add a URL_PREFIX environment variable

this adds the ability to add a prefix to all generated URLs
so placing cabot under a subdirectory of a web server is possible,
such as with a reverse proxy.

resolves #321

cabot/settings.py

@@ -22,6 +22,8 @@ DATABASES = {'default': dj_database_url.parse(os.environ["DATABASE_URL"])}
 if not DEBUG:
     DATABASES['default']['OPTIONS'] = {'autocommit': True}
 
+URL_PREFIX = os.environ.get('URL_PREFIX', '/').rstrip("/")
+
 LOGIN_URL = reverse_lazy('login')
 
 USE_TZ = True
@@ -58,7 +60,7 @@ MEDIA_ROOT = os.path.join(PROJECT_ROOT, 'media/')
 # URL that handles the media served from MEDIA_ROOT. Make sure to use a
 # trailing slash.
 # Examples: "http://media.lawrence.com/media/", "http://example.com/media/"
-MEDIA_URL = '/media/'
+MEDIA_URL = '%s/media/' % URL_PREFIX
 
 # Absolute path to the directory static files should be collected to.
 # Don't put anything in this directory yourself; store your static files
@@ -70,7 +72,7 @@ COMPRESS_ROOT = STATIC_ROOT
 
 # URL prefix for static files.
 # Example: "http://media.lawrence.com/static/"
-STATIC_URL = '/static/'
+STATIC_URL = '%s/static/' % URL_PREFIX
 
 # Additional locations of static files
 STATICFILES_DIRS = [os.path.join(PROJECT_ROOT, 'static')]
@@ -153,7 +155,7 @@ EMAIL_USE_TLS = os.environ.get('SES_USE_TLS', 0)
 
 COMPRESS_OFFLINE = not DEBUG
 
-COMPRESS_URL = '/static/'
+COMPRESS_URL = '%s/static/' % URL_PREFIX
 
 RECOVERY_SNIPPETS_WHITELIST = (
     r'https?://[^.]+\.hackpad\.com/[^./]+\.js',

cabot/urls.py

@@ -165,3 +165,8 @@ def append_plugin_urls():
                 )
 
 append_plugin_urls()
+
+if settings.URL_PREFIX.strip('/'):
+    urlpatterns = patterns('',
+        ('^%s/' % settings.URL_PREFIX.strip('/'), include(urlpatterns))
+    )

conf/development.env.example

@@ -10,6 +10,9 @@ PORT=5001
 
 # You shouldn't need to change anything above this line
 
+# Base path to include before generated URLs.  If not defined, uses `/`
+# URL_PREFIX=/
+
 # Local time zone for this installation. Choices can be found here:
 # http://en.wikipedia.org/wiki/List_of_tz_zones_by_name
 TIME_ZONE=Etc/UTC

conf/production.env.example

@@ -10,6 +10,9 @@ VENV=/home/ubuntu/venv
 
 # You shouldn't need to change anything above this line
 
+# Base path to include before generated URLs.  If not defined, uses `/`
+# URL_PREFIX=/
+
 # Local time zone for this installation. Choices can be found here:
 # http://en.wikipedia.org/wiki/List_of_tz_zones_by_name
 TIME_ZONE=Etc/UTC