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FlexBuffers: The Zero-Copy Data Layer

FlexBuffers, part of Google's FlatBuffers project, is a self-describing binary format that Reaktor uses as its universal data format. Unlike JSON, FlexBuffers data can be accessed without parsing or deserialization, leading to massive performance gains.

The Role of FlexBuffers​

Reaktor uses FlexBuffers in three critical roles:

1. FFI Wire Format​

When data crosses language boundaries (e.g., Kotlin ↔ C++ ↔ JavaScript), it must be serialized.

  • Zero-copy on the reader side: The receiver reads directly from the byte buffer.
  • Language-agnostic: Can be called from Kotlin/Native, Swift, Dart, C#, Erlang, and JavaScript.
  • Schema DSL Integration: Annotated Kotlin schemas generate typed accessors for every language.

2. Object Cache (ObjectStore)​

Reaktor's ObjectStore (reaktor-db) is a key-value store backed by SQLite.

  • Cache hit without deserialization: Reading a byte buffer and accessing fields directly drops access time from ~2ms to 0.1ms.
  • Partial reads: Only the required fields are read, whereas JSON requires parsing the entire string.
  • Cache-to-wire zero-copy: When sending a cached object over the network or FFI, the byte buffer is sent directly.

3. Network Transport​

FlexBuffers is the wire format for all Reaktor transports, including HTTP, Mesh DataChannels, Pub/Sub, and Actor mailboxes. Content negotiation (JSON for debugging, FlexBuffer for production) is handled at the Service layer.

Schema DSL: Single Source of Truth​

Reaktor uses annotated Kotlin data classes with FlexBuffer serialization as the canonical schema definition. These are processed by the reaktor-compiler (KSP) to generate artifacts for every target:

  • Kotlin: Service layer, ObjectStore, and graph port types.
  • TypeScript: Interface, decoder, and JSON type guards.
  • Dart: Flutter bridge classes.
  • Swift: SwiftUI bridge structs.
  • C++: High-performance Highway SIMD accessors.
  • SQL: Database table generation and migration scripts.
  • API Routes: HTTP route handlers and OpenAPI specifications.