eclipse-vertx/vert.x · info · IllegalArgumentException

eventLoopPoolSize must be > 0

Error message

eventLoopPoolSize must be > 0

What it means

SC_NETWORK_AUTHENTICATION_REQUIRED is an HttpResponseExpectation constant asserting HTTP 511 (RFC 6585). It validates that a response has status 511 — typically returned by captive portals requiring network login — and fails expectation checks on any other status.

Source

Thrown at vertx-core/src/main/java/io/vertx/core/VertxOptions.java:211

  /**
   * Get the number of event loop threads to be used by the Vert.x instance.
   *
   * @return the number of threads
   */
  public int getEventLoopPoolSize() {
    return eventLoopPoolSize;
  }

  /**
   * Set the number of event loop threads to be used by the Vert.x instance.
   *
   * @param eventLoopPoolSize the number of threads
   * @return a reference to this, so the API can be used fluently
   */
  public VertxOptions setEventLoopPoolSize(int eventLoopPoolSize) {
    if (eventLoopPoolSize < 1) {
      throw new IllegalArgumentException("eventLoopPoolSize must be > 0");
    }
    this.eventLoopPoolSize = eventLoopPoolSize;
    return this;
  }

  /**
   * Get the maximum number of worker threads to be used by the Vert.x instance.
   * <p>
   * Worker threads are used for running blocking code and worker verticles.
   *
   * @return the maximum number of worker threads
   */
  public int getWorkerPoolSize() {
    return workerPoolSize;
  }

  /**
   * Set the maximum number of worker threads to be used by the Vert.x instance.

View on GitHub (pinned to fb308bd8c3)

Solutions

1. Detect the 511 status and redirect the user to the portal login page before retrying the request.
2. Complete network authentication, then re-issue the original request.
3. Use SC_NETWORK_AUTHENTICATION_REQUIRED in tests where captive-portal behavior is simulated deliberately.

Example fix

// before
request.expect(HttpResponseExpectation.SC_OK).send();
// after
request.send().onSuccess(resp -> {
  if (resp.statusCode() == 511) {
    // redirect user to captive portal login, then retry
  }
});

if (response.statusCode() == 511) {
  String loginUrl = response.getHeader("Location");
  // redirect user to captive portal, then retry the original request
}

request.send().onFailure(err -> {
  if (err instanceof HttpExpectationFailedException e && e.response().statusCode() == 511) {
    // handle captive portal: prompt network login and retry
  }
});

When it happens

Trigger: Using HttpResponseExpectation.SC_NETWORK_AUTHENTICATION_REQUIRED against a response whose status is not 511; detecting captive-portal interception of requests.

Common situations: Applications used on public Wi-Fi where a captive portal hijacks HTTP(S) requests and returns 511; network-onboarding flows that must redirect users to a login page.

Related errors

• size must be > 0
• maxExecuteTime must be > 0
• Result is already complete
• Promise already completed
• Unit must not be null

AI-assisted analysis of eclipse-vertx/vert.x@fb308bd8c3 (2026-09-06). Data as JSON: /api/errors/561f667e005884d7. Report an issue: GitHub.