uvicorn TypeError when connection is closed in connect()

The Fix

Upgrade to version 0.13.1 or later.

Based on closed Kludex/uvicorn issue #244 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -216,6 +216,7 @@ async def asgi_send(self, message):
             elif message_type == "websocket.close":
                 code = message.get("code", 1000)
+                self.close_code = code  # for WebSocketServerProtocol
                 await self.close(code)
                 self.closed_event.set()

repro.py

class Application:
    def __init__(self, scope):
        self.scope = scope

    async def __call__(self, receive, send):
        if self.scope["type"] != "websocket":
            return

        while True:
            # what for the 'websocket.connect' event.
            await receive()

            # Close the connection
            await send({'type': 'websocket.close'})

verify

Re-run: uvicorn asgi:Application --ws websockets

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.13.1 or later.\nWhen NOT to use: This fix should not be applied if the application logic requires immediate connection closure.\n\nOption C — Workaround\nfor this?  I can post more info about what I'm seeing, but it looks like the connection closes and things are fine browser side, but if I call .close() in the .connect() function I end up with type errors in the logs.  Having stack traces in the logs is obviously not ideal, but it would help to clarify that's the extent of the issue...\nWhen NOT to use: This fix should not be applied if the application logic requires immediate connection closure.\n\n

Why This Fix Works in Production

Trigger: result = await asgi(self.asgi_receive, self.asgi_send)
Mechanism: The TypeError occurs when attempting to receive data from a closed WebSocket connection
Why the fix works: Fix failures when ASGI app rejects a connection during handshake, addressing TypeError when connection is closed. (first fixed release: 0.13.1).

Why This Breaks in Prod

Shows up under Python 3.7 in real deployments (not just unit tests).
The TypeError occurs when attempting to receive data from a closed WebSocket connection
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #244
Fix PR: https://github.com/kludex/uvicorn/pull/704
First fixed release: 0.13.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.27

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“> The thing that would help most with progressing this would be to try to replicate the issue in a plain ASGI application, or in…”

@matteing · 2019-10-22 · repro detail · source

“> If anyone's able to reduce the issue like that then I'd be very happy to dig into it”

@adamhooper · 2020-09-08 · source

“Here is a minimal example without using django: To test it, you have to start it with an asgi server an open a websocket connection”

@ostcar · 2019-04-13 · repro detail · source

“The thing that would help most with progressing this would be to try to replicate the issue in a plain ASGI application, or in Starlette,…”

@lovelydinosaur · 2019-10-22 · repro detail · source

Failure Signature (Search String)

result = await asgi(self.asgi_receive, self.asgi_send)

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/uvicorn/protocols/websockets/websockets_impl.py", line 140, in run_asgi
    result = await asgi(self.asgi_receive, self.asgi_send)
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/channels/sessions.py", line 179, in __call__
    return await self.inner(receive, self.send)
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/channels/middleware.py", line 41, in coroutine_call
    await inner_instance(receive, send)
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/channels/consumer.py", line 59, in __call__
    [receive, self.channel_receive], self.dispatch
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/channels/utils.py", line 59, in await_many_dispatch
    await task
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/channels/utils.py", line 51, in await_many_dispatch
    result = task.result()
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/uvicorn/protocols/websockets/websockets_impl.py", line 222, in asgi_receive
    data = await self.recv()
  File "/home/ossi/src/channels-examples/.venv/lib/python3.7/site-packages/websockets/protocol.py", line 419, in recv
    return_when=asyncio.FIRST_COMPLETED,
  File "/usr/lib/py
... (truncated) ...

Stack trace

error.txt

Error Message
-------------
TypeError: An asyncio.Future, a coroutine or an awaitable is required
at ensure_future (/usr/local/lib/python3.6/asyncio/tasks.py:526)
at <setcomp> (/usr/local/lib/python3.6/asyncio/tasks.py:311)
at wait (/usr/local/lib/python3.6/asyncio/tasks.py:311)
at recv (/usr/local/lib/python3.6/site-packages/websockets/protocol.py:419)
at asgi_receive (/usr/local/lib/python3.6/site-packages/uvicorn/protocols/websockets/websockets_impl.py:227)
at await_many_dispatch (/usr/local/lib/python3.6/site-packages/channels/utils.py:51)
at await_many_dispatch (/usr/local/lib/python3.6/site-packages/channels/utils.py:59)
at __call__ (/usr/local/lib/python3.6/site-packages/channels/consumer.py:59)
at run_asgi (/usr/local/lib/python3.6/site-packages/uvicorn/protocols/websockets/websockets_impl.py:147)

Stack trace

error.txt

Error Message
-------------
$ uvicorn asgi:Application --ws websockets
INFO: Started server process [23052]
INFO: Waiting for application startup.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: ('127.0.0.1', 58172) - "WebSocket /" 403
ERROR: Exception in ASGI application
Traceback (most recent call last):
  File "/home/ossi/src/uvicorn_test/venv/lib/python3.7/site-packages/uvicorn/protocols/websockets/websockets_impl.py", line 147, in run_asgi
    result = await asgi(self.asgi_receive, self.asgi_send)
  File "./asgi.py", line 12, in __call__
    await receive()
  File "/home/ossi/src/uvicorn_test/venv/lib/python3.7/site-packages/uvicorn/protocols/websockets/websockets_impl.py", line 227, in asgi_receive
    data = await self.recv()
  File "/home/ossi/src/uvicorn_test/venv/lib/python3.7/site-packages/websockets/protocol.py", line 419, in recv
    return_when=asyncio.FIRST_COMPLETED,
  File "/usr/lib/python3.7/asyncio/tasks.py", line 361, in wait
    fs = {ensure_future(f, loop=loop) for f in set(fs)}
  File "/usr/lib/python3.7/asyncio/tasks.py", line 361, in <setcomp>
    fs = {ensure_future(f, loop=loop) for f in set(fs)}
  File "/usr/lib/python3.7/asyncio/tasks.py", line 592, in ensure_future
    raise TypeError('An asyncio.Future, a coroutine or an awaitable is '
TypeError: An asyncio.Future, a coroutine or an awaitable is required
^CINFO: Shutting down
INFO: Waiting for app
... (truncated) ...

Minimal Reproduction

repro.py

class Application:
    def __init__(self, scope):
        self.scope = scope

    async def __call__(self, receive, send):
        if self.scope["type"] != "websocket":
            return

        while True:
            # what for the 'websocket.connect' event.
            await receive()

            # Close the connection
            await send({'type': 'websocket.close'})

Environment

Python: 3.7

What Broke

Uvicorn raises TypeError during WebSocket connection closure, leading to log clutter.

Why It Broke

The TypeError occurs when attempting to receive data from a closed WebSocket connection

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.13.1 or later.

When NOT to use: This fix should not be applied if the application logic requires immediate connection closure.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Option C — Workaround Temporary workaround

for this? I can post more info about what I'm seeing, but it looks like the connection closes and things are fine browser side, but if I call .close() in the .connect() function I end up with type errors in the logs. Having stack traces in the logs is obviously not ideal, but it would help to clarify that's the extent of the issue...

When NOT to use: This fix should not be applied if the application logic requires immediate connection closure.

Use only if you cannot change versions today. Treat this as a stopgap and remove once upgraded.

Option D — Guard side-effects with OnceOnly Guardrail for side-effects

Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.

Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.

Show example snippet (optional)

onceonly.py

from onceonly import OnceOnly
import os

once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)

# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..."  # replace
key = f"stripe:webhook:{event_id}"

res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
    return {"status": "already_processed"}

# Safe to execute the side-effect exactly once.
handle_event(event_id)

See OnceOnly SDK

When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.

Fix reference: https://github.com/kludex/uvicorn/pull/704

First fixed release: 0.13.1

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the application logic requires immediate connection closure.
Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.

Verify Fix

verify

Re-run: uvicorn asgi:Application --ws websockets

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Version Compatibility Table

Version	Status
0.13.1	Fixed

Related Issues

No related fixes found.

Cluster: uvicorn:ssl-handshake All hubs All clusters

Related clusters: Configuration error Data consistency Race condition

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

uvicorn TypeError when connection is closed in connect() (Fix)

The Fix

Why This Fix Works in Production

Why This Breaks in Prod

Proof / Evidence

Discussion

Failure Signature (Search String)

Error Message

Minimal Reproduction

Environment

What Broke

Why It Broke

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Option C — Workaround Temporary workaround

Option D — Guard side-effects with OnceOnly Guardrail for side-effects

Get updates

When NOT to Use This Fix

Verify Fix

Did This Fix Work in Your Case?

Prevention

Version Compatibility Table

Related Issues

Sources