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deer-flow/backend/packages/harness/deerflow/agents/middlewares/token_usage_middleware.py

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"""Middleware for logging LLM token usage."""
import logging
from typing import override
from langchain.agents import AgentState
from langchain.agents.middleware import AgentMiddleware
from langgraph.runtime import Runtime
logger = logging.getLogger(__name__)
class TokenUsageMiddleware(AgentMiddleware):
"""Logs token usage from model response usage_metadata."""
@override
def after_model(self, state: AgentState, runtime: Runtime) -> dict | None:
return self._log_usage(state)
@override
async def aafter_model(self, state: AgentState, runtime: Runtime) -> dict | None:
return self._log_usage(state)
def _log_usage(self, state: AgentState) -> None:
messages = state.get("messages", [])
if not messages:
return None
last = messages[-1]
usage = getattr(last, "usage_metadata", None)
if usage:
logger.info(
"LLM token usage: input=%s output=%s total=%s",
usage.get("input_tokens", "?"),
usage.get("output_tokens", "?"),
usage.get("total_tokens", "?"),
)
return None