Add support for hostname canonicalization

This commit adds support for hostname canonicalization. It supports the
same config items used in OpenSSH config files, but also provides
options which can be passed directly, without the need to use a config
file. This commit also adds automatic reloading of the config file when
canonicalization is performed, as well as support for match keywords
"canonical" and "final".

This commit also adds support for negation of match keywords. Thanks go
to GitHub user commonism who suggested adding this support and provided
a proposed implementation.

asyncssh/config.py

@@ -60,12 +60,15 @@ class SSHConfig:
     _percent_expand = {'AuthorizedKeysFile'}
     _handlers: Dict[str, Tuple[str, Callable]] = {}
 
-    def __init__(self, last_config: Optional['SSHConfig'], reload: bool):
+    def __init__(self, last_config: Optional['SSHConfig'], reload: bool,
+                 canonical: bool, final: bool):
         if last_config:
             self._last_options = last_config.get_options(reload)
         else:
             self._last_options = {}
 
+        self._canonical = canonical
+        self._final = True if final else None
         self._default_path = Path('~', '.ssh').expanduser()
         self._path = Path()
         self._line_no = 0
@@ -153,35 +156,53 @@ def _match(self, option: str, args: List[str]) -> None:
 
         # pylint: disable=unused-argument
 
+        matching = True
+
         while args:
             match = args.pop(0).lower()
 
+            if match[0] == '!':
+                match = match[1:]
+                negated = True
+            else:
+                negated = False
+
+            if match == 'final' and self._final is None:
+                self._final = False
+
             if match == 'all':
-                self._matching = True
-                continue
+                result = True
+            elif match == 'canonical':
+                result = self._canonical
+            elif match == 'final':
+                result = cast(bool, self._final)
+            else:
+                match_val = self._match_val(match)
 
-            match_val = self._match_val(match)
+                if match != 'exec' and match_val is None:
+                    self._error(f'Invalid match condition {match}')
 
-            if match != 'exec' and match_val is None:
-                self._error('Invalid match condition')
+                try:
+                    arg = args.pop(0)
+                except IndexError:
+                    self._error(f'Missing {match} match pattern')
+
+                if matching:
+                    if match == 'exec':
+                        result = _exec(arg)
+                    elif match in ('address', 'localaddress'):
+                        host_pat = HostPatternList(arg)
+                        ip = ip_address(cast(str, match_val)) \
+                            if match_val else None
+                        result = host_pat.matches(None, match_val, ip)
+                    else:
+                        wild_pat = WildcardPatternList(arg)
+                        result = wild_pat.matches(match_val)
 
-            try:
-                if match == 'exec':
-                    self._matching = _exec(args.pop(0))
-                elif match in ('address', 'localaddress'):
-                    host_pat = HostPatternList(args.pop(0))
-                    ip = ip_address(cast(str, match_val)) \
-                        if match_val else None
-                    self._matching = host_pat.matches(None, match_val, ip)
-                else:
-                    wild_pat = WildcardPatternList(args.pop(0))
-                    self._matching = wild_pat.matches(match_val)
-            except IndexError:
-                self._error(f'Missing {match} match pattern')
+            if matching and result == negated:
+                matching = False
 
-            if not self._matching:
-                args.clear()
-                break
+        self._matching = matching
 
     def _set_bool(self, option: str, args: List[str]) -> None:
         """Set a boolean config option"""
@@ -276,6 +297,23 @@ def _set_address_family(self, option: str, args: List[str]) -> None:
         if option not in self._options:
             self._options[option] = value
 
+    def _set_canonicalize_host(self, option: str, args: List[str]) -> None:
+        """Set a canonicalize host config option"""
+
+        value_str = args.pop(0).lower()
+
+        if value_str in ('yes', 'true'):
+            value: Union[bool, str] = True
+        elif value_str in ('no', 'false'):
+            value = False
+        elif value_str == 'always':
+            value = value_str
+        else:
+            self._error(f'Invalid {option} value: {value_str}')
+
+        if option not in self._options:
+            self._options[option] = value
+
     def _set_rekey_limits(self, option: str, args: List[str]) -> None:
         """Set rekey limits config option"""
 
@@ -295,6 +333,11 @@ def _set_rekey_limits(self, option: str, args: List[str]) -> None:
         if option not in self._options:
             self._options[option] = byte_limit, time_limit
 
+    def has_match_final(self) -> bool:
+        """Return whether this config includes a 'Match final' block"""
+
+        return self._final is not None
+
     def parse(self, path: Path) -> None:
         """Parse an OpenSSH config file and return matching declarations"""
 
@@ -384,10 +427,10 @@ def get_options(self, reload: bool) -> Dict[str, object]:
     @classmethod
     def load(cls, last_config: Optional['SSHConfig'],
              config_paths: ConfigPaths, reload: bool,
-             *args: object) -> 'SSHConfig':
+             canonical: bool, final: bool, *args: object) -> 'SSHConfig':
         """Load a list of OpenSSH config files into a config object"""
 
-        config = cls(last_config, reload, *args)
+        config = cls(last_config, reload, canonical, final, *args)
 
         if config_paths:
             if isinstance(config_paths, (str, PurePath)):
@@ -429,8 +472,9 @@ class SSHClientConfig(SSHConfig):
                        'IdentityFile', 'ProxyCommand', 'RemoteCommand'}
 
     def __init__(self, last_config: 'SSHConfig', reload: bool,
-                 local_user: str, user: str, host: str, port: int) -> None:
-        super().__init__(last_config, reload)
+                 canonical: bool, final: bool, local_user: str,
+                 user: str, host: str, port: int) -> None:
+        super().__init__(last_config, reload, canonical, final)
 
         self._local_user = local_user
         self._orig_host = host
@@ -485,10 +529,10 @@ def _set_request_tty(self, option: str, args: List[str]) -> None:
             value: Union[bool, str] = True
         elif value_str in ('no', 'false'):
             value = False
-        elif value_str not in ('force', 'auto'):
-            self._error(f'Invalid {option} value: {value_str}')
-        else:
+        elif value_str in ('force', 'auto'):
             value = value_str
+        else:
+            self._error(f'Invalid {option} value: {value_str}')
 
         if option not in self._options:
             self._options[option] = value
@@ -531,6 +575,11 @@ def _set_tokens(self) -> None:
 
         ('AddressFamily',                   SSHConfig._set_address_family),
         ('BindAddress',                     SSHConfig._set_string),
+        ('CanonicalDomains',                SSHConfig._set_string_list),
+        ('CanonicalizeFallbackLocal',       SSHConfig._set_bool),
+        ('CanonicalizeHostname',            SSHConfig._set_canonicalize_host),
+        ('CanonicalizeMaxDots',             SSHConfig._set_int),
+        ('CanonicalizePermittedCNAMEs',     SSHConfig._set_string_list),
         ('CASignatureAlgorithms',           SSHConfig._set_string),
         ('CertificateFile',                 SSHConfig._append_string),
         ('ChallengeResponseAuthentication', SSHConfig._set_bool),
@@ -579,9 +628,9 @@ class SSHServerConfig(SSHConfig):
     """Settings from an OpenSSH server config file"""
 
     def __init__(self, last_config: 'SSHConfig', reload: bool,
-                 local_addr: str, local_port: int, user: str,
-                 host: str, addr: str) -> None:
-        super().__init__(last_config, reload)
+                 canonical: bool, final: bool, local_addr: str,
+                 local_port: int, user: str, host: str, addr: str) -> None:
+        super().__init__(last_config, reload, canonical, final)
 
         self._local_addr = local_addr
         self._local_port = local_port
@@ -618,6 +667,11 @@ def _set_tokens(self) -> None:
         ('AuthorizedKeysFile',              SSHConfig._set_string_list),
         ('AllowAgentForwarding',            SSHConfig._set_bool),
         ('BindAddress',                     SSHConfig._set_string),
+        ('CanonicalDomains',                SSHConfig._set_string_list),
+        ('CanonicalizeFallbackLocal',       SSHConfig._set_bool),
+        ('CanonicalizeHostname',            SSHConfig._set_canonicalize_host),
+        ('CanonicalizeMaxDots',             SSHConfig._set_int),
+        ('CanonicalizePermittedCNAMEs',     SSHConfig._set_string_list),
         ('CASignatureAlgorithms',           SSHConfig._set_string),
         ('ChallengeResponseAuthentication', SSHConfig._set_bool),
         ('Ciphers',                         SSHConfig._set_string),