clean up ssh.py submodule

smart_open/ssh.py

@@ -27,6 +27,12 @@
 import logging
 import urllib.parse
 
+from typing import (
+    Dict,
+    Callable,
+    Tuple,
+)
+
 try:
     import paramiko
 except ImportError:
@@ -70,6 +76,25 @@ def _str2bool(string):
         return True
     raise ValueError(f"Expected 'yes' / 'no', got {string}.")
 
+#
+# The parameter names used by Paramiko (and smart_open) slightly differ to
+# those used in ~/.ssh/config, so we use a mapping to bridge the gap.
+#
+# The keys are option names as they appear in Paramiko (and smart_open)
+# The values are a tuples containing:
+#
+# 1. their corresponding names in the ~/.ssh/config file
+# 2. a callable to convert the parameter value from a string to the appropriate type
+#
+_PARAMIKO_CONFIG_MAP: Dict[str, Tuple[str, Callable]] = {
+    "timeout": ("connecttimeout", float),
+    "compress": ("compression", _str2bool),
+    "gss_auth": ("gssapiauthentication", _str2bool),
+    "gss_kex": ("gssapikeyexchange", _str2bool),
+    "gss_deleg_creds": ("gssapidelegatecredentials", _str2bool),
+    "gss_trust_dns": ("gssapitrustdns", _str2bool),
+}
+
 
 def parse_uri(uri_as_string):
     split_uri = urllib.parse.urlsplit(uri_as_string)
@@ -117,57 +142,81 @@ def _maybe_fetch_config(host, username=None, password=None, port=None, transport
         transport_params["connect_kwargs"] = {}
 
     # Attempt to load an OpenSSH config.
-    # NOTE: connections configured in this way are not guaranteed to perform exactly as
-    # they do in typical usage due to mismatches between the set of OpenSSH configuration
-    # options and those that Paramiko supports. We provide a best attempt,
-    # and support:
+    #
+    # Connections configured in this way are not guaranteed to perform exactly
+    # as they do in typical usage due to mismatches between the set of OpenSSH
+    # configuration options and those that Paramiko supports. We provide a best
+    # attempt, and support:
+    #
     # - hostname -> address resolution
     # - username inference
     # - port inference
     # - identityfile inference
     # - connection timeout inference
     # - compression selection
     # - GSS configuration
-    for config_filename in _SSH_CONFIG_FILES:
-        if os.path.exists(config_filename):
+    #
+    connect_params = transport_params["connect_kwargs"]
+    config_files = [f for f in _SSH_CONFIG_FILES if os.path.exists(f)]
+    #
+    # This is the actual name of the host.  The input host may actually be an
+    # alias.
+    #
+    actual_hostname = ""
+
+    for config_filename in config_files:
+        try:
+            cfg = paramiko.SSHConfig.from_path(config_filename)
+        except PermissionError:
+            continue
+
+        if host not in cfg.get_hostnames():
+            continue
+
+        cfg = cfg.lookup(host)
+        if username is None:
+            username = cfg.get("user", None)
+
+        if not actual_hostname:
+            actual_hostname = cfg["hostname"]
+
+        if port is None:
             try:
-                cfg = paramiko.SSHConfig.from_path(config_filename)
-            except PermissionError:
-                continue
-            if host in cfg.get_hostnames():
-                cfg = cfg.lookup(host)
-                host = cfg["hostname"]
-                if username is None:
-                    username = cfg.get("user", None)
-                if port is None and cfg.get("port", None) is not None:
-                    port = int(cfg["port"])
-
-                # Special case, as we can have multiple identity files, so we check that the
-                # identityfile list has len > 0. This should be redundant, but keeping it for safety.
-                if (transport_params["connect_kwargs"].get("key_filename", None) is None
-                    and "identityfile" in cfg and len(cfg.get("identityfile", []))
-                    ):
-                    transport_params["connect_kwargs"]["key_filename"] = cfg["identityfile"]
-
-                # Map parameters from config to their required values for Paramiko's `connect` fn.
-                _connect_kwarg_map = dict(
-                    timeout=dict(key="connecttimeout", type=float),
-                    compress=dict(key="compression", type=_str2bool),
-                    gss_auth=dict(key="gssapiauthentication", type=_str2bool),
-                    gss_kex=dict(key="gssapikeyexchange", type=_str2bool),
-                    gss_deleg_creds=dict(key="gssapidelegatecredentials", type=_str2bool),
-                    gss_trust_dns=dict(key="gssapitrustdns", type=_str2bool)
-                )
-                for target, field in _connect_kwarg_map.items():
-                    if (
-                        transport_params["connect_kwargs"].get(target, None) is None and field["key"] in cfg
-                    ):
-                        transport_params["connect_kwargs"][target] = field["type"](cfg[field["key"]])
+                port = int(cfg["port"])
+            except (IndexError, ValueError):
+                #
+                # Nb. ignore missing/invalid port numbers
+                #
+                pass
+
+        #
+        # Special case, as we can have multiple identity files, so we check
+        # that the identityfile list has len > 0. This should be redundant, but
+        # keeping it for safety.
+        #
+        if connect_params.get("key_filename") is None:
+            identityfile = cfg.get("identityfile", [])
+            if len(identityfile):
+                connect_params["key_filename"] = identityfile
+
+        for param_name, (sshcfg_name, from_str) in _PARAMIKO_CONFIG_MAP.items():
+            if connect_params.get(param_name) is None and sshcfg_name in cfg:
+                connect_params[param_name] = from_str(cfg[sshcfg_name])
+
+        #
+        # Continue working through other config files, if there are any,
+        # as they may contain more options for our host
+        #
 
     if port is None:
         port = DEFAULT_PORT
+
     if not username:
         username = getpass.getuser()
+
+    if actual_hostname:
+        host = actual_hostname
+
     return host, username, password, port, transport_params