template-fastapi/{{project_slug}}/fastapi_init.py.jinja

"""FastAPI application initialization is performed here."""

import os
from contextlib import asynccontextmanager
from typing import NoReturn

from fastapi import FastAPI, Request
from fastapi.middleware.cors import CORSMiddleware
from fastapi.middleware.gzip import GZipMiddleware
from fastapi.openapi.docs import get_swagger_ui_html
from fastapi.responses import JSONResponse

from {{project_slug}}.config import {{ProjectName}}Config
from {{project_slug}}.db.connection.manager import PostgresConnectionManager
from {{project_slug}}.dependencies import connection_manager_dep, logger_dep, metrics_dep
from {{project_slug}}.exceptions.mapper import ExceptionMapper
from {{project_slug}}.handlers.debug import DebugException, DebugExceptionWithParams
from {{project_slug}}.middlewares.exception_handler import ExceptionHandlerMiddleware, HandlerNotFoundError
from {{project_slug}}.middlewares.observability import ObservabilityMiddleware
from {{project_slug}}.observability.logging import configure_logging
from {{project_slug}}.observability.metrics import setup_metrics
from {{project_slug}}.observability.otel_agent import OpenTelemetryAgent
from {{project_slug}}.observability.utils import URLsMapper

from .handlers import list_of_routers
from .version import LAST_UPDATE, VERSION


def bind_routes(application: FastAPI, prefix: str, debug: bool) -> None:
    """Bind all routes to application."""
    for router in list_of_routers:
        if not debug:
            to_remove = []
            for i, route in enumerate(router.routes):
                if "debug" in route.path:
                    to_remove.append(i)
            for i in to_remove[::-1]:
                del router.routes[i]
        if len(router.routes) > 0:
            application.include_router(router, prefix=(prefix if "/" not in {r.path for r in router.routes} else ""))


def get_app(prefix: str = "/api") -> FastAPI:
    """Create application and all dependable objects."""

    if "CONFIG_PATH" not in os.environ:
        raise ValueError("CONFIG_PATH environment variable is not set")
    app_config: {{ProjectName}}Config = {{ProjectName}}Config.from_file(os.getenv("CONFIG_PATH"))

    description = "{{project_description}}"

    application = FastAPI(
        title="{{project_name}}",
        description=description,
        docs_url=None,
        openapi_url=f"{prefix}/openapi",
        version=f"{VERSION} ({LAST_UPDATE})",
        terms_of_service="http://swagger.io/terms/",
        contact={"email": "idu@itmo.ru"},
        license_info={"name": "Apache 2.0", "url": "http://www.apache.org/licenses/LICENSE-2.0.html"},
        lifespan=lifespan,
    )
    bind_routes(application, prefix, app_config.app.debug)

    @application.get(f"{prefix}/docs", include_in_schema=False)
    async def custom_swagger_ui_html():
        return get_swagger_ui_html(
            openapi_url=application.openapi_url,
            title=application.title + " - Swagger UI",
            oauth2_redirect_url=app.swagger_ui_oauth2_redirect_url,
            swagger_js_url="https://unpkg.com/swagger-ui-dist@5.11.7/swagger-ui-bundle.js",
            swagger_css_url="https://unpkg.com/swagger-ui-dist@5.11.7/swagger-ui.css",
        )

    @application.exception_handler(404)
    async def handle_404(request: Request, exc: Exception) -> NoReturn:
        raise HandlerNotFoundError() from exc

    application.add_middleware(
        CORSMiddleware,
        allow_origins=app_config.app.cors.allow_origins,
        allow_credentials=app_config.app.cors.allow_credentials,
        allow_methods=app_config.app.cors.allow_methods,
        allow_headers=app_config.app.cors.allow_headers,
    )
    application.add_middleware(GZipMiddleware, minimum_size=1000, compresslevel=5)

    application.state.config = app_config

    logger = configure_logging(
        app_config.observability.logging,
        tracing_enabled=app_config.observability.jaeger is not None,
    )
    metrics = setup_metrics()

    exception_mapper = ExceptionMapper()
    _register_exceptions(exception_mapper, debug=app_config.app.debug)
    connection_manager = PostgresConnectionManager(
        master=app_config.db.master,
        replicas=app_config.db.replicas,
        logger=logger,
        application_name=f"{{project_slug}}_{VERSION}",
    )
    urls_mapper = URLsMapper()
    urls_mapper.add_routes(application.routes)

    connection_manager_dep.init_dispencer(application, connection_manager)
    metrics_dep.init_dispencer(application, metrics)
    logger_dep.init_dispencer(application, logger)

    application.add_middleware(
        ExceptionHandlerMiddleware,
        debug=app_config.app.debug,
        exception_mapper=exception_mapper,
        urls_mapper=urls_mapper,
        errors_metric=metrics.http.errors,
    )
    application.add_middleware(
        ObservabilityMiddleware,
        metrics=metrics,
        urls_mapper=urls_mapper,
    )

    return application


@asynccontextmanager
async def lifespan(application: FastAPI):
    """Lifespan function.

    Initializes database connection in pass_services_dependencies middleware.
    """
    app_config: {{ProjectName}}Config = application.state.config
    logger = logger_dep.from_app(application)

    await logger.ainfo("application is starting", config=app_config.to_order_dict())

    otel_agent = OpenTelemetryAgent(
        app_config.observability.prometheus,
        app_config.observability.jaeger,
    )

    yield

    otel_agent.shutdown()


def _register_exceptions(mapper: ExceptionMapper, debug: bool) -> None:
    if debug:
        mapper.register_simple(DebugException, 506, "That's how a debug exception look like")
        mapper.register_func(
            DebugExceptionWithParams,
            lambda exc: JSONResponse(
                {"error": "That's how a debug exception with params look like", "message": exc.message},
                status_code=exc.status_code,
            ),
        )
    return mapper


app = get_app()