Add before_routing for Reverse Proxy plugins (#1252)

* Add `before_routing` for Reverse Proxy plugins

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: abhinavsingh

proxy/http/server/plugin.py

@@ -13,8 +13,8 @@
 from abc import ABC, abstractmethod
 from typing import TYPE_CHECKING, Any, Dict, List, Tuple, Union, Optional
 
-from proxy.http.url import Url
 from ..parser import HttpParser
+from ...http.url import Url
 from ..responses import NOT_FOUND_RESPONSE_PKT, okResponse
 from ..websocket import WebsocketFrame
 from ..connection import HttpClientConnection
@@ -161,6 +161,12 @@ def routes(self) -> List[Union[str, Tuple[str, List[bytes]]]]:
         must return the url to serve."""
         raise NotImplementedError()     # pragma: no cover
 
+    def before_routing(self, request: HttpParser) -> Optional[HttpParser]:
+        """Plugins can modify request, return response, close connection.
+
+        If None is returned, request will be dropped and closed."""
+        return request  # pragma: no cover
+
     def handle_route(self, request: HttpParser, pattern: RePattern) -> Url:
         """Implement this method if you have configured dynamic routes."""
         pass

proxy/http/server/reverse.py

@@ -46,6 +46,8 @@ def __init__(self, *args: Any, **kwargs: Any):
             self.plugins.append(plugin)
 
     def handle_upstream_data(self, raw: memoryview) -> None:
+        # TODO: Parse response and implement plugin hook per parsed response object
+        # This will give plugins a chance to modify the responses before dispatching to client
         self.client.queue(raw)
 
     def routes(self) -> List[Tuple[int, str]]:
@@ -57,6 +59,14 @@ def routes(self) -> List[Tuple[int, str]]:
         return r
 
     def handle_request(self, request: HttpParser) -> None:
+        # before_routing
+        for plugin in self.plugins:
+            r = plugin.before_routing(request)
+            if r is None:
+                raise HttpProtocolException('before_routing closed connection')
+            request = r
+
+        # routes
         for plugin in self.plugins:
             for route in plugin.routes():
                 if isinstance(route, tuple):
@@ -73,6 +83,7 @@ def handle_request(self, request: HttpParser) -> None:
                         break
                 else:
                     raise ValueError('Invalid route')
+
         assert self.choice and self.choice.hostname
         port = self.choice.port or \
             DEFAULT_HTTP_PORT \