Support obfuscated feature flag assignment keys by leoromanovsky · Pull Request #3941 · DataDog/dd-sdk-android

leoromanovsky · 2026-10-01T11:28:37Z

Motivation

Readable flag keys can reveal upcoming features. Support obfuscated assignments without changing application evaluation calls.
This reduces readable names in payloads; it does not hide values or prevent dictionary guessing. It is not encryption or response signing.

Changes and Decisions

Advertise support through this header instead of a JSON supported_capabilities field. Existing request fields stay unchanged.

X-DD-FEATURE-FLAGS-CAPABILITIES: assignment-encoding-flag-key-256-v1

Capabilities are sorted and comma-separated. They describe support, not a requirement. The edge still selects plaintext or obfuscated responses through its rollout.

For obfuscated: true, validate obfuscation: {scheme, salt} and hash the application key for lookup. The response scheme remains flag-key-sha256-v1:

lowercase_hex(SHA256(
  UTF8("datadog.feature-flags.flag-key.v1") || 0x00 ||
  decode_hex(salt) || UTF8(application_flag_key)
))

The public salt contains 16 bytes, encoded as 32 lowercase hexadecimal characters. Keys use exact UTF-8 bytes without normalization.

sequenceDiagram
    participant App
    participant SDK as Android Flags client
    participant Edge as Fastly
    SDK->>Edge: Precompute request + capability header
    Edge-->>SDK: Plaintext, or encoded keys + scheme + salt
    SDK->>SDK: Validate and retain assignments with encoding
    App->>SDK: Evaluate original flag key
    SDK->>SDK: Hash lookup key only for encoded assignments
    SDK-->>App: Original value and evaluation details
    SDK->>SDK: Keep original flag key in telemetry

Cache up to 1,024 lookup hashes per descriptor. Do not cache flag values or change exposure deduplication.
Use platform SHA-256. Update assignments and encoding together. Evaluation calls and original-key telemetry stay unchanged.
Notify first-flags listeners only for readable assignments. Return an empty key list for encoded configurations because original keys cannot be enumerated.
Persist encoded assignments under encodedFlags with their metadata and context. Continue reading legacy plaintext caches.
Advertise support only for native Android consumers. Block encoded cache reads until local source detection confirms support. React Native remains excluded.
Reject invalid encoding metadata without a plaintext retry. Preserve existing fallback behavior; failed context-switch behavior remains separate.
Keep API 23 compatibility and the existing JVM test structure. Add no application configuration or release tooling.

Release requires edge support for the new header. This PR does not deploy backend changes.

Related: edge rollout, browser implementation.

datadog-datadog-prod-us1 · 2026-10-01T11:33:32Z

✅ All CI checks and tests passed. Datadog automation helped this PR pass.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🔄 Datadog retried 1 test - 1 passed on retry

🎯 Code Coverage (details)
• Patch Coverage: 90.82%
• Overall Coverage: 71.80% (-0.01%)

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 27ba428 | Docs | View more details | Give us feedback!}

chatgpt-codex-connector · 2026-10-05T22:19:28Z

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-08T14:18:46.163663Z	`27ba428`	New commits
🔒 Security Review	✅ Completed 2026-10-08T14:18:54.224228Z	`27ba428`	New commits

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0xnm · 2026-10-08T07:16:27Z


        sdkCore.getFeature(Feature.FLAGS_FEATURE_NAME)
            ?.withContext(withFeatureContexts = setOf(Feature.RUM_FEATURE_NAME)) { datadogContext ->
+                val supportsObfuscation = datadogContext.source == "android"


why this is needed? the same SDK working in React Native SDK setup changes behavior?

JavaScript consumes the snapshot through the bridge. It cannot decode obfuscated keys yet. A native SDK upgrade alone does not make that JavaScript reader compatible.

How do you think we should handle adding support for this given that the React Native changes have to be layer after this release?

0xnm · 2026-10-08T07:51:27Z

Please also follow the convention for the feature PRs: title should contain JIRA ticket reference, branch should be <user.handle>/<jira-ticket>/<branch-name>.

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linear-code · 2026-10-08T13:42:23Z

FFLSDK-261

leoromanovsky · 2026-10-08T13:54:14Z

Please also follow the convention for the feature PRs: title should contain JIRA ticket reference, branch should be <user.handle>/<jira-ticket>/<branch-name>.

@0xnm I don’t see this branch-naming convention documented in AGENTS.md or CONTRIBUTING.md. If it is required, could you please document it there so contributors can follow it from the start?

I’ve added the associated Linear ticket to the PR description. I’ll keep the existing branch for this PR rather than disrupt the review already in progress. We can follow the documented convention for future work.

0xnm · 2026-10-08T13:56:34Z

@leoromanovsky Can you update your branch? I pushed some updates to AGENTS.md in #3968.

Support obfuscated feature flag assignment keys

d600473

fix(flags): keep capability negotiation independent of versions

185a1fa

leoromanovsky marked this pull request as ready for review October 5, 2026 22:19

leoromanovsky requested review from a team as code owners October 5, 2026 22:19

leoromanovsky requested review from typotter and vjfridge and removed request for a team October 5, 2026 22:19

chatgpt-codex-connector Bot reviewed Oct 5, 2026

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Comment thread ...gs/src/androidTest/kotlin/com/datadog/android/flags/internal/FlagKeyObfuscationDeviceTest.kt Outdated

maciejburda requested a review from satween October 6, 2026 07:05

0xnm reviewed Oct 6, 2026

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Comment thread ...gs/src/androidTest/kotlin/com/datadog/android/flags/internal/FlagKeyObfuscationDeviceTest.kt Outdated

Comment thread features/dd-sdk-android-flags/build.gradle.kts

test(flags): keep obfuscation coverage in JVM suite

b3779f8

chatgpt-codex-connector Bot reviewed Oct 6, 2026

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leoromanovsky added 3 commits October 6, 2026 09:15

Merge origin/develop into flag-key-obfuscation

39ae47b

fix(flags): gate encoded cache reads until source is known

c63e2d6

Use the feature flags capabilities header

16292d0

typotter reviewed Oct 6, 2026

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Comment thread ...id-flags/src/main/kotlin/com/datadog/android/flags/internal/evaluation/EvaluationsManager.kt Outdated

typotter previously approved these changes Oct 6, 2026

View reviewed changes

Comment thread ...android-flags/src/main/kotlin/com/datadog/android/flags/internal/model/FlagKeyObfuscation.kt

Comment thread ...c/main/kotlin/com/datadog/android/flags/internal/net/PrecomputedAssignmentsRequestFactory.kt

fix(flags): cache lookup hashes and strengthen obfuscation regressions

751cb76

leoromanovsky dismissed typotter’s stale review via 751cb76 October 6, 2026 20:34

chatgpt-codex-connector Bot reviewed Oct 6, 2026

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Comment thread ...k-android-flags/src/test/kotlin/com/datadog/android/flags/internal/FlagKeyObfuscationTest.kt Outdated

aarsilv mentioned this pull request Oct 6, 2026

feat(browser): support flag-key obfuscation DataDog/openfeature-js-client#405

Merged

typotter previously approved these changes Oct 7, 2026

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Merge develop and preserve obfuscation with first-flags callbacks

1c1f39f

leoromanovsky dismissed typotter’s stale review via 1c1f39f October 7, 2026 18:00

typotter previously approved these changes Oct 7, 2026

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FFLSDK-254: Merge develop into flag-key-obfuscation

d8a2840

leoromanovsky dismissed typotter’s stale review via d8a2840 October 7, 2026 23:11

leoromanovsky requested a review from 0xnm October 8, 2026 00:34

0xnm requested changes Oct 8, 2026

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leoromanovsky added 6 commits October 8, 2026 07:39

FFLSDK-254: Mark obfuscation test setup, actions, and assertions

65fc35c

FFLSDK-254: Use Mockito annotations in obfuscation tests

3c503fc

FFLSDK-254: Generate incidental obfuscation test fixtures

26d87d6

FFLSDK-254: Limit obfuscation suppressions to specific calls

ad7aa8d

FFLSDK-254: Declare obfuscation parser exceptions

1d236bc

FFLSDK-254: Generate assignment and cache JSON models

71cc4df

chatgpt-codex-connector Bot reviewed Oct 8, 2026

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Comment thread .../src/test/kotlin/com/datadog/android/flags/internal/repository/DefaultFlagsRepositoryTest.kt Outdated

leoromanovsky added 6 commits October 8, 2026 09:58

FFLSDK-261: Add context to generated assignments test

935ada0

FFLSDK-261: Explain obfuscation copy visibility

586f86a

FFLSDK-261: Merge latest develop

36c7d5a

FFLSDK-261: Apply documented Kotlin conventions

723409b

FFLSDK-261: Tighten obfuscation test assertions

f4a6d1f

FFLSDK-261: Keep evaluation tests independent of HTTP

27ba428

leoromanovsky requested a review from 0xnm October 8, 2026 14:19

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