From e77b99c56a3dd4fa386ea49e2ccb4c3e881a45e8 Mon Sep 17 00:00:00 2001
From: kyle <liyuankui@gmail.com>
Date: Wed, 25 Apr 2018 16:46:21 -0400
Subject: [PATCH] Add support for custom context/application root

This adds a new parameter, ARA_APPLICATION_ROOT, which does two things:

1) Maps to Flask's APPLICATION_ROOT [1]
2) Adds a route prefix by supplying the APPLICATION_ROOT value to
   SCRIPT_NAME through a custom WSGI middleware implementation.

[1]: http://flask.pocoo.org/docs/0.12/config/

Story: 2001123
Co-Authored-By: kyle <liyuankui@gmail.com>
Co-Authored-By: David Moreau-Simard <dmsimard@redhat.com>
Change-Id: Icb58a3d64716263718b9cb5a2d4fe46a6d522502
---
 ara/config/base.py            |  5 ++++
 ara/tests/unit/test_config.py |  1 +
 ara/webapp.py                 | 43 +++++++++++++++++++++++++++++++++++
 doc/source/configuration.rst  | 14 ++++++++++++
 4 files changed, 63 insertions(+)

diff --git a/ara/config/base.py b/ara/config/base.py
index 9051a578..427f074e 100644
--- a/ara/config/base.py
+++ b/ara/config/base.py
@@ -39,6 +39,11 @@ class BaseConfig(object):
             True,
             value_type='boolean'
         )
+        self.APPLICATION_ROOT = ara_config(
+            'application_root',
+            'ARA_APPLICATION_ROOT',
+            '/'
+        )
         self.SQLALCHEMY_DATABASE_URI = self.ARA_DATABASE
         self.SQLALCHEMY_TRACK_MODIFICATIONS = False
         self.SQLALCHEMY_ECHO = ara_config(
diff --git a/ara/tests/unit/test_config.py b/ara/tests/unit/test_config.py
index 0232c8ce..5f03d326 100644
--- a/ara/tests/unit/test_config.py
+++ b/ara/tests/unit/test_config.py
@@ -41,6 +41,7 @@ class TestConfig(TestAra):
             'FREEZER_IGNORE_404_NOT_FOUND': True,
             'ARA_DIR': os.path.expanduser('~/.ara'),
             'SQLALCHEMY_DATABASE_URI': db,
+            'APPLICATION_ROOT': '/',
             'ARA_HOST': '127.0.0.1',
             'ARA_AUTOCREATE_DATABASE': True,
             'ARA_PORT': "9191",
diff --git a/ara/webapp.py b/ara/webapp.py
index 4ee5e2e5..f804b033 100644
--- a/ara/webapp.py
+++ b/ara/webapp.py
@@ -62,6 +62,7 @@ def create_app():
     configure_app(app)
     configure_dirs(app)
     configure_logging(app)
+    configure_app_root(app)
     configure_blueprints(app)
     configure_static_route(app)
     configure_db(app)
@@ -88,6 +89,14 @@ def configure_logging(app):
     setup_logging(app.config)
 
 
+def configure_app_root(app):
+    log = logging.getLogger('ara.webapp.configure_app_root')
+    # Don't load the middleware needlessly if the root is actually '/'
+    if app.config['APPLICATION_ROOT'] != '/':
+        app.wsgi_app = AppRootMiddleware(app, app.wsgi_app)
+    log.debug('Application root loaded: %s' % app.config['APPLICATION_ROOT'])
+
+
 def configure_errorhandlers(app):
     @app.errorhandler(404)
     def page_not_found(error):
@@ -309,3 +318,37 @@ def configure_cache(app):
 
     if not getattr(app, '_cache', None):
         app._cache = {}
+
+
+class AppRootMiddleware(object):
+    """
+    Middleware to manage route prefixes, for example when hosting ARA in a
+    subdirectory.
+    """
+    def __init__(self, app, wsgi_app):
+        self.log = logging.getLogger('ara.webapp.AppRootMiddleware')
+        self.log.debug('Initializing AppRootMiddleware')
+        self.app = app
+        self.wsgi_app = wsgi_app
+
+    def __call__(self, environ, start_response):
+        root = self.app.config['APPLICATION_ROOT']
+        if environ['PATH_INFO'].startswith(root):
+            environ['PATH_INFO'] = environ['PATH_INFO'][len(root):]
+            environ['SCRIPT_NAME'] = root
+            self.log.debug('Returning with root %s' % root)
+            return self.wsgi_app(environ, start_response)
+        else:
+            self.log.debug('Returning 404 for %s' % environ['PATH_INFO'])
+            url = "{scheme}://{host}{root}".format(
+                scheme=environ['wsgi.url_scheme'],
+                host=environ['HTTP_HOST'],
+                root=root,
+            )
+            msg = """
+            This URL doesn't belong to an ARA application. <br />
+            <br />
+            Did you mean to browse to <a href='{url}'>{url}</a> instead ?
+            """.format(url=url)
+            start_response('404', [('Content-Type', 'text/html')])
+            return [msg.strip().encode()]
diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index 39c181e1..2056dee7 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -117,6 +117,8 @@ Parameters and their defaults
 +-------------------------------+----------------------------+-------------------------------------------+
 | ARA_PORT_                     | port                       | 9191                                      |
 +-------------------------------+----------------------------+-------------------------------------------+
+| ARA_APPLICATION_ROOT_         | application_root           | /                                         |
++-------------------------------+----------------------------+-------------------------------------------+
 | ARA_LOG_CONFIG_               | logconfig                  | None                                      |
 +-------------------------------+----------------------------+-------------------------------------------+
 | ARA_LOG_FILE_                 | logfile                    | ~/.ara/ara.log                            |
@@ -237,6 +239,18 @@ the ``ara-manage runserver`` command.
 It is equivalent to the ``-p`` or ``--port`` argument of the
 ``ara-manage runserver`` command.
 
+ARA_APPLICATION_ROOT
+~~~~~~~~~~~~~~~~~~~~
+
+The path at which the web application should be loaded.
+
+The default behavior is to load the application at the root (``/``) of your
+host.
+Change this parameter if you'd like to host your application elsewhere.
+
+For example, ``/ara`` would make the application available under
+``http://host/ara`` instead of ``http://host/``.
+
 ARA_LOG_CONFIG
 ~~~~~~~~~~~~~~