uvicorn Httptools trims long urls (Fix)

The Fix

Upgrade to version 0.14.0 or later.

Based on closed Kludex/uvicorn issue #924 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Open PR/Commit

@@ -53,7 +53,7 @@ def get_packages(package):
 extra_requirements = [
     "websockets>=8.*",
-    "httptools==0.1.* ;" + env_marker_cpython,
+    "httptools==0.2.* ;" + env_marker_cpython,
     "uvloop>=0.14.0,!=0.15.0,!=0.15.1; " + env_marker_cpython,

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.14.0 or later.\nWhen NOT to use: This fix is not applicable if the underlying issue is not related to httptools.\n\n

Why This Fix Works in Production

Trigger: url parsing in httptools is still handled by http-parser and llhttp has a long standing enhancement request to provide a way to do it, so using the new…
Mechanism: Httptools does not handle long URLs properly due to reliance on an outdated HTTP parser
Why the fix works: Updated httptools from version 0.1.* to 0.2.* to replace the underlying HTTP parser with llhttp as http-parser is no longer actively maintained. (first fixed release: 0.14.0).

Production impact:

If left unfixed, retries/timeouts can trigger duplicate external side-effects (double charges, duplicate emails, repeated writes).

Why This Breaks in Prod

Httptools does not handle long URLs properly due to reliance on an outdated HTTP parser
Production symptom (often without a traceback): url parsing in httptools is still handled by http-parser and llhttp has a long standing enhancement request to provide a way to do it, so using the new httptools version in fact does not change anything to this issue

Proof / Evidence

GitHub issue: #924
Fix PR: https://github.com/encode/uvicorn/pull/1024
First fixed release: 0.14.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.72

Discussion

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

Jump to Sources Open on GitHub

“jfyk, @victoraugustolls PR was merged, and we have a PR using the new httptools version: https://github.com/encode/uvicorn/pull/1024”

@Kludex · 2021-05-24 · confirmation · source

“closing this a wontfix since it's an issue upstream > upstream (httptools using http-parse for url parsing)”

@euri10 · 2021-06-07 · confirmation · source

“@euri10 There is a pr to move httptools from http-parser tô llhttp. If the bug is in http-parser, this might help!”

@victoraugustolls · 2020-12-29 · source

“Cool, I subscribed to it thanks for the heads up @victoraugustolls !”

@euri10 · 2020-12-29 · source

Failure Signature (Search String)

url parsing in httptools is still handled by http-parser and llhttp has a long standing enhancement request to provide a way to do it, so using the new httptools version in fact

Copy-friendly signature

signature.txt

Failure Signature
-----------------
url parsing in httptools is still handled by http-parser and llhttp has a long standing enhancement request to provide a way to do it, so using the new httptools version in fact does not change anything to this issue

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
url parsing in httptools is still handled by http-parser and llhttp has a long standing enhancement request to provide a way to do it, so using the new httptools version in fact does not change anything to this issue

What Broke

Multiple calls to on_url for long URLs causing unexpected behavior.

Why It Broke

Httptools does not handle long URLs properly due to reliance on an outdated HTTP parser

Fix Options (Details)

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

Upgrade to version 0.14.0 or later.

When NOT to use: This fix is not applicable if the underlying issue is not related to httptools.

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

Fix reference: https://github.com/encode/uvicorn/pull/1024

First fixed release: 0.14.0

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

When NOT to Use This Fix

This fix is not applicable if the underlying issue is not related to httptools.

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
0.14.0	Fixed

Related Issues

No related fixes found.

Cluster: uvicorn:duplicate-processing All hubs All clusters

Related clusters: Configuration error Data consistency Race condition

Sources

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