如何优化Python中处理BadHostKeyException()异常的性能

在Python中处理BadHostKeyException异常的性能优化可以通过以下方法实现：

1. 缓存已经验证的主机密钥：当首次连接一个主机时，Python会检查主机密钥是否存在于默认的.ssh/known_hosts文件中。验证主机密钥是一个计算密集型操作，因此可以通过存储已经验证过的主机密钥来避免重复的验证。

   import paramiko

   known_hosts = paramiko.util.load_host_keys('/path/to/known_hosts')

   def add_host_key(hostname, key):
       known_hosts[hostname] = {'ssh-rsa': key.get_base64()}

   def fingerprint_key(key):
       return '-'.join([key.get_name(), key.get_base64()[:16]])

   def check_host_key(hostname, key):
       fingerprint = fingerprint_key(key)
       if hostname in known_hosts:
           if fingerprint in known_hosts[hostname]:
               return True
           else:
               raise paramiko.BadHostKeyException(hostname, key)

       # Validate the key against the hostname (this is a computation-heavy operation)
       is_valid = validate_key_against_hostname(hostname, key)

       if is_valid:
           add_host_key(hostname, key)
           return True
       else:
           raise paramiko.BadHostKeyException(hostname, key)
   

2. 启用并发验证（Concurrent Validation）：在某些情况下，可以并发验证主机密钥，以提升性能。这可以通过使用多线程或多进程来实现。

   import paramiko
   import concurrent.futures

   known_hosts = paramiko.util.load_host_keys('/path/to/known_hosts')

   def add_host_key(hostname, key):
       known_hosts[hostname] = {'ssh-rsa': key.get_base64()}

   def fingerprint_key(key):
       return '-'.join([key.get_name(), key.get_base64()[:16]])

   def check_host_key(hostname, key):
       fingerprint = fingerprint_key(key)
       if hostname in known_hosts:
           if fingerprint in known_hosts[hostname]:
               return True
           else:
               raise paramiko.BadHostKeyException(hostname, key)

       # Validate the key against the hostname (this is a computation-heavy operation)
       is_valid = validate_key_against_hostname(hostname, key)

       if is_valid:
           add_host_key(hostname, key)
           return True
       else:
           raise paramiko.BadHostKeyException(hostname, key)

   def validate_host_keys(hosts):
       with concurrent.futures.ThreadPoolExecutor() as executor:
           futures = []
           for hostname, key in hosts.items():
               futures.append(executor.submit(check_host_key, hostname, key))
           
           for future in concurrent.futures.as_completed(futures):
               try:
                   result = future.result()
               except paramiko.BadHostKeyException as e:
                   print(f"Failed to validate host key for {e.hostname}: {e.key}")

   # Assume hosts is a dictionary of hostnames and keys
   validate_host_keys(hosts)
   

3. 使用异步编程模型：在Python 3.7及更高版本中，可以使用asyncio库实现异步编程。通过使用异步调用，可以同时进行多个主机密钥的验证，从而提高性能。

   import paramiko
   import asyncio

   known_hosts = paramiko.util.load_host_keys('/path/to/known_hosts')

   def add_host_key(hostname, key):
       known_hosts[hostname] = {'ssh-rsa': key.get_base64()}

   def fingerprint_key(key):
       return '-'.join([key.get_name(), key.get_base64()[:16]])

   async def check_host_key(hostname, key):
       fingerprint = fingerprint_key(key)
       if hostname in known_hosts:
           if fingerprint in known_hosts[hostname]:
               return True
           else:
               raise paramiko.BadHostKeyException(hostname, key)

       # Validate the key against the hostname (this is a computation-heavy operation)
       is_valid = validate_key_against_hostname(hostname, key)

       if is_valid:
           add_host_key(hostname, key)
           return True
       else:
           raise paramiko.BadHostKeyException(hostname, key)

   async def validate_host_keys(hosts):
       tasks = []
       for hostname, key in hosts.items():
           tasks.append(check_host_key(hostname, key))

       await asyncio.gather(*tasks)

   # Assume hosts is a dictionary of hostnames and keys
   asyncio.run(validate_host_keys(hosts))
   

总结起来，优化Python中处理BadHostKeyException异常的性能可以通过缓存已验证的主机密钥、启用并发验证和使用异步编程模型等方法。这些方法都可以根据具体的需求和场景进行选择和应用。