dotnet/aspnetcore · error · Error

Invalid payload for StreamItem message.

Error message

Invalid payload for StreamItem message.

What it means

Thrown by _createStreamItemMessage when the decoded properties array has fewer than 4 elements. A StreamItem is encoded as [MessageType.StreamItem, headers, invocationId, item]. Fewer than 4 means the item slot — the actual streamed value — is missing.

Solutions

1. Confirm the server's streaming hub method emits items correctly with the canonical MessagePack encoder.
2. Match server and client SignalR protocol versions.
3. Reconnect: a malformed stream item invalidates the stream and likely the connection.

Example fix

// before
// server stream emits [2, {}, '42'] — missing item → throws

// after — server must emit [2, {}, '42', itemValue]

function isValidStreamItemProperties(p: unknown[]): boolean {
  return p.length >= 4;
}

function isStreamItemPayload(p: unknown[]): p is [number, unknown, string, unknown] {
  return p.length >= 4;
}

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

When it happens

Trigger: Receiving a StreamItem frame missing the item slot; corrupt bytes decoded to a short array typed as StreamItem; a non-conforming server-side streaming implementation.

Common situations: Server-side streaming bug that emits the headers/id without the item; protocol version drift; wire corruption mid-stream.

Related errors

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

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/97a24669f9422bef. Report an issue: GitHub.

Appendix: source

Thrown at src/SignalR/clients/ts/signalr-protocol-msgpack/src/MessagePackHubProtocol.ts:218

                target: properties[3] as string,
                type: MessageType.Invocation,
            };
        } else {
            return {
                arguments: properties[4],
                headers,
                streamIds: [],
                target: properties[3],
                type: MessageType.Invocation,
            };
        }

    }

    private _createStreamItemMessage(headers: MessageHeaders, properties: any[]): StreamItemMessage {
        // check minimum length to allow protocol to add items to the end of objects in future releases
        if (properties.length < 4) {
            throw new Error("Invalid payload for StreamItem message.");
        }

        return {
            headers,
            invocationId: properties[2],
            item: properties[3],
            type: MessageType.StreamItem,
        } as StreamItemMessage;
    }

    private _createCompletionMessage(headers: MessageHeaders, properties: any[]): CompletionMessage {
        // check minimum length to allow protocol to add items to the end of objects in future releases
        if (properties.length < 4) {
            throw new Error("Invalid payload for Completion message.");
        }

        const resultKind = properties[3];

View on GitHub (pinned to 3600ca084e)