The Fix
Upgrade to version 0.13.0 or later.
Based on closed encode/httpx issue #396 · 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%.
@@ -75,7 +75,7 @@ For a list of all available client-level parameters, see the [`Client` API refer
You can configure an `httpx` client to call directly into a Python web
-application using either the ASGI protocol.
+application using the ASGI protocol.
Option A — Upgrade to fixed release\nUpgrade to version 0.13.0 or later.\nWhen NOT to use: This fix is not applicable if the documentation is already accurate and clear.\n\n
Why This Fix Works in Production
- Trigger: In API design, a parameter should ideally be the smallest, atomic piece of information required from the user that, preferably, doesn't leak…
- Mechanism: Links to the ASGI documentation, addressing issues raised in the documentation for calling into Python web apps.
- Why the fix works: Links to the ASGI documentation, addressing issues raised in the documentation for calling into Python web apps. (first fixed release: 0.13.0).
- 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
- Production symptom (often without a traceback): In API design, a parameter should ideally be the smallest, atomic piece of information required from the user that, preferably, doesn't leak internals/implementations.
Proof / Evidence
- GitHub issue: #396
- Fix PR: https://github.com/encode/httpx/pull/577
- First fixed release: 0.13.0
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.75
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.70
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“At the moment this issue is somewhat defunct, since 0.8 dropped sync (and, correspondingly WSGI)”
“I think https://github.com/encode/httpx/pull/407 mostly resolves this”
“And, as I look back, I see "Review dispatch interface" in the 1.0 blockers issue..”
“> It'd be nice if some less knowledgeable users saw this and expressed their opinion, but that is probably unlikely. Just pitching in to say…”
Failure Signature (Search String)
- In API design, a parameter should ideally be the smallest, atomic piece of information required from the user that, preferably, doesn't leak internals/implementations.
- If it's just the spec APIs leaking into httpx
Copy-friendly signature
Failure Signature
-----------------
In API design, a parameter should ideally be the smallest, atomic piece of information required from the user that, preferably, doesn't leak internals/implementations.
If it's just the spec APIs leaking into httpx
Error Message
Signature-only (no traceback captured)
Error Message
-------------
In API design, a parameter should ideally be the smallest, atomic piece of information required from the user that, preferably, doesn't leak internals/implementations.
If it's just the spec APIs leaking into httpx
What Broke
Users encounter confusion and errors when trying to access WSGIDispatch due to incorrect documentation.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.13.0 or later.
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)
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)
Fix reference: https://github.com/encode/httpx/pull/577
First fixed release: 0.13.0
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix is not applicable if the documentation is already accurate and clear.
- 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.
Version Compatibility Table
| Version | Status |
|---|---|
| 0.13.0 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.