feat(example): add precomputed client demo by leoromanovsky · Pull Request #241 · Eppo-exp/android-sdk

leoromanovsky · 2026-01-28T16:32:00Z

Motivation

Provide an interactive demonstration of the precomputed client in the example app for testing and development purposes.

Changes

Activity Refactoring:

Renamed MainActivity → HomeActivity (launcher with client selection)
Renamed SecondActivity → StandardClientActivity (existing client demo)
Added back navigation to both existing activities

New PrecomputedActivity:

Subject ID input field
Two initialization modes:
- "From Server" - Fetches fresh configuration from edge endpoint
- "From Disk" - Uses only cached configuration (offline mode)
Dynamic subject attributes table:
- Add/remove key-value pairs
- Auto-detects numeric vs string values
- Pre-populated with platform and appVersion
Flag key input with type selector (String, Bool, Int, Num, JSON)
"Get Assignment" button to fetch and display results
Scrollable log showing all operations
Proper lifecycle handling:
- onPause() → pause polling
- onResume() → resume polling
- onDestroy() → stop polling

Layouts:

activity_home.xml - Updated with precomputed client button
activity_precomputed.xml - New layout with all controls

Resources:

Added string for precomputed button

Screen.Recording.2026-02-03.at.5.01.09.PM.mov

Decisions

Two init buttons: Makes it easy to test offline vs online scenarios
Dynamic attributes: More flexible than hardcoded fields
Type selector: Demonstrates all supported flag types
Verbose logging: Helps debug issues during development
Purple button: Visually distinguishes precomputed option

PR Stack

This PR is part of the precomputed client feature, split for easier review:

main
├── precomputed/1-base-cache-file
│   └─┬─ precomputed/3-storage-layer
│     │   └── precomputed/4-client ⬅ (base)
│     │       └── 👉 precomputed/5-example-app (this PR)
│     │
└── precomputed/2-dtos-and-utils ──────┘

Why this structure: Example app changes are purely additive and don't affect the SDK library. Keeping them separate allows the core feature to be merged and released independently if needed.

Merge order: This is the final PR in the stack. Merge PRs 1-4 first.

Full Stack Summary

PR	Title	Status
#237	refactor: extract BaseCacheFile	Ready
#238	feat: add obfuscation utilities and precomputed DTOs	Ready
#239	feat: add precomputed configuration storage	Waiting on #237, #238
#240	feat: add EppoPrecomputedClient	Waiting on #239
#241	feat(example): add precomputed client demo	Waiting on #240

Add the foundational data structures and utilities for the precomputed client feature: - ObfuscationUtils: MD5 hashing for flag key obfuscation - PrecomputedFlag: DTO for precomputed flag assignments - PrecomputedBandit: DTO for precomputed bandit assignments - PrecomputedConfigurationResponse: Wire protocol response parsing - BanditResult: Result container for bandit action lookups - MissingSubjectKeyException: Validation exception Includes comprehensive unit tests for serialization round-trips and MD5 hash consistency.

Replace Integer.toHexString() with a pre-computed hex character lookup table for byte-to-hex conversion. This avoids creating intermediate String objects for each byte, reducing allocations. Mirrors optimization from iOS SDK PR #91/#93.

Add md5HexPrefix() method that only converts the bytes needed for a given prefix length, avoiding unnecessary work when only a prefix is required (e.g., cache file naming uses first 8 chars). Includes unrolled loop for the common 4-byte (8 hex char) case to help compiler optimization, following iOS SDK PR #93 approach.

Extract common file caching functionality from ConfigCacheFile into a new BaseCacheFile base class. This enables reuse for the upcoming precomputed configuration cache without code duplication. - Add BaseCacheFile with common read/write/delete operations - Refactor ConfigCacheFile to extend BaseCacheFile - No functional changes to existing behavior

Add the storage layer for precomputed flag configurations: - PrecomputedCacheFile: Disk cache file extending BaseCacheFile - PrecomputedConfigurationStore: In-memory + disk storage with async save/load operations and proper thread synchronization - Updates in-memory config even if disk write fails for resilience Also adds test data files to Makefile for integration testing. Includes unit tests for cache operations and failure scenarios.

- Return null consistently in loadConfigFromCache for both file-not-found and read-error cases - Use static EMPTY singleton in PrecomputedConfigurationResponse.empty() - Use Collections.singletonMap() in getEnvironment() for memory efficiency

Add the main precomputed client implementation with: - Server-side precomputed flag assignments with instant lookups - Support for all flag types: string, boolean, integer, numeric, JSON - Bandit action support with attribute decoding - Builder pattern with extensive configuration options - Offline mode with initial configuration support - Background polling with configurable interval and jitter - Assignment and bandit logging with deduplication caches - Graceful error handling mode The client fetches precomputed assignments from the edge endpoint, eliminating client-side flag evaluation overhead. Includes comprehensive instrumented tests covering: - All flag type assignments - Assignment logging and deduplication - Bandit actions - Offline mode - SDK test data integration

- Make polling fields volatile for thread safety - Return user's default value on parse failure instead of hardcoded 0 - Extract magic string to NO_ACTION_CACHE_KEY constant - Fix banditActions serialization to match JS SDK wire format - Add comments for hash length and jitter calculation - Rename misleading test to testNonGracefulModeCanBeConfigured

Extract environment prefix from SDK key to automatically construct the correct edge endpoint URL (e.g., https://5qhpgd.fs-edge-assignment.eppo.cloud). This removes the need for users to manually configure the base URL.

Add demonstration of the precomputed client in the example app: - Rename MainActivity -> HomeActivity, SecondActivity -> StandardClientActivity - Add PrecomputedActivity with: - Subject ID input with server/disk initialization options - Dynamic subject attributes table (add/remove key-value pairs) - Flag key input with type selection (string, bool, int, numeric, JSON) - Assignment log display - Proper lifecycle handling for polling (pause/resume/stop) - Add back navigation to all activities - Update layouts and strings This provides a complete interactive demo of the precomputed client for testing and development purposes.

Address PR review feedback by removing redundant inline comments that simply restated what the test assertions already conveyed.

sameerank · 2026-02-05T00:08:15Z

example/src/main/java/cloud/eppo/androidexample/PrecomputedActivity.java

+    Button removeButton = new Button(this);
+    removeButton.setText("X");
+    removeButton.setMinWidth(0);
+    removeButton.setMinHeight(0);
+    removeButton.setMinimumWidth(0);
+    removeButton.setMinimumHeight(0);
+    removeButton.setPadding(16, 8, 16, 8);


Is it common to create UI components programmatically like this in Android? 😮

Also .setMinWidth and .setMinimumWidth are different?

sameerank · 2026-02-05T00:22:05Z

example/src/main/java/cloud/eppo/androidexample/PrecomputedActivity.java

+        // JSON assignments return JsonNode - for simplicity, we show as string
+        appendToLog("JSON assignment for '" + flagKey + "': (use getJSONAssignment() API)");


Could you do

JsonNode jsonResult = precomputedClient.getJSONAssignment(flagKey, null);

and stringify it with jsonResult.toString()?

leoromanovsky force-pushed the precomputed/4-client branch from fa04c22 to 7524fa0 Compare January 28, 2026 16:44

leoromanovsky force-pushed the precomputed/5-example-app branch from 2a2e1bc to 63b0d58 Compare January 28, 2026 16:44

leoromanovsky force-pushed the precomputed/4-client branch from 7524fa0 to 1abb120 Compare February 2, 2026 20:10

leoromanovsky force-pushed the precomputed/5-example-app branch from 63b0d58 to 95a40f0 Compare February 2, 2026 20:10

leoromanovsky added 4 commits February 2, 2026 15:13

style: apply spotless formatting

dd5309f

leoromanovsky force-pushed the precomputed/4-client branch from 1abb120 to f85971f Compare February 2, 2026 20:14

leoromanovsky force-pushed the precomputed/5-example-app branch 2 times, most recently from 328f129 to 5d88392 Compare February 2, 2026 20:14

leoromanovsky added 4 commits February 2, 2026 21:34

fix: address PR #239 feedback

4741881

- Return null consistently in loadConfigFromCache for both file-not-found and read-error cases - Use static EMPTY singleton in PrecomputedConfigurationResponse.empty() - Use Collections.singletonMap() in getEnvironment() for memory efficiency

Merge branch 'main' into precomputed/3-storage-layer

75dcdc4

perf: use md5HexPrefix for cache file naming

590804e

leoromanovsky force-pushed the precomputed/4-client branch from 42bc3da to 590804e Compare February 3, 2026 02:45

leoromanovsky force-pushed the precomputed/5-example-app branch from 5d88392 to d15bde0 Compare February 3, 2026 20:55

leoromanovsky marked this pull request as ready for review February 3, 2026 21:24

feat: derive precomputed client base URL from SDK key

4239fa0

Extract environment prefix from SDK key to automatically construct the correct edge endpoint URL (e.g., https://5qhpgd.fs-edge-assignment.eppo.cloud). This removes the need for users to manually configure the base URL.

leoromanovsky requested review from sameerank and typotter February 3, 2026 22:05

leoromanovsky force-pushed the precomputed/5-example-app branch from d15bde0 to dd5c86d Compare February 3, 2026 22:06

chore: remove self-evident comments in UtilsTest

f81109a

Address PR review feedback by removing redundant inline comments that simply restated what the test assertions already conveyed.

Base automatically changed from precomputed/4-client to main February 4, 2026 15:31

Merge branch 'main' into precomputed/5-example-app

801950c

leoromanovsky enabled auto-merge (squash) February 4, 2026 15:35

leoromanovsky disabled auto-merge February 4, 2026 15:35

sameerank approved these changes Feb 5, 2026

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feat(example): add precomputed client demo#241

feat(example): add precomputed client demo#241
leoromanovsky wants to merge 15 commits intomainfrom
precomputed/5-example-app

leoromanovsky commented Jan 28, 2026 •

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		// JSON assignments return JsonNode - for simplicity, we show as string
		appendToLog("JSON assignment for '" + flagKey + "': (use getJSONAssignment() API)");

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leoromanovsky commented Jan 28, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Motivation

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PR Stack

Full Stack Summary

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sameerank Feb 5, 2026

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leoromanovsky commented Jan 28, 2026 •

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