是否可以刷新请求中的会话？答案

【问题标题】：Is it possible to refresh a session in requests?是否可以刷新请求中的会话？
【发布时间】：2016-04-17 06:28:36
【问题描述】：

我使用requests.Session() 创建了一个会话。由于某种原因，服务器端关闭了这个连接，所以我必须重新连接。问题是，这个会话用在很多地方，所以我想知道是否可以重建一个 TCP 连接但保留会话对象以便我仍然可以使用它？

例子：

s = requests.Session()

class B:
    def __init__(self, session):
        self._session = session

    def get(self):
        self._session.get('some_url')

b1 = B(s)
b2 = B(s)
b3 = B(s)

# some get calls
...
# then connection is closed

# some get calls
...

如果我可以保留 seesion 对象，则无需替换每个 B 实例中的每个 _session。

错误日志：

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 376, in _make_request
    httplib_response = conn.getresponse(buffering=True)
TypeError: getresponse() got an unexpected keyword argument 'buffering'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 559, in urlopen
    body=body, headers=headers)
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 378, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 1174, in getresponse
    response.begin()
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 282, in begin
    version, status, reason = self._read_status()
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 243, in _read_status
    line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/socket.py", line 571, in readinto
    return self._sock.recv_into(b)
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 924, in recv_into
    return self.read(nbytes, buffer)
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 786, in read
    return self._sslobj.read(len, buffer)
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 570, in read
    v = self._sslobj.read(len, buffer)
ConnectionResetError: [Errno 54] Connection reset by peer

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/requests/adapters.py", line 376, in send
    timeout=timeout
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 609, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/util/retry.py", line 247, in increment
    raise six.reraise(type(error), error, _stacktrace)
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/packages/six.py", line 309, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 559, in urlopen
    body=body, headers=headers)
  File "/usr/local/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 378, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 1174, in getresponse
    response.begin()
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 282, in begin
    version, status, reason = self._read_status()
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 243, in _read_status
    line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/socket.py", line 571, in readinto
    return self._sock.recv_into(b)
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 924, in recv_into
    return self.read(nbytes, buffer)
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 786, in read
    return self._sslobj.read(len, buffer)
  File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 570, in read
    v = self._sslobj.read(len, buffer)
requests.packages.urllib3.exceptions.ProtocolError: ('Connection aborted.', ConnectionResetError(54, 'Connection reset by peer'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/laike9m/ICT/zhihu-analysis/dynamic/main.py", line 108, in <module>
    main()
  File "/Users/laike9m/ICT/zhihu-analysis/dynamic/main.py", line 89, in main
    m.detect_new_question()
  File "/Users/laike9m/ICT/zhihu-analysis/dynamic/monitor.py", line 32, in detect_new_question
    question = latest_question = next(it)
  File "/usr/local/lib/python3.5/site-packages/zhihu/topic.py", line 269, in questions
    res = self._session.get(question_url, params=params)
  File "/usr/local/lib/python3.5/site-packages/requests/sessions.py", line 480, in get
    return self.request('GET', url, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/sessions.py", line 468, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/sessions.py", line 576, in send
    r = adapter.send(request, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/adapters.py", line 426, in send
    raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', ConnectionResetError(54, 'Connection reset by peer'))

这是一个非常常见的问题：Python handling socket.error: [Errno 104] Connection reset by peer。我无法控制服务器，所以我不知道为什么或如何发生这种情况。

服务器确实支持keep-alive，因为我可以发出数百个请求（持续一个小时或更长时间）。

【问题讨论】：

HTTP 连接是无状态，因此即使使用 Keep-Alive 关闭也是常态。您是否将 cookie 过期与可能关闭的连接混淆了？
除非您使用的是 HTTP 协议的新版本 HTTP/2.x，否则 @MartijnPieters 所说的是正确的。但是看看 Python 是否确实对请求库实现“刷新”以更好地匹配 HTTP/2.x 会很有趣。
@Torxed：requests 库不支持 HTTP/2.x。无论如何，还没有。
@MartijnPieters 很好的说明。我只是为未来的读者和那些试图以严格模式（不启用旧协议）运行网络服务器的人发表评论。并表示，考虑到协议以PING 的形式支持它，将来看看 Python 是否确实实现了这样的功能将会很有趣。我猜将来官方的 Python lib 会以最完整的形式支持该协议，所以我想我的评论是多余的。
@laike9m：会话对象根据需要从池中创建连接并支持保持活动状态。如果服务器声称支持keep-alive但过早关闭连接而没有传达此信息，则服务器已损坏。

标签： python http session python-requests

【解决方案1】：

要么将您的B() 设为单例，要么将会话设为类属性（从而有效地成为全局属性）。

例如，仅当您创建至少一个实例时才将其设为类属性可能如下所示：

class B:
    def __init__(self):
        if not hasattr(type(self), '_session'):
            self._create_session()

    @classmethod
    def _create_session(cls):
        cls._session = requests.Session()

    def get(self):
        self._session.get('some_url')

如果使用会话会因为服务器没有正确关闭会话连接而引发异常，则只需在那时重新创建会话即可：

    def __init__(self):
        if not hasattr(type(self), '_session'):
            self._create_session()

    @classmethod
    def _create_session(cls):
        cls._session = requests.Session()

    def get(self):
        retries = 5
        while retries:
            try:
                return self._session.get('some_url')
            except requests.ConnectionException as e:
                last_connection_exception = e
                retries -= 1
        raise last_connection_exception

以上示例最多重试 5 次。您确实不需要每次都需要重新创建会话。如果连接已关闭，即使出现异常，会话对象也会为下一个请求创建一个 new TCP/IP 连接。

如果您发现会话对象以某种方式被拍摄并且不再能够创建新连接，而新会话确实有效，那么这将是一个错误。请使用合适的 MCVE 向项目报告。

【讨论】：

是的，我刚刚在自己的服务器上验证了会话将使用requests lib 自动重新创建。无需重新创建甚至打扰监控损坏的管道/会话。然而，我确实开始怀疑 OP 的实际问题是什么。
@Torxed 一个常见问题：stackoverflow.com/questions/1434451/…。 requests 无法处理，但会引发异常。
@laike9m 这就是我们想要告诉你的。服务器可能不支持keep-alive，因此会丢弃 TCP 会话。造成这种情况的其他原因可能是网络峰值、wifi 连接不稳定或网络中其他不可恢复的致命错误。无论哪种方式，requests 库都会处理这些问题，如果没有，请说明您的实际错误消息，而不是您遇到的问题。