如何知道paramiko SSH通道是否断开连接？

Question

我正在设计使用paramiko进行SSH连接的测试用例。测试用例通常包含有包装器的paramiko.exec_command()调用（称为run_command()）。这里self.ssh是paramiko.SSHClient()的维持。在每次调用之前，我使用decorator检查ssh连接。（self.get_ssh()协商连接）

def check_connections(function):
    ''' A decorator to check SSH connections. '''
    def deco(self, *args, **kwargs):
        if self.ssh is None:
            self.ssh = self.get_ssh()
        else:
            ret = getattr(self.ssh.get_transport(), 'is_active', None)
            if ret is None or (ret is not None and not ret()):
                self.ssh = self.get_ssh()
        return function(self, *args, **kwargs)
    return deco

@check_connections
def run_command(self, command):
    ''' Executes command via SSH. '''
    stdin, stdout, stderr = self.ssh.exec_command(command)
    stdin.flush()
    stdin.channel.shutdown_write()
    ret = stdout.read()
    err = stderr.read()
    if ret:
        return ret
    elif err:
        return err
    else:
        return None

它在我的远程节点重新启动之前工作得很好，这有时会发生。当它发生时，下一个run_command()调用生成一个socket.error异常。问题是，paramiko.Transport对象似乎一直处于活动状态，直到引发异常：

Python 2.7.3 (default, Mar  7 2013, 14:03:36)
[GCC 4.3.4 [gcc-4_3-branch revision 152973]] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> import paramiko
>>> ssh = paramiko.SSHClient()
>>> print ssh
<paramiko.SSHClient object at 0x7f2397b96d50>
>>> print ssh.get_transport()
None
>>> ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
>>> ssh.load_host_keys(os.path.expanduser('~') + '/.ssh/known_hosts')
>>> ssh.connect(hostname = '172.31.77.57', username = 'root', password = 'rootroot', timeout = 5.0)
>>> print ssh
<paramiko.SSHClient object at 0x7f2397b96d50>
>>> print ssh.get_transport()
<paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 0 open channel(s))>
>>> print ssh.get_transport().is_active()
True
>>> ssh.exec_command('ls')
(<paramiko.ChannelFile from <paramiko.Channel 1 (open) window=2097152 -> <paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 1 open channel(s))>>>, <paramiko.ChannelFile from <paramiko.Channel 1 (open) window=2097152 -> <paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 1 open channel(s))>>>, <paramiko.ChannelFile from <paramiko.Channel 1 (open) window=2097152 -> <paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 1 open channel(s))>>>)
>>> print ssh
<paramiko.SSHClient object at 0x7f2397b96d50>
>>> print ssh.get_transport()
<paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 0 open channel(s))>
>>> print ssh.get_transport().is_active()
True
>>> ssh.exec_command('reboot')
(<paramiko.ChannelFile from <paramiko.Channel 2 (open) window=2097152 -> <paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 1 open channel(s))>>>, <paramiko.ChannelFile from <paramiko.Channel 2 (open) window=2097152 -> <paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 1 open channel(s))>>>, <paramiko.ChannelFile from <paramiko.Channel 2 (open) window=2097152 -> <paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 1 open channel(s))>>>)
>>> print ssh
<paramiko.SSHClient object at 0x7f2397b96d50>
>>> print ssh.get_transport()
<paramiko.Transport at 0x97537550L (cipher aes128-ctr, 128 bits) (active; 0 open channel(s))>
>>> print ssh.get_transport().is_active()
True
>>> ssh.exec_command('ls')
No handlers could be found for logger "paramiko.transport"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pytest/lib/python2.7/site-packages/paramiko/client.py", line 370, in exec_command
    chan = self._transport.open_session()
  File "/home/pytest/lib/python2.7/site-packages/paramiko/transport.py", line 662, in open_session
    return self.open_channel('session')
  File "/home/pytest/lib/python2.7/site-packages/paramiko/transport.py", line 764, in open_channel
    raise e
socket.error: [Errno 104] Connection reset by peer
>>> print ssh
<paramiko.SSHClient object at 0x7f2397b96d50>
>>> print ssh.get_transport()
<paramiko.Transport at 0x97537550L (unconnected)>
>>> print ssh.get_transport().is_active()
False
>>>

问题：如何确定连接是否处于活动状态？

Answer 1

我的解决方案与你的基本相同，只是组织方式不同：

def connection(self):
    if not self.is_connected():
        self._ssh = paramiko.SSHClient()
        self._ssh.connect(self.server, self.port,
                          username = self.username, password = self.password)

    return self._ssh

def is_connected(self):
    transport = self._ssh.get_transport() if self._ssh else None
    return transport and transport.is_active()

def do_something(self):
    self.connection().exec_command('ls')

Answer 2

在python中，它是easier to ask for forgiveness than permission。

将每个调用包装为ssh.exec_command，如下所示：

try:
    ssh.exec_command('ls')
except socket.error as e:
    # Crap, it's closed. Perhaps reopen and retry?

Answer 3

这是有效的：

import paramiko
client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())        # Setting the missing host policy to auto add it
client.connect('192.168.1.16', port=22, username='admin', password='admin', timeout=3, banner_timeout=2)

channel = client.invoke_shell()                 # Request an interactive shell session on this channel. If the server allows it, the channel will then be directly connected to the stdin, stdout, and stderr of the shell.
print channel.closed          # False
command = 'reboot'
channel.send(command + '\n')
# wait a while
print channel.closed          # True