Aleksei Sokol
b4632c27d3
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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
80 lines
3.0 KiB
Django/Jinja
80 lines
3.0 KiB
Django/Jinja
"""Exception handling middleware is defined here."""
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import itertools
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import traceback
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from fastapi import FastAPI, HTTPException, Request
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from fastapi.responses import JSONResponse
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from starlette.middleware.base import BaseHTTPMiddleware
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from {{project_slug}}.exceptions.mapper import ExceptionMapper
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from .observability import ObservableException
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class ExceptionHandlerMiddleware(BaseHTTPMiddleware): # pylint: disable=too-few-public-methods
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"""Handle exceptions, so they become http response code 500 - Internal Server Error.
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If debug is activated in app configuration, then stack trace is returned, otherwise only a generic error message.
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Message is sent to logger error stream anyway.
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"""
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def __init__(
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self,
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app: FastAPI,
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debug: list[bool],
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exception_mapper: ExceptionMapper,
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):
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"""Passing debug as a list with single element is a hack to be able to change the value on the fly."""
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super().__init__(app)
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self._debug = debug
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self._mapper = exception_mapper
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async def dispatch(self, request: Request, call_next):
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try:
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return await call_next(request)
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except Exception as exc: # pylint: disable=broad-except
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additional_headers: dict[str, str] | None = None
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if isinstance(exc, ObservableException):
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additional_headers = {"X-Trace-Id": exc.trace_id, "X-Span-Id": str(exc.span_id)}
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exc = exc.__cause__
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status_code = 500
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detail = "exception occured"
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if isinstance(exc, HTTPException):
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status_code = exc.status_code # pylint: disable=no-member
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detail = exc.detail # pylint: disable=no-member
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if self._debug[0]:
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if (res := self._mapper.apply_if_known(exc)) is not None:
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response = res
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else:
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response = JSONResponse(
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{
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"code": status_code,
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"detail": detail,
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"error": str(exc),
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"error_type": type(exc).__name__,
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"path": request.url.path,
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"params": request.url.query,
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"tracebacks": _get_tracebacks(exc),
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},
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status_code=status_code,
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)
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else:
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response = self._mapper.apply(exc)
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if additional_headers is not None:
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response.headers.update(additional_headers)
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return response
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def _get_tracebacks(exc: Exception) -> list[list[str]]:
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tracebacks: list[list[str]] = []
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while exc is not None:
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tracebacks.append(
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list(itertools.chain.from_iterable(map(lambda x: x.split("\n"), traceback.format_tb(exc.__traceback__))))
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)
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tracebacks[-1].append(f"{exc.__class__.__module__}.{exc.__class__.__qualname__}: {exc}")
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exc = exc.__cause__
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return tracebacks
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