Add entrypoint of Kuryr

This patch adds the entrypoint of Kuryr libnetwork remote driver, which
works as a JSON-oriented Flask app.

Change-Id: Idd6a8d5e72fd4c619bfa88c01edf1f0e19391f91
Signed-off-by: Taku Fukushima <f.tac.mac@gmail.com>

__init__.py

@@ -15,5 +15,4 @@
 import pbr.version
 
 
-__version__ = pbr.version.VersionInfo(
-    'kuryr').version_string()
+__version__ = pbr.version.VersionInfo('kuryr').version_string()

kuryr/__init__.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 # Licensed under the Apache License, Version 2.0 (the "License"); you may
 # not use this file except in compliance with the License. You may obtain
 # a copy of the License at
@@ -12,8 +10,11 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import pbr.version
+import logging
+import sys
 
+from kuryr.utils import make_json_app
 
-__version__ = pbr.version.VersionInfo(
-    'kuryr').version_string()
+app = make_json_app(__name__)
+app.logger.addHandler(logging.StreamHandler(sys.stdout))
+app.logger.setLevel(logging.INFO)

kuryr/utils.py

@@ -0,0 +1,47 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from flask import Flask, jsonify
+from werkzeug.exceptions import default_exceptions
+from werkzeug.exceptions import HTTPException
+
+
+# Return all errors as JSON. From http://flask.pocoo.org/snippets/83/
+def make_json_app(import_name, **kwargs):
+    """Creates a JSON-oriented Flask app.
+
+    All error responses that you don't specifically manage yourself will have
+    application/json content type, and will contain JSON that follows the
+    libnetwork remote driver protocol.
+
+
+    { "Err": "405: Method Not Allowed" }
+
+
+    See:
+      - https://github.com/docker/libnetwork/blob/3c8e06bc0580a2a1b2440fe0792fbfcd43a9feca/docs/remote.md#errors  # noqa
+    """
+    def make_json_error(ex):
+        response = jsonify({"Err": str(ex)})
+        response.status_code = (ex.code
+                                if isinstance(ex, HTTPException)
+                                else 500)
+        content_type = 'application/vnd.docker.plugins.v1+json; charset=utf-8'
+        response.headers['Content-Type'] = content_type
+        return response
+
+    app = Flask(import_name, **kwargs)
+
+    for code in default_exceptions.iterkeys():
+        app.error_handler_spec[None][code] = make_json_error
+
+    return app