*
   * @since 19.0
   */
  public Optional<Long> sizeIfKnown() {
    return Optional.absent();
  }

  /**
   * Returns the size of this source in bytes, even if doing so requires opening and traversing an
   * entire stream. To avoid a potentially expensive operation, see {@link #sizeIfKnown}.
   *

   *         .put("one", 1)
   *         .put("two", 2)
   *         .put("three", 3)
   *         .buildOrThrow();
   * }</pre>
   *
   * <p>For <i>small</i> immutable maps, the {@code ImmutableMap.of()} methods are even more
   * convenient.
   *
   * <p>By default, a {@code Builder} will generate maps that iterate over entries in the order they
   * were inserted into the builder, equivalently to {@code LinkedHashMap}. For example, in the

   *         .put("one", 1)
   *         .put("two", 2)
   *         .put("three", 3)
   *         .buildOrThrow();
   * }</pre>
   *
   * <p>For <i>small</i> immutable maps, the {@code ImmutableMap.of()} methods are even more
   * convenient.
   *
   * <p>By default, a {@code Builder} will generate maps that iterate over entries in the order they
   * were inserted into the builder, equivalently to {@code LinkedHashMap}. For example, in the

// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License

      Work (including but not limited to damages for loss of goodwill,
      work stoppage, computer failure or malfunction, or any and all
      other commercial damages or losses), even if such Contributor
      has been advised of the possibility of such damages.

   9. Accepting Warranty or Additional Liability. While redistributing
      the Work or Derivative Works thereof, You may choose to offer,

      Work (including but not limited to damages for loss of goodwill,
      work stoppage, computer failure or malfunction, or any and all
      other commercial damages or losses), even if such Contributor
      has been advised of the possibility of such damages.

   9. Accepting Warranty or Additional Liability. While redistributing
      the Work or Derivative Works thereof, You may choose to offer,

      Work (including but not limited to damages for loss of goodwill,
      work stoppage, computer failure or malfunction, or any and all
      other commercial damages or losses), even if such Contributor
      has been advised of the possibility of such damages.

   9. Accepting Warranty or Additional Liability. While redistributing
      the Work or Derivative Works thereof, You may choose to offer,

        acceptConnections()
      } catch (e: Throwable) {
        logger.log(Level.WARNING, "$this failed unexpectedly", e)
      }

      // Release all sockets and all threads, even if any close fails.
      serverSocket?.closeQuietly()

      val openClientSocket = openClientSockets.iterator()
      while (openClientSocket.hasNext()) {
        openClientSocket.next().closeQuietly()

// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License

 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public