urllib3 [1.26] Coverage dropped below 100% when vendoring

The Fix

pip install urllib3==1.26.9

Based on closed urllib3/urllib3 issue #2543 · PR/commit linked

Open PR/Commit

@@ -117,7 +117,7 @@ jobs:
           python -m coverage combine
           python -m coverage html --skip-covered --skip-empty
-          python -m coverage report -i --fail-under=100 
+          python -m coverage report --ignore-errors --show-missing --fail-under=100

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.26.9\nWhen NOT to use: This fix is not suitable if complete coverage is required without exceptions.\n\n

Why This Fix Works in Production

Trigger: [1.26] Coverage dropped below 100% when vendoring ssl_match_hostname
Mechanism: Coverage report command did not show missing lines due to incorrect flags
Why the fix works: Addresses the coverage drop by modifying the coverage report command to show missing lines. (first fixed release: 1.26.9).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

Coverage report command did not show missing lines due to incorrect flags
Production symptom (often without a traceback): [1.26] Coverage dropped below 100% when vendoring ssl_match_hostname

Proof / Evidence

GitHub issue: #2543
Fix PR: https://github.com/urllib3/urllib3/pull/2540
First fixed release: 1.26.9
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
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

“Thanks @pquentin for the issue”

@hramezani · 2022-01-20 · source

“@pquentin I think we can close this now!”

@hramezani · 2022-01-30 · source

“To cover UnicodeError except: https://github.com/urllib3/urllib3/blob/b1f60e44d43b13e5272d5b6003f125af9c25c8ad/src/urllib3/util/ssl_match_hostname.py#L118-L122 As UnicodeError is a subclass of ValueError, and in both except blocks we have host_ip = None, I wou”

@hramezani · 2022-01-21 · source

Failure Signature (Search String)

[1.26] Coverage dropped below 100% when vendoring ssl_match_hostname
https://github.com/urllib3/urllib3/blob/b1f60e44d43b13e5272d5b6003f125af9c25c8ad/src/urllib3/util/ssl_match_hostname.py#L118-L122

Copy-friendly signature

signature.txt

Failure Signature
-----------------
[1.26] Coverage dropped below 100% when vendoring ssl_match_hostname
https://github.com/urllib3/urllib3/blob/b1f60e44d43b13e5272d5b6003f125af9c25c8ad/src/urllib3/util/ssl_match_hostname.py#L118-L122

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
[1.26] Coverage dropped below 100% when vendoring ssl_match_hostname
https://github.com/urllib3/urllib3/blob/b1f60e44d43b13e5272d5b6003f125af9c25c8ad/src/urllib3/util/ssl_match_hostname.py#L118-L122

Why It Broke

Coverage report command did not show missing lines due to incorrect flags

Fix Options (Details)

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

pip install urllib3==1.26.9

When NOT to use: This fix is not suitable if complete coverage is required without exceptions.

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

Fix reference: https://github.com/urllib3/urllib3/pull/2540

First fixed release: 1.26.9

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

When NOT to Use This Fix

This fix is not suitable if complete coverage is required without exceptions.

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
1.26.9	Fixed

Related Issues

No related fixes found.

Cluster: urllib3:data-consistency urllib3 hub urllib3 best practices All hubs All clusters

Related clusters: Configuration error SSL handshake Other

Sources

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

urllib3 [1.26] Coverage dropped below 100% when vendoring ssl_match_hostname (Fix)