Make middleware-types read only. (#106)

mateusz834 · web-flow · commit 806da0bca05d · 2026-03-31T11:56:13.000+02:00
In the README, we modified the request within a middleware, which is a bad practice.
Middleware should treat the request as immutable, since middleware earlier in
the chain may depend on the original request state.

And to avoid such mistakes, lets make all middleware-related types read-only.
diff --git a/splunklib/ai/README.md b/splunklib/ai/README.md
@@ -476,8 +476,14 @@ class ExampleMiddleware(AgentMiddleware):
     async def model_middleware(
         self, request: ModelRequest, handler: ModelMiddlewareHandler
     ) -> ModelResponse:
-        request.system_message = request.system_message.replace("SECRET", "[REDACTED]")
-        return await handler(request)
+        return await handler(
+            ModelRequest(
+                system_message=request.system_message.replace(
+                    "SECRET", "[REDACTED]"
+                ),
+                state=request.state,
+            )
+        )
 
     @override
     async def tool_middleware(
@@ -535,8 +541,14 @@ from splunklib.ai.middleware import (
 async def redact_system_prompt(
     request: ModelRequest, handler: ModelMiddlewareHandler
 ) -> ModelResponse:
-    request.system_message = request.system_message.replace("SECRET", "[REDACTED]")
-    return await handler(request)
+    return await handler(
+        ModelRequest(
+            system_message=request.system_message.replace(
+                "SECRET", "[REDACTED]"
+            ),
+            state=request.state,
+        )
+    )
 ```
 
 Example tool middleware:
diff --git a/splunklib/ai/middleware.py b/splunklib/ai/middleware.py
@@ -42,27 +42,27 @@ class AgentState:
     token_count: float
 
 
-@dataclass
+@dataclass(frozen=True)
 class ToolRequest:
     call: ToolCall
     state: AgentState
 
 
-@dataclass
+@dataclass(frozen=True)
 class ToolResponse:
     result: ToolResult | ToolFailureResult
 
 
 ToolMiddlewareHandler = Callable[[ToolRequest], Awaitable[ToolResponse]]
 
 
-@dataclass
+@dataclass(frozen=True)
 class SubagentRequest:
     call: SubagentCall
     state: AgentState
 
 
-@dataclass
+@dataclass(frozen=True)
 class SubagentResponse:
     result: SubagentStructuredResult | SubagentTextResult | SubagentFailureResult
 
@@ -73,13 +73,13 @@ class SubagentResponse:
 ]
 
 
-@dataclass
+@dataclass(frozen=True)
 class ModelRequest:
     system_message: str
     state: AgentState
 
 
-@dataclass
+@dataclass(frozen=True)
 class ModelResponse:
     message: AIMessage
     structured_output: Any | None = None
@@ -88,7 +88,7 @@ class ModelResponse:
 ModelMiddlewareHandler = Callable[[ModelRequest], Awaitable[ModelResponse]]
 
 
-@dataclass
+@dataclass(frozen=True)
 class AgentRequest:
     messages: list[BaseMessage]
 
