proxy: use FrontEndApp.proxy_route_request() to determine proxy route

Extensions can override this function to provide custom proxy routing
Update docs

docs/manual/configuring.rst

@@ -478,11 +478,11 @@ The following are all the available proxy options -- only ``coll`` is required::
     use_banner: true
     use_head_insert: true
 
-(A final option, ``override_route``, allows setting a custom prefix to which to which the proxy requested will be routed.
+The HTTP/S functionality is provided by the separate :mod:`wsgiprox` utility which provides HTTP/S proxy routing
-If set, this option overrides the proxy collection and all other settings, and it is intended for use when extending pywb with custom routing.)
+to any WSGI application.
 
-The HTTP/S functionality is provided by the separate :mod:`wsgiprox` utility which provides HTTP/S proxy
+Using ``wsgiprox``, pywb sets ``FrontEndApp.proxy_route_request()`` as the proxy resolver, and this function returns the full collection path that pywb uses to route each proxy request.
-for any WSGI application.
+Extensions to pywb can override ``proxy_route_request()`` to provide custom handling, such as setting the collection dynamically or based on external data sources.
 
 See the `wsgiprox README <https://github.com/webrecorder/wsgiprox/blob/master/README.rst>`_ for additional details on how it works.
 

pywb/apps/frontendapp.py

@@ -380,6 +380,7 @@ class FrontEndApp(object):
 
     def init_proxy(self, config):
         proxy_config = config.get('proxy')
+        self.proxy_prefix = None
         if not proxy_config:
             return
 
@@ -407,17 +408,24 @@ class FrontEndApp(object):
         else:
             logging.info('Proxy enabled for collection "{0}"'.format(proxy_coll))
 
-        if proxy_config.get('override_route'):
+        if proxy_config.get('use_head_insert', True):
-            prefix = proxy_config.get('override_route')
+            self.proxy_prefix = '/{0}/bn_/'.format(proxy_coll)
-        elif proxy_config.get('use_head_insert', True):
-            prefix = '/{0}/bn_/'.format(proxy_coll)
         else:
-            prefix = '/{0}/id_/'.format(proxy_coll)
+            self.proxy_prefix = '/{0}/id_/'.format(proxy_coll)
 
-        self.handler = WSGIProxMiddleware(self.handle_request, prefix,
+        self.handler = WSGIProxMiddleware(self.handle_request,
+                                  self.proxy_route_request,
                                   proxy_host=proxy_config.get('host', 'pywb.proxy'),
                                   proxy_options=proxy_config)
 
+    def proxy_route_request(self, url, environ):
+        """ Return the full url that this proxy request will be routed to
+        The 'environ' PATH_INFO and REQUEST_URI will be modified based on the returned url
+
+        Default is to use the 'proxy_prefix' to point to the proxy collection
+        """
+        return self.proxy_prefix + url
+
 
 # ============================================================================
 class MetadataCache(object):

tests/test_proxy.py

@@ -127,7 +127,7 @@ class TestRecordingProxy(CollsDirMixin, BaseTestProxy):
     def test_proxy_replay_recorded(self, scheme):
         manager(['reindex', 'test'])
 
-        self.app.handler.prefix_resolver.fixed_prefix = '/test/bn_/'
+        self.app.proxy_prefix = '/test/bn_/'
 
         res = requests.get('{0}://httpbin.org/'.format(scheme),
                            proxies=self.proxies,
@@ -137,7 +137,7 @@ class TestRecordingProxy(CollsDirMixin, BaseTestProxy):
         assert 'httpbin(1)' in res.text
 
     def test_proxy_record_keep_percent(self, scheme):
-        self.app.handler.prefix_resolver.fixed_prefix = '/test/record/bn_/'
+        self.app.proxy_prefix = '/test/record/bn_/'
 
         res = requests.get('{0}://example.com/path/%2A%2Ftest'.format(scheme),
                            proxies=self.proxies,