python：烧瓶url_for将'http'添加到动态url的路径

Question

我有一个通过此功能实现的动态网址：

@results.route("/crawled/<domain_name>")
def show_results(domain_name):
    #do some work

我正在尝试向用户发送一封包含此动态URL链接的电子邮件。这是发送电子邮件功能：

def send_email(email, domain_name):
    with create_app().test_request_context():
        msg = Message('Crawl Complete View the Results',
                      sender='noreply@demo.com',
                      recipients=[email])
        msg.body = render_template('results_email.html',name=domain_name)
        mail.send(msg)

这是我正在使用的电子邮件模板：

#results_email.html


The crawl for your requested domain is complete. To view the results visit the following link:
{{ url_for('results.show_results', domain_name=domain_name, _external=True) }}

If you did not make this request please ignore this email.

这里的问题是url_for函数使url的路径成为完整的url。这是电子邮件示例：

The crawl for your requested domain is complete. To view the results visit the following link:
http://localhost/crawled/http://techxpecs.com/

If you did not make this request please ignore this email.

我无法弄清楚这是怎么回事。我对网站的“忘记密码”部分使用了类似的方法，并且url_for在该网站上可以正常工作。它们之间的唯一区别是create_app().test_request_context()。我必须在这里使用它，因为如果不使用url_for会抛出此错误：

'Application was not able to create a URL adapter for request'
RuntimeError: Application was not able to create a URL adapter for request independent URL generation. You might be able to fix this by setting the SERVER_NAME config variable.

即使经过大量的搜索，我也无法弄清楚这里出了什么问题。