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checksum.md

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Tx-Chain Checksum

This project uses a transaction-chain checksum (sha256) to ensure both client and server process the same sequence of normalized transactions.

Key Concepts

  • Each tx only includes :block/uuid, :block/parent, :block/page, and :block/title (still ignoring :block/tx-id and RTC ignore attrs) before being turned into a deterministic string.
  • The checksum for a tx is sha256(prev-checksum + tx-string), with a fixed initial-checksum seed.
  • The server persists the latest checksum in sync_meta and recomputes it from tx_log when needed.
  • The client stores the checksum alongside its local metadata and validates pull/ok and tx/batch/ok responses before applying txs.

Failure Handling

  • When a pull or tx batch includes a checksum, the client compares it to the computed chain; mismatches throw :db-sync/checksum-mismatch.
  • The server includes the checksum in both pull/ok and tx/batch/ok responses so clients can stay in sync while applying retries or pending batches.

Testing

  • Coverage lives in src/test/frontend/worker/db_sync_test.cljs.
  • Run bb dev:test -v frontend.worker.db-sync-test.