feat: add precomputed configuration storage#239
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leoromanovsky merged 8 commits intomainfrom Feb 3, 2026
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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.
sameerank
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The empty-vs-null behavior returned by loadConfigFromCache is the main one that was confusing to me. The rest are nits. Looks good overall!
eppo/src/main/java/cloud/eppo/android/PrecomputedConfigurationStore.java
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eppo/src/main/java/cloud/eppo/android/dto/PrecomputedConfigurationResponse.java
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| return CompletableFuture.completedFuture(null); | ||
| } | ||
| return cacheLoadFuture = | ||
| CompletableFuture.supplyAsync( |
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Nothing to fix here, but just noting that there's a race condition due to a sync check and async read. You've handled it by ensuring that exceptions are caught so it's not dangerous.
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Yea absolutely thanks for mentioning; I'm being kind of lazy and copying the same pattern as exists in the local-eval configuration store.
eppo/src/main/java/cloud/eppo/android/dto/PrecomputedConfigurationResponse.java
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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.
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- 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
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* feat: add obfuscation utilities and precomputed DTOs 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. * perf: optimize MD5 hex conversion with lookup table 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. * perf: add md5HexPrefix for efficient partial hash 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. * refactor: extract BaseCacheFile for reuse 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 * feat: add precomputed configuration storage 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. * style: apply spotless formatting * fix: address PR #239 feedback - 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 * feat: add EppoPrecomputedClient 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 * perf: use md5HexPrefix for cache file naming * fix: address PR review feedback for EppoPrecomputedClient - 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 * feat: derive precomputed client base URL from SDK key 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. * chore: remove self-evident comments in UtilsTest Address PR review feedback by removing redundant inline comments that simply restated what the test assertions already conveyed.
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Motivation
The precomputed client needs to store configuration both in-memory for fast access and on disk for offline/startup scenarios. This PR adds the storage layer that manages this caching.
Changes
Storage:
PrecomputedCacheFile- Disk cache file extendingBaseCacheFilewith precomputed-specific namingPrecomputedConfigurationStore- Thread-safe storage manager with:Build:
Makefileto download precomputed test data files from sdk-test-dataTests:
PrecomputedConfigurationStoreTest- Unit tests for:Decisions
volatilefor configuration field to ensure visibility across threads without locking on readscacheLock) and load future management (cacheLoadLock)PR Stack
This PR is part of the precomputed client feature, split for easier review:
Why this structure: The storage layer depends on both the base cache infrastructure (PR 1) and the DTOs (PR 2). It's isolated from the client implementation, making it easier to review the caching logic independently.
Merge order: PR 1 and PR 2 must be merged first, then this PR's base updated to
main.