langchain/dist/agents/nodes/middleware.js

Typescript bindings for langchain

import { RunnableCallable } from "../RunnableCallable.js";
import { derivePrivateState } from "./utils.js";
import { getHookConstraint } from "../middleware/utils.js";
import { interopParse } from "@langchain/core/utils/types";

//#region src/agents/nodes/middleware.ts
/**
* Named class for context objects to provide better error messages
*/
var AgentContext = class {};
var AgentRuntime = class {};
var MiddlewareNode = class extends RunnableCallable {
	#options;
	constructor(fields, options) {
		super(fields);
		this.#options = options;
	}
	async invokeMiddleware(invokeState, config) {
		/**
		* Filter context based on middleware's contextSchema
		*/
		let filteredContext = {};
		/**
		* Parse context using middleware's contextSchema to apply defaults and validation
		*/
		if (this.middleware.contextSchema) {
			/**
			* Extract only the fields relevant to this middleware's schema
			*/
			const schemaShape = this.middleware.contextSchema?.shape;
			if (schemaShape) {
				const relevantContext = {};
				const invokeContext = config?.context || {};
				for (const key of Object.keys(schemaShape)) if (key in invokeContext) relevantContext[key] = invokeContext[key];
				/**
				* Parse to apply defaults and validation, even if relevantContext is empty
				* This will throw if required fields are missing and no defaults exist
				*/
				filteredContext = interopParse(this.middleware.contextSchema, relevantContext);
			}
		}
		const state = {
			...this.#options.getState(),
			...invokeState,
			messages: invokeState.messages
		};
		/**
		* ToDo: implement later
		*/
		const runtime = {
			context: filteredContext,
			writer: config?.writer,
			interrupt: config?.interrupt,
			signal: config?.signal
		};
		const result = await this.runHook(
			state,
			/**
			* assign runtime and context values into empty named class
			* instances to create a better error message.
			*/
			Object.freeze(Object.assign(new AgentRuntime(), {
				...runtime,
				context: Object.freeze(Object.assign(new AgentContext(), filteredContext))
			}))
		);
		/**
		* If result is undefined, return current state
		*/
		if (!result) return {
			...state,
			jumpTo: void 0
		};
		/**
		* Verify that the jump target is allowed for the middleware
		*/
		let jumpToConstraint;
		let constraint;
		if (this.name?.startsWith("BeforeAgentNode_")) {
			jumpToConstraint = getHookConstraint(this.middleware.beforeAgent);
			constraint = "beforeAgent.canJumpTo";
		} else if (this.name?.startsWith("BeforeModelNode_")) {
			jumpToConstraint = getHookConstraint(this.middleware.beforeModel);
			constraint = "beforeModel.canJumpTo";
		} else if (this.name?.startsWith("AfterAgentNode_")) {
			jumpToConstraint = getHookConstraint(this.middleware.afterAgent);
			constraint = "afterAgent.canJumpTo";
		} else if (this.name?.startsWith("AfterModelNode_")) {
			jumpToConstraint = getHookConstraint(this.middleware.afterModel);
			constraint = "afterModel.canJumpTo";
		}
		if (typeof result.jumpTo === "string" && !jumpToConstraint?.includes(result.jumpTo)) {
			const suggestion = jumpToConstraint && jumpToConstraint.length > 0 ? `must be one of: ${jumpToConstraint?.join(", ")}.` : constraint ? `no ${constraint} defined in middleware ${this.middleware.name}` : "";
			throw new Error(`Invalid jump target: ${result.jumpTo}, ${suggestion}.`);
		}
		/**
		* If result is a control action, handle it
		*/
		if (typeof result === "object" && "type" in result) {
			if (result.type === "terminate") {
				if (result.error) throw result.error;
				return {
					...state,
					...result.result || {},
					jumpTo: result.jumpTo
				};
			}
			throw new Error(`Invalid control action: ${JSON.stringify(result)}`);
		}
		/**
		* If result is a state update, merge it with current state
		*/
		return {
			...state,
			...result,
			jumpTo: result.jumpTo
		};
	}
	get nodeOptions() {
		return { input: derivePrivateState(this.middleware.stateSchema) };
	}
};

//#endregion
export { MiddlewareNode };
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