httpx Does detection of lost connections implicitly depend

The Fix

Upgrade to version 0.7.3 or later.

Based on closed encode/httpx issue #346 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Open PR/Commit

@@ -81,7 +81,7 @@ def __init__(
                 dispatch = WSGIDispatch(app=app)
             else:
-                dispatch = ASGIDispatch(app=app)
+                dispatch = ASGIDispatch(app=app, backend=backend)

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.7.3 or later.\nWhen NOT to use: This fix is not suitable for non-asyncio backends that do not support the trio concurrency model.\n\n

Why This Fix Works in Production

Trigger: Connections may be incorrectly marked as reusable, leading to potential request failures.
Mechanism: httpx's connection pooling relies on asyncio's behavior to detect stale connections, which is not optimal
Why the fix works: Adds a trio concurrency backend to handle connection pooling, addressing the issue of detecting lost connections in a more reliable manner. (first fixed release: 0.7.3).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

httpx's connection pooling relies on asyncio's behavior to detect stale connections, which is not optimal
Production symptom (often without a traceback): Connections may be incorrectly marked as reusable, leading to potential request failures.

Proof / Evidence

GitHub issue: #346
Fix PR: https://github.com/encode/httpx/pull/276
First fixed release: 0.7.3
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.83

Discussion

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

Jump to Sources Open on GitHub

“Yes, I think I understand that there’s actually not really a dependency there. Thanks for clarifying!”

@florimondmanca · 2019-09-15 · source

“Yeah, the current way of detecting stale connections on asyncio isn't *optimal*, in the sense that it will occasionally think a connection is ok when…”

@njsmith · 2019-09-15 · source

“It seems I tangled myself up on the previous discussions and the counter-intuitive notion of *readability*”

@florimondmanca · 2019-09-15 · source

Failure Signature (Search String)

Connections may be incorrectly marked as reusable, leading to potential request failures.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Connections may be incorrectly marked as reusable, leading to potential request failures.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Connections may be incorrectly marked as reusable, leading to potential request failures.

What Broke

Connections may be incorrectly marked as reusable, leading to potential request failures.

Why It Broke

httpx's connection pooling relies on asyncio's behavior to detect stale connections, which is not optimal

Fix Options (Details)

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

Upgrade to version 0.7.3 or later.

When NOT to use: This fix is not suitable for non-asyncio backends that do not support the trio concurrency model.

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

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/encode/httpx/pull/276

First fixed release: 0.7.3

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

When NOT to Use This Fix

This fix is not suitable for non-asyncio backends that do not support the trio concurrency model.
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.

Did This Fix Work in Your Case?

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

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.
Track RSS + object counts after deployments; alert on monotonic growth and GC pressure.
Add a long-running test that repeats the failing call path and asserts stable memory.

Version Compatibility Table

Version	Status
0.7.3	Fixed

Related Issues

No related fixes found.

Cluster: httpx:configuration-error All hubs All clusters

Related clusters: Data consistency Other Timeout

Sources

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

httpx Does detection of lost connections implicitly depend on asyncio? (Fix)