119-Introduce-CompactedKeyEncoder

[leekeiabstraction]

Purpose

Linked issue: close #119

Brief change log

• Added CompactedKeyEncoder
• Added CompactedKeyWriter
• Added FieldGetter
• Added Value enum (not in Java) to allow more graceful/polymorphic BinaryWriter implementations

Several TODOs that may benefit from being broken up into smaller task to prevent PR from becoming too large:

1. BinaryWriter functions to return Result<?> for exception handling instead of panic!
2. Decimal, Timestamp, Date, InternalArray, Row and other data type's BinaryWriter functions, FieldGetter etc. implementation
3. CompactedKeyEncoder's all data type unit test

Tests

• Added CompactedKeyEncoder UTs similar to Java UTs

[leekeiabstraction]

@luoyuxia @Kelvinyu1117 Would appreciate review here.

[Copilot]

Pull request overview

This PR introduces the CompactedKeyEncoder infrastructure to encode key columns of rows into compact binary format. The implementation closely follows the Java reference implementation and provides a foundation for encoding primary keys for various data lake formats.

Key Changes

• Added CompactedKeyEncoder with support for basic data types (integers, floats, strings, bytes, binary, boolean)
• Introduced BinaryWriter trait and ValueWriter abstraction for extensible binary serialization
• Added FieldGetter trait to extract typed field values from rows
• Extended Datum enum with BorrowedBlob variant to support borrowed byte slices

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 19 comments.

Show a summary per file

File	Description
crates/fluss/src/row/mod.rs	Added module declarations for binary, encode, and field_getter; added helper method to create GenericRow from data
crates/fluss/src/row/field_getter.rs	New file implementing FieldGetter trait and type-specific getters for extracting fields from rows
crates/fluss/src/row/encode/mod.rs	New file defining KeyEncoder trait and factory method for creating encoders based on data lake format
crates/fluss/src/row/encode/compacted_key_encoder.rs	Core implementation of CompactedKeyEncoder with comprehensive unit tests
crates/fluss/src/row/datum.rs	Added BorrowedBlob variant and corresponding From implementation for borrowed byte slices
crates/fluss/src/row/compacted/mod.rs	Exposed CompactedKeyWriter module
crates/fluss/src/row/compacted/compacted_key_writer.rs	Wrapper around CompactedRowWriter that rejects null values for key encoding
crates/fluss/src/row/binary/mod.rs	New module defining BinaryRowFormat enum and re-exporting binary writer types
crates/fluss/src/row/binary/binary_writer.rs	Defines BinaryWriter and ValueWriter traits with implementations for all basic data types
crates/fluss/src/metadata/datatype.rs	Added test helper methods to create RowType from data types and field names
crates/fluss/Cargo.toml	Added delegate crate dependency for delegation pattern

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[leekeiabstraction]

Copilot comments have been addressed

[luoyuxia]

@leekeiabstraction Thanks for the pr. Left minor comment. PTAL

[leekeiabstraction]

@luoyuxia Addressed all comments, PTAL!