[posthog]

💡 Motivation and Context

Contract: get-feature-flag-payload — "Malformed serialized payloads return no payload" — and its bulk counterpart in get-feature-flags-and-payloads ("Bulk payload decoding agrees with single-flag APIs"). The same rule is referenced by evaluate-flags and get-feature-flag-result.

The spec requires that a serialized payload be validated as JSON before public access: malformed, empty, or whitespace-only input must be logged and treated as an absent payload, never surfaced raw and never thrown to the caller — and "a payload decoding failure MUST NOT discard the associated flag value, healthy sibling payloads, or the combined result."

The sdk-specs compliance matrix for this SDK records this as a single shared root behind four non-compliant rows (Evaluate Flags, Get Feature Flag Payload, Get Feature Flag Result, Get Feature Flags And Payloads):

An unguarded JsonDocument.Parse in both FeatureFlag factories means a malformed payload throws during flag construction — discarding the flag's correctly evaluated local value on one path and the entire remote response on the other. […] Replace both JsonDocument.Parse(...) calls in FeatureFlag.cs with a TryParsePayload helper that trims, rejects empty/whitespace-only input, logs once, and yields Payload = null — the same result the SDK already produces for a flag with no payload — so neither the flag's value nor its siblings are lost.

📝 What changed

• FeatureFlag.CreateFromFlagsApi and FeatureFlag.CreateFromLocalEvaluation now decode payloads through a shared private ParsePayloadOrNull guard instead of calling JsonDocument.Parse directly. A null payload stays null as before; empty/whitespace-only input and a JsonException both log a warning and yield Payload = null.
• Both factories take an optional ILogger?, threaded from the existing loggers at the three call sites (FlagsApiResultExtensions.ToFlagsResult, LocalEvaluator.EvaluateAllFlags, PostHogClient.GetFeatureFlagAsync), so the failure is attributable to a flag key in SDK diagnostics.

Before this change, one bad payload byte in a /flags response threw out of FlagsApiResult.ToFlagsResult's projection and EvaluateFlagsAsync's catch discarded the whole response — every healthy flag value and sibling payload with it — and nothing in the logs distinguished it from a transport failure. On the local-evaluation path the per-flag catch swallowed it, lost the flag's correctly evaluated value, and forced an unnecessary remote fallback.

✅ Why this is backwards-compatible

Behavior changes only for payloads that are already unusable. A payload that parses today parses identically; a payload that threw today now resolves to Payload = null, which is the SDK's existing representation for a flag with no payload, and which callers already have to handle. The raw malformed string is never exposed (JsonDocument? makes that impossible). No public API surface changes — both factories are internal, the new parameters are optional, and PublicAPI.*.txt is untouched.

💚 How did you test it?

• New unit tests on both factories: {broken, "", and " " each yield Payload = null while Key, IsEnabled, and VariantKey are preserved.
• New EvaluateFlagsAsync tests covering both evaluation paths with the same three inputs, mirroring the spec's scenario outlines: a malformed remote payload leaves the sibling flag's value and payload intact, and a malformed locally-evaluated payload no longer triggers a remote /flags fallback.
• All 12 new cases were confirmed to fail against main's FeatureFlag.cs and pass with the fix.
• Full CI flow locally: dotnet restore --locked-mode, bin/fmt --check, dotnet build --configuration Release, dotnet test --configuration Release — green on both net8.0 and netcoreapp3.1 (1235 / 1225 passed, 2 skipped, 0 failed).

➡️ Follow-up work (not in this PR)

The compliance notes list two further gaps on these rows that are deliberately out of scope here, to keep this change to the single contract:

• No standalone GetFeatureFlagPayloadAsync(key, distinctId, matchValue?) API — the only routes to a payload still require an already-evaluated flag or snapshot.
• No negative-knowledge retention for keys absent from both local definitions and a clean /flags response, so such keys re-probe on every call.

📝 Checklist

• 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 pnpm changeset to generate a changeset file

🤖 Agent context

Autonomy: Fully autonomous

Produced by the scheduled sdk-specs compliance run (Claude Code). The run reads the compliance matrices in PostHog/sdk-specs, ranks the open 🟡/❌ cells by safety, impact and scope, and implements exactly one per run. This cell was picked because its backwards-compatibility verdict is "Backward-compatible", it is user-facing (feature flag payload reads), and one guard resolves four matrix rows at a shared root. Breaking-verdict and Unknown cells are left for humans.

Scope decisions: the parse guard only, not the two follow-ups listed above, which are separate contracts/API additions. The logger is passed as an optional parameter rather than a static or ambient logger, to match how LocalEvaluator and PostHogClient already thread ILogger. Empty/whitespace input is reported with a distinct message from a parse failure so the two causes stay separable in logs.

Agent-authored — please review rather than rubber-stamp. No manual/sample-app testing was performed beyond the automated suite described above.

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Created with PostHog Desktop

🤖 Generated with Claude Code

[github-actions]

posthog-dotnet Compliance Report

Date: 2026-10-09T06:10:34.236760+00:00
Duration: 124965ms

✅ All Tests Passed!

47/47 tests passed

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Capture Tests

✅ 30/30 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	256ms
Format Validation.Event Has Uuid	✅	127ms
Format Validation.Event Has Lib Properties	✅	110ms
Format Validation.Distinct Id Is String	✅	115ms
Format Validation.Token Is Present	✅	111ms
Format Validation.Custom Properties Preserved	✅	117ms
Format Validation.Event Has Timestamp	✅	111ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	✅	120ms
Retry Behavior.Retries On 503	✅	8125ms
Retry Behavior.Does Not Retry On 400	✅	2117ms
Retry Behavior.Does Not Retry On 401	✅	2114ms
Retry Behavior.Respects Retry After Header	✅	8120ms
Retry Behavior.Implements Backoff	✅	22132ms
Retry Behavior.Retries On 500	✅	6117ms
Retry Behavior.Retries On 502	✅	6116ms
Retry Behavior.Retries On 504	✅	6117ms
Retry Behavior.Max Retries Respected	✅	22119ms
Deduplication.Generates Unique Uuids	✅	117ms
Deduplication.Preserves Uuid On Retry	✅	6117ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	13126ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6121ms
Deduplication.No Duplicate Events In Batch	✅	116ms
Deduplication.Different Events Have Different Uuids	✅	111ms
Compression.Sends Gzip When Enabled	✅	110ms
Batch Format.Uses Proper Batch Structure	✅	109ms
Batch Format.Flush With No Events Sends Nothing	✅	106ms
Batch Format.Multiple Events Batched Together	✅	114ms
Error Handling.Does Not Retry On 403	✅	2112ms
Error Handling.Does Not Retry On 413	✅	2112ms
Error Handling.Retries On 408	✅	6117ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	147ms
Request Payload.Flags Request Uses V2 Query Param	✅	109ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	108ms
Request Payload.Flags Request Omits Authorization Header	✅	110ms
Request Payload.Token In Flags Body Matches Init	✅	110ms
Request Payload.Groups Round Trip	✅	113ms
Request Payload.Groups Default To Empty Object	✅	110ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	107ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	110ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	110ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	109ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	213ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	112ms
Retry Behavior.Retries Flags On 502	✅	1113ms
Retry Behavior.Retries Flags On 504	✅	1111ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	212ms