Allow reaching the backend over a unix socket via API_SOCKET

CHANGELOG.md

@@ -10,6 +10,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 headers that will be sent with every request from a connection. This setting
 accepts a mapping of header names to `connection.header.Header` objects which
 can retrieve values from get params, cookies etc.
+- The `X-Real-IP` header of the connection is now forwarded to the backend by
+default. Without it the backend attributes every request to the host High
+Templar dials it from, rather than to the client that opened the websocket.
+- An `API_SOCKET` setting was added that makes requests to the backend go over
+the given unix socket rather than over TCP. This is for deployments where the
+backend is otherwise only reachable back through a proxy, which overwrites
+`X-Real-IP` with the address of the machine dialling it. `API_URL` is still
+required, and must be an `http://` url: the socket does not speak TLS, the path
+prefix is still prepended to every request, and the host, while it no longer
+decides where the connection goes, is still sent as the `Host` header and so
+must be one the backend accepts.
+
+### Removed
+- The `FORWARD_IP` setting has been removed. It read the value of the given key
+from the WSGI request environment and sent it on as `X-Forwarded-For`. The
+request environment has not existed since the rewrite to Quart, which dropped
+the code that read the setting but left the setting itself in place, so it has
+had no effect since. `X-Real-IP` is now forwarded by default instead; note that
+this is a different header, chosen because a proxy overwrites it rather than
+appending to it, and so it cannot be set by the client.
 
 ### Fixed
 - The message consumer queue is now declared `exclusive` instead of

high_templar/asgi.py

@@ -5,8 +5,8 @@
 
 class Settings:
     API_URL = os.environ.get('CY_BINDER_INTERNAL', 'http://wiremock:8080/api/')
+    API_SOCKET = os.environ.get('CY_BINDER_SOCKET')
     USER_ID_PATH = ['user', 'data', 'id']
-    FORWARD_IP = 'HTTP_X_REAL_IP'
     CONNECTION_HEADERS = {
         # 'X-Session-Token': header.Param('session_token'),
     }

high_templar/backend_adapter/binder.py

@@ -1,5 +1,5 @@
 # from aiohttp_requests import requests
-from aiohttp import ClientSession
+from aiohttp import ClientSession, UnixConnector
 from .interface import NoBackendConnectionException, BackendAdapter, UnparsableBackendPermissionsException
 from high_templar.authentication import Authentication, Permission
 from . import header
@@ -8,6 +8,9 @@
 DEFAULT_HEADERS = {
     'cookie': header.Key('Cookie'),
     'user-agent': header.Key('User-Agent'),
+    # Without this the backend attributes the connection to whichever host we
+    # dial it from, rather than to the client that opened the websocket.
+    'x-real-ip': header.Key('X-Real-IP'),
     'x-csrftoken': header.Cookie('csrftoken'),
     'authorization': header.Param('token').map('Token {}'.format),
 }
@@ -20,10 +23,15 @@ class BinderAdapter(BackendAdapter, ClientSession):
     '''
 
     def __init__(self, app):
-        super().__init__()
+        # API_SOCKET reaches the backend over a unix socket, so the request does
+        # not pass back through the proxy that fronts API_URL. API_URL is still
+        # prepended to every request and must be http:// -- the socket does not
+        # speak TLS -- and its host, though no longer dialled, is still sent as
+        # the Host header.
+        socket = app.config.get('API_SOCKET')
+        super().__init__(connector=UnixConnector(path=socket) if socket else None)
         self.app = app
         self.base_url = app.config['API_URL']
-        self.forward_ip = app.config.get('FORWARD_IP')
         self.header_definition = {**DEFAULT_HEADERS, **app.config.get('CONNECTION_HEADERS', {})}
 
     async def get_authentication(self, websocket) -> Authentication:

install/serve.py

@@ -19,9 +19,11 @@
 
 
 class Settings:
-    API_URL = os.environ.get('BINDER_INTERNAL', app_url)
+    API_SOCKET = os.environ.get('BINDER_SOCKET')
+    API_URL = os.environ.get('BINDER_INTERNAL') or (
+        'http://localhost/api/' if API_SOCKET else app_url
+    )
     USER_ID_PATH = ['user', 'data', 'id']
-    FORWARD_IP = 'HTTP_X_REAL_IP'
     CONNECTION_HEADERS = {
         'X-Session-Token': header.Param('session_token'),
         'Referer': header.Fixed(app_url), # Needed in production for online/offline notification (see T25664)