[ioannisj]

💡 Motivation and Context

Part of PostHog/posthog-android#577

The SDK can't read the payload of a remote config feature flag. This adds a public function, PostHog.FeatureFlags.get_remote_config_payload/2, which fetches it from GET /api/projects/@current/feature_flags/{key}/remote_config with the existing secret_key option.

• Returns {:ok, payload} with the decoded JSON value. The endpoint sends the payload as a JSON string, so a string result is parsed a second time and stays a string if that parse fails.
• Returns {:ok, nil} when the flag has no payload. PostHog answers that with a 200 and an empty body, so an empty or whitespace-only 2xx body isn't an error.
• Returns {:ok, nil} without a request when the instance is disabled.
• Returns {:error, exception} when secret_key is missing, the flag key is "", ., or .., the status isn't 2xx, the body isn't JSON, or the request fails.
• Percent-encodes the flag key as one path segment, so a key with /, ?, or # can't change the request.
• Makes one request per call, with no retry, no cache, and no $feature_flag_called event.

Three things differ from posthog-node:

• A non-2xx status is an error here. posthog-node returns the error body as the payload.
• The flag key is encoded. posthog-node sends it as is.
• An empty 2xx body returns {:ok, nil}. posthog-node throws a SyntaxError on that response today, from await response.json() at packages/node/src/client.ts:2272 (480395c4).

With the default client, the request turns off Req's body decoding and the SDK parses the body itself. With Req's decoding, a 200 with a non-JSON content type (an HTML page from a proxy, for example) comes back as a plain string, and that looks the same as a decoded JSON string payload.

A custom api_client_module returns a decoded body, so the SDK doesn't decode the response again there and only parses the stored payload string. Both clients give the same result for the same payload, but with a custom client the SDK can't tell that a body wasn't JSON.

A Finch pool checkout timeout, which Finch raises, comes back as {:error, exception} like any other failed request.

💚 How did you test it?

Unit tests in test/posthog/feature_flags/remote_config_payload_test.exs and test/posthog/api/client_test.exs cover the request (path, encoded key, token param, bearer header, one request on a 503), the payload parsing, the empty and whitespace-only 200 bodies, and each error case (a 404 with an empty body and a pool checkout timeout included). The payload cases run against both the default client and a custom client that decodes the body.

mix test, mix format --check-formatted, mix credo --strict, and mix posthog.public_api --check pass. I didn't test against a live PostHog project.

📝 Checklist

• All commits are signed (see Commit signing)
• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

🤖 Agent context

DRI: @ioannisj
Autonomy: Human-driven (agent-assisted)

[github-actions]

posthog-elixir Compliance Report

Date: 2026-11-13T20:57:06.242395+00:00
Duration: 108382ms

⚠️ Some Tests Failed

40/47 tests passed, 7 failed

---

Capture Tests

⚠️ 29/30 tests passed, 1 failed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	606ms
Format Validation.Event Has Uuid	✅	608ms
Format Validation.Event Has Lib Properties	✅	607ms
Format Validation.Distinct Id Is String	✅	606ms
Format Validation.Token Is Present	✅	607ms
Format Validation.Custom Properties Preserved	✅	607ms
Format Validation.Event Has Timestamp	✅	607ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	❌	607ms
Retry Behavior.Retries On 503	✅	5613ms
Retry Behavior.Does Not Retry On 400	✅	2611ms
Retry Behavior.Does Not Retry On 401	✅	2610ms
Retry Behavior.Respects Retry After Header	✅	5612ms
Retry Behavior.Implements Backoff	✅	15615ms
Retry Behavior.Retries On 500	✅	5614ms
Retry Behavior.Retries On 502	✅	5614ms
Retry Behavior.Retries On 504	✅	5614ms
Retry Behavior.Max Retries Respected	✅	15623ms
Deduplication.Generates Unique Uuids	✅	616ms
Deduplication.Preserves Uuid On Retry	✅	5615ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10617ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5614ms
Deduplication.No Duplicate Events In Batch	✅	611ms
Deduplication.Different Events Have Different Uuids	✅	609ms
Compression.Sends Gzip When Enabled	✅	607ms
Batch Format.Uses Proper Batch Structure	✅	608ms
Batch Format.Flush With No Events Sends Nothing	✅	605ms
Batch Format.Multiple Events Batched Together	✅	611ms
Error Handling.Does Not Retry On 403	✅	2609ms
Error Handling.Does Not Retry On 413	✅	2609ms
Error Handling.Retries On 408	✅	5612ms

Failures

format_validation.non_utc_event_timestamp_is_converted_to_utc

Event 0 field 'timestamp' instant '2026-11-13T20:55:22.266799Z' != expected '2025-01-02T03:04:05Z'

Feature_Flags Tests

⚠️ 11/17 tests passed, 6 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	6ms
Request Payload.Flags Request Uses V2 Query Param	✅	4ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	5ms
Request Payload.Flags Request Omits Authorization Header	✅	4ms
Request Payload.Token In Flags Body Matches Init	✅	5ms
Request Payload.Groups Round Trip	✅	4ms
Request Payload.Groups Default To Empty Object	❌	5ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	4ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	4ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	4ms
Request Lifecycle.No Flags Request On Init Alone	✅	2ms
Request Lifecycle.No Flags Request On Normal Capture	✅	610ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	17ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	4ms
Retry Behavior.Retries Flags On 502	❌	308ms
Retry Behavior.Retries Flags On 504	❌	308ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	607ms

Failures

request_payload.groups_default_to_empty_object

Field 'groups' not found in /flags request body at path 'groups'. Available keys: ['distinct_id', 'api_key', 'flag_keys_to_evaluate']

request_payload.disable_geoip_omitted_defaults_to_false

Field 'geoip_disable' not found in /flags request body at path 'geoip_disable'. Available keys: ['distinct_id', 'api_key', 'flag_keys_to_evaluate']

request_lifecycle.mock_response_value_is_returned_to_caller

Last action result missing field 'value'. Keys: ['error', 'success']

retry_behavior.retries_flags_on_502

Last action result missing field 'value'. Keys: ['error', 'success']

retry_behavior.retries_flags_on_504

Last action result missing field 'value'. Keys: ['error', 'success']

side_effect_events.get_feature_flag_captures_feature_flag_called_event

Expected 1 events with name '$feature_flag_called', got 0

[posthog]

PostHog Review · Deep · reviewed 9479f5e

Posted 3 findings: 1 Should fix, 2 Consider.

Step	Status	Result
Prepare the diff	done	4 files, 1 chunk
Pick perspectives	done	3 perspectives
Run review passes	done	6 issues (+1 blind-spot)
Merge overlapping findings	done	7 → 5
Validate findings	done	3 kept, 2 dismissed
Publish	done	3 posted (view review)

[posthog]

See this review and its findings in PostHog Review.

[veria-ai]

PR overview

No security issues were found in this pull request.

Reviews

• beb4fae — No new issues
• 2d4a147 — No new issues