Asyncio获取邮件python3

Question

我正在用异步模块进行测试，但是我需要提示/建议如何以异步方式获取大型电子邮件。

我有一个包含邮件帐户用户名和密码的列表。

data = [
    {'usern': 'foo@bar.de', 'passw': 'x'},
    {'usern': 'foo2@bar.de', 'passw': 'y'},
    {'usern': 'foo3@bar.de', 'passw': 'z'} (...)
]

我想：

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait([get_attachment(d) for d in data]))
loop.close()

然而，很长的一部分是下载电子邮件附件。

电子邮件：

@asyncio.coroutine
def get_attachment(d):
    username = d['usern']
    password = d['passw']

    connection = imaplib.IMAP4_SSL('imap.bar.de')
    connection.login(username, password)
    connection.select()

    # list all available mails
    typ, data = connection.search(None, 'ALL')

    for num in data[0].split():
        # fetching each mail
        typ, data = connection.fetch(num, '(RFC822)')
        raw_string = data[0][1].decode('utf-8')
        msg = email.message_from_string(raw_string)
        for part in msg.walk():
            if part.get_content_maintype() == 'multipart':
                continue

            if part.get('Content-Disposition') is None:
                continue

            if part.get_filename():
                body = part.get_payload(decode=True)
                # do something with the body, async?

    connection.close()
    connection.logout()

我如何以异步方式处理所有(下载附件)邮件？

Answer 1

如果您没有基于异步I/O的imap库，您可以只使用concurrent.futures.ThreadPoolExecutor在线程中执行I/O。Python将在I/O期间发布GIL，因此您将获得真正的并发性：

def init_connection(d):    
    username = d['usern']
    password = d['passw']

    connection = imaplib.IMAP4_SSL('imap.bar.de')
    connection.login(username, password)
    connection.select()
    return connection

local = threading.local() # We use this to get a different connection per thread
def do_fetch(num, d, rfc):
    try:
        connection = local.connection
    except AttributeError:
        connnection = local.connection = init_connection(d)
    return connnection.fetch(num, rfc)

@asyncio.coroutine
def get_attachment(d, pool):
    connection = init_connection(d)    
    # list all available mails
    typ, data = connection.search(None, 'ALL')

    # Kick off asynchronous tasks for all the fetches
    loop = asyncio.get_event_loop()
    futs = [asyncio.create_task(loop.run_in_executor(pool, do_fetch, num, d, '(RFC822)'))
                for num in data[0].split()]

    # Process each fetch as it completes
    for fut in asyncio.as_completed(futs):
        typ, data = yield from fut
        raw_string = data[0][1].decode('utf-8')
        msg = email.message_from_string(raw_string)
        for part in msg.walk():
            if part.get_content_maintype() == 'multipart':
                continue

            if part.get('Content-Disposition') is None:
                continue

            if part.get_filename():
                body = part.get_payload(decode=True)
                # do something with the body, async?

    connection.close()
    connection.logout()    


loop = asyncio.get_event_loop()
pool = ThreadPoolExecutor(max_workers=5)  # You can probably increase max_workers, because the threads are almost exclusively doing I/O.
loop.run_until_complete(asyncio.wait([get_attachment(d, pool) for d in data]))
loop.close()

这并不像真正基于异步I/O的解决方案那么好，因为您仍然有创建线程的开销，这限制了可伸缩性并增加了额外的内存开销。由于所有包装实际I/O调用的代码，您也会遇到一些GIL减速。尽管如此，如果你处理的邮件少于数千封，它的表现应该还不错。

我们使用run_in_executor作为异步事件循环的一部分使用ThreadPoolExecutor，使用asyncio.async包装在asyncio.Future中返回的coroutine对象，并使用as_completed按照它们完成的顺序迭代未来。

编辑

看起来imaplib并不是线程安全的。我已经编辑了我的答案，通过threading.local使用线程本地存储，它允许我们每个线程创建一个连接对象，它可以在线程的整个生命周期中被重用(这意味着您只创建num_workers连接对象，而不是为每个fetch创建一个新连接)。

Answer 2

我也有同样的需求:用python 3完全异步获取电子邮件。如果这里的其他人感兴趣，我在这里推出了异步IMAP库：https://github.com/bamthomas/aioimaplib

你可以这样使用它：

import asyncio
from aioimaplib import aioimaplib

@asyncio.coroutine
def wait_for_new_message(host, user, password):
    imap_client = aioimaplib.IMAP4(host=host)
    yield from imap_client.wait_hello_from_server()

    yield from imap_client.login(user, password)
    yield from imap_client.select()

    asyncio.async(imap_client.idle())
    id = 0
    while True:
        msg = yield from imap_client.wait_server_push()
        print('--> received from server: %s' % msg)
        if 'EXISTS' in msg:
            id = msg.split()[0]
            imap_client.idle_done()
            break

    result, data = yield from imap_client.fetch(id, '(RFC822)')
    email_message = email.message_from_bytes(data[0])

    attachments = []
    body = ''
    for part in email_message.walk():
        if part.get_content_maintype() == 'multipart':
            continue
        if part.get_content_maintype() == 'text' and 'attachment' not in part.get('Content-Disposition', ''):
            body = part.get_payload(decode=True).decode(part.get_param('charset', 'ascii')).strip()
        else:
            attachments.append(
                {'type': part.get_content_type(), 'filename': part.get_filename(), 'size': len(part.as_bytes())})

    print('attachments : %s' % attachments)
    print('body : %s' % body)
    yield from imap_client.logout()



if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(wait_for_new_message('my.imap.server', 'user', 'pass'))

带有附件的大型电子邮件也是通过异步下载的。