 5 means required fields (typically target or arguments) are missing.

Solutions

1. Verify the server runs a compatible SignalR MessagePack protocol version.
2. Inspect the decoded properties array contents to identify the missing slot.
3. Treat as connection-poisoning: close and reconnect.

Example fix

// before
// server emits [1, {}, '42', 'Send']  — missing arguments → throws

// after — server must include all required slots
// emit [1, {}, '42', 'Send', [], []]  (arguments, streamIds)

function isValidInvocationProperties(p: unknown[]): boolean {
  return p.length >= 5;
}

function isInvocationPayload(p: unknown[]): p is [number, unknown, string | null, string, unknown[], unknown[]?] {
  return p.length >= 5;
}

try { return protocol.parseMessages(buf, logger); }
catch (e) {
  if (/Invalid payload for Invocation/.test((e as Error).message)) {
    logger.log(LogLevel.Error, 'Malformed Invocation — reconnecting');
    await connection.stop(); await connection.start();
  } else throw e;
}

When it happens

Trigger: A server/peer sent an Invocation frame missing the target or arguments slot; corrupt bytes that decoded to an array of length 1-4 but were typed as Invocation; a non-conforming hub method invocation.

Common situations: Protocol version mismatch (older/newer server with a different Invocation layout); corrupted wire data; malicious peer; testing the parser with truncated arrays.

Related errors

• Invalid payload for Close message.
• Invalid payload for Completion message.
• Invalid payload.
• Invalid payload for Ping message.
• Invalid payload for StreamItem message.

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/b34b4e26d6466794. Report an issue: GitHub.

Appendix: source

Thrown at src/SignalR/clients/ts/signalr-protocol-msgpack/src/MessagePackHubProtocol.ts:190

        } as HubMessage;
    }

    private _createPingMessage(properties: any[]): HubMessage {
        // check minimum length to allow protocol to add items to the end of objects in future releases
        if (properties.length < 1) {
            throw new Error("Invalid payload for Ping message.");
        }

        return {
            // Ping messages have no headers.
            type: MessageType.Ping,
        } as HubMessage;
    }

    private _createInvocationMessage(headers: MessageHeaders, properties: any[]): InvocationMessage {
        // check minimum length to allow protocol to add items to the end of objects in future releases
        if (properties.length < 5) {
            throw new Error("Invalid payload for Invocation message.");
        }

        const invocationId = properties[2] as string;
        if (invocationId) {
            return {
                arguments: properties[4],
                headers,
                invocationId,
                streamIds: [],
                target: properties[3] as string,
                type: MessageType.Invocation,
            };
        } else {
            return {
                arguments: properties[4],
                headers,
                streamIds: [],
                target: properties[3],

View on GitHub (pinned to 3600ca084e)