Always look up a "front end" name in the SSH config file and possibly…

… translate it.

If a "HostName" directive is specified in the SSH config file, the host name or
IP address following it are used in stead of the "frontend =" value from the
GC3Pie config file.

This was supposed to happen since SSH config lookups were implemented, but a
wrong code path resulted in overwriting the output of the "HostName" directive
with the value read in GC3Pie's config file.

Thanks to Kyle Robertson for reporting the bug!

gc3libs/backends/shellcmd.py

@@ -485,7 +485,7 @@ def fget(self):
 
         def fset(self, value):
             self._frontend = value
-            self.transport.remote_frontend = value
+            self.transport.set_connection_params(value)
         return locals()
 
     def _gather_machine_specs(self):

gc3libs/backends/transport.py

@@ -438,32 +438,38 @@ def __init__(self, remote_frontend,
         Additional arguments ``user``, ``port``, ``keyfile``, and
         ``timeout``, if given, override the above settings.
         """
-        self.remote_frontend = remote_frontend
-        self.port = port
-        self.username = username
-
         self.ssh = paramiko.SSHClient()
         self.ignore_ssh_host_keys = ignore_ssh_host_keys
         self.sftp = None
         self._is_open = False
         self.transport_channel = None
 
         # use SSH options, if available
-        sshcfg = paramiko.SSHConfig()
+        self._ssh_config = paramiko.SSHConfig()
         config_filename = os.path.expanduser(ssh_config or gc3libs.Default.SSH_CONFIG_FILE)
         if os.path.exists(config_filename):
             with open(config_filename, 'r') as config_file:
-                sshcfg.parse(config_file)
-            # check if we have an ssh configuration stanza for this host
-            ssh_options = sshcfg.lookup(self.remote_frontend)
-        else:
-            # no options
-            ssh_options = {}
+                self._ssh_config.parse(config_file)
+
+        self.set_connection_params(remote_frontend, username, keyfile, port, timeout)
+
+
+    def set_connection_params(self, hostname, username=None, keyfile=None,
+                               port=None, timeout=None):
+        """
+        Set remote host name and other parameters used for new connections.
+        Currently-established connections are not affected.
+
+        The host name is the only mandatory argument; any other parameter will
+        be read from the SSH configuration file (unless explicitly provided to
+        this function).
+        """
+        # check if we have an ssh configuration stanza for this host
+        ssh_options = self._ssh_config.lookup(hostname)
 
         # merge SSH options from the SSH config file with parameters
         # we were given in this method call
-        if 'hostname' in ssh_options:
-            self.remote_frontend = ssh_options['hostname']
+        self.remote_frontend = ssh_options.get('hostname', hostname)
 
         if username is None:
             self.username = ssh_options.get('user', None)
@@ -854,6 +860,19 @@ def __init__(self):
         # into `.remote_frontend`
         self.remote_frontend = (platform.node() or 'localhost')
 
+    # pylint: disable=too-many-arguments,unused-argument
+    def set_connection_params(self, hostname, username=None, keyfile=None,
+                              port=None, timeout=None):
+        """
+        Set the host name stored in this `LocalTransport` instance.
+        Any other argument is ignored.
+
+        This method exists only for interface compatibility with
+        :class:`SshTranport`, which see.
+        """
+        self.remote_frontend = hostname
+
+
     def get_proc_state(self, pid):
         """
         Getting process state.