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/starlette/server.py

@@ -7,7 +7,7 @@
 """
 Server implementation using the starlette webserver framework.
 """
-from typing import Any, Type, Optional, Mapping
+from typing import Any, Optional, Mapping, Callable, cast, Coroutine
 from pathlib import Path
 
 from starlette.applications import Starlette
@@ -16,58 +16,50 @@ from starlette.exceptions import HTTPException
 from starlette.responses import Response
 from starlette.requests import Request
 
-from nominatim.api import NominatimAPIAsync, StatusResult
+from nominatim.api import NominatimAPIAsync
 import nominatim.api.v1 as api_impl
 
-CONTENT_TYPE = {
-  'text': 'text/plain; charset=utf-8',
-  'xml': 'text/xml; charset=utf-8'
-}
-
-def parse_format(request: 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.
+class ParamWrapper(api_impl.ASGIAdaptor):
+    """ Adaptor class for server glue to Starlette framework.
     """
-    fmt = request.query_params.get('format', default=default)
 
-    if not api_impl.supports_format(rtype, fmt):
-        raise HTTPException(400, detail="Parameter 'format' must be one of: " +
-                                        ', '.join(api_impl.list_formats(rtype)))
-
-    request.state.format = fmt
+    def __init__(self, request: Request) -> None:
+        self.request = request
 
 
-def format_response(request: Request, result: Any) -> Response:
-    """ Render response into a string according.
-    """
-    fmt = request.state.format
-    return Response(api_impl.format_result(result, fmt),
-                    media_type=CONTENT_TYPE.get(fmt, 'application/json'))
+    def get(self, name: str, default: Optional[str] = None) -> Optional[str]:
+        return self.request.query_params.get(name, default=default)
 
 
-async def on_status(request: Request) -> Response:
-    """ Implementation of status endpoint.
-    """
-    parse_format(request, StatusResult, 'text')
-    result = await request.app.state.API.status()
-    response = format_response(request, result)
-
-    if request.state.format == 'text' and result.status:
-        response.status_code = 500
-
-    return response
+    def get_header(self, name: str, default: Optional[str] = None) -> Optional[str]:
+        return self.request.headers.get(name, default)
 
 
-V1_ROUTES = [
-    Route('/status', endpoint=on_status)
-]
+    def error(self, msg: str) -> HTTPException:
+        return HTTPException(400, detail=msg)
+
+
+    def create_response(self, status: int, output: str, content_type: str) -> Response:
+        return Response(output, status_code=status, media_type=content_type)
+
+
+def _wrap_endpoint(func: api_impl.EndpointFunc)\
+        -> Callable[[Request], Coroutine[Any, Any, Response]]:
+    async def _callback(request: Request) -> Response:
+        return cast(Response, await func(request.app.state.API, ParamWrapper(request)))
+
+    return _callback
+
 
 def get_application(project_dir: Path,
                     environ: Optional[Mapping[str, str]] = None) -> Starlette:
     """ Create a Nominatim falcon ASGI application.
     """
-    app = Starlette(debug=True, routes=V1_ROUTES)
+    routes = []
+    for name, func in api_impl.ROUTES:
+        routes.append(Route(f"/{name}", endpoint=_wrap_endpoint(func)))
+
+    app = Starlette(debug=True, routes=routes)
 
     app.state.API = NominatimAPIAsync(project_dir, environ)