Add charset=utf-8 to JSON responses on the orjson (bytes) path

[wbarnha]

Note: Before submitting this pull request, please review our contributing guidelines.

Description

Fixes #557.

Web.json() serializes with faust.utils.json.dumps, which returns str with stdlib json but bytes with orjson. The two paths produced different content-types:

• str path → Response(text=...) → aiohttp appends ; charset=utf-8.
• bytes path (orjson) → Response(body=...) → aiohttp does not add a charset.

So with orjson installed, every JSON response was served as application/json (no charset), while the same app on stdlib json served application/json; charset=utf-8. This explains the reporter-vs-maintainer "can't reproduce" — it depends on whether orjson is installed.

Fix

Build the bytes-path Response directly with an explicit charset="utf-8" (verified: Response(body=..., content_type="application/json", charset="utf-8") → application/json; charset=utf-8). The generic bytes() helper is left unchanged — binary responses shouldn't be forced to utf-8.

Tests

• Updated test_json__from_bytes for the new implementation (builds Response(..., charset="utf-8")).
• Added test_json_content_type_has_charset_for_both_backends: asserts the real Content-Type header is application/json; charset=utf-8 whether dumps returns bytes (orjson) or str (stdlib).
• Verified it catches the bug: reverting the fix makes the bytes case assert application/json (no charset).
• flake8 / black --check / isort --check-only clean.

🤖 Generated with Claude Code

---

Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.15%. Comparing base (3073eb9) to head (26d34f0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #696   +/-   ##
=======================================
  Coverage   94.14%   94.15%           
=======================================
  Files         104      104           
  Lines       11136    11137    +1     
  Branches     1201     1201           
=======================================
+ Hits        10484    10486    +2     
+ Misses        551      550    -1     
  Partials      101      101           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.