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

@@ -4,63 +4,58 @@ import socket
 from collections.abc import Awaitable, Callable
 from urllib.parse import urlsplit, urlunsplit
 
-Resolver = Callable[[str, int], Awaitable[list[str]]]
 
-
-class UnsafeTarget(ValueError):
+class UnsafeTargetError(ValueError):
     pass
 
 
-async def system_resolver(host: str, port: int) -> list[str]:
-    def resolve() -> list[str]:
-        records = socket.getaddrinfo(host, port, type=socket.SOCK_STREAM)
+Resolver = Callable[[str, int], Awaitable[list[str]]]
+
+
+async def resolve_addresses(host: str, port: int) -> list[str]:
+    loop = asyncio.get_running_loop()
+    records = await loop.run_in_executor(
+        None, lambda: socket.getaddrinfo(host, port, type=socket.SOCK_STREAM)
+    )
     return sorted({record[4][0] for record in records})
 
-    try:
-        return await asyncio.to_thread(resolve)
-    except socket.gaierror as exc:
-        raise OSError(f"DNS resolution failed: {exc}") from exc
 
-
-def _require_global(address: str) -> None:
-    try:
-        ip = ipaddress.ip_address(address)
-    except ValueError as exc:
-        raise UnsafeTarget("DNS returned an invalid address") from exc
-    if not ip.is_global:
-        raise UnsafeTarget("target resolves to a non-public address")
-
-
-async def validate_target(url: str, resolver: Resolver = system_resolver) -> None:
+async def assert_safe_url(
+    url: str, allowed_ports: frozenset[int], resolver: Resolver = resolve_addresses
+) -> str:
     parsed = urlsplit(url)
-    if parsed.scheme not in {"http", "https"}:
-        raise UnsafeTarget("only HTTP(S) targets are allowed")
+    if parsed.scheme not in {"http", "https"} or not parsed.hostname:
+        raise UnsafeTargetError("only HTTP(S) targets with a hostname are allowed")
     if parsed.username is not None or parsed.password is not None:
-        raise UnsafeTarget("URL credentials are not allowed")
-    if not parsed.hostname:
-        raise UnsafeTarget("target has no hostname")
+        raise UnsafeTargetError("target credentials are not allowed")
     try:
-        literal = ipaddress.ip_address(parsed.hostname)
-    except ValueError:
-        addresses = await resolver(parsed.hostname, parsed.port or (443 if parsed.scheme == "https" else 80))
+        port = parsed.port or (443 if parsed.scheme == "https" else 80)
+    except ValueError as exc:
+        raise UnsafeTargetError("target port is invalid") from exc
+    if port not in allowed_ports:
+        raise UnsafeTargetError("target port is not allowed")
+    try:
+        addresses = await resolver(parsed.hostname, port)
+    except (OSError, UnicodeError) as exc:
+        raise UnsafeTargetError("target hostname could not be resolved") from exc
     if not addresses:
-            raise OSError("DNS resolution returned no addresses")
-        for address in addresses:
-            _require_global(address)
-    else:
-        _require_global(str(literal))
-
-
-def redact_url(url: str) -> str:
-    """Retain scheme/host/port/path, never credentials, query, or fragment."""
-    parsed = urlsplit(url)
-    host = parsed.hostname or ""
-    if ":" in host and not host.startswith("["):
-        host = f"[{host}]"
-    netloc = host
+        raise UnsafeTargetError("target hostname returned no addresses")
+    for value in addresses:
         try:
-        if parsed.port is not None:
-            netloc = f"{host}:{parsed.port}"
+            address = ipaddress.ip_address(value)
+        except ValueError as exc:
+            raise UnsafeTargetError("resolver returned an invalid address") from exc
+        if not address.is_global:
+            raise UnsafeTargetError("target resolves to a non-public address")
+    return url
+
+
+def redacted_url(url: str) -> str:
+    parsed = urlsplit(url)
+    host = parsed.hostname or "invalid"
+    try:
+        port = parsed.port
     except ValueError:
-        netloc = host
+        port = None
+    netloc = f"{host}:{port}" if port else host
     return urlunsplit((parsed.scheme, netloc, parsed.path, "", ""))