Initial commit

This is a FastAPI backend microservice template used with `copier` utility.

Features of applied template are:
- Configuration file processing logic
- Metrics and tracing (both optional) configuration available
- Debug endpoints
- Database migration commands, prepared Alembic environment
- Database usage example in ping_db endpoint
- gitea sanity check pipeline

{{project_slug}}/middlewares/exception_handler.py.jinja

@@ -0,0 +1,79 @@
+"""Exception handling middleware is defined here."""
+
+import itertools
+import traceback
+
+from fastapi import FastAPI, HTTPException, Request
+from fastapi.responses import JSONResponse
+from starlette.middleware.base import BaseHTTPMiddleware
+
+from {{project_slug}}.exceptions.mapper import ExceptionMapper
+
+from .observability import ObservableException
+
+
+class ExceptionHandlerMiddleware(BaseHTTPMiddleware):  # pylint: disable=too-few-public-methods
+    """Handle exceptions, so they become http response code 500 - Internal Server Error.
+
+    If debug is activated in app configuration, then stack trace is returned, otherwise only a generic error message.
+    Message is sent to logger error stream anyway.
+    """
+
+    def __init__(
+        self,
+        app: FastAPI,
+        debug: list[bool],
+        exception_mapper: ExceptionMapper,
+    ):
+        """Passing debug as a list with single element is a hack to be able to change the value on the fly."""
+        super().__init__(app)
+        self._debug = debug
+        self._mapper = exception_mapper
+
+    async def dispatch(self, request: Request, call_next):
+        try:
+            return await call_next(request)
+        except Exception as exc:  # pylint: disable=broad-except
+            additional_headers: dict[str, str] | None = None
+            if isinstance(exc, ObservableException):
+                additional_headers = {"X-Trace-Id": exc.trace_id, "X-Span-Id": str(exc.span_id)}
+                exc = exc.__cause__
+            status_code = 500
+            detail = "exception occured"
+
+            if isinstance(exc, HTTPException):
+                status_code = exc.status_code  # pylint: disable=no-member
+                detail = exc.detail  # pylint: disable=no-member
+
+            if self._debug[0]:
+                if (res := self._mapper.apply_if_known(exc)) is not None:
+                    response = res
+                else:
+                    response = JSONResponse(
+                        {
+                            "code": status_code,
+                            "detail": detail,
+                            "error": str(exc),
+                            "error_type": type(exc).__name__,
+                            "path": request.url.path,
+                            "params": request.url.query,
+                            "tracebacks": _get_tracebacks(exc),
+                        },
+                        status_code=status_code,
+                    )
+            else:
+                response = self._mapper.apply(exc)
+            if additional_headers is not None:
+                response.headers.update(additional_headers)
+            return response
+
+
+def _get_tracebacks(exc: Exception) -> list[list[str]]:
+    tracebacks: list[list[str]] = []
+    while exc is not None:
+        tracebacks.append(
+            list(itertools.chain.from_iterable(map(lambda x: x.split("\n"), traceback.format_tb(exc.__traceback__))))
+        )
+        tracebacks[-1].append(f"{exc.__class__.__module__}.{exc.__class__.__qualname__}: {exc}")
+        exc = exc.__cause__
+    return tracebacks