httpx Reverting #2354 (Fix)

The Fix

Upgrade to version 0.23.1 or later.

Based on closed encode/httpx issue #2712 · 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%.

Jump to Verify Open PR/Commit

@@ -540,7 +540,7 @@ def __init__(
         if value is None or isinstance(value, (str, bytes)):
             value = value.decode("ascii") if isinstance(value, bytes) else value
-            self._dict = parse_qs(value)
+            self._dict = parse_qs(value, keep_blank_values=True)
         elif isinstance(value, QueryParams):

repro.py

Params means we want an acceptable format "key=val&", but when we combine this with the string supplied into the uri, I don't believe there is a server that will recognize such a format.

Overriding queries passed into the string if they are not in "key=value" format is much more expected behavior, in my opinion.

For example

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 0.23.1 or later.\nWhen NOT to use: This fix should not be applied if the application relies on the previous behavior of merging query parameters.\n\n

Why This Fix Works in Production

Trigger: because they fail to distinguish query data from path data when
Mechanism: The handling of empty query parameters was incorrect, leading to unexpected URL formats
Why the fix works: Fixes the handling of empty query parameters by allowing blank values in query strings. (first fixed release: 0.23.1).

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

The handling of empty query parameters was incorrect, leading to unexpected URL formats
Production symptom (often without a traceback): because they fail to distinguish query data from path data when

Proof / Evidence

GitHub issue: #2712
Fix PR: https://github.com/encode/httpx/pull/2354
First fixed release: 0.23.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.55

Discussion

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

Jump to Sources Open on GitHub

“There are several helpful links related to this issue. The initial issue that represents this problem: https://github.com/encode/httpx/issues/2331 The pull request that 'fixed' the #2331: https://github.com/encode/httpx/pull/2354”

@karpetrosyan · 2023-05-21 · source

“There are two different aspects you're highlighting here..”

@lovelydinosaur · 2023-05-22 · source

“I had no idea why we were merging 'params' with queries passed into strings in this manner”

@karpetrosyan · 2023-05-21 · source

Failure Signature (Search String)

because they fail to distinguish query data from path data when
So when our uri is 'http://example.com?test' with params={'key':'value'} we should either override "?test" or raise an exception because merging these two formats does not make

Copy-friendly signature

signature.txt

Failure Signature
-----------------
because they fail to distinguish query data from path data when
So when our uri is 'http://example.com?test' with params={'key':'value'} we should either override "?test" or raise an exception because merging these two formats does not make sense.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
because they fail to distinguish query data from path data when
So when our uri is 'http://example.com?test' with params={'key':'value'} we should either override "?test" or raise an exception because merging these two formats does not make sense.

Minimal Reproduction

repro.py

Params means we want an acceptable format "key=val&", but when we combine this with the string supplied into the uri, I don't believe there is a server that will recognize such a format.

Overriding queries passed into the string if they are not in "key=value" format is much more expected behavior, in my opinion.

For example

What Broke

Requests with query parameters resulted in malformed URLs, causing potential request failures.

Why It Broke

The handling of empty query parameters was incorrect, leading to unexpected URL formats

Fix Options (Details)

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

Upgrade to version 0.23.1 or later.

When NOT to use: This fix should not be applied if the application relies on the previous behavior of merging query parameters.

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

Fix reference: https://github.com/encode/httpx/pull/2354

First fixed release: 0.23.1

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

When NOT to Use This Fix

This fix should not be applied if the application relies on the previous behavior of merging query parameters.

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.

Version Compatibility Table

Version	Status
0.23.1	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.