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/checker.py

@@ -1,50 +1,76 @@
 import logging
-from time import monotonic
+import time
+from datetime import UTC, datetime
 from urllib.parse import urljoin
 
 import httpx
 
-from .config import Settings
+from app.config import Settings
-from .logging import log_event, redacted_url
+from app.models import MonitorState, StatusSnapshot
-from .models import CheckSnapshot, State, now
+from app.security import Resolver, UnsafeTarget, redact_url, system_resolver, validate_target
-from .security import UnsafeDestination, validate_destination
 
-logger = logging.getLogger("endpoint_monitor.checker")
+logger = logging.getLogger("monitor.checker")
 
 
-async def check_url(url: str, timeout: float, settings: Settings,
+class EndpointChecker:
-                    transport: httpx.AsyncBaseTransport | None = None) -> CheckSnapshot:
+    def __init__(
-    started = monotonic()
+        self, settings: Settings, resolver: Resolver = system_resolver,
-    current = url
+        transport: httpx.AsyncBaseTransport | None = None,
-    try:
+    ) -> None:
-        async with httpx.AsyncClient(transport=transport, follow_redirects=False,
+        self.settings = settings
-                                     timeout=httpx.Timeout(timeout)) as client:
+        self.resolver = resolver
-            for redirect_count in range(settings.max_redirects + 1):
+        self.transport = transport
-                await validate_destination(current)
+
-                response = await client.get(current)
+    async def check(self, monitor_id: str, url: str) -> StatusSnapshot:
-                if response.is_redirect:
+        started = time.perf_counter()
-                    location = response.headers.get("location")
+        current = url
-                    if not location:
+        try:
-                        break
+            timeout = httpx.Timeout(
-                    if redirect_count == settings.max_redirects:
+                self.settings.check_timeout_seconds,
-                        raise httpx.TooManyRedirects("redirect limit exceeded")
+                connect=self.settings.connect_timeout_seconds,
-                    current = urljoin(current, location)
+            )
-                    continue
+            async with httpx.AsyncClient(
-                elapsed = round((monotonic() - started) * 1000, 3)
+                timeout=timeout, transport=self.transport, follow_redirects=False,
-                state = State.up if 200 <= response.status_code < 400 else State.down
+            ) as client:
-                result = CheckSnapshot(state=state, checked_at=now(), latency_ms=elapsed,
+                for hop in range(self.settings.max_redirects + 1):
-                                       http_status=response.status_code)
+                    await validate_target(current, self.resolver)
-                log_event(logger, "check_complete", url=redacted_url(current), state=state,
+                    async with client.stream("GET", current) as response:
-                          latency_ms=elapsed, http_status=response.status_code)
+                        if response.is_redirect:
-                return result
+                            location = response.headers.get("location")
-        raise httpx.RemoteProtocolError("redirect response missing location")
+                            if not location:
-    except UnsafeDestination:
+                                return self._result(MonitorState.ERROR, started, error="bad_redirect")
-        log_event(logger, "check_blocked", url=redacted_url(current))
+                            if hop == self.settings.max_redirects:
-        raise
+                                return self._result(MonitorState.ERROR, started, error="too_many_redirects")
-    except (httpx.HTTPError, TimeoutError) as exc:
+                            current = urljoin(current, location)
-        elapsed = round((monotonic() - started) * 1000, 3)
+                            continue
-        result = CheckSnapshot(state=State.error, checked_at=now(), latency_ms=elapsed,
+                        state = MonitorState.UP if 200 <= response.status_code < 400 else MonitorState.DOWN
-                               error=type(exc).__name__)
+                        result = self._result(state, started, response.status_code)
-        log_event(logger, "check_error", url=redacted_url(current), state=State.error,
+                        self._log(monitor_id, url, result)
-                  error=type(exc).__name__, latency_ms=elapsed)
+                        return result
+        except UnsafeTarget as exc:
+            result = self._result(MonitorState.BLOCKED, started, error=str(exc))
+        except httpx.TimeoutException:
+            result = self._result(MonitorState.ERROR, started, error="timeout")
+        except httpx.HTTPError:
+            result = self._result(MonitorState.ERROR, started, error="transport_error")
+        self._log(monitor_id, url, result)
         return result
+
+    @staticmethod
+    def _result(
+        state: MonitorState, started: float, status: int | None = None,
+        error: str | None = None,
+    ) -> StatusSnapshot:
+        return StatusSnapshot(
+            state=state, checked_at=datetime.now(UTC),
+            latency_ms=round((time.perf_counter() - started) * 1000, 3),
+            http_status=status, error=error,
+        )
+
+    @staticmethod
+    def _log(monitor_id: str, url: str, result: StatusSnapshot) -> None:
+        logger.info("check_complete", extra={
+            "monitor_id": monitor_id, "target": redact_url(url),
+            "state": result.state, "latency_ms": result.latency_ms,
+            "http_status": result.http_status, "error": result.error,
+        })