86 lines
2.9 KiB
Python
86 lines
2.9 KiB
Python
"""
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Middleware for managing Unity instance selection per session.
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This middleware intercepts all tool calls and injects the active Unity instance
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into the request-scoped state, allowing tools to access it via ctx.get_state("unity_instance").
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"""
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from threading import RLock
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from typing import Optional
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from fastmcp.server.middleware import Middleware, MiddlewareContext
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# Global instance for access from tools
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_unity_instance_middleware: Optional['UnityInstanceMiddleware'] = None
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def get_unity_instance_middleware() -> 'UnityInstanceMiddleware':
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"""Get the global Unity instance middleware."""
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if _unity_instance_middleware is None:
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raise RuntimeError("UnityInstanceMiddleware not initialized. Call set_unity_instance_middleware first.")
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return _unity_instance_middleware
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def set_unity_instance_middleware(middleware: 'UnityInstanceMiddleware') -> None:
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"""Set the global Unity instance middleware (called during server initialization)."""
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global _unity_instance_middleware
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_unity_instance_middleware = middleware
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class UnityInstanceMiddleware(Middleware):
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"""
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Middleware that manages per-session Unity instance selection.
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Stores active instance per session_id and injects it into request state
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for all tool calls.
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"""
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def __init__(self):
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super().__init__()
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self._active_by_key: dict[str, str] = {}
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self._lock = RLock()
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def _get_session_key(self, ctx) -> str:
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"""
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Derive a stable key for the calling session.
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Uses ctx.session_id if available, falls back to 'global'.
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"""
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session_id = getattr(ctx, "session_id", None)
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if isinstance(session_id, str) and session_id:
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return session_id
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client_id = getattr(ctx, "client_id", None)
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if isinstance(client_id, str) and client_id:
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return client_id
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return "global"
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def set_active_instance(self, ctx, instance_id: str) -> None:
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"""Store the active instance for this session."""
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key = self._get_session_key(ctx)
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with self._lock:
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self._active_by_key[key] = instance_id
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def get_active_instance(self, ctx) -> Optional[str]:
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"""Retrieve the active instance for this session."""
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key = self._get_session_key(ctx)
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with self._lock:
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return self._active_by_key.get(key)
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async def on_call_tool(self, context: MiddlewareContext, call_next):
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"""
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Intercept tool calls and inject the active Unity instance into request state.
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"""
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# Get the FastMCP context
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ctx = context.fastmcp_context
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# Look up the active instance for this session
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active_instance = self.get_active_instance(ctx)
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# Inject into request-scoped state (accessible via ctx.get_state)
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if active_instance is not None:
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ctx.set_state("unity_instance", active_instance)
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# Continue with tool execution
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return await call_next(context)
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