Fix double URL-encoding of context param in remote feature flags

[corleymj]

Summary

RemoteFeatureFlagsProvider._prepare_query_params manually URL-encodes the JSON context string via urllib.parse.quote() before passing it as an httpx query parameter. Since httpx also URL-encodes all query parameter values when constructing the request URL, the context parameter ends up double-encoded:

Character	Expected	Actual (double-encoded)
{	%7B	%257B
"	%22	%2522
:	%3A	%253A

This causes the Mixpanel /flags API to return 400 Bad Request because it cannot parse the garbled context.

Before (broken)

context_json = json.dumps(context).encode("utf-8")
url_encoded_context = urllib.parse.quote(context_json)
params["context"] = url_encoded_context
# httpx then encodes again → %257B%2522distinct_id%2522...

After (fixed)

params["context"] = json.dumps(context)
# httpx handles encoding once → %7B%22distinct_id%22...

Changes

• mixpanel/flags/remote_feature_flags.py: Remove manual urllib.parse.quote() and .encode("utf-8") in _prepare_query_params. Pass the raw JSON string and let httpx handle URL encoding.
• mixpanel/flags/test_remote_feature_flags.py: Add TestPrepareQueryParams test class covering:
  • Context value is a plain JSON string (not pre-encoded)
  • Context value is str, not bytes
  • flag_key presence/absence
  • End-to-end check that the request URL is not double-encoded

Test plan

• All 31 existing + new tests pass (pytest mixpanel/flags/test_remote_feature_flags.py)
• New test_request_url_has_properly_encoded_context asserts no %257B (double-encode) or b%27 (bytes literal) in the outgoing URL
• Verified against live Mixpanel /flags API — 400s resolve with this fix applied

Made with Cursor

[lajohn4747]

Nice I found the same issue in #175

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.58%. Comparing base (58d9c38) to head (d341dbe).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #177      +/-   ##
==========================================
+ Coverage   94.50%   94.58%   +0.07%     
==========================================
  Files          12       12              
  Lines        1947     1975      +28     
  Branches      116      116              
==========================================
+ Hits         1840     1868      +28     
  Misses         70       70              
  Partials       37       37              

Flag	Coverage Δ
openfeature-provider	53.82% <0.00%> (+0.05%)	⬆️

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