Python: [Bug]: aiohttp.http_exceptions.LineTooLong: 400, message: Got more than 524288 bytes when reading: b'data:

[lakshaydulani]

Description

Hi
I am calling the agent created using Copilot Studio.
Whenever I make a request to the Salesforce connector , it gives the following issue -

Code Sample

import asyncio
from agent_framework.microsoft import CopilotStudioAgent
from msal import PublicClientApplication, ConfidentialClientApplication
import traceback

async def main():        

    agent = CopilotStudioAgent(
        environment_id=ENVIRONMENT_ID,
        agent_identifier="new_sf",
        tenant_id=TENANT_ID,
        client_id=CLIENT_ID,
        token=TOKEN
    )


    try:
        result = await agent.run("hi")
        print(f"Result: {result}")
        result1 = await agent.run("tell me the open opportunities in salesforce")
        print(f"Result: {result1}")
    except Exception as e:
        traceback.print_exc()

asyncio.run(main())

Error Messages / Stack Traces

result1 = await agent.run("tell me the open opportunities in salesforce")
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\agent_framework_copilotstudio\_agent.py", line 258, in _run_impl
    response_messages = [message async for message in self._process_activities(activities, streaming=False)]
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\agent_framework_copilotstudio\_agent.py", line 330, in _process_activities
    async for activity in activities:
    ...<9 lines>...
            )
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\microsoft_agents\copilotstudio\client\copilot_client.py", line 78, in ask_question
    async for activity in self.ask_question_with_activity(activity):
        yield activity
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\microsoft_agents\copilotstudio\client\copilot_client.py", line 105, in ask_question_with_activity
    async for activity in self.post_request(url, data, headers):
        yield activity
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\microsoft_agents\copilotstudio\client\copilot_client.py", line 39, in post_request
    async for line in response.content:
    ...<9 lines>...
            yield activity
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\aiohttp\streams.py", line 46, in __anext__
    rv = await self.read_func()
         ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\aiohttp\streams.py", line 370, in readline
    return await self.readuntil(max_size=max_line_length)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Z00583RM\Documents\tech\mafcs\.venv\Lib\site-packages\aiohttp\streams.py", line 401, in readuntil
    raise LineTooLong(chunk[:100] + b"...", max_size)
aiohttp.http_exceptions.LineTooLong: 400, message:
  Got more than 524288 bytes when reading: b'data: {"type":"event","id":"3da033af-d972-49d7-9880-628da9340178","timestamp":"2026-07-22T11:33:41.3...'.

Package Versions

agent-framework - 1.10.0, agent-framework-copilotstudio - 1.0.0b260521

Python Version

3.14.3

Additional Context

No response

[github-actions]

🤖 Automated triage reproduction notes (agent-authored — trust but verify)

Agent analysis

Repro: CopilotClient.post_request() in python/.venv/lib/python3.13/site-packages/microsoft_agents/copilotstudio/client/copilot_client.py line 39 uses async for line in response.content: which triggers aiohttp's readline() with a hardcoded 524288-byte max_line_length. When Copilot Studio returns an SSE data: line exceeding 512KB (e.g. from a Salesforce connector), LineTooLong is raised. Minimal repro: start a test server returning an SSE line >524288 bytes and call client.post_request(); fix must replace line-based iteration with chunk-based reading or increase/remove the line limit.

• Failing test: python/packages/copilotstudio/tests/test_line_too_long_bug.py
• Files examined: python/.venv/lib/python3.13/site-packages/microsoft_agents/copilotstudio/client/copilot_client.py, python/packages/copilotstudio/agent_framework_copilotstudio/_agent.py, python/packages/copilotstudio/tests/test_copilot_agent.py, python/packages/copilotstudio/pyproject.toml, python/packages/copilotstudio/tests/conftest.py
• Tests run: python/packages/copilotstudio/tests/test_line_too_long_bug.py
• Reported version: agent-framework-copilotstudio 1.0.0b260521
• Current version: 1.0.0b260721

[Mahajan-Sachin]

Hi Giles Odigwe (@giles17) Evan Mattson (@moonbox3),

I have submitted a PR #7321 to address this issue.

How it was resolved:

Since microsoft-agents-copilotstudio-client is an external dependency, we cannot modify its source code directly. To fix the LineTooLong error within the framework, we did the following:

1. Monkeypatched CopilotClient.post_request inside the agent-framework-copilotstudio package (_agent.py).
2. The patched function reads the response stream in chunks using response.content.iter_any() instead of line-by-line iteration. We buffer the chunks and split on \n manually. This completely bypasses aiohttp's default 512 KB line limit.
3. Added a regression test test_line_too_long_bug.py that starts a local mock SSE server returning a 600 KB data line, verifying that it gets successfully parsed.

All tests and code checks (poe check including Ruff, Pyright, MyPy) are passing successfully. Please take a look at PR #7321.