Allow processing of a specific configuration file for the connection

Depending on the destination, libssh might need to be configured in a
way, that the algorithms and methods need to be adjusted. Instead of
adding each possible configuration option into the wrapper, including
a config file (as it exists for ordinary OpenSSH) is much easier. This
allows ansible to connect to devices with less well supported
algorithms.

Author: lutz

src/pylibsshext/includes/libssh.pxd

@@ -163,6 +163,7 @@ cdef extern from "libssh/libssh.h" nogil:
     int ssh_options_get(ssh_session session, ssh_options_e type, char **value)
     int ssh_options_get_port(ssh_session session, unsigned int * port_target)
     int ssh_options_set(ssh_session session, ssh_options_e type, const void *value)
+    int ssh_options_parse_config(ssh_session session, const char *filename)
 
     int ssh_get_server_publickey(ssh_session session, ssh_key *key)
     void ssh_key_free(ssh_key key)

src/pylibsshext/session.pyx

@@ -241,6 +241,16 @@ cdef class Session(object):
             if (key in OPTS_MAP or key in OPTS_DIR_MAP) and (kwargs[key] is not None):
                 self.set_ssh_options(key, kwargs[key])
 
+        if 'config_file' in kwargs:
+            file_name = kwargs['config_file']
+            rc = libssh.ssh_options_parse_config(self._libssh_session, file_name.encode())
+            if rc != libssh.SSH_OK or self._get_session_error_str() != "":
+                libssh.ssh_disconnect(self._libssh_session)
+                raise LibsshSessionException(
+                    "parsing ssh config failed: %s: %s" %
+                    (file_name, self._get_session_error_str())
+                )
+
         if libssh.ssh_connect(self._libssh_session) != libssh.SSH_OK:
             libssh.ssh_disconnect(self._libssh_session)
             raise LibsshSessionException("ssh connect failed: %s" % self._get_session_error_str())