public VirtualHostBuilder virtualHost(int port) {
        checkArgument(port >= 1 && port <= 65535, "port: %s (expected: 1-65535)", port);

        // Look for a virtual host that has already been made and reuse it.
        final Optional<VirtualHostBuilder> vhost =
                virtualHostBuilders.stream()
                                   .filter(v -> v.port() == port && v.defaultVirtualHost())
                                   .findFirst();
        if (vhost.isPresent()) {
            return vhost.get();
        }

        final VirtualHostBuilder virtualHostBuilder = new VirtualHostBuilder(this, port);
        virtualHostBuilders.add(virtualHostBuilder);
        return virtualHostBuilder;
    }
Adds the <a href="https://en.wikipedia.org/wiki/Virtual_hosting#Port-based">port-based virtual host</a>
with the specified {@code port}. The returned virtual host will have a catch-all (wildcard host) name
pattern that allows all host names.

<p>Note that you cannot configure TLS to the port-based virtual host. Configure it to the
{@link ServerBuilder} or a {@linkplain #virtualHost(String) name-based virtual host}.

@param port the port number that this virtual host binds to
@return {@link VirtualHostBuilder} for building the virtual host
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java