mastra-ai/mastra · error · MastraClientErrorClass

A2A ${method} stream response did not include a body (status

Error message

A2A ${method} stream response did not include a body (status: ${response.status} ${response.statusText})

What it means

requireResponseBody guards A2A streaming calls (sendMessageStream, resubscribeTask): a streaming response must expose a ReadableStream body. When body is null, it throws a MastraClientError including status, statusText, sanitized headers, and (when available) response text to aid debugging.

Source

Thrown at client-sdks/client-js/src/resources/a2a.ts:116

    .join(', ');

  let responseText = '';
  try {
    responseText = await response.text();
  } catch {
    // Ignore body read failures and surface the rest of the response context.
  }

  const details = [
    `A2A ${method} stream response did not include a body`,
    `(status: ${response.status} ${response.statusText})`,
    headerSummary ? `headers: ${headerSummary}` : '',
    responseText ? `body: ${responseText}` : '',
  ]
    .filter(Boolean)
    .join(' ');

  throw new MastraClientErrorClass(response.status, response.statusText, details);
}

/**
 * Class for interacting with an agent via the A2A protocol
 */
export class A2A extends BaseResource {
  constructor(
    options: ClientOptions,
    private agentId: string,
  ) {
    super(options);
  }

  /**
   * Get the agent card with metadata about the agent.
   * @param options - Optional Agent Card verification settings
   * @returns Promise containing the agent card information
   */

View on GitHub (pinned to 75dd419e61)

Solutions

1. Read the status/details embedded in the thrown MastraClientError (headers, body text) to identify the server-side cause.
2. Confirm the A2A server supports streaming responses for the invoked method.
3. Use a runtime with native streaming fetch (Node 18+, modern browsers).
4. For persistent failures, fall back to the non-streaming sendMessage and poll for task updates.

function hasBody(res: Response): res is Response & { body: ReadableStream<Uint8Array> } {
  return res.body !== null;
}

try {
  const events = await a2a.sendMessageStream(msg);
} catch (e) {
  if (e instanceof MastraClientError && e.message.includes('did not include a body')) {
    // fall back to non-streaming sendMessage + task polling
  }
  throw e;
}

When it happens

Trigger: Calling a2a.sendMessageStream(...) or resubscribeTask(...) where the HTTP response has no body: 204/304-style empty responses, server not supporting streaming, or a runtime/polyfill producing bodyless Response objects.

Common situations: A2A server returning a non-streaming error response with empty body; fetch polyfill in a constrained runtime; middleware consuming the stream before the client sees it.

Related errors

• Failed to stream background tasks: ${response.statusText}
• Response body is null
• Failed to stream agent builder action: ${response.statusText
• Response body is null
• Failed to observe agent builder action stream: ${response.st

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/a89007714c9836ad. Report an issue: GitHub.