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}}/fastapi_init.py.jinja

@@ -0,0 +1,150 @@
+"""FastAPI application initialization is performed here."""
+
+import os
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+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
+from {{project_slug}}.exceptions.mapper import ExceptionMapper
+from {{project_slug}}.handlers.debug import DebugException, DebugExceptionWithParams
+from {{project_slug}}.middlewares.exception_handler import ExceptionHandlerMiddleware
+from {{project_slug}}.middlewares.observability import ObservabilityMiddleware
+from {{project_slug}}.observability.metrics import init_metrics
+from {{project_slug}}.observability.otel_agent import OpenTelemetryAgent
+from {{project_slug}}.utils.observability import URLsMapper, configure_logging
+
+from .handlers import list_of_routers
+from .version import LAST_UPDATE, VERSION
+
+
+def _get_exception_mapper(debug: bool) -> ExceptionMapper:
+    mapper = ExceptionMapper()
+    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
+
+
+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.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.state.config = app_config
+
+    exception_mapper = _get_exception_mapper(app_config.app.debug)
+    metrics = init_metrics()
+    urls_mapper = URLsMapper(app_config.observability.prometheus.urls_mapping)
+
+    application.add_middleware(
+        ObservabilityMiddleware,
+        exception_mapper=exception_mapper,
+        metrics=metrics,
+        urls_mapper=urls_mapper,
+    )
+    application.add_middleware(
+        ExceptionHandlerMiddleware,
+        debug=[False],  # reinitialized on startup
+        exception_mapper=exception_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
+    loggers_dict = {logger_config.filename: logger_config.level for logger_config in app_config.logging.files}
+    logger = configure_logging(app_config.logging.level, loggers_dict)
+
+    await logger.ainfo("application is being configured", config=app_config.to_order_dict())
+
+    connection_manager = PostgresConnectionManager(
+        master=app_config.db.master,
+        replicas=app_config.db.replicas,
+        logger=logger,
+        application_name=f"{{project_slug}}_{VERSION}",
+    )
+    connection_manager_dep.init_dispencer(application, connection_manager)
+    logger_dep.init_dispencer(application, logger)
+
+    for middleware in application.user_middleware:
+        if middleware.cls == ExceptionHandlerMiddleware:
+            middleware.kwargs["debug"][0] = app_config.app.debug
+
+    otel_agent = OpenTelemetryAgent(
+        app_config.observability.prometheus,
+        app_config.observability.jaeger,
+    )
+
+    yield
+
+    otel_agent.shutdown()
+
+
+app = get_app()