eclipse-vertx/vert.x · error · IllegalArgumentException

multiplexingLimit must be > 0 or -1 (disabled)

Error message

multiplexingLimit must be > 0 or -1 (disabled)

What it means

Configuration validation in Http3ClientConfig.setMultiplexingLimit: the limit on concurrent HTTP/3 streams per connection must be positive or -1 (sentinel meaning 'use the server's initial SETTINGS value'). Other negative values are rejected.

Source

Thrown at vertx-core/src/main/java/io/vertx/core/http/Http3ClientConfig.java:64

   */
  public int getMultiplexingLimit() {
    return multiplexingLimit;
  }

  /**
   * Set a client limit of the number concurrent streams for each HTTP/3 connection, this limits the number
   * of streams the client can create for a connection. The effective number of streams for a
   * connection is the min of this value and the server's initial settings.
   * <p/>
   * Setting the value to {@code -1} means to use the value sent by the server's initial settings.
   * {@code -1} is the default value.
   *
   * @param limit the maximum concurrent for an HTTP/3 connection
   * @return a reference to this, so the API can be used fluently
   */
  public Http3ClientConfig setMultiplexingLimit(int limit) {
    if (limit == 0 || limit < -1) {
      throw new IllegalArgumentException("multiplexingLimit must be > 0 or -1 (disabled)");
    }
    this.multiplexingLimit = limit;
    return this;
  }

  /**
   * @return the keep alive timeout value in seconds for HTTP/3 connections
   */
  public Duration getKeepAliveTimeout() {
    return keepAliveTimeout;
  }

  /**
   * <p>Set the keep alive timeout for HTTP/3 connections. This value determines how long a connection remains
   * unused in the pool before being evicted and closed. A timeout of zero or {@code null} means there is no timeout.</p>
   *
   * @param keepAliveTimeout the timeout, in seconds
   * @return a reference to this, so the API can be used fluently

View on GitHub (pinned to fb308bd8c3)

Solutions

1. Pass -1 or a value >= 1
2. Validate configuration before building the HTTP/3 client

When it happens

Trigger: Thrown at vertx-core/src/main/java/io/vertx/core/http/Http3ClientConfig.java:64 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of eclipse-vertx/vert.x@fb308bd8c3 (2026-09-06). Data as JSON: /api/errors/d069f2c99f080670. Report an issue: GitHub.