httpx Document the `extensions` API. (Fix)

The Fix

Upgrade to version 0.27.0 or later.

Based on closed encode/httpx issue #2599 · PR/commit linked

Production note: Watch p95/p99 latency and retry volume; timeouts can turn into retry storms and duplicate side-effects.

Jump to Verify Open PR/Commit

@@ -0,0 +1,201 @@
@@ -0,0 +1,201 @@
+# Extensions
+
+Request and response extensions provide a untyped space where additional information may be added.

repro.py

# You'll probably want to use `httpx` (or an httpx client instance) here instead of `httpcore`.
# The extension works the same way...
with httpcore.stream("GET", "https://www.example.com") as response:
    network_stream = response.extensions["network_stream"]

    ssl_object = network_stream.get_extra_info("ssl_object")
    print("TLS version", ssl_object.version())

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 0.27.0 or later.\nWhen NOT to use: This fix is not applicable if the documentation is already sufficient.\n\n

Why This Fix Works in Production

Trigger: timeout=timeout) as client:`
Mechanism: Missing documentation for the `extensions` API in httpx
Why the fix works: Added documentation for the `extensions` API in httpx, addressing issue #2599. (first fixed release: 0.27.0).

Why This Breaks in Prod

Missing documentation for the `extensions` API in httpx
Production symptom (often without a traceback): timeout=timeout) as client:`

Proof / Evidence

GitHub issue: #2599
Fix PR: https://github.com/encode/httpx/pull/3080
First fixed release: 0.27.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.69

Discussion

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

Jump to Sources Open on GitHub

“Take a look at the 'network_stream' extension”

@lovelydinosaur · 2023-03-03 · source

“Another user asking the same question, but looking for the server_addr info... https://github.com/encode/httpx/discussions/2633”

@lovelydinosaur · 2023-03-27 · source

“I cannot assert that using extensions will help solve my problem”

@al3x4kov · 2023-03-02 · source

Failure Signature (Search String)

timeout=timeout) as client:`
timeout = 30.0

Copy-friendly signature

signature.txt

Failure Signature
-----------------
timeout=timeout) as client:`
timeout = 30.0

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
timeout=timeout) as client:`
timeout = 30.0

Minimal Reproduction

repro.py

# You'll probably want to use `httpx` (or an httpx client instance) here instead of `httpcore`.
# The extension works the same way...
with httpcore.stream("GET", "https://www.example.com") as response:
    network_stream = response.extensions["network_stream"]

    ssl_object = network_stream.get_extra_info("ssl_object")
    print("TLS version", ssl_object.version())

What Broke

Users unable to utilize the `extensions` API effectively due to lack of documentation.

Why It Broke

Missing documentation for the `extensions` API in httpx

Fix Options (Details)

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

Upgrade to version 0.27.0 or later.

When NOT to use: This fix is not applicable if the documentation is already sufficient.

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/3080

First fixed release: 0.27.0

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 sufficient.
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

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.
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
0.27.0	Fixed

Related Issues

No related fixes found.

Cluster: httpx:ssl-handshake All hubs All clusters

Related clusters: Configuration error Data consistency Other

Sources

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