Improve support for Windows pathnames when using ProxyCommand

This commit changes the parsing of a proxy_command (or ProxyCommand in
SSH config files) to better cope with backslashes that might appear in
pathnames on Windows. Thanks go to GitHub user chipolux for reporting
the issue and investigating the existing OpenSSH parsing behavior.

Author: ronf

asyncssh/config.py

@@ -425,7 +425,7 @@ class SSHClientConfig(SSHConfig):
     """Settings from an OpenSSH client config file"""
 
     _conditionals = {'host', 'match'}
-    _no_split = {'remotecommand'}
+    _no_split = {'proxycommand', 'remotecommand'}
     _percent_expand = {'CertificateFile', 'IdentityAgent',
                        'IdentityFile', 'ProxyCommand', 'RemoteCommand'}
 
@@ -559,7 +559,7 @@ def _set_tokens(self) -> None:
         ('PKCS11Provider',                  SSHConfig._set_string),
         ('PreferredAuthentications',        SSHConfig._set_string),
         ('Port',                            SSHConfig._set_int),
-        ('ProxyCommand',                    SSHConfig._set_string_list),
+        ('ProxyCommand',                    SSHConfig._set_string),
         ('ProxyJump',                       SSHConfig._set_string),
         ('PubkeyAuthentication',            SSHConfig._set_bool),
         ('RekeyLimit',                      SSHConfig._set_rekey_limits),

asyncssh/connection.py

@@ -115,7 +115,7 @@
 from .misc import TermModesArg, TermSizeArg
 from .misc import async_context_manager, construct_disc_error
 from .misc import get_symbol_names, ip_address, map_handler_name
-from .misc import parse_byte_count, parse_time_interval
+from .misc import parse_byte_count, parse_time_interval, split_args
 
 from .packet import Boolean, Byte, NameList, String, UInt32, PacketDecodeError
 from .packet import SSHPacket, SSHPacketHandler, SSHPacketLogger
@@ -231,7 +231,7 @@ async def create_server(self, session_factory: TCPListenerFactory,
 _GlobalRequestResult = Tuple[int, SSHPacket]
 _KeyOrCertOptions = Mapping[str, object]
 _ListenerArg = Union[bool, SSHListener]
-_ProxyCommand = Optional[Sequence[str]]
+_ProxyCommand = Optional[Union[str, Sequence[str]]]
 _RequestPTY = Union[bool, str]
 
 _TCPServerHandlerFactory = Callable[[str, int], SSHSocketSessionFactory]
@@ -7144,11 +7144,13 @@ def prepare(self, config: SSHConfig, # type: ignore
         self.tunnel = tunnel if tunnel != () else config.get('ProxyJump')
         self.passphrase = passphrase
 
+        if proxy_command == ():
+            proxy_command = cast(Optional[str], config.get('ProxyCommand'))
+
         if isinstance(proxy_command, str):
-            proxy_command = shlex.split(proxy_command)
+            proxy_command = split_args(proxy_command)
 
-        self.proxy_command = proxy_command if proxy_command != () else \
-            cast(Sequence[str], config.get('ProxyCommand'))
+        self.proxy_command = proxy_command
 
         self.family = cast(int, family if family != () else
             config.get('AddressFamily', socket.AF_UNSPEC))
@@ -9224,7 +9226,7 @@ async def create_server(server_factory: _ServerFactory,
 async def get_server_host_key(
         host = '', port: DefTuple[int] = (), *,
         tunnel: DefTuple[_TunnelConnector] = (),
-        proxy_command: DefTuple[str] = (), family: DefTuple[int] = (),
+        proxy_command: DefTuple[_ProxyCommand] = (), family: DefTuple[int] = (),
         flags: int = 0, local_addr: DefTuple[HostPort] = (),
         sock: Optional[socket.socket] = None,
         client_version: DefTuple[BytesOrStr] = (),
@@ -9368,7 +9370,7 @@ def conn_factory() -> SSHClientConnection:
 async def get_server_auth_methods(
         host = '', port: DefTuple[int] = (), username: DefTuple[str] = (), *,
         tunnel: DefTuple[_TunnelConnector] = (),
-        proxy_command: DefTuple[str] = (), family: DefTuple[int] = (),
+        proxy_command: DefTuple[_ProxyCommand] = (), family: DefTuple[int] = (),
         flags: int = 0, local_addr: DefTuple[HostPort] = (),
         sock: Optional[socket.socket] = None,
         client_version: DefTuple[BytesOrStr] = (),

asyncssh/misc.py

@@ -23,6 +23,7 @@
 import functools
 import ipaddress
 import re
+import shlex
 import socket
 import sys
 
@@ -269,6 +270,18 @@ def parse_time_interval(value: str) -> float:
     return _parse_units(value, _time_units, 'time interval')
 
 
+def split_args(command: str) -> Sequence[str]:
+    """Split a command string into a list of arguments"""
+
+    lex = shlex.shlex(command, posix=True)
+    lex.whitespace_split = True
+
+    if sys.platform == 'win32': # pragma: no cover
+        lex.escape = []
+
+    return list(lex)
+
+
 _ACM = TypeVar('_ACM', bound=AsyncContextManager, covariant=True)
 
 class _ACMWrapper(Generic[_ACM]):