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/security.py

@@ -1,29 +1,55 @@
 import asyncio
 import ipaddress
 import socket
-from urllib.parse import urlsplit
+from collections.abc import Awaitable, Callable
+from urllib.parse import urlsplit, urlunsplit
+
+Resolver = Callable[[str, int], Awaitable[list[str]]]
 
 
-class UnsafeDestination(ValueError):
+class UnsafeTarget(ValueError):
     pass
 
 
-async def validate_destination(url: str) -> None:
-    parsed = urlsplit(url)
-    if parsed.scheme not in {"http", "https"} or not parsed.hostname:
-        raise UnsafeDestination("only HTTP(S) URLs with a hostname are allowed")
-    if parsed.username or parsed.password:
-        raise UnsafeDestination("URL credentials are not allowed")
+def redact_url(url: str) -> str:
+    parts = urlsplit(url)
+    host = parts.hostname or "invalid"
+    if ":" in host:
+        host = f"[{host}]"
+    port = f":{parts.port}" if parts.port else ""
+    return urlunsplit((parts.scheme, f"{host}{port}", parts.path, "", ""))
+
+
+async def system_resolver(host: str, port: int) -> list[str]:
+    def resolve() -> list[str]:
+        rows = socket.getaddrinfo(host, port, type=socket.SOCK_STREAM)
+        return list({row[4][0] for row in rows})
+
+    return await asyncio.to_thread(resolve)
+
+
+async def validate_target(url: str, resolver: Resolver = system_resolver) -> None:
+    parts = urlsplit(url)
+    if parts.scheme not in {"http", "https"} or not parts.hostname:
+        raise UnsafeTarget("invalid_scheme_or_host")
+    if parts.username is not None or parts.password is not None:
+        raise UnsafeTarget("credentials_not_allowed")
+    host = parts.hostname.rstrip(".").lower()
+    if host == "localhost" or host.endswith(".localhost"):
+        raise UnsafeTarget("non_global_target")
+    port = parts.port or (443 if parts.scheme == "https" else 80)
     try:
-        literal = ipaddress.ip_address(parsed.hostname)
-        addresses = [literal]
+        literal = ipaddress.ip_address(host)
+        addresses = [str(literal)]
     except ValueError:
-        loop = asyncio.get_running_loop()
         try:
-            infos = await loop.getaddrinfo(parsed.hostname, parsed.port,
-                                           type=socket.SOCK_STREAM)
-        except socket.gaierror as exc:
-            raise UnsafeDestination("destination DNS resolution failed") from exc
-        addresses = list({ipaddress.ip_address(info[4][0]) for info in infos})
-    if not addresses or any(not address.is_global for address in addresses):
-        raise UnsafeDestination("destination resolves to a non-public address")
+            addresses = await resolver(host, port)
+        except (OSError, socket.gaierror) as exc:
+            raise UnsafeTarget("dns_resolution_failed") from exc
+    if not addresses:
+        raise UnsafeTarget("dns_resolution_failed")
+    try:
+        if any(not ipaddress.ip_address(address).is_global for address in addresses):
+            raise UnsafeTarget("non_global_target")
+    except ValueError as exc:
+        raise UnsafeTarget("invalid_dns_answer") from exc