improve error message on missing modules from nominatim_api

[nominatim.git] / src / nominatim_api / result_formatting.py

diff --git a/src/nominatim_api/result_formatting.py b/src/nominatim_api/result_formatting.py
index fc22fc0f28ba4c1c430d78601aa7d92d9b258904..50f086f3fb281fbf89108c40241e809dd216a747 100644 (file)
--- a/src/nominatim_api/result_formatting.py
+++ b/src/nominatim_api/result_formatting.py
@@ -7,19 +7,28 @@
 """
 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
+
+from .server.content_types import CONTENT_JSON
 
 T = TypeVar('T') # pylint: disable=invalid-name
 FormatFunc = Callable[[T, Mapping[str, Any]], str]
+ErrorFormatFunc = Callable[[str, str, int], str]
 
 
 class FormatDispatcher:
-    """ Helper class to conveniently create formatting functions in
-        a module using decorators.
+    """ Container for formatting functions for results.
+        Functions can conveniently be added by using decorated functions.
     """
 
-    def __init__(self) -> None:
+    def __init__(self, content_types: Optional[Mapping[str, str]] = None) -> None:
+        self.error_handler: ErrorFormatFunc = lambda ct, msg, status: f"ERROR {status}: {msg}"
+        self.content_types: Dict[str, str] = {}
+        if content_types:
+            self.content_types.update(content_types)
         self.format_functions: Dict[Type[Any], Dict[str, FormatFunc[Any]]] = defaultdict(dict)
 
 
@@ -35,6 +44,15 @@ class FormatDispatcher:
         return decorator
 
 
+    def error_format_func(self, func: ErrorFormatFunc) -> ErrorFormatFunc:
+        """ Decorator for a function that formats error messges.
+            There is only one error formatter per dispatcher. Using
+            the decorator repeatedly will overwrite previous functions.
+        """
+        self.error_handler = func
+        return func
+
+
     def list_formats(self, result_type: Type[Any]) -> List[str]:
         """ Return a list of formats supported by this formatter.
         """
@@ -54,3 +72,56 @@ class FormatDispatcher:
             `list_formats()`.
         """
         return self.format_functions[type(result)][fmt](result, options)
+
+
+    def format_error(self, content_type: str, msg: str, status: int) -> str:
+        """ Convert the given error message into a response string
+            taking the requested content_type into account.
+
+            Change the format using the error_format_func decorator.
+        """
+        return self.error_handler(content_type, msg, status)
+
+
+    def set_content_type(self, fmt: str, content_type: str) -> None:
+        """ Set the content type for the given format. This is the string
+            that will be returned in the Content-Type header of the HTML
+            response, when the given format is choosen.
+        """
+        self.content_types[fmt] = content_type
+
+
+    def get_content_type(self, fmt: str) -> str:
+        """ Return the content type for the given format.
+
+            If no explicit content type has been defined, then
+            JSON format is assumed.
+        """
+        return self.content_types.get(fmt, CONTENT_JSON)
+
+
+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)