make API formatter loadable from project directory

src/nominatim_api/result_formatting.py

@@ -7,8 +7,10 @@
 """
 Helper classes and functions for formatting results into API responses.
 """
-from typing import Type, TypeVar, Dict, List, Callable, Any, Mapping
+from typing import Type, TypeVar, Dict, List, Callable, Any, Mapping, Optional, cast
 from collections import defaultdict
+from pathlib import Path
+import importlib
 
 T = TypeVar('T') # pylint: disable=invalid-name
 FormatFunc = Callable[[T, Mapping[str, Any]], str]
@@ -54,3 +56,30 @@ class FormatDispatcher:
             `list_formats()`.
         """
         return self.format_functions[type(result)][fmt](result, options)
+
+
+def load_format_dispatcher(api_name: str, project_dir: Optional[Path]) -> FormatDispatcher:
+    """ Load the dispatcher for the given API.
+
+        The function first tries to find a module api/<api_name>/format.py
+        in the project directory. This file must export a single variable
+        `dispatcher`.
+
+        If the function does not exist, the default formatter is loaded.
+    """
+    if project_dir is not None:
+        priv_module = project_dir / 'api' / api_name / 'format.py'
+        if priv_module.is_file():
+            spec = importlib.util.spec_from_file_location(f'api.{api_name},format',
+                                                          str(priv_module))
+            if spec:
+                module = importlib.util.module_from_spec(spec)
+                # Do not add to global modules because there is no standard
+                # module name that Python can resolve.
+                assert spec.loader is not None
+                spec.loader.exec_module(module)
+
+                return cast(FormatDispatcher, module.dispatch)
+
+    return cast(FormatDispatcher,
+                importlib.import_module(f'nominatim_api.{api_name}.format').dispatch)

src/nominatim_api/server/falcon/server.py

@@ -17,8 +17,7 @@ from falcon.asgi import App, Request, Response
 from ...config import Configuration
 from ...core import NominatimAPIAsync
 from ... import v1 as api_impl
-from ...result_formatting import FormatDispatcher
-from ...v1.format import dispatch as formatting
+from ...result_formatting import FormatDispatcher, load_format_dispatcher
 from ... import logging as loglib
 from ..asgi_adaptor import ASGIAdaptor, EndpointFunc
 
@@ -64,10 +63,12 @@ class ParamWrapper(ASGIAdaptor):
     """ Adaptor class for server glue to Falcon framework.
     """
 
-    def __init__(self, req: Request, resp: Response, config: Configuration) -> None:
+    def __init__(self, req: Request, resp: Response,
+                 config: Configuration, formatter: FormatDispatcher) -> None:
         self.request = req
         self.response = resp
         self._config = config
+        self._formatter = formatter
 
 
     def get(self, name: str, default: Optional[str] = None) -> Optional[str]:
@@ -96,23 +97,26 @@ class ParamWrapper(ASGIAdaptor):
         return self._config
 
     def formatting(self) -> FormatDispatcher:
-        return formatting
+        return self._formatter
 
 
 class EndpointWrapper:
     """ Converter for server glue endpoint functions to Falcon request handlers.
     """
 
-    def __init__(self, name: str, func: EndpointFunc, api: NominatimAPIAsync) -> None:
+    def __init__(self, name: str, func: EndpointFunc, api: NominatimAPIAsync,
+                 formatter: FormatDispatcher) -> None:
         self.name = name
         self.func = func
         self.api = api
+        self.formatter = formatter
 
 
     async def on_get(self, req: Request, resp: Response) -> None:
         """ Implementation of the endpoint.
         """
-        await self.func(self.api, ParamWrapper(req, resp, self.api.config))
+        await self.func(self.api, ParamWrapper(req, resp, self.api.config,
+                                               self.formatter))
 
 
 class FileLoggingMiddleware:
@@ -182,8 +186,9 @@ def get_application(project_dir: Path,
     app.add_error_handler(asyncio.TimeoutError, timeout_error_handler)
 
     legacy_urls = api.config.get_bool('SERVE_LEGACY_URLS')
+    formatter = load_format_dispatcher('v1', project_dir)
     for name, func in api_impl.ROUTES:
-        endpoint = EndpointWrapper(name, func, api)
+        endpoint = EndpointWrapper(name, func, api, formatter)
         app.add_route(f"/{name}", endpoint)
         if legacy_urls:
             app.add_route(f"/{name}.php", endpoint)

src/nominatim_api/server/starlette/server.py

@@ -24,8 +24,7 @@ from starlette.middleware.cors import CORSMiddleware
 from ...config import Configuration
 from ...core import NominatimAPIAsync
 from ... import v1 as api_impl
-from ...result_formatting import FormatDispatcher
-from ...v1.format import dispatch as formatting
+from ...result_formatting import FormatDispatcher, load_format_dispatcher
 from ..asgi_adaptor import ASGIAdaptor, EndpointFunc
 from ... import logging as loglib
 
@@ -73,7 +72,7 @@ class ParamWrapper(ASGIAdaptor):
 
 
     def formatting(self) -> FormatDispatcher:
-        return formatting
+        return cast(FormatDispatcher, self.request.app.state.API.formatter)
 
 
 def _wrap_endpoint(func: EndpointFunc)\
@@ -171,6 +170,7 @@ def get_application(project_dir: Path,
                     on_shutdown=[_shutdown])
 
     app.state.API = NominatimAPIAsync(project_dir, environ)
+    app.state.formatter = load_format_dispatcher('v1', project_dir)
 
     return app