factor out common server implementation code

Most of the server implementation of V1 API now resides in
api.v1.server_glue. The webframeworks only supply some glue code
which is independent to changes in the API code.

nominatim/server/falcon/server.py

@@ -7,70 +7,66 @@
 """
 Server implementation using the falcon webserver framework.
 """
-from typing import Type, Any, Optional, Mapping
+from typing import Optional, Mapping, cast
 from pathlib import Path
 
 import falcon
-import falcon.asgi
+from falcon.asgi import App, Request, Response
 
-from nominatim.api import NominatimAPIAsync, StatusResult
+from nominatim.api import NominatimAPIAsync
 import nominatim.api.v1 as api_impl
 
-CONTENT_TYPE = {
-  'text': falcon.MEDIA_TEXT,
-  'xml': falcon.MEDIA_XML
-}
 
-class NominatimV1:
-    """ Implementation of V1 version of the Nominatim API.
+class ParamWrapper(api_impl.ASGIAdaptor):
+    """ Adaptor class for server glue to Falcon framework.
     """
 
-    def __init__(self, project_dir: Path, environ: Optional[Mapping[str, str]]) -> None:
-        self.api = NominatimAPIAsync(project_dir, environ)
+    def __init__(self, req: Request, resp: Response) -> None:
+        self.request = req
+        self.response = resp
 
 
-    def parse_format(self, req: falcon.asgi.Request, rtype: Type[Any], default: str) -> None:
-        """ Get and check the 'format' parameter and prepare the formatter.
-            `rtype` describes the expected return type and `default` the
-            format value to assume when no parameter is present.
+    def get(self, name: str, default: Optional[str] = None) -> Optional[str]:
+        return cast(Optional[str], self.request.get_param(name, default=default))
+
+
+    def get_header(self, name: str, default: Optional[str] = None) -> Optional[str]:
+        return cast(Optional[str], self.request.get_header(name, default=default))
+
+
+    def error(self, msg: str) -> falcon.HTTPBadRequest:
+        return falcon.HTTPBadRequest(description=msg)
+
+
+    def create_response(self, status: int, output: str, content_type: str) -> None:
+        self.response.status = status
+        self.response.text = output
+        self.response.content_type = content_type
+
+
+class EndpointWrapper:
+    """ Converter for server glue endpoint functions to Falcon request handlers.
+    """
+
+    def __init__(self, func: api_impl.EndpointFunc, api: NominatimAPIAsync) -> None:
+        self.func = func
+        self.api = api
+
+
+    async def on_get(self, req: Request, resp: Response) -> None:
+        """ Implementation of the endpoint.
         """
-        req.context.format = req.get_param('format', default=default)
-
-        if not api_impl.supports_format(rtype, req.context.format):
-            raise falcon.HTTPBadRequest(
-                description="Parameter 'format' must be one of: " +
-                            ', '.join(api_impl.list_formats(rtype)))
-
-
-    def format_response(self, req: falcon.asgi.Request, resp: falcon.asgi.Response,
-                        result: Any) -> None:
-        """ Render response into a string according to the formatter
-            set in `parse_format()`.
-        """
-        resp.text = api_impl.format_result(result, req.context.format)
-        resp.content_type = CONTENT_TYPE.get(req.context.format, falcon.MEDIA_JSON)
-
-
-    async def on_get_status(self, req: falcon.asgi.Request, resp: falcon.asgi.Response) -> None:
-        """ Implementation of status endpoint.
-        """
-        self.parse_format(req, StatusResult, 'text')
-
-        result = await self.api.status()
-
-        self.format_response(req, resp, result)
-        if result.status and req.context.format == 'text':
-            resp.status = 500
+        await self.func(self.api, ParamWrapper(req, resp))
 
 
 def get_application(project_dir: Path,
-                    environ: Optional[Mapping[str, str]] = None) -> falcon.asgi.App:
-    """ Create a Nominatim falcon ASGI application.
+                    environ: Optional[Mapping[str, str]] = None) -> App:
+    """ Create a Nominatim Falcon ASGI application.
     """
-    app = falcon.asgi.App()
+    api = NominatimAPIAsync(project_dir, environ)
 
-    api = NominatimV1(project_dir, environ)
-
-    app.add_route('/status', api, suffix='status')
+    app = App()
+    for name, func in api_impl.ROUTES:
+        app.add_route('/' + name, EndpointWrapper(func, api))
 
     return app