The Fix
Upgrade to version 0.28.0 or later.
Based on closed Kludex/starlette issue #847 · PR/commit linked
@@ -3,7 +3,7 @@
from starlette.background import BackgroundTask
-from starlette.requests import Request
+from starlette.requests import ClientDisconnect, Request
from starlette.responses import ContentStream, Response, StreamingResponse
repro.py
app = Starlette()
class ParseRequestMiddleware(BaseHTTPMiddleware):
async def dispatch(self, request: Request, call_next: RequestResponseEndpoint):
# payload = await request.json() # This will cause test() to hang
response = await call_next(request)
payload = await request.json() # Hangs forever
return response
async def test(scope: Scope, receive: Receive, send: Send):
request = Request(scope=scope, receive=receive)
data = await request.json()
response = Response(status_code=405)
await response(scope, receive, send)
app.mount("/test", test)
app.add_middleware(ParseRequestMiddleware)
verify
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
fix.md
Option A — Upgrade to fixed release\nUpgrade to version 0.28.0 or later.\nWhen NOT to use: This fix is not suitable if the application requires distinct Request objects for each middleware.\n\nOption C — Workaround\nfor me right now but the more apps I add (especially third party ones) the more of a problem this will become.\nWhen NOT to use: This fix is not suitable if the application requires distinct Request objects for each middleware.\n\n
Why This Fix Works in Production
- Trigger: Middleware Request parse Hangs forever
- Mechanism: The middleware and ASGI app use different Request objects, exhausting the stream on the first read
- Why the fix works: Reuses the request's body buffer for call_next in BaseHTTPMiddleware, preventing the request from hanging forever when the body is read multiple times. (first fixed release: 0.28.0).
Production impact:
- If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).
Why This Breaks in Prod
- Dependency interaction matters here: httpx v1.0.
- The middleware and ASGI app use different Request objects, exhausting the stream on the first read
- Surfaces as: Middleware Request parse Hangs forever
Proof / Evidence
- GitHub issue: #847
- Fix PR: https://github.com/kludex/starlette/pull/1692
- First fixed release: 0.28.0
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.75
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.61
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Awesome, thanks Tom! I'm willing to help wherever I can. If you think my approach in #944 isn't the way to go I am willing…”
“We use starlette in combination with fastapi”
“This is my work around right now”
“Ok I think I found a solution here. See PR #848”
Failure Signature (Search String)
- Middleware Request parse Hangs forever
Error Message
Stack trace
error.txt
Error Message
-------------
Middleware Request parse Hangs forever
Minimal Reproduction
repro.py
app = Starlette()
class ParseRequestMiddleware(BaseHTTPMiddleware):
async def dispatch(self, request: Request, call_next: RequestResponseEndpoint):
# payload = await request.json() # This will cause test() to hang
response = await call_next(request)
payload = await request.json() # Hangs forever
return response
async def test(scope: Scope, receive: Receive, send: Send):
request = Request(scope=scope, receive=receive)
data = await request.json()
response = Response(status_code=405)
await response(scope, receive, send)
app.mount("/test", test)
app.add_middleware(ParseRequestMiddleware)
Environment
- httpx: 1.0
What Broke
Request parsing hangs indefinitely when the body is read multiple times.
Why It Broke
The middleware and ASGI app use different Request objects, exhausting the stream on the first read
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.28.0 or later.
When NOT to use: This fix is not suitable if the application requires distinct Request objects for each middleware.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option C — Workaround Temporary workaround
for me right now but the more apps I add (especially third party ones) the more of a problem this will become.
When NOT to use: This fix is not suitable if the application requires distinct Request objects for each middleware.
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.
- This does NOT fix data corruption; it only prevents duplicate side-effects.
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)
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/starlette/pull/1692
First fixed release: 0.28.0
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix is not suitable if the application requires distinct Request objects for each middleware.
- 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 the minimal reproduction on your broken version, then apply the fix and re-run.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
- Pin production dependencies and upgrade only with a reproducible test that hits the failing path.
Version Compatibility Table
| Version | Status |
|---|---|
| 0.28.0 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.