Importing & Executing a BrowserBased Agent in Langgraph Studio

[KateZhang98]

Async Browser reports handler is closed

Problem

To illustrate the problem, I copied the NavigateTool from langchain-community into local. When I tried to run the simplified agent as illustrated in the code, I got the error

RuntimeError('unable to perform operation on <WriteUnixTransport closed=True reading=False 0xffff8ff9ec20>; the handler is closed')

The error is not reported when I do not have anything after the page.goto(url). However, if I add

response = await page.goto(url)
print("here is the response", response)

The above error appeared.

Screen.Recording.2025-01-25.at.12.50.32.PM.mov

import asyncio

#from langchain_community.tools.playwright.navigate import NavigateTool
from langgraph.graph import START, MessagesState, StateGraph
from playwright.async_api import Page, async_playwright

from .navigate_tool import NavigateTool


async def start_browser():
    playwright = await async_playwright().start()
    browser = await playwright.chromium.launch(headless=True)
    context = await browser.new_context()
    await context.new_page()
    return browser


def build_graph(browser):
    builder = StateGraph(MessagesState)
    # Pass browser to test node
    navigate_tool = NavigateTool.from_browser(async_browser=browser)
    builder.add_node("navigate", navigate_tool)
    builder.add_edge(START, "navigate")
    return builder.compile()


async def create_graph():
    browser = await start_browser()
    return build_graph(browser)


graph = asyncio.run(create_graph())

Sync Browser not allowed for BrowserTool

Problem

Take NavigateTool as an example. For the sync code below, I got the below error if input a url and click submit. Why is async browser required for it?

ValueError('Asynchronous browser not provided to navigate_browser')

Screen.Recording.2025-01-25.at.12.42.35.PM.mov

def start_browser():
    playwright = sync_playwright().start()
    browser = playwright.chromium.launch(headless=True)
    context = browser.new_context()
    context.new_page()
    return browser


def build_graph(browser):
    builder = StateGraph(UrlState)
    # Pass browser to test node
    navigate_tool = NavigateTool.from_browser(sync_browser=browser)
    builder.add_node("navigate", navigate_tool)
    builder.add_edge(START, "navigate")
    return builder.compile()


def create_graph():
    browser = start_browser()
    return build_graph(browser)


graph = create_graph()