[ADD] base_external_system: Implement interface/adapter (#993)

* [ADD] base_external_system: Implement interface/adapter for external systems

* base_external_system: Fix OS model, add inherits, add validate

* base_external_system: Usability and private key pass

* base_external_system: Use contextmanager in adapter client

* base_external_system: Move contextmanager to interface

* base_external_system: Include contextmanager on adapter and system

* base_external_system: Unify client

* Use password widget for password field

* Add tests & security

* Fix lint

* Add plaintext note

base_external_system/models/external_system_adapter.py

@@ -0,0 +1,71 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 LasLabs Inc.
+# License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl.html).
+
+from contextlib import contextmanager
+
+from odoo import api, fields, models, _
+from odoo.exceptions import UserError
+
+
+class ExternalSystemAdapter(models.AbstractModel):
+    """This is the model that should be inherited for new external systems.
+
+    Methods provided are prefixed with ``external_`` in order to keep from
+    """
+
+    _name = 'external.system.adapter'
+    _description = 'External System Adapter'
+    _inherits = {'external.system': 'system_id'}
+
+    system_id = fields.Many2one(
+        string='System',
+        comodel_name='external.system',
+        required=True,
+        ondelete='cascade',
+    )
+
+    @api.multi
+    @contextmanager
+    def client(self):
+        """Client object usable as a context manager to include destruction.
+
+        Yields the result from ``external_get_client``, then calls
+        ``external_destroy_client`` to cleanup the client.
+
+        Yields:
+            mixed: An object representing the client connection to the remote
+             system.
+        """
+        client = self.external_get_client()
+        try:
+            yield client
+        finally:
+            self.external_destroy_client(client)
+
+    @api.multi
+    def external_get_client(self):
+        """Return a usable client representing the remote system."""
+        self.ensure_one()
+
+    @api.multi
+    def external_destroy_client(self, client):
+        """Perform any logic necessary to destroy the client connection.
+
+        Args:
+            client (mixed): The client that was returned by
+             ``external_get_client``.
+        """
+        self.ensure_one()
+
+    @api.multi
+    def external_test_connection(self):
+        """Adapters should override this method, then call super if valid.
+
+        If the connection is invalid, adapters should raise an instance of
+        ``odoo.ValidationError``.
+
+        Raises:
+            odoo.exceptions.UserError: In the event of a good connection.
+        """
+        raise UserError(_('The connection was a success.'))