flask 异步发送邮件 --

异步发送邮件

当使用SMTP的方式发送电子邮件时，如果你手动使用浏览器测试程序的注册功能，在提交注册表单后，浏览器会有几秒钟的不响应。因为这时候程序正在发送电子邮件，发信的操作阻断了请求--响应循环，直到发信的send_mail()函数调用结束后，视图函数才会返回响应。这几秒的延迟带了不好的用户体验，为了避免这个延迟，我们可以将发信函数放入后台线程异步执行，以Flask-Mail为例：

app.py: 异步发送电子邮件

from threading import Thread

def _send_async_mail(app, message):
    with app.app_context():
        mail.send(message)

def send_mail(subject, to, body):
    message = Message(subject, recipients=[to], body = body)
    thr = Thread(target=_send_async_mail, args=[app, message])
    thr.start()
    return thr

因为Flask-Mail的send()方法内部的调用逻辑中使用了current_app变量，而这个变量只在激活的程序上下文中才存在，这里在后台线程调用发信函数，但是后台线程并没有程序上下文存在。为了正常实现发信功能，我们传入app作为参数，并调用app.app_context()手动激活程序上下文。

app.py文件增加相关的类和函数

#send over SMTP
def send_smtp_mail(subject, to, body):
    message = Message(subject, recipients=[to], body=body)
    mail.send(message)

class EmailForm(FlaskForm):
    to = StringField('To', validators=[DataRequired(),Email()])
    subject = StringField('Subject', validators=[DataRequired()])
    body = TextAreaField('Body', validators=[DataRequired()])
    submit_smtp = SubmitField('Send with SMTP')
    submit_async = SubmitField('Send with SMTP asynchronously')

#send email asynchronously
def _send_async_mail(app, message):
    with app.app_context():
        mail.send(message)

def send_async_mail(subject, to ,body):
    message = Message(subject, recipients=[to],body=body)
    thr = Thread(target=_send_async_mail, args=[app, message])
    thr.start()
    return thr

@app.route('/', methods=['GET','POST'])
def index():
    form = EmailForm()
    if form.validate_on_submit():
        to = form.to.data
        subject = form.subject.data
        body = form.body.data
        if form.submit_smtp.data:
            send_smtp_mail(subject, to, body)
            print "request.form:",request.form
            method = request.form.get('submit_smtp')  #提交按钮的文字
        else:
            send_async_mail(subject, to, body)
            print "request.form:", request.form
            method = request.form.get('submit_async')  #提交按钮的文字
            print "method:",method
            print "method.split():",method.split()
        flash('Email sent %s! Check your inbox.' % ' '.join(method.split()[1:]))  #把按钮上的问题的前一个单词去掉，显示剩下的，用来提示发送方式
        return redirect(url_for('index'))
    form.subject.data = 'Keep on learning Flask!'
    form.body.data = 'Across the Great Wall we can reach every corner in the world.'
    return render_template('index.html', form=form)

if __name__ == '__main__':
    print app.config
    app.run(debug = True)

新建index.html:

{% extends 'base.html' %}
{% from 'macros.html' import form_field %}

{% block content %}
<h2>Send an Email to Yourself</h2>
<p>or subscribe <a href="{{ url_for('subscribe') }}">the fake newsletter</a></p>

<form method="post">
    {{ form.csrf_token }}
    {{ form_field(form.to, placeholder='xiaxiaoxu1987@163.com') }}
    {{ form_field(form.subject, size=30) }}
    {{ form_field(form.body, rows=5, cols=50) }}<br>
    {{ form.submit_smtp(class='btn') }}
    {{ form.submit_async(class='btn') }}
</form>
{% endblock %}

在测试前，确保在demos/email目录下添加一个.env文件，保存发送邮件所需要的MAIL_SERVER、MAIL_USERNAME、MAIL_PASSWORD的值。准备好后，访问index页面，在表单To字段里填入你的邮箱地址，然后单击下面的按钮发送邮件，Send with SMTP将通过普通的SMTP方式发信，Send with SMTP asynchronously则会以异步的方式通过SMTP发信。