decomposer: generate deliverable files for Define the service contract and project architecture for the FastAPI endpoint monitoring service.; Implement the typed monitor CRUD API and concurrency-safe in-memory state according to the service design.; Implement secure on-demand endpoint checks with status updates, latency measurement, robust error handling, and redacted structured logs.; Add operational API endpoints and environment-driven runtime configuration to the monitoring service.; Create automated tests for the monitoring service.; Package the service with Docker and developer documentation.; Validate the complete project.

app/main.py

@@ -1,50 +1,156 @@
 import logging
 from contextlib import asynccontextmanager
 from typing import AsyncIterator
+from uuid import UUID
 
-from fastapi import FastAPI, HTTPException, Request
-from fastapi.exceptions import RequestValidationError
+from fastapi import FastAPI, Request, Response, status
 from fastapi.responses import JSONResponse
 
-from app.api import router
-from app.checker import EndpointChecker
-from app.settings import Settings, get_settings
-from app.store import MonitorStore
+from app.checker import (
+    CheckNetworkError,
+    CheckTimeoutError,
+    EndpointChecker,
+    TooManyRedirectsError,
+    UnsafeTargetError,
+)
+from app.config import Settings, get_settings
+from app.logging_config import configure_logging
+from app.models import CheckResult, CurrentStatus, Monitor, MonitorInput, State, utcnow
+from app.store import CapacityError, MonitorStore, NotFoundError, StaleCheckError
+
+logger = logging.getLogger("monitor.check")
 
 
-def configure_logging(level: str) -> None:
-    logging.basicConfig(level=level.upper(), format="%(message)s")
+def error(status_code: int, code: str, message: str) -> JSONResponse:
+    return JSONResponse(status_code=status_code, content={
+        "error": {"code": code, "message": message}
+    })
 
 
 def create_app(settings: Settings | None = None) -> FastAPI:
     config = settings or get_settings()
 
     @asynccontextmanager
-    async def lifespan(application: FastAPI) -> AsyncIterator[None]:
+    async def lifespan(app: FastAPI) -> AsyncIterator[None]:
         configure_logging(config.log_level)
-        application.state.store = MonitorStore()
-        application.state.checker = EndpointChecker(config)
+        app.state.store = MonitorStore(config.max_monitors)
+        app.state.checker = EndpointChecker(
+            config.request_timeout_seconds, config.max_redirects
+        )
+        app.state.ready = True
         yield
+        app.state.ready = False
 
-    application = FastAPI(title="Endpoint Monitor", version="1.0.0", lifespan=lifespan)
-    application.include_router(router)
+    api = FastAPI(title="Endpoint Monitor API", version="1.0.0", lifespan=lifespan)
 
-    @application.exception_handler(HTTPException)
-    async def http_error(_request: Request, exc: HTTPException) -> JSONResponse:
-        if isinstance(exc.detail, tuple):
-            code, message = exc.detail
-        else:
-            code, message = "http_error", str(exc.detail)
-        return JSONResponse(status_code=exc.status_code,
-                            content={"error": {"code": code, "message": message}},
-                            headers=exc.headers)
+    @api.exception_handler(NotFoundError)
+    async def not_found(_: Request, __: NotFoundError) -> JSONResponse:
+        return error(404, "monitor_not_found", "monitor does not exist")
 
-    @application.exception_handler(RequestValidationError)
-    async def validation_error(_request: Request, _exc: RequestValidationError) -> JSONResponse:
-        return JSONResponse(status_code=422, content={"error": {
-            "code": "validation_error", "message": "Request validation failed"}})
+    @api.exception_handler(CapacityError)
+    async def capacity(_: Request, __: CapacityError) -> JSONResponse:
+        return error(409, "capacity_exceeded", "monitor capacity reached")
 
-    return application
+    @api.get("/healthz")
+    async def health() -> dict[str, str]:
+        return {"status": "ok"}
+
+    @api.get("/readyz")
+    async def readiness(request: Request) -> JSONResponse | dict[str, str]:
+        if not getattr(request.app.state, "ready", False):
+            return error(503, "not_ready", "service is not ready")
+        return {"status": "ok"}
+
+    @api.post("/monitors", response_model=Monitor, status_code=status.HTTP_201_CREATED)
+    async def create(data: MonitorInput, request: Request) -> Monitor:
+        return await request.app.state.store.create(data)
+
+    @api.get("/monitors", response_model=list[Monitor])
+    async def list_monitors(request: Request) -> list[Monitor]:
+        return await request.app.state.store.list()
+
+    @api.get("/monitors/{monitor_id}", response_model=Monitor)
+    async def get_monitor(monitor_id: UUID, request: Request) -> Monitor:
+        return await request.app.state.store.get(monitor_id)
+
+    @api.put("/monitors/{monitor_id}", response_model=Monitor)
+    async def replace(monitor_id: UUID, data: MonitorInput, request: Request) -> Monitor:
+        return await request.app.state.store.replace(monitor_id, data)
+
+    @api.delete("/monitors/{monitor_id}", status_code=204)
+    async def delete(monitor_id: UUID, request: Request) -> Response:
+        await request.app.state.store.delete(monitor_id)
+        return Response(status_code=204)
+
+    @api.get("/monitors/{monitor_id}/status", response_model=CurrentStatus)
+    async def current_status(monitor_id: UUID, request: Request) -> CurrentStatus:
+        return (await request.app.state.store.get(monitor_id)).current_status
+
+    @api.post("/monitors/{monitor_id}/check", response_model=CheckResult)
+    async def check(monitor_id: UUID, request: Request) -> CheckResult | JSONResponse:
+        store: MonitorStore = request.app.state.store
+        item = await store.get(monitor_id)
+        checked_url = str(item.url)
+        logger.info("check_started", extra={"fields": {"url": checked_url, "monitor_id": monitor_id}})
+        try:
+            outcome = await request.app.state.checker.check(checked_url)
+            current = CurrentStatus(
+                state=State.UP if 200 <= outcome.status_code < 400 else State.DOWN,
+                checked_at=utcnow(), latency_ms=outcome.latency_ms,
+                status_code=outcome.status_code,
+            )
+            await store.publish_status(monitor_id, checked_url, current)
+            logger.info("check_finished", extra={"fields": {
+                "url": checked_url, "monitor_id": monitor_id,
+                "status_code": outcome.status_code, "latency_ms": outcome.latency_ms,
+            }})
+            return CheckResult(monitor_id=monitor_id, **current.model_dump())
+        except UnsafeTargetError:
+            return await publish_error(store, monitor_id, checked_url, "unsafe_target", 400)
+        except CheckTimeoutError as exc:
+            return await publish_error(
+                store, monitor_id, checked_url, "check_timeout", 504, exc.latency_ms
+            )
+        except CheckNetworkError as exc:
+            return await publish_error(
+                store, monitor_id, checked_url, "network_error", 502, exc.latency_ms
+            )
+        except TooManyRedirectsError as exc:
+            return await publish_error(
+                store, monitor_id, checked_url, "redirect_limit", 502, exc.latency_ms
+            )
+        except StaleCheckError:
+            return error(409, "stale_check", "monitor URL changed during check")
+
+    return api
+
+
+async def publish_error(
+    store: MonitorStore,
+    monitor_id: UUID,
+    checked_url: str,
+    code: str,
+    http_status: int,
+    latency_ms: float | None = None,
+) -> JSONResponse:
+    current = CurrentStatus(
+        state=State.ERROR, checked_at=utcnow(), latency_ms=latency_ms, error_code=code
+    )
+    try:
+        await store.publish_status(monitor_id, checked_url, current)
+    except StaleCheckError:
+        return error(409, "stale_check", "monitor URL changed during check")
+    logger.warning("check_failed", extra={"fields": {
+        "url": checked_url, "monitor_id": monitor_id, "error_code": code,
+        "latency_ms": latency_ms,
+    }})
+    messages = {
+        "unsafe_target": "target is not permitted",
+        "check_timeout": "target request timed out",
+        "network_error": "target request failed",
+        "redirect_limit": "target exceeded redirect limit",
+    }
+    return error(http_status, code, messages[code])
 
 
 app = create_app()