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protocol

The wire contract for LEDGERD: the SBE (Simple Binary Encoding) schema and the generated flyweight codecs that every other module uses to talk to the cluster and the read replica. This module is the contract only; it holds no business logic.

Responsibility

  • Define all on-wire and IPC messages in an SBE schema.
  • Generate zero-copy flyweight encoders and decoders (no reflection, little endian, fixed binary layout with backward-compatible optional fields).
  • Provide stream identifiers and shared wire constants.

Key contents

  • src/main/resources/messages.xml - the SBE schema (source of truth for the wire format).
  • Generated codecs under the module build output (encoders/decoders for CommandEnvelope, CommandResult, snapshot records, domain event journal records, and QueryRequest / QueryResponse).
  • QueryStreams.java - default channel and stream ids for the read-side query protocol.

Message families

  • Ingress: CommandEnvelope (command plus correlation: clientId, clientSeq, commandId, assetId) and TransferBatch (a group of transfer legs with a linked flag, ADR 0012).
  • Egress: CommandResult (deterministic result for exactly one command) and TransferBatchResult (one result per leg, ADR 0012).
  • Snapshot: SnapshotHeader, BalanceEntry, AllowanceEntry, DedupEntry, AssetSupplyEntry, BatchDedupEntry, SnapshotFooter.
  • Domain event journal (ADR 0011): BalanceChangedEvent, ReservedEvent, CapturedEvent, ReleasedEvent, TransferEvent, AllowanceChangedEvent, CommandRejectedEvent.
  • Read path: QueryRequest, QueryResponse.

Design notes

  • Flyweights hold no state: wrap(buffer, offset, blockLength, version) per message, decode fields in place, never build an intermediate POJO.
  • Little endian only, matching SBE default and native x86/ARM order.
  • Schema evolution is via optional fields, so newer and older peers interoperate.

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