Support passing a policy file to the proxy on startup.

proxy/common/config_manager.py

@@ -0,0 +1,63 @@
+"""Common Configurations for the Proxy Server."""
+
+import os
+import threading
+
+from invariant.analyzer import Policy
+
+
+class ProxyConfig:
+    """Common configurations for the Proxy Server."""
+
+    def __init__(self):
+        print("hello in init of ProxyConfig")
+        self.policies = self._load_policies()
+
+    def _load_policies(self) -> str:
+        """
+        Loads and validates policies from the file specified in POLICIES_FILE_PATH.
+        Returns the policy file content as a string if valid; otherwise, raises an error.
+        """
+        print("hello in load_policies")
+        policies_file = os.getenv("POLICIES_FILE_PATH", "")
+
+        if not policies_file:
+            print("Warning: POLICIES_FILE_PATH is not set. Using empty policies.")
+            return ""
+
+        try:
+            with open(policies_file, "r", encoding="utf-8") as f:
+                policy_file_content = f.read()
+            _ = Policy.from_string(policy_file_content)
+            return policy_file_content
+
+        except (FileNotFoundError, PermissionError, OSError) as e:
+            raise ValueError(
+                f"Error: Unable to read policies file ({policies_file}): {e}"
+            ) from e
+
+        except Exception as e:
+            raise ValueError(f"Invalid policy content in {policies_file}: {e}") from e
+
+    def __repr__(self) -> str:
+        return f"ProxyConfig(policies={repr(self.policies)})"
+
+
+class ProxyConfigManager:
+    """Manager for Proxy Configuration."""
+
+    _config_instance = None
+    _lock = threading.Lock()
+
+    @classmethod
+    def get_config(cls):
+        """Initializes and returns the proxy configuration using double-checked locking."""
+        local_config = cls._config_instance
+
+        if local_config is None:
+            with cls._lock:
+                local_config = cls._config_instance
+                if local_config is None:
+                    local_config = ProxyConfig()
+                    cls._config_instance = local_config
+        return local_config